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Oct 19, 2016 - Abstract: The prostate is a developmental model system study of prostate growth regulation. Historically the research focus was on androgen ...
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Hedgehog Signaling in Prostate Development, Regeneration and Cancer Wade Bushman Department of Urology, Carbone Comprehensive Cancer Center, University of Wisconsin, Madison, WI 53705, USA; [email protected]; Tel.: +1-608-262-5440; Fax: +1-608-262-6453 Academic Editors: Henk Roelink and Simon J. Conway Received: 17 August 2016; Accepted: 4 October 2016; Published: 19 October 2016

Abstract: The prostate is a developmental model system study of prostate growth regulation. Historically the research focus was on androgen regulation of development and growth and instructive interactions between the mesenchyme and epithelium. The study of Hh signaling in prostate development revealed important roles in ductal morphogenesis and in epithelial growth regulation that appear to be recapitulated in prostate cancer. This overview of Hh signaling in the prostate will address the well-described role of paracrine signaling prostate development as well as new evidence suggesting a role for autocrine signaling, the role of Hh signaling in prostate regeneration and reiterative activities in prostate cancer. Keywords: Hedgehog; prostate; cancer

1. Prostate Development The prostate is a male sex-accessory gland that contributes secretions to the ejaculate. The mouse prostate is comprised of a highly branched ductal network in a loose fibro-vascular stroma arranged into anterior, dorsolateral and ventral lobes. The overall appearance and ratio of epithelium and stroma varies significantly between species but the basic mechanisms controlling prostate development appear to be conserved as evidenced by tissue recombination studies using mouse, rat, rabbit, and human prostate mesenchyme and epithelia [1]. The most widely used animal model for prostate development and morphogenesis is the mouse. The prostate develops from the urogenital sinus (UGS), a derivative of endodermal tissue. The first morphological event in prostate development is budding of urogenital sinus epithelium (UGE) into the surrounding urogenital sinus mesenchyme (UGM). This occurs in the mouse at embryonic day 16.5 (E16.5). During prenatal development, these epithelial buds elongate and form solid, unbranched ducts. Postnatal, the solid epithelial ducts elongate, canalize, and undergo branching morphogenesis. Extensive branching occurs by postnatal day 15 (P15) and is largely completed by P30 [2]. This morphogenetic process results in a mature prostate with an intricate branched ductal system that consists of three paired lobes: the ventral prostate (VP), the anterior prostate (AP), and the dorsolateral prostate (DLP). Each prostatic lobe has a distinct branching pattern [2]. 2. Hedgehog Signaling in the Developing Prostate In the developing prostate, Shh and Ihh are expressed by the UGS epithelium and induce Hh target gene expression in the adjacent mesenchyme (Figure 1; [3–7]). Mesenchymal target genes include the conserved Hh targets Ptc, Gli1, Ptc2 and Hip1 [5] but also include a number of specific genes such as IGFBP-6, Angiopoetin4 (Agpt4), IGFBP-3, Inhibin beta-B and TIMP3 [8,9]. Several investigators noted minor expression of Ptc and Gli1 at the tips of the growing ducts suggesting a minor component of autocrine signaling [10,11].

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Figure 1. Whole mount in situ hybridization and sections of the P1 urogenital sinus (UGS). Figure 1. Whole mount in situ [4]. hybridization and sections of the P1 urogenital sinus (UGS). (m) (m) mesenchyme (e) epithelium mesenchyme (e) epithelium [4]

