[Autophagy 4:5, 574-580; 1 July 2008]; ©2008 Landes Bioscience
Review Series: Autophagy in Higher Eukaryotes—A Matter of Survival or Death
Autophagy Maria Høyer-Hansen and Marja Jäättelä*
st r
Apoptosis Department and Centre for Genotoxic Stress Research; Institute of Cancer Biology; Danish Cancer Society; Copenhagen, Denmark
di
Key words: autophagy, cancer, cell death, survival, lysosomes, cancer-therapy
no t
Autophagy-Dependent Control of Cell Survival and Cell Death
.D
o
The critical role of autophagy in maintaining cell viability upon shortage of external nutritional sources was first documented in yeast, whose autophagy-defective mutants are viable under normal growth conditions but contrary to their wild type counterparts die rapidly during starvation.1,4,5 Later, a similar cytoprotective role of autophagy-dependent production of metabolites during nutrient starvation or growth factor deprivation was also demonstrated in mammalian cells lacking essential atg genes.6-8 The mechanisms by which autophagy promotes cell survival are, however, not restricted to the maintenance of cellular energy homeostasis. Autophagy is also involved in removing damaged or over-activated and thereby potentially dangerous organelles (mitochondria, endoplasmatic reticulum, peroxisomes and lysosomes) as well as cytotoxic protein aggregates from the cell thereby promoting cell survival.9-14 Mice deficient of known autophagic signaling molecules die either during embryonic development or within one day after the birth indicating that autophagy can also prolong the life of multicellular organisms.1518 Furthermore, the autophagy-mediated removal of intracellular pathogens and protein aggregates has been suggested to prolong the life of individuals exposed to infectious diseases and neurodegenerative processes, respectively.11,19-21 Paradoxically, autophagy has also been implicated in cell death called autophagic or type II programmed cell death, which was originally described on the basis of morphological studies detecting autophagic vacuoles during tissue involution.22-24 It should be noted that this definition does not distinguish whether autophagy directly contributes to death or whether it is a failed effort to preserve cell viability. Furthermore, most of the earlier studies that support autophagy as an execution pathway have been defined by the ability of 3-methyladenine, an inhibitor of class III PI3K (a kinase essential for autophagosome formation), to block programmed cell death. However, at the concentrations used this chemical regulates several other cellular enzymes that may also affect cell survival.25 Thus, it is only the recent identification of the atg family of genes controlling autophagosome formation, which has allowed the confirmation of the role of autophagy in cell death signaling. Studies based on atg gene depletion have shown autophagy-dependent death of cultured cells exposed for example to endoplasmatic reticulum stress, caspase inhibition, oxidative stress, growth factor deprivation, interferon-γ, anti-cancer drugs, p53 activation, oncogene activation, radiation
en ce
Macroautophagy (hereafter referred to as autophagy) is a lysosomal catabolic pathway whereby cells recycle macromolecules and organelles. The capacity of autophagy to maintain cellular metabolism under starvation conditions and to remove damaged organelles under stress conditions improves the survival of cells. Yet, autophagy appears to suppress tumorigenesis. In this review we discuss recent data that begin to elucidate the molecular basis for this apparent controversy. First, we summarize our current knowledge on the autophagy-mediated control of both cell survival and cell death in general. Then, we highlight the common cancer-associated changes in autophagy induction, regulation and execution. And finally we discuss the potential of pro- as well as anti-autophagic signaling pathways as targets for future cancer therapy.
ib u
te .
An emerging target for cancer therapy
© 20
08
La
nd
es
B
io s
ci
Autophagy is an evolutionarily highly conserved catabolic pathway that degrades cellular macromolecules and organelles. 1-3 It is regulated by the atg genes (autophagy-related genes) that control the formation of autophagosomes; cytoplasmic vesicles with a double membrane surrounding a cargo. The autophagosomes fuse with lysosomes to form autolysosomes, in which lysosomal hydrolases digest the cargo to metabolites that are released back to the cytosol for recycling. Starvation, hypoxia and various other stresses increase autophagic activity above the low basal level observed in unstressed cells, where it is kept down by the mammalian target of rapamycin complex 1 (mTORC1). The key upstream regulators of mTORC1 include the class I phosphoinositide 3-kinase (PI3K) —Akt pathway that keeps mTORC1 active in cells with sufficient growth factors and AMP-activated protein kinase (AMPK) pathway that inhibits mTORC1 upon starvation and calcium signals (Fig. 1). The recent molecular characterization and functional evaluation of both of these upstream pathways as well as that of the autophagosome formation and maturation have revealed numerous cancer-associated genetic changes that regulate the autophagic process. Here, we discuss the emerging connections between autophagy regulation and cell fate with special emphasis on cancer development and therapy response. *Correspondence to: Marja Jäättelä; Apoptosis Department and Centre for Genotoxic Stress Research; Institute of Cancer Biology; Danish Cancer Society; Strandboulevarden 49; Copenhagen 2100 Denmark; Tel.: +4535257318, Fax: +4535257721; Email:
[email protected] Submitted: 01/21/08; Revised: 03/17/08; Accepted: 03/17/08 Previously published online as an Autophagy E-publication: http://www.landesbioscience.com/journals/autophagy/article/5921 574
