Inhibition of epithelial ductal branching in the prostate by sonic hedgehog is indirectly mediated by stromal cells

Unique and complimentary activities of the Gli transcription factors in Hedgehog signaling

The Gli family of transcription factors (Gli1, 2 and 3) mediate the Hedgehog morphogenetic signal by regulating the expression of downstream target genes. Aberrations in Hedgehog signaling seriously affect vertebrate development. Postnatally, Hedgehog signaling has been postulated to play a pivotal role in healing and repair processes and inappropriate pathway activation has been implicated in several types of cancers. To better understand both the upstream regulation of the Gli transcription factors, as well as their unique and combinatorial roles in regulating the expression of Hedgehog target genes, we have characterized embryonic fibroblasts (MEFs) from Gli mutant mice. Stimulation of wild-type MEFs by Sonic Hedgehog (Shh) peptide elicited unique profiles of induction of Hedgehog target genes Gli1, Ptc1, and Hip1. Gli2 loss-of-function was associated with diminished Shh-induced target gene expression, while Gli3 loss-of-function was associated with increased basal and Shh-induced target gene expression. The loss of Gli1 alone had no effect on target gene induction but did diminish Shh-induced target gene expression when combined with the loss of Gli2 or Gli3. Additionally, overexpression of Gli1 induced target gene expression in Gli2(-/-)3(-/-) MEFs, while Shh stimulation did not. Using MEFs expressing only Gli2 or Gli3, we found that both cyclopamine and the PKA activator forskolin inhibited target gene induction mediated by Gli2 and Gli3. These results demonstrate that Gli2 and Gli3 share common regulatory mechanisms and modulate Hedgehog target gene expression directly and independently while also regulating Gli1 expression, which in specific contexts, coordinately contributes to target gene activation.

Cytotoxic effects induced by a combination of cyclopamine and gefitinib, the selective hedgehog and epidermal growth factor receptor signaling inhibitors, in prostate cancer cells

Although the blockade of the hedgehog cascade by using cyclopamine has been reported to inhibit the growth of some cancer cell types, few studies on the mechanism by which this drug alone or in combination with other cytotoxic agents induces its cytotoxic effect have been reported. In our study, we evaluate, for the first time, the antiproliferative and cytotoxic effects induced by a combination of selective SMO inhibitor, cyclopamine and epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, gefitinib on metastatic prostate cancer (PC) cells. The results revealed that cyclopamine, alone or at a lower concentration in combination with gefitinib, inhibited the growth of sonic hedgehog- (SHH), epidermal growth factor- (EGF) and serum-stimulated androgen-sensitive LNCaP-C33 and LNCaP-LN3 and androgen-independent LNCaP-C81, DU145 and PC3 cells. The antiproliferative effect of cyclopamine and gefitinib, alone or in combination, was mediated via a blockade of the PC3 cells in the G1 phase of the cell cycle. Importantly, the combined cyclopamine and gefitinib also caused a higher rate of apoptotic death of PC cells compared to single agents. The cytotoxic effect induced by these drugs in PC3 cells appears to be mediated at least, in part, via the mitochondrial pathway through the depolarization of the mitochondrial membrane and the release of cytochrome c and reactive oxygen species into the cytosol. This was also accompanied by the activation of caspase cascades, PARP cleavage and DNA fragmentation. Additionally, the combined cyclopamine and gefitinib were more effective at suppressing the invasiveness of PC3 cells through matrigel in vitro as the drugs alone. These findings indicate that the simultaneous blockade of SHH-GLI-1 and EGF-EGFR signaling, which results in the growth arrest and massive rate of apoptotic cell death, represents a promising strategy for a more effective treatment of metastatic PC forms.

Notch signaling is required for normal prostatic epithelial cell proliferation and differentiation

Notch pathway is crucial for stem/progenitor cell maintenance, growth and differentiation in a variety of tissues. Using a transgenic cell ablation approach, we found in our previous study that cells expressing Notch1 are crucial for prostate early development and re-growth. Here, we further define the role of Notch signaling in regulating prostatic epithelial cell growth and differentiation using biochemical and genetic approaches in ex vivo or in vivo systems. Treatment of developing prostate grown in culture with inhibitors of gamma-secretase/presenilin, which is required for Notch cleavage and activation, caused a robust increase in proliferation of epithelial cells co-expressing cytokeratin 8 and 14, lack of luminal/basal layer segregation and dramatically reduced branching morphogenesis. Using conditional Notch1 gene deletion mouse models, we found that inactivation of Notch1 signaling resulted in profound prostatic alterations, including increased tufting, bridging and enhanced epithelial proliferation. Cells within these lesions co-expressed both luminal and basal cell markers, a feature of prostatic epithelial cells in predifferentiation developmental stages. Microarray analysis revealed that the gene expression in a number of genetic networks was altered following Notch1 gene deletion in prostate. Furthermore, expression of Notch1 and its effector Hey-1 gene in human prostate adenocarcinomas were found significantly down-regulated compared to normal control tissues. Taken together, these data suggest that Notch signaling is critical for normal cell proliferation and differentiation in the prostate, and deregulation of this pathway may facilitate prostatic tumorigenesis.