3. Requirement for Prostate Development 3. Requirement for Prostate Development Shh is the most abundantly expressed Hh ligand in the developing prostate [12]. Shh expression Shh is the most abundantly expressed Hh ligand in the developing prostate [12]. Shh expression in the UGS epithelium increases with the onset of ductal budding. Abundant gene expression is in the UGS epithelium increases with the onset of ductal budding. Abundant gene expression is maintained until the beginning of ductal branching at which point Shh begins to steadily decrease maintained until the beginning of ductal branching at which point Shh begins to steadily decrease and eventually taper off to a low but detectable level in the adult [3,4]. Shh expression is localized to and eventually taper off to a low but detectable level in the adult [3,4]. Shh expression is localized to the epithelium at the distal tip as the ducts elongate and branch. During this time Ptc1 and Gli1 are the epithelium at the distal tip as the ducts elongate and branch. During this time Ptc1 and Gli1 are localized to the mesenchyme directly around the emerging buds [4]. Several laboratories have studied localized to the mesenchyme directly around the emerging buds [4]. Several laboratories have the role of Hh signaling in prostate development. The earliest studies used a polyclonal antibody studied the role of Hh signaling in prostate development. The earliest studies used a polyclonal to neutralize Shh signaling and noted inhibition of prostate morphogenesis in the grafted UGS [3]. antibody to neutralize Shh signaling and noted inhibition of prostate morphogenesis in the grafted Subsequent studies showed prostate development was not dependent on Shh signaling since the UGS UGS [3]. Subsequent studies showed prostate development was not dependent on Shh signaling since from a Shh null embryo exhibited normal prostate morphogenesis when grafted [5–7]. However; the UGS from a Shh null embryo exhibited normal prostate morphogenesis when grafted [5–7]. we then observed that Ihh expression was increased in the Shh null UGS and provided functional However; we then observed that Ihh expression was increased in the Shh null UGS and provided redundancy that rescued Hh signaling [12]. Whether Hh signaling is strictly required for prostate functional redundancy that rescued Hh signaling [12]. Whether Hh signaling is strictly required for morphogenesis remains to be determined. prostate morphogenesis remains to be determined. 4. Effects on Growth and Ductal Morphogenesis 4. Effects on Growth and Ductal Morphogenesis Initially it was reported that chemical inhibition of Hh signaling in the cultured UGS resulted Initially was reported that chemical inhibition of HhHowever, signaling later in thestudies cultured UGS resulted in in decreaseditepithelial proliferation and branching [4]. reported a myriad decreased epithelial proliferation and branching [4]. However, later studies reported a myriad of of effects on branching during experimental approaches to increase or decrease Hh signaling in the effects on branching during experimental approaches to increase or decrease Hh signaling in the cultured postnatal prostate[5–7]. Wang reported inhibition of Hh signaling increased overall epithelial cultured postnatal prostate[5–7]. Wang inhibition ofduct. Hh In signaling increased overall proliferation [5]. However, the effects were reported regionalized along the fact, epithelial proliferation epithelial proliferation [5]. However, the effects were regionalized along the duct. In fact, epithelial was significantly and selectively decreased in the distal, less differentiated part of the duct [5,6]. proliferation was significantly selectively decreased in the distal, less might differentiated part of We postulated that inconstant and findings reported by different laboratories be attributed tothe the duct [5,6]. We postulated that inconstant findings reported by different laboratories might studies being done at different stages of prostate development [5]. This was subsequently shown tobe be attributed to thea combination studies beingof done at different prostate development [5]. This of was the case. Using chemical inhibitionstages of Hh of signaling and transgenic activation Hh subsequently shown to bethat theparacrine case. Using combination of chemical inhibition of Hh signaling and signaling, it was shown Hhasignaling promotes epithelial proliferation and budding transgenic activation of Hh signaling, it was shown that paracrine Hh signaling promotes epithelial proliferation and budding prenatally while inhibiting epithelial proliferation and branching