Autophagy
2008; Vol. 4 Issue 5
Autophagy—An emerging target for cancer therapy
© 20
08
La
nd
es
B
io s
ci
ib u st r di no t o .D
en ce
and various cancer drugs.26-36 More importantly, recent studies have also verified the existence of Atg-dependent cell death in more physiological circumstances, i.e., during the ecdysone-mediated involution of Drosophila salivary gland and the differentiation factor-controlled life cycle of the protist Dictyostelium discoideum.37,38 The data available today strongly supports the view that the capacity of autophagy to maintain cellular metabolism under starvation conditions and to remove damaged organelles under stress conditions improves the survival capacity of the normal cells. How can autophagy then during some conditions turn to a cell death mechanism? Even though we are still far from fully understanding what determines the final outcome of autophagy, it is clear that it does not depend solely on either the cell-type or the stimulus. For example, autophagy protects HeLa cervix carcinoma cells against starvation but contributes to the death of the same cells following treatment with interferon-γ,6,32 and tunicamycin-induced autophagy enhances the survival of colon cancer cells but contributes to the killing of immortalized murine embryonic fibroblasts.28 Alternatively, it may be the level of autophagy that determines the final outcome, the moderate induction supporting cell survival and the massive and/or prolonged induction leading to the opposite outcome when the cell literally “eats itself ” to death.39 In that way autophagy would act as a self-limited survival mechanism. Contradictory to this theory, recent data indicate that autophagosome formation is not enough, but the formation of autolysosomes is required for autophagic cell death in resveratrol-treated cancer cells.40 Thus, it will be interesting to test whether the autolysosomes themselves play a role in the autophagic cell death pathway by leaking lysosomal hydrolases into the the cytosol where they can induce either apoptosis- or necrosis-like cell death depending on the amount of the leakage.41 Additionally, studies on apoptosis defective cells suggest that autophagy as well as lysosomal membrane permeabilization can emerge as a cell death mechanism upon treatment with various anti-cancer drugs once the primary cell death pathway is inhibited.42 Thus, cancer cells that accumulate defects in their apoptotic machinery may be more prone to succumb by autophagy than their normal counterparts. Finally, the differences in the upstream signaling pathways activating the autophagic machinery are likely to contribute to the final outcome. Firstly, the induction of autophagy via pathways that inhibit the potent survival kinase Akt (Fig. 1) sensitizes cells to other forms of cell death.43 Secondly, autophagy can facilitate the caspase-dependent execution of the cell in conditions where autophagic and apoptotic proteases are simultaneously activated.38 And thirdly, the different signaling pathways may result in different cargo-specificity of the autophagosomes. For example,
te .
Figure 1. A schematic presentation of the two major signaling pathways controlling the activity of mTORC1 and autophagy. Green and red colors indicate molecules whose activation leads to the activation and inhibition of autophagy, respectively.
www.landesbioscience.com
selective autophagic degradation of catalase has been reported in fibroblasts treated with the pan-caspase inhibitor zVAD-fmk but not in the same cells during starvation-induced autophagy.26,36 Specific removal of catalase then contributes to zVAD-fmk-induced autophagic cell death via the accumulation of reactive oxygen species, membrane lipid oxidation and loss of membrane integrity.
Cancer-Associated Changes in the Autophagic Process In cancer the autophagic process is commonly altered at the levels of induction, regulation and lysosomal degradation (Fig. 2). Firstly, the low levels of oxygen and nutrients in the tumor environment enhance the autophagy signaling in cancer tissue.44 Secondly, several cancer-associated genetic alterations in genes that either regulate the mTORC1 activity or the autophagic process itself increase the threshold to autophagy induction.44,45 And thirdly, the completion of the autophagic process requires lysosomes whose activity and trafficking are greatly altered during tumorgenesis.41 These changes and their contribution to the final level of autophagic degradation in cancer tissue are discussed below. Tumor environment induces autophagy. The tumor environment is characterized by reduced levels of oxygen and nutrients. For example the median level of oxygen and glucose in normal breast tissue is 10 kPa and 5 mM as compared to 4 kPa and 0–2 mM in breast cancer tissue.46 This suggests that cancer cells, in addition to a high level of glycolysis,47 also increase autophagy for energy
Autophagy
575
no t
di
st r
ib u
te .
Autophagy—An emerging target for cancer therapy
.D
