Influence of the interaction between long noncoding RNAs and ...

Tumor Biol. (2016) 37:1379–1385 DOI 10.1007/s13277-015-4457-0

REVIEW

Influence of the interaction between long noncoding RNAs and hypoxia on tumorigenesis Jun Dong 1 & Jiangbing Xu 1 & Xiang Wang 1 & Bilian Jin 1

Received: 4 August 2015 / Accepted: 17 November 2015 / Published online: 25 November 2015 # International Society of Oncology and BioMarkers (ISOBM) 2015

Abstract The interaction between cancer and its microenvironment is crucial for survival and development of cancerous cells. Tumor microenvironment is usually under hypoxia, which promotes tumor aggressiveness like growth, angiogenesis, and metastasis. How cancer cells respond to hypoxia and the resultant impact on tumorigenesis are not yet fully explored. Long noncoding RNAs (lncRNAs) have been attracting more and more attention since their functions in regulating gene expression at chromatic, transcriptional, and posttranscriptional levels were found. lncRNAs are dysregulated in cancer and act as oncogenes or tumor suppressors. Moreover, emerging evidence has been provided that the expression of lncRNAs changes with the stimulus of hypoxia and they in turn produce a significant influence on the hypoxia-inducible factor (HIF), the most common transcription regulator in response to hypoxia. In this review, we discuss the recent findings of hypoxia-responsive lncRNAs and summarize their interaction with hypoxia to further understand their roles in cancer growth, metabolism, angiogenesis, and metastasis and their potential for cancer diagnosis and treatment. Keywords Hypoxia . Long noncoding RNA . Hypoxia-inducible factor . Interaction . Tumorigenesis . Biomarker

* Xiang Wang [email protected] * Bilian Jin [email protected]; [email protected] 1

Institute of Cancer Stem Cell, Dalian Medical University, Dalian 116044, Liaoning, China

Introduction Cancer consists of all kinds of interacting cells, some of which are cancerous cells or not, possessing different functions for cancer initiation and progression [1]. As a result, the interacting cells make up a strong microenvironment that, in return, promote survival and development of these cells [2]. Tumor microenvironment is usually under hypoxia, because of aberrant new-generating blood vessels and poor blood flow [3]. Being the most common and significant environmental factor, hypoxia facilitates cancer formation and progression through multiple signaling pathways, especially the hypoxiainducible factor (HIF) pathway [3]. At the same time, cancer cells have to adapt to the hypoxic environment to sustain their growth advantage. Specifically, cancer metabolism shifts from tricarboxylic acid cycle (TCA cycle) to glycolysis. It leads to a significant change of the tumor microenvironment like the pH concentration, promoting invasion of primary tumors into their surrounding tissues [4]. However, more comprehensive mechanisms of cancer cells interacting with hypoxic microenvironment are required to be discovered. Long noncoding RNAs (lncRNAs) are a new class of RNA transcripts larger than 200 bp in length, which include antisense RNAs, transcribed ultraconserved regions (T-UCR), intergenic lncRNAs, and noncoding pseudogenes, lacking the ability to translate protein [5]. Increased evidence has demonstrated that lncRNAs play pivotal roles in regulating gene expression at several levels, including the chromatin (the X chromosome silencing, genomic imprinting, and chromatin modification) [6]; transcription (transcription activation or inactivation) [7]; and post-transcription (splicing, messenger RNA (mRNA) turnover, translation, and RNA interference) [8], being closely linked with the initiation and progression of human diseases particularly cancer [9]. More recently, lncRNAs in response to hypoxia have been identified to

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regulate tumor biological behavior-like growth and metastasis [10, 11]. However, the mechanisms of how lncRNAs interact with hypoxia in cancer are still in demand to be further elucidated. In this review, we will summarize the latest findings about the interaction between lncRNAs and hypoxia to better understand the role of hypoxia-responsive lncRNAs in cancer initiation and progression, providing implications for cancer diagnosis and therapy.