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postnatally. These differential effectsproliferation were mirrored stage-specific differences in Hh targeteffects gene prenatally while inhibiting epithelial and by branching postnatally. These differential regulation [8]. by These studies established Hhgene signaling as a [8]. primary of ductal were mirrored stage-specific differencesparacrine in Hh target regulation These regulator studies established morphogenesis and epithelial proliferation. Stage dependent effects are associated withproliferation. an evolving paracrine Hh signaling as a primary regulator of ductal morphogenesis and epithelial palettedependent of target gene regulation and reveal the effects of paracrine signaling are dependent Stage effects are associated with that an evolving palette of targetHh gene regulation and reveal uponthe theeffects mesenchymal microenvironment. that of paracrine Hh signaling are dependent upon the mesenchymal microenvironment. Beachy and colleagues performed elegant studies localizing Hh ligand expression and pathway morphogenesis in the regenerating regenerating prostate prostate [13]. [13]. They found both Shh and activity during branching morphogenesis Ihh to be expressed at significant levels but observed focally decreased Hh expression and pathway activity at sites of ductal branching. Manipulations to decrease Hh pathway activity increased ductal branching and this was associated with increased stromal expression of hepatocyte growth factor (HFG) a positive regulator of ductal ductal branching. branching. Ongoing studies are yielding additional evidence of other regulators regulators of of prostate prostate development. development. Shh expression is diminished diminished cross-talk between Hh and other but prolonged prolonged in in FoxA1 FoxA1 deficient deficient mice mice [10]. [10]. Pu et al. [11] in Sox9 genetically deficient mice [14] but exogenous Shh Shh decreased decreased FGF10 FGF10 expression expression in in cultured cultured prostate prostatetissues. tissues. demonstrated that exogenous 5. Autocrine AutocrineSignaling Signaling We in the the prostate. prostate. We performed performed preliminary preliminary studies to examine the role of autocrine Hh signaling in lacZ reporter mice to localize Hh pathway lacZ and Using Ptc1 and Gli1 Gli1lacZ Ptc1lacZ reporter mice to localize Hh pathway activation, we observed robust lacZ in the urogenital mesenchyme. Most epithelium was unstained, but lacZ and expression and Gli1lacZ expression of of Ptc1 Ptc1lacZ in the urogenital mesenchyme. Most epithelium was we observed strong lacZ lacZ staining stainingin inaasmall smallnumber numberofofepithelial epithelialcells cellsinin the nascent prostate ducts the nascent prostate ducts at at and (Figure2).2).Staining Stainingofofthe theadult adultprostate prostate showed showed relatively relatively infrequent infrequent and scattered P1P1 and P5P5(Figure epithelial notnot shown). These observations suggestsuggest that autocrine Hh pathway epithelial staining staining(data (data shown). These observations that autocrine Hh activation pathway occurs in aoccurs small number of number epithelial specifically during prostate development. activation in a small ofcells epithelial cells specifically during prostate development.

lacZ mice lacZPtc1 lacZ Figure 2. staining of P1/P5 prostate fromfrom Gli1lacZ and showed strong positive Figure 2. X-gal/PanCK X-gal/PanCK staining of P1/P5 prostate Gli1 and Ptc1 mice showed strong beta-gal beta-gal activity activity (blue) in the in mesenchyme generally andand in ainlimited number cells positive (blue) the mesenchyme generally a limited numberofofepithelial epithelial cells (brown) in the nascent ducts (arrowheads). N = 3, scale bar = 40 µm (brown) in the nascent ducts (arrowheads). N = 3, scale bar = 40 µm.

To examine the role of autocrine signaling specifically, we abrogated epithelial Hh signaling by To examine the role of autocrine signaling specifically, we abrogated epithelial Hh signaling by cre construct conditional deletion of the essential pathway component Smoothened (Smo) using a Shhcre conditionaltm1(EGFP/cre)Cjt deletion of the essential pathway component Smoothened (Smo) using a Shh construct B6.Cg-Shh /J (stock 005622). We have previously shown that Shh mRNA expression in the B6.Cg-Shhtm1(EGFP/cre)Cjt /J (stock 005622). We have previously showncre that Shh mRNA expression developing prostate is restricted to the epithelium [3,4]. When the Shh mouse was bred to the lacZ in the developing prostate is restricted to the epithelium [3,4]. When the Shhcre mouse was bred to reporter mouse Rosa26 (B6.129S4-Gt(ROSA)26Sor/J 003474) X-gal staining of the UGS from the cre lacZ reporter mouse Rosa26 (B6.129S4-Gt(ROSA)26Sor/J 003474) X-gal staining of the Shh ;Rosa26 mice exhibited robust positive staining restricted to the epithelium (Figure 3) and Mehta cre ;Rosa26 UGS from Shhcre mice exhibited robust positive staining restricted to the epithelium (Figure 3) et al. [15]. Shh was bred cre to Smoc/c (Smoc/c : STOCK Smotm2Amc/J 004526)tm2Amc/J to selectively delete Smo from and Mehta et al. [15]. Shh was bred to Smoc/c (Smoc/c : STOCK Smo 004526) to selectively cre c/c all cells expressing Shh, including the UGS epithelium. Shh ;Smo mutantcrepups were small with delete Smo from all cells expressing Shh, including the UGS epithelium. Shh ;Smoc/c mutant pups abnormalities in limb, digits and tail and died as newborns (data not shown). The P1 UGS from were small with abnormalities in limb, digits and tail and died as newborns (data not shown). The P1 Shhcre;Smoc/c mutants and controls were grafted under the renal capsule of adult nude males [12,16]. UGS from Shhcre ;Smoc/c mutants and controls were grafted under the renal capsule of adult nude Histologic examination after eight weeks showed well-developed ductal structures and males [12,16]. Histologic examination after eight weeks showed well-developed ductal structures and differentiated epithelium and stroma in both groups (Figure 4, top panels). differentiated epithelium and stroma in both groups (Figure 4, top panels).