during starvation and other stressful conditions? Recent data suggest that it is, in fact, the enhanced survival and adaptation capacity of autophagy competent cells that may suppress tumorigenicity.7,48,49 Autophagy diminishes necrotic cell lysis in apoptosis-defective cells7 and therefore limits tumor inflammation in apoptosis-compromised tumors. Since the inflammation response has been linked to increased tumorigenesis,61 the increased necrotic cell death in autophagy defective tumors may enhance the tumorigenic potential of the surviving cells. Furthermore, the ability of autophagy to mitigate genome damage and mutation rate upon metabolic stress in tumor cells in which cell cycle checkpoints are inactivated is likely to slow down the tumor progression.48,49 Additionally, autophagy may simply suppress the growth of tumors. This hypothesis is supported by the data showing that breast cancer cells overexpressing Beclin 1 grow slower than parental cells,62 and mice heterozygous for Beclin 1 have increased number of proliferating cells in mammary ducts as compared to wildtype mice.18,63 Lastly, the death-promoting activity of autophagy could contribute to the tumor suppression. So far, there is, however, no experimental in vivo evidence to support autophagy as an important cell death pathway in normal or pre-malignant tissue in mammals. Cancer-associated lysosomal changes might influence the autophagic process. The ability of autophagosomes to fuse with lysosomes as well as the lysosomal degradative capacity are crucial for the completion of the autophagic process, i.e., the recycling of amino acids, fatty acids and other cellular metabolites. Thus, it is interesting to note that cancer is associated with prominent changes in lysosomal composition and trafficking.41,64,65 Oncogenic transformation increases the level and activity of cysteine cathepsins,66 which is expected to increase the lysosomal degradation capacity and thereby the turnover of autophagosomes. Increased cysteine cathepsin activity in cancer cell lysosomes leads, however, to the proteolytic degradation of lysosomal membrane-associated proteins (LAMP-1 and -2) (Nicole Fehrenbacher and MJ, unpublished data), both of which have been suggested to be essential for the fusion with autophagosomes.67 Thus, the final outcome of the increased cysteine cathepsin
© 20
08
La
nd
es
B
io s
ci
en ce
production. Accordingly, autophagosomes are found in vivo in insufficiently vascularised metabolically stressed regions of the tumor,7 and the prevention of the autophagic response in apoptosis-compromised tumor tissues leads to necrotic cell death.7 These data strongly suggest that in agreement with findings from cell culture experiments, autophagy is an essential mechanism for providing nutrients in tumor tissue.6,8 Genetic alterations in tumors. Contradicting the fact that autophagy has a prominent role in sustaining cell viability in metabolically stressed tumor cells, it serves as a tumor suppressive mechanism.6-8,48,49 This became first evident from data showing a high frequency of monoallelic deletions of Beclin 1 in breast, prostate and ovarian cancers, and the tumor prone phenotype of autophagy-defective mice.17,18,50 Accordingly, several of the known tumor-suppressor genes (p53, PTEN, DAPK, LKB1, TSC1/2 and p27KIP) and cancer-causing oncogenes (Bcl-2, class I PI3K, mTOR and Akt)—in addition to their other cancer-regulating functions— also stimulate or inhibit autophagy, respectively.45,51-54 Interestingly, damage-regulated autophagy modulator (DRAM), UV irradiation resistance-associated gene (UVRAG) and Atg4C constitute a new group of potential tumor suppressor genes with the only known function in autophagy regulation.29,50,55 This provides evidence for a decrease in the autophagic capacity in cancers. However, even though cancer cells are less sensitive toward autophagic induction as compared to non-malignant cells, samples from cancers of various origins still show autophagic vacuoles and activity.56,57 Furthermore, contrary to most known tumor suppressor genes, beclin 1 has never been found biallelically mutated or silenced.17,18,58 This suggests that tumors rely on a certain level of autophagy, possibly to protect them against the hostile tumor environment that is low in oxygen, and nutrients as discussed above. Interestingly, removing the majority of Beclin 1 or Atg5 protein from human cancer cells by RNA interference inhibits tumor growth also under in vitro conditions that provide sufficient nutrients and oxygen.29,59,60 How can autophagy suppress tumor development even though one of its best-characterized functions is to enhance cellular adaptation
o
Figure 2. A schematic presentation of the autophagic process and its regulation in cancer. Green and red colors indicate common cancer-associated changes that enhance and inhibit autophagic process, respectively.
576
Autophagy
2008; Vol. 4 Issue 5
Autophagy—An emerging target for cancer therapy
© 20
08
La
nd
es
B
io s
ci
The question whether we should try to enhance or inhibit autophagy in future cancer treatment is not straightforward and the answer is hard to predict before we have specific autophagy modulators to be tested in a clinical setting. While lacking such autophagy specific drugs, several compounds developed for other purposes and having profound affects on autophagy may teach us important lessons on the usability of autophagy modulators in cancer treatment (Table 1). Autophagy inhibitors in cancer treatment. Due to the cancerassociated mutations that decrease the autophagic capacity, a substantial block of autophagy might be easier to achieve in cancer cells than in normal cells. Thus, it is interesting to note that even though Beclin 1 is a haplo-insufficient tumor suppressor, removal of the remaining Beclin 1 in vitro induces a growth arrest in cancer cells.59 This suggests that a certain level of autophagy is required for tumor growth. In line with this depletion of Atg5 induces growth arrest in cancer cells suggesting that autophagic inhibitors could have relevant anti-cancer effects even when applied alone.29,60 They are, however, more likely to succeed in combination with cytotoxic drugs that activate a protective autophagy (that is an autophagic response that pro-long cell survival upon treatment). A potential synergistic effect would be expected when combining autophagy inhibition with other metabolic inhibitors, since tumor cells have high energy consumption simultaneous with a decreased oxidative phosphorylation.47 To compensate for this, cancer cells increase glycolysis and activate autophagy. Thus, a combination of angiogenesis or glucose uptake inhibitors with an autophagy block could prove as a potential anti-cancer strategy. In addition to the essential function of autophagy in metabolism, it also serves to remove damaged and thereby potential dangerous organelles from the cell. Therefore, combining organelle-damaging drugs with an www.landesbioscience.com