Sonic hedgehog signaling regulates the expression of insulin-like growth factor binding protein-6 during fetal prostate development

At the onset of ductal morphogenesis in the developing prostate, Shh expression condenses at evaginations of urogenital sinus epithelium and activates Gli transcription factors in the adjacent mesenchyme. Abrogation of Hedgehog signaling disrupts proper prostatic budding, ductal growth, and branching. We now show that Hedgehog signaling regulates the expression of insulin-like growth factor binding protein-6 (Igfbp-6) in the developing mouse prostate. Igfbp-6 is a secreted factor that specifically binds insulin-like growth factor-II (IGF-II), prevents its binding to the IGF-I receptor, and is thought to regulate the activity of IGF-II in growth and differentiation. Igfbp-6 is expressed in both the developing and adult prostate. In the urogenital sinus, Igfbp-6 mRNA colocalized with Ptc1 and Gli1 mRNA in the mesenchyme, while Igfbp-6 protein was found in both the mesenchymal and epithelial layers. Exogenous Shh peptide induced expression of Igfbp-6 in the developing prostate while the chemical inhibitor of Hedgehog signaling, cyclopamine, reduced its expression. These studies show that Igfbp-6 is an actual target of Shh signaling in the urogenital sinus and provide the first evidence for a linkage between the Hedgehog and IGF signaling pathways in prostate development.

Forkhead box A1 regulates prostate ductal morphogenesis and promotes epithelial cell maturation

We have previously shown that a forkhead transcription factor Foxa1 interacts with androgen signaling and controls prostate differentiated response. Here, we show the mouse Foxa1 expression marks the entire embryonic urogenital sinus epithelium (UGE), contrasting with Shh and Foxa2, which are restricted to the basally located cells during prostate budding. The Foxa1-deficient mouse prostate shows a severely altered ductal pattern that resembles primitive epithelial cords surrounded by thick stromal layers. Characterization of these mutant cells indicates a population of basal-like cells similar to those found in the embryonic UGE, whereas no differentiated or mature luminal epithelial cells are found in Foxa1-deficient epithelium. These phenotypic changes are accompanied with molecular aberrations, including focal epithelial activation of Shh and elevated Foxa2 and Notch1 in the null epithelium. Perturbed epithelial-stromal interactions induced by Foxa1-deficient epithelium is evident, as demonstrated by the expansion of surrounding smooth muscle and elevated levels of stromal factors (Bmp4, Fgf7, Fgf10 and Gli). The prostatic homeobox protein Nkx3.1, a known proliferation inhibitor, was downregulated in Foxa1-deficient epithelial cells, while several prostate-specific androgen-regulated markers, including a novel Foxa1 target, are absent in the null prostate. These data indicate that Foxa1 plays a pivotal role in controlling prostate morphogenesis and cell differentiation.

Expression of Foxa transcription factors in the developing and adult murine prostate

BACKGROUND

The Foxa family (a1, a2, and a3) of proteins are transcription factors that are central to endodermal development. Recently, Foxa1 has been shown to regulate the transcription of several murine and human prostate specific genes involved in differentiated function by interacting with DNA promoter sequences and androgen receptors. Currently, the developmental expression pattern of Foxa proteins in the murine prostate is unknown.

METHODS

Male CD-1 mice (embryonic, prepubertal, pubertal, and adult) were used for immunohistochemical analysis of Foxa1, a2, and a3. Immunofluorescence was also performed for androgen receptor and cytokeratin 14 expression. Prostate tissue from pre-pubertal, pubertal, and adult mice were analyzed by Western blot and RT-PCR analysis for Foxa1, a2, and a3 expression.

RESULTS

Strong Foxa1 immunoreactivity was observed in epithelial cells throughout prostate development, growth, and adult differentiation. Prominent Foxa2 protein expression was only observed in the early stages of prostate development and was exclusively localized to epithelial cells of the forming buds. RT-PCR analysis identified low Foxa2 mRNA expression levels in the ventral and dorsolateral lobes of the adult prostate, with Foxa2 epithelial cell expression being localized to periurethral regions of the murine adult prostatic complex. Foxa3 expression was not observed in the murine prostate.