LncRNAs interacting with hypoxia The role of hypoxia in regulating lncRNA expression Emerging studies have showed that lncRNAs in cancer are dysregulated in response to hypoxia (Table 1). Of these lncRNAs, H19, linc-ROR, lincRNA-p21, and NEAT1 are upregulated whereas lncRNA-LET and ENST00000480739 are downregulated. In hypoxic conditions, the HIF complex is a crucial transcription factor comprising an O2-responsive α subunit HIF-1α or HIF-2α and a stable β subunit HIF-1β. Based on their relevance to the HIF complex, the hypoxiaresponsive lncRNAs can be classified as HIF-dependent and HIF-independent. Till now, only sONE, an antisense transcript to endothelial nitric-oxide synthase (eNOS) mRNA induced by hypoxia, is found to be HIF-independent [12], but no studies have determined the involvement of sONE in tumorigenesis. Therefore, our discussion is focused on HIF-dependent lncRNAs, which can be further categorized into HIF directly regulating lncRNAs and HIF indirectly regulating lncRNAs. Analogous to protein-coding genes and microRNAs (miRNAs), HIF directly regulating lncRNAs can be transcriptionally regulated through hypoxia response elements (HREs) usually located in their promoter regions [13]. Many hypoxiaresponsive lncRNAs have been demonstrated to contain HREs by both bioinformatical analysis and experiments like electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP). As an example, lncRNA-UCA1 is predicted to have two putative HREs for HIF-1α in its promoter region by using the bioinformatical software MatInspector and subsequently, the putative HREs were validated by EMSA and ChIP [10]. Similarly, the EFNA3 promoter is bound significantly by HIF, resulting in high expression of EFNA3 lncRNAs [14]. The most recent study showed that HIF-1α also specifically targeted HOTAIR promoter by binding with putative HREs to promote HOTAIR transcription in lung cancer [15]. In addition to HIF-1α, Dr. Mole’s group revealed that HIF-2α also bound with lncRNA promoters even in a higher proportion than HIF-1α by analyzing the ChIP-seq data in human MCF-7 breast cancer cells [16]. Afterwards, the loss of function assays proved that HIF-2α was a main regulator of NEAT1, one of the most highly upregulated lncRNAs in

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MCF-7 [17]. Taken together, these studies provide evidence that the hypoxia-responsive lncRNAs can be directly regulated by HIF-1α and/or HIF-2α in different types of cancers. The present data also disclose that lncRNAs may be indirectly influenced by HIF, probably through epigenetic mechanisms. As a powerful transcription factor, the HIF complex activates expression of multiple genes, some of which are involved in epigenetic modifications. For instance, HDAC3, one of the HIF-1α-regulating gene [18], represses the lncRNA-LET expression by reducing histone H3 and H4 acetylation levels in the lncRNA-LET promoter region [19], indicating that the expression of lncRNA-LET is indirectly affected by HIF-1α. Similarly, WT1 lncRNA is activated by HIF through upregulating DNA demethylating enzymes TET2 and TET3 in myeloid leukemia cells [20]. These studies together suggest that epigenetic mechanisms may take an important part in the expression of HIF indirectly regulating lncRNAs. The role of lncRNAs in regulating HIF expression LncRNAs have a crucial role in regulating gene expression through different mechanisms such as guide, scaffold, decoy, and sponge [21]. It has been documented that antisense lncRNAs are pervasive in mammalian cells [22] and can inhibit their opposite sense genes [23]. Recent studies have demonstrated that the HIF gene can be modulated by its corresponding antisense lncRNAs. Bertozzi et al. found two antisense transcripts of HIF-1α, 5 aHIF-1α, and 3 aHIF-1α, were implicated in chromatin inactivation or mRNA degradation of the HIF-1α gene [24]. Another important machinery of lncRNAs regulating the HIF gene is that lncRNAs activate their nearby genes in cis. Wang et al. found that lncRNA HIF2PUT, transcribed from the upstream of the HIF-2α promoter, activated HIF-2α in osteosarcoma [25]. However, more lncRNAs are demonstrated to regulate HIF in an indirect way. A novel lncRNA ENST00000480739, which is usually in low expression in human pancreatic ductal adenocarcinoma (PDAC), can inhibit the expression of HIF1α by increasing the protein level of OS-9 [26] that destabilizes HIF-1α by promoting the interaction between HIF-1α and proline hydroxylase domain (PHD) proteins [27]. PHDs are capable of hydroxylating HIF-1α and thus promoting HIF1α degradation [28]. It has been reported that RERT-lncRNA suppresses the HIF-1α expression by activating PHD1 at the transcriptional level [29]. Intriguingly, lincRNA-p21 and lncRNA-LET regulate HIF reciprocally to form a positive feedback loop under hypoxia [30, 31]. In low-oxygen conditions, HIF-1α directly activates lincRNA-p21 at transcriptional level, while lincRNA-p21 stabilizes HIF-1α through disrupting the HIF-1α-VHL interaction [30]. In contrast, HIF-1α represses the lncRNA-LET expression, while

Tumor Biol. (2016) 37:1379–1385 Table 1

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The role of hypoxia-responsive lncRNAs in tumorigenesis

lncRNA

Function

Cancer type

Interaction with hypoxia

Cancer phenotype

References

lncRNA-UCA1

Oncogene

Bladder cancer

Upregulated by HIF-1α

[10]