te .
ib u
st r
di
no t
o
.D
Should We Switch Autophagy On or Off in Order to Combat Cancer?
autophagy inhibitor might be an effective way of inducing cell death. For example, cancer cell death induced by the lysosome-damaging drug siramesine (a sigma-2 receptor agonist presently under preclinical development as an anti-cancer drug) is increased when autophagy is blocked either by removal of Atg proteins or treatment with microtubule destabilizing drugs.13,73 In line with this, ER stress induced by thapsigargin and tunicamycin, triggers a cell death in cancer cells that is increased when autophagy is inhibited.28,74 Moreover, autophagyblock sensitizes breast cancer cells toward camptothecin induced mitochondrial damage and cell death.75 The present list of clinically relevant drugs with proven autophagy inhibitory capacity is as yet very short and limited to compounds that affect the lysosomal compartment (Table 1). Importantly, emerging data from animal tumor models encourage clinical trials combining such inhibitors with other anti-cancer drugs. The inhibition of lysosomal function (and thereby autophagy) in murine cancer models has shown additive or synergistic effects in following combination treatments; a proton pump inhibitor omeprazole and cisplatin,76 choloriquine (currently used as an anti-malaria drug) and p53 activation or alkylating agents,77 as well as vincristine and siramesine.73 One major concern for administration of autophagy inhibitors in patients is that they might act as promoters of tumor development.7,17,18,48 However, if the tumor-promoting effect of autophagy inhibition relies on the necrotic cell lysis and the following inflammatory response as discussed above, co-treatment with an immunosuppressive drug could prevent this undesirable effect. Autophagy inducers in cancer treatment. Several chemo-therapeutic agents (alkylating agents, actinomycin D and arsenic trioxide), hormonal therapies (tamoxifen and vitamin D analogues), natural compounds (resveratrol), cytokines (IFNγ), gene therapies (p53 and p27Kip1), radiation and photodynamic therapy have been shown to trigger autophagic cell death in various cancer cells in vitro, whereas the contribution of autophagy to their anti-tumor effects in vivo still waits experimental evidence.29,32,40,59,78-85 Most of the cellular systems where autophagy has been proven to contribute to cell death are defect in the apoptosis signaling pathways.26,27,31,33,35,36,59 Thus, autophagy appears to serve as a death program primarily when the apoptotic machinery is defect, as is the case in most tumors. Therefore, even though autophagy most likely serves as a pro-survival response in normal cell homeostasis, it might be able to signal cell death in tumor cells. If this hypothesis is correct, drugs that specifically trigger autophagic cell death should be well-tolerated due to highly specific killing of cancer cells. Moreover, autophagic cell death is a tempting way to circumvent apoptosis-resistance. What could be the problems in inducing autophagy in cancer patients? Autophagy-inducing drugs may protect tumors against cell death triggered by nutrient-deprivation in the tumor environment or by other simultaneous anti-cancer therapies. For instance, radiation-induced apoptosis is inhibited by rapamycin-triggered autophagy,86 and the non-apoptotic lysosomal cell death pathway induced by siramesine is enhanced by depletion of Beclin1.13,87 On the other hand, increased sensitivity to autophagic cell death may also be obtained by combining two therapies that trigger autophagy by differerent means. For example vitamin D analogue EB1089 potentiates the response of breast cancer cells to radiation.88 Thus, great care should be taken in designing combination therapies when autophagy-inducing drugs are included in the cocktail. The frequent
en ce
activity may paradoxically be a decrease in autophagosome turnover and subsequent reduction in the autophagic capacity. However, there is still no evidence in literature that tumors are blocked at the fusion step between autophagosomes and lysosomes. On the other hand, the cancer-associated upregulation of Rab geranylgeranyltransferases (RabGGTs) may enhance the autophagosome—lysosome fusion by activating members of the Rab family of small GTPases that stimulate membrane fusion events.68-70 Finally, the sustained activation of the ERK pathway by the MEK1 oncoprotein alters autophagy selectively by inhibiting the maturation of autolysosomes.71 It is still speculative what the final outcome of all these lysosomal changes is on the overall autophagic process in cancers. Since the lysosomal changes influence the half-live of autophagosomes, measuring the autophagic flux rather than the steady state level of autophagosomes will be needed to address this issue appropriately. Similarly, the combined effect of cancer-associated changes in autophagic stimuli, signaling, regulation, fusion and degradation on the autophagic process waits proper experimental testing. So far, the measurement of constitutive autophagic flow has only been assessed in liver cancer cells isolated from rats, which show reduced autophagic protein degradation.56,72 In vitro analysis fails, however, to take into the account the effect of tumor environment, which is likely to activate autophagy as discussed above.
Autophagy
577
Autophagy—An emerging target for cancer therapy
Clinically relevant compounds that modulate autophagy
La
nd
es
B
io s
ci
en ce
.D
o
no t
di
st r