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Figure 3.Staining Stainingfor for beta-gal in E16 mice. Note recombination Figure for beta-gal in UGS of Shhcrecre;Rosa26R ;Rosa26R mice. Noteefficient efficient recombination cre Shh Figure3.3. Staining beta-gal in E16 UGSUGS of Shhof ;Rosa26R mice. Note efficient recombination through through the UGS epithelium (UGE) bladder epithelium. UGM: UGS mesenchyme; n = 3. through the UGS epithelium (UGE) and bladder epithelium. UGM: UGS mesenchyme; n = 3. the UGS epithelium (UGE) and bladder epithelium. UGM: UGS mesenchyme; n = 3.

Figure 4. In vivo subcapsular grafts of P1 UGS from control and Shhcre;Smoc/c mutants. Histologic appearance weeks growth (top), two weeks after castration (middle) and two weeks after Figure 4. Inafter vivoeight subcapsular grafts of P1 UGS from control and Shhcre ;Smoc/c mutants. Histologic Figure 4. In vivo subcapsular grafts of P1 UGS from control and Shhcre;Smoc/c mutants. Histologic testosterone supplement. n = 3.growth (top), two weeks after castration (middle) and two weeks after appearance after eight weeks

appearance after eight weeks growth (top), two weeks after castration (middle) and two weeks after testosterone supplement. n = 3. testosterone supplement. n = 3.