EFNA3

Oncogene

Breast cancer

Upregulated by HIF

HOTAIR

Oncogene

NSCLC

Upregulated by HIF-1α

NEAT1 lncRNA-LET

Oncogene Tumor suppressor

Breast cancer HCC, CRC, LC

WT1 5 aHIF-1α, 3 aHIF-1α HIF2PUT

Oncogene Oncogene Oncogene

Myeloid leukemia Kidney cancer Osteosarcoma

Upregulated by HIF-1α and HIF-2α Downregulate HIF-1α reciprocally Regulated by HIF Upregulate HIF-1α Upregulate HIF-2α

Cell proliferation, apoptosis, migration, invasion Cell extravasation, dissemination, metastasis Cell proliferation, migration and invasion Cell proliferation, apoptosis Metastasis and invasion

[20] [24] [25]

ENST00000480739 RERT-lncRNA lincRNA-p21

Tumor suppressor Oncogene Oncogene

PDAC HCC Cervical cancer, LC

Downregulate HIF-1α Downregulate HIF Upregulate HIF-1 reciprocally

linc-ROR

Oncogene

HCC

uc.475 H19

Oncogene Oncogene or tumor suppressor Oncogene

Colon cancer HCC, bladder cancer

Upregulated by hypoxia, upregulate HIF-1 Upregulated by HIF-1 Upregulated by HIF-1

NA NA CSC proliferation, migration, self-renewal Invasion NA Cell glycolysis, apoptosis, tumorigenecity Cell viability, tumor growth

[35] [41, 42]

GC

Induced by hypoxia

Cell proliferation Cell proliferation, angiogenesis, metastasis Migration, invasion

AK058003

[14] [15] [17] [19, 31]

[26] [29] [30] [32]

[56]

NSCLC nonsmall cell lung carcinoma, HCC hepatocellular cancer, CRC colorectal cancer, LC lung cancer, NA no annotation, CSC cancer stem cell, PDAC pancreatic ductal adenocarcinoma, GC Gastric cancer

lncRNA-LET destabilizes the HIF-1α mRNA through degrading nuclear factor 90 [31]. A recent research found that linc-ROR was induced by hypoxia and in return, linc-ROR modulated HIF-1α expression by sponging endogenous microRNA-145 [32] that targeted P70S6K1, a critical regulator in protein synthesis [33]. It suggests that there may be a network of lncRNAs and microRNAs, also known as competing endogenous RNAs (ceRNAs), for regulating the expression of HIF-1α. So far, some lncRNA databases such as starBase and DIANA-LncBase have already been built up to predict the relationship between lncRNAs and miRNAs. It will be of much significance to dig out potential lncRNAs co-working with miRNAs in hypoxia from these databases. In summary, the key regulator of hypoxic response, HIF, can be significantly influenced by lncRNAs directly or indirectly. With the development of sequencing and labeling methodologies, we believe more HIF regulating lncRNAs will be revealed.

Functions of hypoxia-responsive lncRNAs in cancer In 2000, Hanahan and Weinberg proposed that cancer cells had six hallmarks including sustaining proliferative signaling, resisting cell death, enabling replicative immortality, evading growth suppressors, inducing angiogenesis, and activating invasion and metastasis [34]. Over decades of years, mounting

evidence has supported the notion that the biological behavior of cancer is determined by not only the cancer cells themselves but also their interactions with the microenvironment such as hypoxia. Although we know the critical role of hypoxia in cancer, there are still many unknown factors to be exploited. With the emergence of lncRNAs and deep understanding of their biological function, accumulating data indicate that hypoxia-responsive lncRNAs are involved in regulating tumor growth, angiogenesis, invasion, and metastasis (Fig. 1).

Cell proliferation Recent researches have demonstrated that cell proliferation of cancer can be regulated by hypoxia-induced lncRNAs. For example, Dr. Mole et al. showed that knockdown of NEAT1 inhibited cell proliferation in both normoxic and hypoxic conditions and the effect of inhibition was more remarkable under hypoxia [17]. Similar effect is also observed for lncRNAUCA1 and hypoxia-induced noncoding ultraconserved transcripts (HINCUTs) [10, 35]. One possible mechanism of lncRNA-UCA1 promoting cellular proliferation of cancer is via the activation of Akt/protein kinase B pathway [36, 37]. However, some lncRNAs play a contrary role in proliferation. For instance, Wang et al. exhibited that suppression of HIF2PUT accelerated the proliferation of the human osteosarcoma cell line MG63 [25]. Till now, the intimate mechanisms for most hypoxia-induced lncRNAs to regulate cell