ib u
te .
Table 1
© 20
08
mutations in genes that regulate the autophagic pathway may cause another therapeutical problem, i.e., reduced sensitivity toward autophagic cell death. In line with this, restoring beclin 1 level in human breast cancer cells heterozygous for beclin 1 gene increases EB1089-induced autophagic cell death.59 Adding drugs that upregulate Beclin 1 or other Atg proteins (e.g., ROS generating agents89) to the treatment may help to circumvent this problem.
Conclusions/Perspectives As discussed above, our knowledge on the molecular control of autophagy has increased enormously during the last decade. Yet, several major questions concerning the consequences of autophagy modulation in vivo remain to be answered, and it is still speculative 578
whether autophagy is a suitable target for cancer treatment. In order to assess this question, better autophagy detection methods and specific modulators suitable for in vivo use are urgently needed. It should be noted that all the autophagy modulators available today control also other important processes in the cell (for examples see Table 1). Therefore, a major task is to develop modulators that specifically target the autophagy core machinery. Putative drug targets include kinases (e.g., class III PI3K), proteases (e.g., Atg4B and C) and E1 or E2-like enzymes (Atg7 and Atg10) that are involved in the autophagosome formation and phosphatases (e.g., myotubularin) that inhibit it.90 Due to a high degree of redundancy in the mammalian autophagic machinery, a combination of specific inhibitors might, however, be required for an efficient autophagy block. In the
Autophagy
2008; Vol. 4 Issue 5
Autophagy—An emerging target for cancer therapy
te .
ib u
st r
di
References
© 20
08
La
nd
es
B
io s
ci
en ce
1. Levine B, Klionsky DJ. Development by self-digestion: molecular mechanisms and biological functions of autophagy. Dev Cell 2004; 6:463-77. 2. Høyer-Hansen M, Jaattela M. AMP-activated protein kinase: a universal regulator of autophagy? Autophagy 2007; 3:381-3. 3. Meijer AJ, Codogno P. Signalling and autophagy regulation in health, aging and disease. Mol Aspects Med 2006; 27:411-25. 4. Ohsumi Y. Molecular dissection of autophagy: two ubiquitin-like systems. Nat Rev Mol Cell Biol 2001; 2:211-6. 5. Tsukada M, Ohsumi Y. Isolation and characterization of autophagy-defective mutants of Saccharomyces cerevisiae. FEBS Lett 1993; 333:169-74. 6. Boya P, Gonzalez-Polo RA, Casares N, Perfettini JL, Dessen P, Larochette N, Metivier D, Meley D, Souquere S, Yoshimori T, Pierron G, Codogno P, Kroemer G. Inhibition of macroautophagy triggers apoptosis. Mol Cell Biol 2005; 25:1025-40. 7. Degenhardt K, Mathew R, Beaudoin B, Bray K, Anderson D, Chen G, Mukherjee C, Shi Y, Gelinas C, Fan Y, Nelson DA, Jin S, White E. Autophagy promotes tumor cell survival and restricts necrosis, inflammation, and tumorigenesis. Cancer Cell 2006; 10:51-64. 8. Lum JJ, Bauer DE, Kong M, Harris MH, Li C, Lindsten T, Thompson CB. Growth factor regulation of autophagy and cell survival in the absence of apoptosis. Cell 2005; 120:23748. 9. Rodriguez-Enriquez S, He L, Lemasters JJ. Role of mitochondrial permeability transition pores in mitochondrial autophagy. Int J Biochem Cell Biol 2004; 36:2463-72. 10. Bernales S, McDonald KL, Walter P. Autophagy counterbalances endoplasmic reticulum expansion during the unfolded protein response. PLoS Biol 2006; 4:423. 11. Ravikumar B, Duden R, Rubinsztein DC. Aggregate-prone proteins with polyglutamine and polyalanine expansions are degraded by autophagy. Hum Mol Genet 2002; 11:110717. 12. Iwata J, Ezaki J, Komatsu M, Yokota S, Ueno T, Tanida I, Chiba T, Tanaka K, Kominami E. Excess peroxisomes are degraded by autophagic machinery in mammals. J Biol Chem 2006; 281:4035-41. 13. Ostenfeld MS, Høyer-Hansen M, Bastholm L, Fehrenbacher N, Olsen OD, Groth-Pedersen L, Puustinen P, Kirkegaard Sorensen T, Nylandsted J, Farkas T, Jaattela M. Anti-cancer agent siramesine is a lysosomotropic detergent that induces cytoprotective autophagosome accumulation. Autophagy 2008; 4. 14. Høyer-Hansen M, Jaattela M. Connecting endoplasmic reticulum stress to autophagy by unfolded protein response and calcium. Cell Death Differ 2007; 14:1576-82. 15. Kuma A, Hatano M, Matsui M, Yamamoto A, Nakaya H, Yoshimori T, Ohsumi Y, Tokuhisa T and Mizushima N. The role of autophagy during the early neonatal starvation period. Nature 2004; 432:1032-6. 16. Komatsu M, Waguri S, Ueno T, Iwata J, Murata S, Tanida I, Ezaki J, Mizushima N, Ohsumi Y, Uchiyama Y, Kominami E, Tanaka K, Chiba T. Impairment of starvation-induced and constitutive autophagy in Atg7-deficient mice. J Cell Biol 2005; 169:425-34. 17. Yue Z, Jin S, Yang C, Levine AJ, Heintz N. Beclin 1, an autophagy gene essential for early embryonic development, is a haploinsufficient tumor suppressor. Proc Natl Acad Sci USA 2003; 100:15077-82. 18. Qu X, Yu J, Bhagat G, Furuya N, Hibshoosh H, Troxel A, Rosen J, Eskelinen EL, Mizushima N, Ohsumi Y, Cattoretti G, Levine B. Promotion of tumorigenesis by heterozygous disruption of the beclin 1 autophagy gene. J Clin Invest 2003; 112:1809-20. 19. Kirkegaard K, Taylor MP, Jackson WT. Cellular autophagy: surrender, avoidance and subversion by microorganisms. Nat Rev Microbiol 2004; 2:301-14. 20. Kouroku Y, Fujita E, Tanida I, Ueno T, Isoai A, Kumagai H, Ogawa S, Kaufman RJ, Kominami E, Momoi T. ER stress (PERK/eIF2alpha phosphorylation) mediates the polyglutamine-induced LC3 conversion, an essential step for autophagy formation. Cell Death Differ 2006. 21. Ravikumar B, Vacher C, Berger Z, Davies JE, Luo S, Oroz LG, Scaravilli F, Easton DF, Duden R, O’Kane CJ, Rubinsztein DC. Inhibition of mTOR induces autophagy and reduces toxicity of polyglutamine expansions in fly and mouse models of Huntington disease. Nat Genet 2004; 36:585-95. 22. Schweichel JU, Merker HJ. The morphology of various types of cell death in prenatal tissues. Teratology 1973; 7:253-66. 23. Clarke PG. Developmental cell death: morphological diversity and multiple mechanisms. Anat Embryol (Berl) 1990; 181:195-213.