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6. Prostate Regeneration Development and maintenance of the prostate is exquisitely dependent on androgen. Castration of the adult results in widespread epithelial apoptosis and glandular involution. Regeneration of the prostate occurs with administration of exogenous testosterone and involves robust cell proliferation, branching morphogenesis and complete reconstitution prostate architecture and differentiation. J. Dev. Biol. 2016,regenerative 4, 30 5 of 8 cells in this The prostate’s unique capacity has stimulated interest in the role of progenitor process and6.the study of prostate stem cells has been an active area of investigation. We performed Prostate Regeneration studies showing that castration induces a selective expansion of slow-cycling progenitor cells. Development and maintenance of the prostate is exquisitely dependent on androgen. Castration The implication of this finding is that these are “androgen-independent” progenitor cellsofthat of the adult results in widespread epithelial apoptosis and glandular involution. Regeneration the could play prostate occurs with administration of exogenous testosterone and involves robust cell proliferation, an important role in prostate regeneration. Interestingly, we found that both Shh and Gli expression branching morphogenesis and complete reconstitution prostate architecture and differentiation. The are increased significantly in response to castration [17] and observed robust Hh signaling when prostate’s unique regenerative capacity has stimulated interest in the role of progenitor cells in this progenitor cells areand grown in anchorage independent findings suggested a role for process the study of prostate stem cells has been culture an active [18]. area ofThese investigation. We performed studies showing thatcell castration inducesand a selective expansion of prostate slow-cycling progenitor cells. The Hh signaling in progenitor expansion the capacity for regeneration. implication of this finding is that these are “androgen-independent” progenitor cells that could play A role for Hh signaling in prostate regeneration has been previously recognized [19] demonstrated an important role in prostate regeneration. Interestingly, we found that both Shh and Gli expression that inhibition of Hh signaling didHhnot distinguish between are increased significantly abrogated in response toprostate castration regeneration [17] and observedbut robust signaling when cre ;Smo c/c mutants progenitor cellssignaling. are grown inUsing anchorage independent culture findings suggested and a rolecontrols, we autocrine and paracrine grafted P1 UGS from[18]. ShhThese forthe Hh signaling progenitor cell expansionsignaling and the capacity forresponse prostate regeneration. characterized effect ofindisrupted autocrine on the to castration and testosterone A role for Hh signaling in prostate regeneration has been previously recognized [19] supplement.demonstrated Eight weeks after grafting, mice were castrated and examined 14 days later. We observed that inhibition of Hh signaling abrogated prostate regeneration but did not distinguish a truly striking difference. Whereas control grafts exhibited well-formed ducts and with cuboidal between autocrine and paracrinethe signaling. Using grafted P1 UGS from Shhcre;Smoc/c mutants controls, we characterized the effect of disrupted autocrine signaling on the response to castration epithelium, the mutant grafts lacked well defined cuboidal epithelial cells. Grafted tissues castrated and testosterone supplement. Eight weeks after grafting, mice were castrated and examined 14 days x 14 days and then testosterone supplemented x 14 days revealed an equally exciting disparity in later. We observed a truly striking difference. Whereas the control grafts exhibited well-formed ducts re-growth. with Whereas control grafts recovered morphology comparable toGrafted the intact tissue, cuboidal epithelium, the mutant grafts normal lacked well defined cuboidal epithelial cells. tissues castrated x 14 days and then testosterone supplemented x 14 days revealed an equally exciting the mutant grafts exhibited an atrophic appearance with fewer, dilated ductal lumen and minimal disparity in re-growth. Whereas control grafts recovered normal morphology comparable to the epithelial re-growth (Figure 4, bottom panels). These previously unpublished observations indicate intact tissue, the mutant grafts exhibited an atrophic appearance with fewer, dilated ductal lumen that disruption of autocrine signaling not4,perturb prostate development but exaggerates the and minimal epithelial re-growthmay (Figure bottom panels). These previously unpublished that disruption of autocrine mayto not perturb prostateAdevelopment response to observations castrationindicate and impairs regeneration insignaling response testosterone. proposed model for exaggerates the response castration and regeneration in response to testosterone. the complexbut roles of autocrine and to paracrine Hh impairs signaling in prostate development andAcapacity for proposed model for the complex roles of autocrine and paracrine Hh signaling in prostate regenerationdevelopment is shown and (Figure 5). capacity for regeneration is shown (Figure 5).

Figure 5. Hh signaling in the developing prostate involves both autocrine and paracrine signaling. Figure 5. Hh signaling in the developing prostate involves both autocrine and paracrine signaling. Autocrine signaling drives proliferation of (androgen independent) progenitor cells at the bud tip. Autocrine signaling drives proliferation of (androgen independent) progenitor cells at the bud tip. Paracrine signaling elicits a complex transcriptional response, determined by the stage of Paracrine signaling elicits complex transcriptional response, determined by the stage In ofthe development, development, thata exerts a variety of effects on epithelial proliferation and differentiation. Hh pathway activity proliferation drives epithelialand proliferation and ductalIn growth. In the that exerts aprenatal varietyprostate, of effects on epithelial differentiation. the prenatal prostate, postnatal prostate, Hh pathway activity inhibits epithelial proliferation and ductal growth. Androgen Hh pathway activity drives epithelial proliferation and ductal growth. In the postnatal prostate, Hh pathway activity inhibits epithelial proliferation and ductal growth. Androgen independent progenitor cells generated by autocrine Hh signaling during development are able to survive castration and enable prostate regeneration in response to testosterone supplement.

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J. Dev.independent Biol. 2016, 4, 30progenitor cells generated by autocrine Hh signaling during development are able to 6 of 8

survive castration and enable prostate regeneration in response to testosterone supplement.