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Fig. 1 Functions and mechanisms of hypoxiaresponsive lncRNAs in tumorigenesis and metastasis. HRE hypoxia response element

proliferation are still unknown, which need to be further clarified in the future. Apoptosis Tumorigenesis can be regarded as a process of interruption of the balance between cell division and cell death particularly apoptosis [38]. To date, the most studied protein-coding genes involved in cell apoptosis are p53 and Bcl-2 [39]. p53 has been known as a tumor suppressor gene, which can activate cell cycle arrest and initiate apoptosis [40]. On the contrary, Bcl-2 is an oncogene, which can suppress apoptosis. Hypoxiaresponsive lncRNAs may adjust apoptosis through p53 or Bcl-2 pathway. For example, H19, aberrantly expressed in various types of tumors, possesses a remarkable inhibitory impact on tumor cell apoptosis [41]. Additionally, H19 can be suppressed by p53 that is usually vacant in cancers [42]. These evidence indicates that H19 may play a crucial role in the process of apoptosis under regulation of p53 [43]. In Xue et al.’s study, knockdown of lncRNA-UCA1 inhibited human bladder cancer cell apoptosis in hypoxic conditions [10]. The subsequent experiment proved that this effect was mediated through upregulation of Bax and downregulation of Bcl-2 [44]. Obviously, hypoxia-responsive lncRNAs can influence tumor growth via interfering with apoptosis, although the underlying mechanisms are still largely unknown. Metabolism When exposed to hypoxic environment, cells shift their metabolism from TAC cycle to glycolysis to get energy. In particular, cancer cells can take glycolysis even in the existence of oxygen, which is called Warburg effect [45]. The Warburg effect not only meets high energy demands of cancer cells, but also minimizes their oxygen consumption, consequently providing cancers with a growth advantage [46]. It is well documented that HIF-1 plays a crucial role in cancer cell metabolism [47]. The hypoxia-responsive lncRNA has a strong

impact on the expression or stabilization of HIF-1, indicating that they probably influence tumor metabolism. It is evidenced by the finding that lincRNA-p21 promotes glycolysis via HIF-1α that regulates the expression of Glut1 and LDHA [30]. Nevertheless, lncRNAs may also regulate cancer metabolism in an HIF-independent way. Ferdin et al. manifested that another hypoxia-responsive lncRNA uc.475 promoted the expression of O-linked N-acetylglucosamine transferase (OGT) that catalyzed polypeptide glycosylation [35]. In general, lncRNAs affect cancer metabolism by mediating key enzymes of the process in hypoxic microenvironment. Angiogenesis Angiogenesis is essential for cancer metastasis [48] and is closely related with hypoxia. When tumors expand, new blood vessels are generated in order to supply adequate oxygen and metabolites for proliferating tumor cells [49]. Meanwhile, oxygen diffusion from the existing vessels decreases, which leads to hypoxia [50]. In return, the hypoxic environment promotes angiogenesis via a series of hypoxia-inducible molecules (such as HIF-1 and HIF-2) and signaling pathways [51]. Among the regulators, HIF1 plays a vital role in the hypoxia-induced angiogenesis. Many HIF-1 target genes like VEGF and ANG have been documented to regulate angiogenesis by promoting endothelial cellular activities [52]. As mentioned earlier, some lncRNAs like linc-ROR may regulate HIF-1 activity, suggesting they probably regulate cancer angiogenesis through HIF-1 pathway. More recently, H19 RNA has been shown to modulate angiogenesis by targeting ANG in hepatocellular carcinoma [41]. In addition, MALAT1, which was first discovered as one of the cancer-associated lncRNAs [53], has been recently reported to be significantly increased in hypoxia and regulate vascular growth in vivo [54]. Therefore, hypoxia-induced lncRNAs, particularly those interacting with HIFs, may take an important part in tumor angiogenesis.

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Invasion and metastasis Metastasis is a primary cause of cancer death [55]. In the process of cancer growth and development, if cancer cells leave the primary site, they will continue growing through lymph node, blood vessels, or body cavity, thereafter forming metastasis focuses. During the past decades, numerous studies have been done to explore the entire process on how cancer cells transfer from the primary site to the targeted region and dozens of genes have been identified and clarified to participate in this process. Furthermore, as hypoxic microenvironment has a critical role in cancer metastasis, hypoxiaresponsive lncRNAs may be involved in the metastasis. To date, some lncRNAs, in response to hypoxia, have been shown to affect cancer invasion and metastasis. Matouk et al. disclosed that under hypoxia, lncRNA H19 increased Slug protein expression and suppressed E-cadherin expression to promote cell migration and cancer metastasis, and they also found that Slug could bind promoter of H19 to activate its expression, thus forming a positive feedback loop between H19 and Slug [11]. Hypoxia-inducible lncRNA-AK058003 contributed to gastric cancer (GC) metastasis by targeting γsynuclein [56]. It is predictable that more hypoxia-responsive lncRNAs may play as critical regulators in the process of cancer invasion and metastasis, although awaiting further investigation.