no t
The authors’ own work is supported by grants from the Danish Cancer Society, the Danish Medical Research Council, the Danish National Research Foundation, and the Novo Nordisk Foundation.
o
Acknowledgements
24. Kroemer G, El-Deiry WS, Golstein P, Peter ME, Vaux D, Vandenabeele P, Zhivotovsky B, Blagosklonny MV, Malorni W, Knight RA, Piacentini M, Nagata S, Melino G. Classification of cell death: recommendations of the Nomenclature Committee on Cell Death. Cell Death Differ 2005; 12:1463-7. 25. Tolkovsky AM, Xue L, Fletcher GC, Borutaite V. Mitochondrial disappearance from cells: a clue to the role of autophagy in programmed cell death and disease? Biochimie 2002; 84:233-40. 26. Yu L, Alva A, Su H, Dutt P, Freundt E, Welsh S, Baehrecke EH, Lenardo MJ. Regulation of an ATG7-beclin 1 Program of Autophagic Cell Death by Caspase-8. Science 2004; 304:1500-2. 27. Li C, Capan E, Zhao Y, Zhao J, Stolz D, Watkins SC, Jin S, Lu B. Autophagy is induced in CD4+ T cells and important for the growth factor-withdrawal cell death. J Immunol 2006; 177:5163-8. 28. Ding WX, Ni HM, Gao W, Hou YF, Melan MA, Chen X, Stolz DB, Shao ZM, Yin XM. Differential effects of endoplasmic reticulum stress-induced autophagy on cell survival. J Biol Chem 2006. 29. Crighton D, Wilkinson S, O’Prey J, Syed N, Smith P, Harrison PR, Gasco M, Garrone O, Crook T, Ryan KM. DRAM, a p53-induced modulator of autophagy, is critical for apoptosis. Cell 2006; 126:121-34. 30. Reef S, Zalckvar E, Shifman O, Bialik S, Sabanay H, Oren M, Kimchi A. A short mitochondrial form of p19ARF induces autophagy and caspase-independent cell death. Mol Cell 2006; 22:463-75. 31. Shimizu S, Kanaseki T, Mizushima N, Mizuta T, Arakawa-Kobayashi S, Thompson CB, Tsujimoto Y. Role of Bcl-2 family proteins in a non-apoptotic programmed cell death dependent on autophagy genes. Nat Cell Biol 2004; 6:1221-8. 32. Pyo JO, Jang MH, Kwon YK, Lee HJ, Jun JI, Woo HN, Cho DH, Choi B, Lee H, Kim JH, Mizushima N, Oshumi Y, Jung YK. Essential roles of Atg5 and FADD in autophagic cell death: dissection of autophagic cell death into vacuole formation and cell death. J Biol Chem 2005; 280:20722-9. 33. Xu Y, Kim SO, Li Y, Han J. Autophagy contributes to caspase-independent macrophage cell death. J Biol Chem 2006; 281:19179-87. 34. Djavaheri Mergny M, Amelotti M, Mathieu J, Besancon F, Bauvy C, Souquere S, Pierron G, Codogno P. NF{kappa}B Activation Represses Tumor Necrosis Factor-{alpha}-induced Autophagy. J Biol Chem 2006; 281:30373-82. 35. Kim KW, Mutter RW, Cao C, Albert JM, Freeman M, Hallahan DE, Lu B. Autophagy for cancer therapy through inhibition of proapoptotic proteins and mTOR signaling. J Biol Chem 2006; 281:36883-90. 36. Yu L, Wan F, Dutta S, Welsh S, Liu Z, Freundt E, Baehrecke EH, Lenardo M. Autophagic programmed cell death by selective catalase degradation. Proc Natl Acad Sci USA 2006; 103:4952-7. 37. Lam D, Kosta A, Luciani MF, Golstein P. The IP3 Receptor Is Required to Signal Autophagic Cell Death. Mol Biol Cell 2007. 38. Berry DL, Baehrecke EH. Growth arrest and autophagy are required for salivary gland cell degradation in Drosophila. Cell 2007; 131:1137-48. 39. Xue L, Fletcher GC, Tolkovsky AM. Mitochondria are selectively eliminated from eukaryotic cells after blockade of caspases during apoptosis. Curr Biol 2001; 11:361-5. 40. Trincheri NF, Follo C, Nicotra G, Peracchio C, Castino R, Isidoro C. Resveratrol-induced Apoptosis Depends on the Lipid Kinase Activity of Vps34 and on the Formation of Autophagolysosomes. Carcinogenesis 2007. 41. Kroemer G, Jaattela M. Lysosomes and autophagy in cell death control. Nat Rev Cancer 2005; 5:886-97. 42. Foghsgaard L, Wissing D, Mauch D, Lademann U, Bastholm L, Boes M, Elling F, Leist M, Jaattela M. Cathepsin B acts as a dominant execution protease in tumor cell apoptosis induced by tumor necrosis factor. J Cell Biol 2001; 153:999-1010. 43. Martelli AM, Tazzari PL, Evangelisti C, Chiarini F, Blalock WL, Billi AM, Manzoli L, McCubrey JA, Cocco L. Targeting the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin module for acute myelogenous leukemia therapy: from bench to bedside. Curr Med Chem 2007; 14:2009-23. 44. Mathew R, Karantza Wadsworth V, White E. Role of autophagy in cancer. Nat Rev Cancer 2007; 7:961-7. 45. Gozuacik D, Kimchi A. Autophagy as a cell death and tumor suppressor mechanism. Oncogene 2004; 23:2891-906. 46. Scriven P, Brown NJ, Pockley AG, Wyld L. The unfolded protein response and cancer: a brighter future unfolding? J Mol Med 2007; 85:331-41. 47. Moreno Sanchez R, Rodriguez Enriquez S, Marin Hernandez A, Saavedra E. Energy metabolism in tumor cells. Febs J 2007; 274:1393-418. 48. Karantza Wadsworth V, Patel S, Kravchuk O, Chen G, Mathew R, Jin S, White E. Autophagy mitigates metabolic stress and genome damage in mammary tumorigenesis. Genes Dev 2007; 21:1621-35. 49. Mathew R, Kongara S, Beaudoin B, Karp CM, Bray K, Degenhardt K, Chen G, Jin S, White E. Autophagy suppresses tumor progression by limiting chromosomal instability. Genes Dev 2007; 21:1367-81. 50. Marino G, Salvador Montoliu N, Fueyo A, Knecht E, Mizushima N, Lopez Otin C. Tissue-specific autophagy alterations and increased tumorigenesis in mice deficient in Atg4C/autophagin-3. J Biol Chem 2007; 282:18573-83.
.D
meanwhile, the existing less-specific autophagy activators (rapamycin analogues) and inhibitors (chloroquine and omeprazole) that are reasonably well-tolerated may enlighten the efficacy of autophagy modulation in cancer therapy.
www.landesbioscience.com
Autophagy
579
Autophagy—An emerging target for cancer therapy
.D
o
no t
di
st r
ib u
te .