ProstateCancer Cancer 7. Prostate signaling is active in human prostate cancer and evidence for both autocrine and paracrine Hh signaling cancer has been presented. This appears to involve ligand-dependent signaling in inhuman humanprostate prostate cancer has been presented. This appears to both involve both ligandsignaling assignaling well as non-canonical pathway activation. Paracrine signaling has been modeled dependent as well as non-canonical pathway activation. Paracrine signaling has using been xenograft using studiesxenograft and shown to promote tumor growth [20]. Interestingly, a correlation analysis of modeled studies and shown to promote tumor growth [20]. Interestingly, a Shh target gene expression in human prostate cancer revealed dichotomous expression of prenatal correlation analysis of Shh target gene expression in human prostate cancer revealed dichotomous and postnatal genesand in the tumors. target In thosegenes tumors myofibroblastic resembling expression of target prenatal postnatal in with the atumors. In thosestroma tumors with a the mesenchymestroma of the resembling developing prostate, Shh and of Gli1 correlated myofibroblastic the mesenchyme theexpression developing prostate,with Shhexpression and Gli1 of prenatal correlated target genes. those with more mature, was expression withInexpression of aprenatal target myofibroblast genes. In thosepoor withstroma, a morethere mature, correlation with expression of postnatal target genes. These findings suggest that genes. the effect of myofibroblast poor stroma, there was correlation with expression of postnatal target These paracrinesuggest signaling in the prostate as in development, dependent upon stromal context findings that effectcancer of paracrine signaling in is prostate cancer as the in development, is and microenvironment in which it and occurs. The role of autocrine cancer is dependent upon the stromal context microenvironment in whichsignaling it occurs. in Theprostate role of autocrine debated. Several studies appeared to show autocrine signaling in prostate cancer cell lines cultured signaling in prostate cancer is debated. Several studies appeared to show autocrine signaling in in vitro [19,21] but this has been contested by two other studies [22,23]. Hh signaling appears to be prostate cancer cell lines cultured in vitro [19,21] but this has been contested by two other studies consistently up-regulated in metastatic and hormone refractory cancer and several studies [22,23]. Hh signaling appears to be consistently up-regulated in prostate metastatic and hormone refractory suggest cancer that Hhand pathway may be critical step in tumor metastasis and progression to prostate severalactivation studies suggest thata Hh pathway activation may be a critical step in tumor androgen independence [19,21,24]. A proposed model for the roles of autocrine and paracrine Hh metastasis and progression to androgen independence [19,21,24]. A proposed model for the roles of signaling in prostate cancer shown (Figure 6). cancer is shown (Figure 6). autocrine and paracrine Hh is signaling in prostate

Figure 6. The target genes activated by paracrine Hh signaling in the adult prostate and the effect on Figure 6. The target genes activated by paracrine Hh signaling in the adult prostate and the effect epithelial/tumor cell proliferation is determined by the phenotype of the stroma. In the normal adult on epithelial/tumor cell proliferation is determined by the phenotype of the stroma. In the normal prostate and prostate cancers with awith normal fibroblastic stroma the target gene gene profile resembles that adult prostate and prostate cancers a normal fibroblastic stroma the target profile resembles of theofpostnatal prostate and the effect of paracrine Hh signaling is homeostatic. In prostate cancers that the postnatal prostate and the effect of paracrine Hh signaling is homeostatic. In prostate with a so-called “reactive” (myofibrobastic) stroma, the target gene profile resembles that of that the cancers with a so-called “reactive” (myofibrobastic) stroma, the target gene profile resembles prenatal prostate and the effect of paracrine signaling is to promote epithelial/tumor cell proliferation. of the prenatal prostate and the effect of paracrine signaling is to promote epithelial/tumor cell Autocrine signaling in tumor stem cells may these cellsthese to survive and enable proliferation. Autocrine signaling in tumor stemenable cells may enable cells to castration survive castration and androgen independent tumor growth. enable androgen independent tumor growth.

8. Summary and Conclusion 8. Summary and Conclusions Shh is the dominantly expressed ligand in the developing prostate. In absence of Shh, Ihh Shh is the dominantly expressed ligand in the developing prostate. In absence of Shh, Ihh expression is up-regulated and provides functional compensation. In the regenerating adult prostate, expression is up-regulated and provides functional compensation. In the regenerating adult prostate, both Shh and Ihh contribute to pathway activity and inhibit ductal branching by restricting the both Shh and Ihh contribute to pathway activity and inhibit ductal branching by restricting the expression of HGF. expression of HGF. Paracrine signaling in the developing prostate plays an important role in regulating growth and ductal development. The growth effects and target gene regulation are stage-dependent.