Potential clinical implications of hypoxia-responsive lncRNAs Cancer diagnostic biomarkers As diagnostic biomarkers, lncRNAs have some following advantages: (1) some lncRNAs play important roles in tumor

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growth and progression; (2) analogous to miRNAs, lncRNAs can be easily detected from the body fluid such as blood or urine [57]; (3) some lncRNAs show restricted tissue-specific and cancer-specific features [58]. In addition, hypoxia is associated with aggressive tumor phenotypes [59]. Hence, hypoxia-responsive lncRNAs may have great potential as cancer diagnostic markers (Fig. 2). LncRNA-UCA1, robustly increased in hypoxic conditions, has been identified as a highly sensitive and specific biomarker for bladder carcinoma [10, 60]. Recent discoveries show that lncRNA-UCA1 is also highly expressed in GC and acute myeloid leukemia [61, 62], indicating the potential as a valuable marker for hypoxic microenvironment in many types of cancers. Another study exhibits that H19 can be used as a new biomarker for GC diagnosis by detecting its level in plasma [63]. Yet, compared to other large biomolecules, many lncRNAs are very unstable and easily degraded. Therefore, further studies are in demand to search for more stable lncRNAs, to be used as cancer diagnostic markers.

Cancer therapy Hypoxia-responsive lncRNAs can act not only as tumor markers, but also as potential cancer therapeutic targets due to their crucial roles in tumor growth and progression. For example, H19 has been demonstrated as a key oncogene in hepatocellular carcinoma (HCC) growth and metastasis [11, 41, 42], implicating a potential target for the therapy of HCC. Till now, the following methods have been developed to target lncRNAs for cancer therapy: (1) inhibiting the expression of lncRNAs by RNA interference technology; (2) blocking functional pathways of lncRNAs; (3) destructing lncRNA structure; and (4) transferring some Bgood^ lncRNAs which are usually tumor suppressors into specific cells [64]. Numerous pre-clinical tests have implicated that lncRNAs can be used as

Fig. 2 Hypoxia-responsive lncRNAs like H19 or UCA1 may be used as cancer diagnosis by collecting samples from patients, extracting RNA from the sample, and detecting expression of the lncRNA by RT-qPCR

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targets for cancer therapy [65]. A phase I/IIa clinical trial showed patients with bladder cancer receiving a plasmid targeting H19 got complete or partial remission without serious side reactions [66]. With in-depth investigation of both hypoxic microenvironment and lncRNA functions, we believe that more hypoxia-responsive lncRNAs will be exploited as targets and be widely applied in the treatment of cancer in the near future.

Conclusion and perspective Hypoxia, as a common and crucial tumor microenvironment, has the profound influence on tumor growth and development. In recent years, more and more lncRNAs have been identified to regulate expression of many protein-coding genes and affect tumorigenesis, cancer invasion, and metastasis, hence providing a novel class of biomarkers for the early detection and prognosis of cancer as well as new targets for cancer therapy. However, the research on hypoxia-responsive lncRNAs is still at the initial stage, and more difficulties will be faced, such as relatively few effective research methods to simulate the real hypoxic tumor microenvironment in human and to identify cell- and tissue-specific lncRNAs, and unclear mechanisms of majority of hypoxia-responsive lncRNAs functioning in cancer. It is urgent to overcome these difficulties in order to reveal molecular mechanisms of hypoxiaresponsive lncRNAs in cancer growth and development and contribute to improving cancer diagnosis and therapy. Acknowledgments This work was supported by grants from the National Natural Science Foundation of China (nos. 81372713, 81402048).

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Compliance with ethical standards Conflicts of interest None

18.

19.

References 1.

2.

3. 4. 5. 6.

Lodish H, Berk A, Zipursky SL et al. (2000) Tumor cells and the onset of cancer; Molecular cell biology, ed4. New York, W. H. Freeman Wels J, Kaplan RN, Rafii S, Lyden D. Migratory neighbors and distant invaders: tumor-associated niche cells. Genes Dev. 2008;22:559–74. Harris AL. Hypoxia—a key regulatory factor in tumour growth. Nat Rev Cancer. 2002;2:38–47. Quail DF, Joyce JA. Microenvironmental regulation of tumor progression and metastasis. Nat Med. 2013;19:1423–37. Prensner JR, Chinnaiyan AM. The emergence of lncRNAs in cancer biology. Cancer discovery. 2011;1:391–407. Autuoro JM, Pirnie SP, Carmichael GG. Long noncoding RNAs in imprinting and x chromosome inactivation. Biomolecules. 2014;4: 76–100.