77. Amaravadi RK, Yu D, Lum JJ, Bui T, Christophorou MA, Evan GI, Thomas-Tikhonenko A, Thompson CB. Autophagy inhibition enhances therapy-induced apoptosis in a Mycinduced model of lymphoma. J Clin Invest 2007; 117:326-36. 78. Bursch W, Ellinger A, Kienzl H, Torok L, Pandey S, Sikorska M, Walker R, Hermann RS. Active cell death induced by the anti-estrogens tamoxifen and ICI 164 384 in human mammary carcinoma cells (MCF-7) in culture: the role of autophagy. Carcinogenesis 1996; 17:1595-607. 79. Kanzawa T, Kondo Y, Ito H, Kondo S, Germano I. Induction of autophagic cell death in malignant glioma cells by arsenic trioxide. Cancer Res 2003; 63:2103-8. 80. Kanzawa T, Germano IM, Komata T, Ito H, Kondo Y, Kondo S. Role of autophagy in temozolomide-induced cytotoxicity for malignant glioma cells. Cell Death Differ 2004; 11:448-57. 81. Buytaert E, Callewaert G, Hendrickx N, Scorrano L, Hartmann D, Missiaen L, Vandenheede JR, Heirman I, Grooten J, Agostinis P. Role of endoplasmic reticulum depletion and multidomain proapoptotic BAX and BAK proteins in shaping cell death after hypericin-mediated photodynamic therapy. Faseb J 2006; 20:756-8. 82. Tavera Mendoza L, Wang TT, Lallemant B, Zhang R, Nagai Y, Bourdeau V, Ramirez Calderon M, Desbarats J, Mader S, White JH. Convergence of vitamin D and retinoic acid signalling at a common hormone response element. EMBO Rep 2006; 7:180-5. 83. Komata T, Kanzawa T, Takeuchi H, Germano IM, Schreiber M, Kondo Y, Kondo S. Antitumour effect of cyclin-dependent kinase inhibitors (p16(INK4A), p18(INK4C), p19(INK4D), p21(WAF1/CIP1) and p27(KIP1)) on malignant glioma cells. Br J Cancer 2003; 88:1277-80. 84. Kanzawa T, Zhang L, Xiao L, Germano IM, Kondo Y, Kondo S. Arsenic trioxide induces autophagic cell death in malignant glioma cells by upregulation of mitochondrial cell death protein BNIP3. Oncogene 2005; 24:980-91. 85. Opipari AW, Jr., Tan L, Boitano AE, Sorenson DR, Aurora A, Liu JR. Resveratrol-induced autophagocytosis in ovarian cancer cells. Cancer Res 2004; 64:696-703. 86. Ravikumar B, Berger Z, Vacher C, O’Kane CJ, Rubinsztein DC. Rapamycin pre-treatment protects against apoptosis. Hum Mol Genet 2006; 15:1209-16. 87. Ostenfeld MS, Fehrenbacher N, Høyer-Hansen M, Thomsen C, Farkas T, Jaattela M. Effective tumor cell death by sigma-2 receptor ligand siramesine involves lysosomal leakage and oxidative stress. Cancer Res 2005; 65:8975-83. 88. Demasters G, Di X, Newsham I, Shiu R, Gewirtz DA. Potentiation of radiation sensitivity in breast tumor cells by the vitamin D3 analogue, EB 1089, through promotion of autophagy and interference with proliferative recovery. Mol Cancer Ther 2006; 5:2786-97. 89. Chen Y, McMillan Ward E, Kong J, Israels SJ, Gibson SB. Oxidative stress induces autophagic cell death independent of apoptosis in transformed and cancer cells. Cell Death Differ 2008; 15:171-82. 90. Walker DM, Urbe S, Dove SK, Tenza D, Raposo G, Clague MJ. Characterization of MTMR3. an inositol lipid 3-phosphatase with novel substrate specificity. Curr Biol 2001; 11:1600-5. 91. Shao Y, Gao Z, Marks PA, Jiang X. Apoptotic and autophagic cell death induced by histone deacetylase inhibitors. Proc Natl Acad Sci USA 2004; 101:18030-5. 92. Paglin S, Hollister T, Delohery T, Hackett N, McMahill M, Sphicas E, Domingo D, Yahalom J. A novel response of cancer cells to radiation involves autophagy and formation of acidic vesicles. Cancer Res 2001; 61:439-44. 93. Nguyen TM, Subramanian IV, Kelekar A, Ramakrishnan S. Kringle 5 of human plasminogen, an angiogenesis inhibitor, induces both autophagy and apoptotic death in endothelial cells. Blood 2007; 109:4793-802. 94. Ertmer A, Huber V, Gilch S, Yoshimori T, Erfle V, Duyster J, Elsasser HP, Schatzl HM. The anticancer drug imatinib induces cellular autophagy. Leukemia 2007; 21:936-42. 95. Fujiwara K, Iwado E, Mills GB, Sawaya R, Kondo S, Kondo Y. Akt inhibitor shows anticancer and radiosensitizing effects in malignant glioma cells by inducing autophagy. Int J Oncol 2007; 31:753-60. 96. Gills JJ, Lopiccolo J, Tsurutani J, Shoemaker RH, Best CJ, Abu Asab MS, Borojerdi J, Warfel NA, Gardner ER, Danish M, Hollander MC, Kawabata S, Tsokos M, Figg WD, Steeg PS, Dennis PA. Nelfinavir, A lead HIV protease inhibitor, is a broad-spectrum, anticancer agent that induces endoplasmic reticulum stress, autophagy, and apoptosis in vitro and in vivo. Clin Cancer Res 2007; 13:5183-94. 97. Noda T, Ohsumi Y. Tor, a phosphatidylinositol kinase homologue, controls autophagy in yeast. J Biol Chem 1998; 273:3963-6.