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There is evidence for autocrine signaling in the developing prostate but its role is unclear. Preliminary studies suggest it may have an important role in the capacity to survive castration and enable ductal regeneration. The role of Hh signaling in development and regeneration is recapitulated in cancer. There is strong evidence for paracrine signaling in prostate cancer. The effect of paracrine signaling may be critically dependent on the phenotype of the tumor stroma. This has major implications for the design of clinical trials of Hh inhibitors in prostate cancer. The role of autocrine signaling remains ill-defined. Our studies suggest a link between autocrine signaling and the capacity of epithelial cells to survive castration and there is a suggestion of pathway activation in high grade, androgen independent prostate cancer. It is as yet unclear if this is ligand-dependent or due to non-canonical activation mechanisms. Acknowledgments: I wish to gratefully acknowledge Min Yu’s provision of the data presented in Figures 2 and 3. Conflicts of Interest: The author declares no conflict of interest.

References 1.

2. 3. 4.

5.

6.

7.

8. 9. 10.

11.

12. 13. 14.

Cunha, G.R.; Sekkingstad, M.; Meloy, B.A. Heterospecific induction of prostatic development in tissue recombinants prepared with mouse, rat, rabbit and human tissues. Differentiation 1983, 24, 174–180. [CrossRef] [PubMed] Sugimura, Y.; Cunha, G.R.; Donjacour, A.A. Morphogenesis of ductal networks in the mouse prostate. Biol. Reprod. 1986, 34, 961–971. [CrossRef] [PubMed] Podlasek, C.A.; Barnett, D.H.; Clemens, J.Q.; Bak, P.M.; Bushman, W. Prostate development requires Sonic hedgehog expressed by the urogenital sinus epithelium. Dev. Biol. 1999, 209, 28–39. [CrossRef] [PubMed] Lamm, M.L.; Catbagan, W.S.; Laciak, R.J.; Barnett, D.H.; Hebner, C.M.; Gaffield, W.; Walterhouse, D.; Iannaccone, P.; Bushman, W. Sonic hedgehog activates mesenchymal Gli1 expression during prostate ductal bud formation. Dev. Biol. 2002, 249, 349–366. [CrossRef] [PubMed] Wang, B.E.; Shou, J.; Ross, S.; Koeppen, H.; de Sauvage, F.J.; Gao, W.Q. Inhibition of epithelial ductal branching in the prostate by sonic hedgehog is indirectly mediated by stromal cells. J. Biol. Chem. 2003, 278, 18506–18513. [CrossRef] [PubMed] Freestone, S.H.; Marker, P.; Grace, O.C.; Tomlinson, D.C.; Cunha, G.R.; Harnden, P.; Thomson, A.A. Sonic hedgehog regulates prostatic growth and epithelial differentiation. Dev. Biol. 2003, 264, 352–362. [CrossRef] [PubMed] Berman, D.M.; Desai, N.; Wang, X.; Karhadkar, S.S.; Reynon, M.; Abate-Shen, C.; Beachy, P.A.; Shen, M.M. Roles for Hedgehog signaling in androgen production and prostate ductal morphogenesis. Dev. Biol. 2004, 267, 387–398. [CrossRef] [PubMed] Yu, M.; Bushman, W. Differential stage-dependent regulation of prostatic epithelial morphogenesis by Hedgehog signaling. Dev. Biol. 2013, 380, 87–98. [CrossRef] [PubMed] Yu, M.; Gipp, J.; Yoon, J.W.; Iannaccone, P.; Walterhouse, D.; Bushman, W. Sonic hedgehog-responsive genes in the fetal prostate. J. Biol. Chem. 2009, 284, 5620–5629. [CrossRef] [PubMed] Gao, N.; Ishii, K.; Mirosevich, J.; Kuwajima, S.; Oppenheimer, S.R.; Roberts, R.L.; Jiang, M.; Yu, X.; Shappell, S.B.; Caprioli, R.M.; et al. Forkhead box A1 regulates prostate ductal morphogenesis and promotes epithelial cell maturation. Development 2005, 132, 3431–3443. [CrossRef] [PubMed] Pu, Y.; Huang, L.; Prins, G.S. Sonic hedgehog-patched Gli signaling in the developing rat prostate gland: Lobe-specific suppression by neonatal estrogens reduces ductal growth and branching. Dev. Biol. 2004, 273, 257–275. [CrossRef] [PubMed] Doles, J.; Cook, C.; Shi, X.; Valosky, J.; Lipinski, R.; Bushman, W. Functional compensation in Hedgehog signaling during mouse prostate development. Dev. Biol. 2006, 295, 13–25. [CrossRef] [PubMed] Lim, A.; Shin, K.; Zhao, C.; Kawano, S.; Beachy, P.A. Spatially restricted Hedgehog signalling regulates HGF-induced branching of the adult prostate. Nat. Cell Biol. 2014, 16, 1135–1145. [CrossRef] [PubMed] Thomsen, M.K.; Francis, J.C.; Swain, A. The role of Sox9 in prostate development. Differentiation 2008, 76, 728–735. [CrossRef] [PubMed]