20.

21. 22. 23. 24.

25.

Kornienko AE, Guenzl PM, Barlow DP, Pauler FM. Gene regulation by the act of long non-coding RNA transcription. BMC Biol. 2013;11:59. Yoon JH, Abdelmohsen K, Gorospe M. Posttranscriptional gene regulation by long noncoding RNA. J Mol Biol. 2013;425:3723–30. Shi X, Sun M, Liu H, Yao Y, Song Y. Long non-coding RNAs: a new frontier in the study of human diseases. Cancer Lett. 2013;339: 159–66. Xue M, Li X, Li Z, Chen W. Urothelial carcinoma associated 1 is a hypoxia-inducible factor-1alpha-targeted long noncoding RNA that enhances hypoxic bladder cancer cell proliferation, migration, and invasion. Oncogene. 2014;35:6901–12. Matouk IJ, Raveh E, Abu-lail R, Mezan S, Gilon M, Gershtain E, et al. Oncofetal h19 RNA promotes tumor metastasis. Biochim Biophys Acta. 1843;2014:1414–26. Fish JE, Matouk CC, Yeboah E, Bevan SC, Khan M, Patil K, et al. Hypoxia-inducible expression of a natural cis-antisense transcript inhibits endothelial nitric-oxide synthase. J Biol Chem. 2007;282: 15652–66. Shen XH, Qi P, Du X. Long non-coding RNAs in cancer invasion and metastasis. Modern pathology: an official journal of the United States and Canadian Academy of Pathology, Inc, 2015;28:4–13. Gomez-Maldonado L, Tiana M, Roche O, Prado-Cabrero A, Jensen L, Fernandez-Barral A, et al. EFNA3 long noncoding RNAs induced by hypoxia promote metastatic dissemination. Oncogene. 2014;34(20):2609–200. Zhou C, Ye L, Jiang C, Bai J, Chi Y, Zhang H: Long noncoding RNA HOTAIR, a hypoxia-inducible factor-1alpha activated driver of malignancy, enhances hypoxic cancer cell proliferation, migration, and invasion in non-small cell lung cancer. Tumour biology: the journal of the International Society for Oncodevelopmental Biology and Medicine 2015 (in press) Choudhry H, Schodel J, Oikonomopoulos S, Camps C, Grampp S, Harris AL, et al. Extensive regulation of the non-coding transcriptome by hypoxia: role of HIF in releasing paused RNAPOL2. EMBO Rep. 2014;15:70–6. Choudhry H, Albukhari A, Morotti M, Hider S, Moralli D, Smythies J, Schodel J, Green CM, Camps C, Buffa F, Ratcliffe P, Ragoussis J, Harris AL, Mole DR: Tumor hypoxia induces nuclear paraspeckle formation through HIF-2alpha dependent transcriptional activation of NEAT1 leading to cancer cell survival. Oncogene. 2015;34:4482–90. Wu MZ, Tsai YP, Yang MH, Huang CH, Chang SY, Chang CC, et al. Interplay between HDAC3 and WDR5 is essential for hypoxia-induced epithelial-mesenchymal transition. Mol Cell. 2011;43:811–22. Yang F, Huo XS, Yuan SX, Zhang L, Zhou WP, Wang F, et al. Repression of the long noncoding RNA-LET by histone deacetylase 3 contributes to hypoxia-mediated metastasis. Mol Cell. 2013;49:1083–96. McCarty G, Loeb DM. Hypoxia-sensitive epigenetic regulation of an antisense-oriented lncRNA controls wt1 expression in myeloid leukemia cells. PLoS One. 2015;10:e0119837. Wang KC, Chang HY. Molecular mechanisms of long noncoding RNAs. Mol Cell. 2011;43:904–14. He Y, Vogelstein B, Velculescu VE, Papadopoulos N, Kinzler KW. The antisense transcriptomes of human cells. Science. 2008;322:1855–7. Villegas VE, Zaphiropoulos PG. Neighboring gene regulation by antisense long non-coding RNAs. Int J Mol Sci. 2015;16:3251–66. Bertozzi D, Iurlaro R, Sordet O, Marinello J, Zaffaroni N, Capranico G. Characterization of novel antisense HIF-1alpha transcripts in human cancers. Cell Cycle. 2011;10:3189–97. Georgetown, Tex. Wang Y, Yao J, Meng H, Yu Z, Wang Z, Yuan X, et al. A novel long non-coding RNA, hypoxia-inducible factor-2alpha promoter