© 20
08
La
nd
es
B
io s
ci
en ce
51. Høyer-Hansen M, Bastholm L, Szyniarowski P, Campanella M, Szabadkai G, Farkas T, Bianchi K, Fehrenbacher N, Elling F, Rizzuto R, Mathiasen IS, Jaattela M. Control of macroautophagy by calcium, calmodulin-dependent kinase kinase-beta, and Bcl-2. Mol Cell 2007; 25:193-205. 52. Pattingre S, Tassa A, Qu X, Garuti R, Liang XH, Mizushima N, Packer M, Schneider MD, Levine B. Bcl-2 antiapoptotic proteins inhibit beclin 1-dependent autophagy. Cell 2005; 122:927-39. 53. Liang J, Shao SH, Xu ZX, Hennessy B, Ding Z, Larrea M, Kondo S, Dumont DJ, Gutterman JU, Walker CL, Slingerland JM, Mills GB. The energy sensing LKB1-AMPK pathway regulates p27(kip1) phosphorylation mediating the decision to enter autophagy or apoptosis. Nat Cell Biol 2007; 9:218-24. 54. Feng Z, Zhang H, Levine AJ, Jin S. The coordinate regulation of the p53 and mTOR pathways in cells. Proc Natl Acad Sci USA 2005; 102:8204-9. 55. Liang C, Feng P, Ku B, Dotan I, Canaani D, Oh BH, Jung JU. Autophagic and tumour suppressor activity of a novel Beclin1-binding protein UVRAG. Nat Cell Biol 2006; 8:688-99. 56. Schwarze PE, Seglen PO. Reduced autophagic activity, improved protein balance and enhanced in vitro survival of hepatocytes isolated from carcinogen-treated rats. Exp Cell Res 1985; 157:15-28. 57. Alva AS, Gultekin SH, Baehrecke EH. Autophagy in human tumors: cell survival or death? Cell Death Differ 2004; 11:1046-8. 58. Aita VM, Liang XH, Murty VV, Pincus DL, Yu W, Cayanis E, Kalachikov S, Gilliam TC, Levine B. Cloning and genomic organization of beclin 1, a candidate tumor suppressor gene on chromosome 17q21. Genomics 1999; 59:59-65. 59. Høyer-Hansen M, Bastholm L, Mathiasen IS, Elling F, Jaattela M. Vitamin D analog EB1089 triggers dramatic lysosomal changes and Beclin 1-mediated autophagic cell death. Cell Death Differ 2005; 12:1297-309. 60. Yousefi S, Perozzo R, Schmid I, Ziemiecki A, Schaffner T, Scapozza L, Brunner T, Simon HU. Calpain-mediated cleavage of Atg5 switches autophagy to apoptosis. Nat Cell Biol 2006; 8:1124-32. 61. Karin M, Greten FR. NFkappaB: linking inflammation and immunity to cancer development and progression. Nat Rev Immunol 2005; 5:749-59. 62. Liang XH, Jackson S, Seaman M, Brown K, Kempkes B, Hibshoosh H, Levine B. Induction of autophagy and inhibition of tumorigenesis by beclin 1. Nature 1999; 402:672-6. 63. Marx J. Autophagy: is it cancer’s friend or foe? Science 2006; 312:1160-1. 64. Sloane BF, Yan S, Podgorski I, Linebaugh BE, Cher ML, Mai J, Cavallo-Medved D, Sameni M, Dosescu J, Moin K. Cathepsin B and tumor proteolysis: contribution of the tumor microenvironment. Semin Cancer Biol 2005; 15:149-57. 65. Gocheva V, Joyce JA. Cysteine cathepsins and the cutting edge of cancer invasion. Cell Cycle 2007; 6:60-4. 66. Fehrenbacher N, Gyrd-Hansen M, Poulsen B, Felbor U, Kallunki T, Boes M, Weber E, Leist M, Jaattela M. Sensitization to the lysosomal cell death pathway upon immortalization and transformation. Cancer Res 2004; 64:5301-10. 67. Eskelinen EL, Schmidt CK, Neu S, Willenborg M, Fuertes G, Salvador N, Tanaka Y, Lullmann Rauch R, Hartmann D, Heeren J, von Figura K, Knecht E, Saftig P. Disturbed cholesterol traffic but normal proteolytic function in LAMP-1/LAMP-2 double-deficient fibroblasts. Mol Biol Cell 2004; 15:3132-45. 68. Jager S, Bucci C, Tanida I, Ueno T, Kominami E, Saftig P, Eskelinen EL. Role for Rab7 in maturation of late autophagic vacuoles. J Cell Sci 2004; 117:4837-48. 69. Munafo DB, Colombo MI. Induction of autophagy causes dramatic changes in the subcellular distribution of GFP-Rab24. Traffic 2002; 3:472-82. 70. Lackner MR, Kindt RM, Carroll PM, Brown K, Cancilla MR, Chen C, de Silva H, Franke Y, Guan B, Heuer T, Hung T, Keegan K, Lee JM, Manne V, O’Brien C, Parry D, Perez Villar JJ, Reddy RK, Xiao H, Zhan H, Cockett M, Plowman G, Fitzgerald K, Costa M, RossMacdonald P. Chemical genetics identifies Rab geranylgeranyl transferase as an apoptotic target of farnesyl transferase inhibitors. Cancer Cell 2005; 7:325-36. 71. Corcelle E, Nebout M, Bekri S, Gauthier N, Hofman P, Poujeol P, Fenichel P, Mograbi B. Disruption of autophagy at the maturation step by the carcinogen lindane is associated with the sustained mitogen-activated protein kinase/extracellular signal-regulated kinase activity. Cancer Res 2006; 66:6861-70. 72. Kisen GO, Tessitore L, Costelli P, Gordon PB, Schwarze PE, Baccino FM, Seglen PO. Reduced autophagic activity in primary rat hepatocellular carcinoma and ascites hepatoma cells. Carcinogenesis 1993; 14:2501-5. 73. Groth Pedersen L, Ostenfeld MS, Høyer-Hansen M, Nylandsted J, Jaattela M. Vincristine induces dramatic lysosomal changes and sensitizes cancer cells to lysosome-destabilizing siramesine. Cancer Res 2007; 67:2217-25. 74. Ogata M, Hino SI, Saito A, Morikawa K, Kondo S, Kanemoto S, Murakami T, Taniguchi M, Tanii I, Yoshinaga K, Shiosaka S, Hammarback JA, Urano F, Imaizumi K. Autophagy is activated for cell survival after ER stress. Mol Cell Biol 2006; 26:9220-31. 75. Abedin MJ, Wang D, McDonnell MA, Lehmann U, Kelekar A. Autophagy delays apoptotic death in breast cancer cells following DNA damage. Cell Death Differ 2007; 14:500-10. 76. Luciani F, Spada M, De Milito A, Molinari A, Rivoltini L, Montinaro A, Marra M, Lugini L, Logozzi M, Lozupone F, Federici C, Iessi E, Parmiani G, Arancia G, Belardelli F, Fais S. Effect of proton pump inhibitor pretreatment on resistance of solid tumors to cytotoxic drugs. J Natl Cancer Inst 2004; 96:1702-13.
580
Autophagy
2008; Vol. 4 Issue 5