J. Dev. Biol. 2016, 4, 30

15.

16.

17. 18. 19.

20.

21.

22. 23. 24.

8 of 8

Mehta, V.; Schmitz, C.T.; Keil, K.P.; Joshi, P.S.; Abler, L.L.; Lin, T.M.; Taketo, M.M.; Sun, X.; Vezina, C.M. Beta-catenin (CTNNB1) induces Bmp expression in urogenital sinus epithelium and participates in prostatic bud initiation and patterning. Dev. Biol. 2013, 376, 125–135. [CrossRef] [PubMed] Doles, J.D.; Vezina, C.M.; Lipinski, R.J.; Peterson, R.E.; Bushman, W. Growth, morphogenesis, and differentiation during mouse prostate development in situ, in renal grafts, and in vitro. Prostate 2005, 65, 390–399. [CrossRef] [PubMed] Yu, M.; Bushman, W. University of Wisconsin, Madison, WI, USA. Unpublished work, 2013. Shi, X.; Gipp, J.; Bushman, W. Anchorage-independent culture maintains prostate stem cells. Dev. Biol. 2007, 312, 396–406. [CrossRef] [PubMed] Karhadkar, S.S.; Bova, G.S.; Abdallah, N.; Dhara, S.; Gardner, D.; Maitra, A.; Isaacs, J.T.; Berman, D.M.; Beachy, P.A. Hedgehog signalling in prostate regeneration, neoplasia and metastasis. Nature 2004, 431, 707–712. [CrossRef] [PubMed] Fan, L.; Pepicelli, C.V.; Dibble, C.C.; Catbagan, W.; Zarycki, J.L.; Laciak, R.; Gipp, J.; Shaw, A.; Lamm, M.L.; Munoz, A.; et al. Hedgehog signaling promotes prostate xenograft tumor growth. Endocrinology 2004, 145, 3961–3970. [CrossRef] [PubMed] Sanchez, P.; Hernández, A.M.; Stecca, B.; Kahler, A.J.; DeGueme, A.M.; Barrett, A.; Beyna, M.; Datta, M.W.; Datta, S.; Ruiz i Altaba, A. Inhibition of prostate cancer proliferation by interference with SONIC HEDGEHOG-GLI1 signaling. Proc. Natl. Acad. Sci. USA 2004, 101, 12561–12566. [CrossRef] [PubMed] Zhang, J.; Lipinski, R.; Shaw, A.; Gipp, J.; Bushman, W. Lack of demonstrable autocrine hedgehog signaling in human prostate cancer cell lines. J. Urol. 2007, 177, 1179–1185. [CrossRef] [PubMed] McCarthy, F.R.; Brown, A.J. Autonomous Hedgehog signalling is undetectable in PC-3 prostate cancer cells. Biochem. Biophys. Res. Commun. 2008, 373, 109–112. [CrossRef] [PubMed] Sheng, T.; Li, C.; Zhang, X.; Chi, S.; He, N.; Chen, K.; McCormick, F.; Gatalica, Z.; Xie, J. Activation of the hedgehog pathway in advanced prostate cancer. Mol. Cancer 2004, 3, 29. [CrossRef] [PubMed] © 2016 by the author; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).