Tumor Biol. (2016) 37:1379–1385 upstream transcript, functions as an inhibitor of osteosarcoma stem cells in vitro. Mol Med Rep. 2015;11:2534–40. 26. Sun YW, Chen YF, Li J, Huo YM, Liu DJ, Hua R, et al. A novel long non-coding RNA ENST00000480739 suppresses tumour cell invasion by regulating OS-9 and HIF-1alpha in pancreatic ductal adenocarcinoma. Br J Cancer. 2014;111:2131–41. 27. Baek JH, Mahon PC, Oh J, Kelly B, Krishnamachary B, Pearson M, et al. Os-9 interacts with hypoxia-inducible factor 1alpha and prolyl hydroxylases to promote oxygen-dependent degradation of HIF-1alpha. Mol Cell. 2005;17:503–12. 28. Wong BW, Kuchnio A, Bruning U, Carmeliet P. Emerging novel functions of the oxygen-sensing prolyl hydroxylase domain enzymes. Trends Biochem Sci. 2013;38:3–11. 29. Zhu Z, Gao X, He Y, Zhao H, Yu Q, Jiang D, et al. An insertion/ deletion polymorphism within RERT-lncRNA modulates hepatocellular carcinoma risk. Cancer Res. 2012;72:6163–72. 30. Yang F, Zhang H, Mei Y, Wu M. Reciprocal regulation of HIF1alpha and lincRNA-p21 modulates the Warburg effect. Mol Cell. 2014;53:88–100. 31. Ma MZ, Kong X, Weng MZ, Zhang MD, Qin YY, Gong W, et al. Long non-coding RNA-LET is a positive prognostic factor and exhibits tumor-suppressive activity in gallbladder cancer. Mol Carcinog. 2014;54(11):1397–406. 32. Takahashi K, Yan IK, Haga H, Patel T. Modulation of hypoxiasignaling pathways by extracellular linc-ror. J Cell Sci. 2014;127: 1585–94. 33. Xu Q, Liu LZ, Qian X, Chen Q, Jiang Y, Li D, et al. Mir-145 directly targets p70s6k1 in cancer cells to inhibit tumor growth and angiogenesis. Nucleic Acids Res. 2012;40:761–74. 34. Hanahan D, Weinberg RA. The hallmarks of cancer. Cell. 2000;100:57–70. 35. Ferdin J, Nishida N, Wu X, Nicoloso MS, Shah MY, Devlin C, et al. HINCUTS in cancer: hypoxia-induced noncoding ultraconserved transcripts. Cell Death Differ. 2013;20:1675–87. 36. Nolte D, Muller U. Human o-GlcNAc transferase (OGT): genomic structure, analysis of splice variants, fine mapping in xq13.1. Mammalian genome: official journal of the International Mammalian Genome Society. 2002;13:62–4. 37. Kreppel LK, Blomberg MA, Hart GW. Dynamic glycosylation of nuclear and cytosolic proteins. Cloning and characterization of a unique o-GlcNAc transferase with multiple tetratricopeptide repeats. J Biol Chem. 1997;272:9308–15. 38. Lowe SW, Lin AW. Apoptosis in cancer. Carcinogenesis. 2000;21: 485–95. 39. Goldar S, Khaniani MS, Derakhshan SM, Baradaran B. Molecular mechanisms of apoptosis and roles in cancer development and treatment. Asian Pacific journal of cancer prevention: APJCP. 2015;16: 2129–44. 40. Soussi T. The p53 tumor suppressor gene: from molecular biology to clinical investigation. Ann N Y Acad Sci. 2000;910:121–37. discussion 137–129. 41. Matouk IJ, DeGroot N, Mezan S, Ayesh S, Abu-lail R, Hochberg A, et al. The h19 non-coding RNA is essential for human tumor growth. PLoS One. 2007;2:e845. 42. Matouk IJ, Mezan S, Mizrahi A, Ohana P, Abu-Lail R, Fellig Y, et al. The oncofetal h19 RNA connection: hypoxia, p53 and cancer. Biochim Biophys Acta. 1803;2010:443–51. 43. Rossi MN, Antonangeli F. LncRNAs: new players in apoptosis control. International journal of cell biology. 2014;2014: 473857. 44. Maddika S, Ande SR, Panigrahi S, Paranjothy T, Weglarczyk K, Zuse A, et al. Cell survival, cell death and cell cycle pathways are interconnected: implications for cancer therapy. Drug resistance updates : reviews and commentaries in antimicrobial and anticancer chemotherapy. 2007;10:13–29.

1385 45. Warburg O. On the origin of cancer cells. Science. 1956;123:309–14. 46. Bartrons R, Caro J. Hypoxia, glucose metabolism and the Warburg’s effect. J Bioenerg Biomembr. 2007;39:223–9. 47. Zeng W, Liu P, Pan W, Singh SR, Wei Y. Hypoxia and hypoxia inducible factors in tumor metabolism. Cancer Lett. 2015;356:263–7. 48. Bikfalvi A. Angiogenesis and invasion in cancer. Handb Clin Neurol. 2012;104:35–43. 49. Raghunand N, Gatenby RA, Gillies RJ. Microenvironmental and cellular consequences of altered blood flow in tumours. Br J Radiol. 2003;76 Spec No 1:S11–22. 50. Carmeliet P, Jain RK. Angiogenesis in cancer and other diseases. Nature. 2000;407:249–57. 51. Chen L, Endler A, Shibasaki F. Hypoxia and angiogenesis: regulation of hypoxia-inducible factors via novel binding factors. Exp Mol Med. 2009;41:849–57. 52. Mizukami Y, Kohgo Y, Chung DC. Hypoxia inducible factor-1 independent pathways in tumor angiogenesis. Clinical cancer research: an official journal of the American Association for Cancer Research. 2007;13:5670–4. 53. Ji P, Diederichs S, Wang W, Boing S, Metzger R, Schneider PM, et al. MALAT-1, a novel noncoding RNA, and thymosin beta4 predict metastasis and survival in early-stage non-small cell lung cancer. Oncogene. 2003;22:8031–41. 54. Michalik KM, You X, Manavski Y, Doddaballapur A, Zornig M, Braun T, et al. Long noncoding RNA MALAT1 regulates endothelial cell function and vessel growth. Circ Res. 2014;114:1389–97. 55. Weigelt B, Peterse JL, Veer LJ v ’t. Breast cancer metastasis: markers and models. Nat Rev Cancer. 2005;5:591–602. 56. Wang Y, Liu X, Zhang H, Sun L, Zhou Y, Jin H, et al. Hypoxiainducible lncRNA-ak058003 promotes gastric cancer metastasis by targeting gamma-synuclein. Neoplasia. 2014;16:1094–106. 57. Van Roosbroeck K, Pollet J, Calin GA. MiRNAs and long noncoding RNAs as biomarkers in human diseases. Expert Rev Mol Diagn. 2013;13:183–204. 58. Yan X, Hu Z, Feng Y, Hu X, Yuan J, Zhao SD, et al. Comprehensive genomic characterization of long non-coding RNAs across human cancers. Cancer Cell. 2015;28:529–40. 59. Vaupel P. Hypoxia and aggressive tumor phenotype: implications for therapy and prognosis. Oncologist. 2008;13 Suppl 3:21–6. 60. Zhang Q, Su M, Lu G, Wang J. The complexity of bladder cancer: long noncoding RNAs are on the stage. Mol Cancer. 2013;12:101. 61. Zheng Q, Wu F, Dai WY, Zheng DC, Zheng C, Ye H, Zhou B, Chen JJ, Chen P: Aberrant expression of UCA1 in gastric cancer and its clinical significance. Clinical & translational oncology: official publication of the Federation of Spanish Oncology Societies and of the National Cancer Institute of Mexico. Clin Transl Oncol. 2015;17:640–6. 62. Hughes JM, Legnini I, Salvatori B, Masciarelli S, Marchioni M, Fazi F, et al. C/EBPalpha-p30 protein induces expression of the oncogenic long non-coding RNA UCA1 in acute myeloid leukemia. Oncotarget. 2015;6(21):18534–44. 63. Zhou X, Yin C, Dang Y, Ye F, Zhang G. Identification of the long non-coding RNA h19 in plasma as a novel biomarker for diagnosis of gastric cancer. Sci Rep. 2015;5:11516. 64. Li CH, Chen Y. Targeting long non-coding RNAs in cancers: progress and prospects. Int J Biochem Cell Biol. 2013;45:1895–910. 65. Qi P, Du X. The long non-coding RNAs, a new cancer diagnostic and therapeutic gold mine. Modern pathology: an official journal of the United States and Canadian Academy of Pathology, Inc. 2013;26:155–65. 66. Smaldone MC, Davies BJ. Bc-819, a plasmid comprising the h19 gene regulatory sequences and diphtheria toxin a, for the potential targeted therapy of cancers. Curr Opin Mol Ther. 2010;12:607–16.