CONCLUSIONS

Foxa proteins represent epithelial cell markers in the murine prostate gland. The early expression of Foxa1 and a2 proteins in prostate formation suggests that these proteins play an important role in normal prostate development, in addition to differentiated secretory function.

Prostate cancer and the met hepatocyte growth factor receptor

The hepatocyte growth factor/scatter factor (HGF/SF) and its receptor, the Met protein tyrosine kinase, form a classic ligand-receptor system for epithelial-mesenchymal communications in the normal and cancerous prostate. This review illustrates the expression and activities of HGF/SF and Met during prostate development, homeostasis, and carcinogenesis. The participation of HGF/SF in the morphogenetic program of rodent prostate development, the role of Met in normal human prostate epithelium, and underlying mechanisms of deregulated Met expression in localized and metastatic prostate cancer are discussed. On the basis of the commonly observed overexpression of Met in metastatic prostate cancer, HGF/SF-Met-targeted imaging and therapeutic agents can now be applied toward diagnosis and treatment.

Sonic hedgehog regulates early human thymocyte differentiation by counteracting the IL-7-induced development of CD34+ precursor cells

The Hedgehog (Hh) family of signaling molecules normally functions in the development of numerous tissues by regulating cellular differentiation and proliferation. Recent results have demonstrated that the different components of the Hh signaling pathway are expressed in the human thymus. In this study, we investigate the potential role of Sonic hedgehog (Shh) in human intrathymic T cell maturation. Results show that the expression of the two components of the Hh receptor, Patched and Smoothened, is mostly restricted to CD34+ precursor cells that are committing to the T cell lineage. Shh significantly increased the viability of CD34+ T cell precursors modulating bcl-2 and bax protein expression, and also inhibited their proliferation. The treatment of chimeric human-mouse fetal thymus organ cultures with Shh resulted in an arrested thymocyte differentiation and an accumulation of CD34+ progenitor cells. This effect was mainly attributed to the ability of Shh to counteract the IL-7-induced proliferation and differentiation of CD34+ cells. Shh down-regulated in the precursor cell population the expression of IL-7R as well as stromal-derived factor-1 chemokine receptor, CXCR4, and inhibited IL-7-dependent STAT5 phosphorylation. Therefore, Shh may function as a maintenance factor for intrathymic CD34+ precursor cells.

Activation of the hedgehog pathway in advanced prostate cancer

BACKGROUND

The hedgehog pathway plays a critical role in the development of prostate. However, the role of the hedgehog pathway in prostate cancer is not clear. Prostate cancer is the second most prevalent cause of cancer death in American men. Therefore, identification of novel therapeutic targets for prostate cancer has significant clinical implications.

RESULTS

Here we report that activation of the hedgehog pathway occurs frequently in advanced human prostate cancer. We find that high levels of hedgehog target genes, PTCH1 and hedgehog-interacting protein (HIP), are detected in over 70% of prostate tumors with Gleason scores 8-10, but in only 22% of tumors with Gleason scores 3-6. Furthermore, four available metastatic tumors all have high expression of PTCH1 and HIP. To identify the mechanism of the hedgehog signaling activation, we examine expression of Su(Fu) protein, a negative regulator of the hedgehog pathway. We find that Su(Fu) protein is undetectable in 11 of 27 PTCH1 positive tumors, two of them contain somatic loss-of-function mutations of Su(Fu). Furthermore, expression of sonic hedgehog protein is detected in majority of PTCH1 positive tumors (24 out of 27). High levels of hedgehog target genes are also detected in four prostate cancer cell lines (TSU, DU145, LN-Cap and PC3). We demonstrate that inhibition of hedgehog signaling by smoothened antagonist, cyclopamine, suppresses hedgehog signaling, down-regulates cell invasiveness and induces apoptosis. In addition, cancer cells expressing Gli1 under the CMV promoter are resistant to cyclopamine-mediated apoptosis. All these data suggest a significant role of the hedgehog pathway for cellular functions of prostate cancer cells.

CONCLUSION

Our data indicate that activation of the hedgehog pathway, through loss of Su(Fu) or overexpression of sonic hedgehog, may involve tumor progression and metastases of prostate cancer. Thus, targeted inhibition of hedgehog signaling may have significant implications of prostate cancer therapeutics.

Sonic hedgehog-patched Gli signaling in the developing rat prostate gland: lobe-specific suppression by neonatal estrogens reduces ductal growth and branching

While prostate gland development is dependent on androgens, other hormones including retinoids and estrogens can influence this process. Brief exposure to high-dose estrogen during the neonatal period in rats leads to permanent, lobe-specific aberrations in the prostate gland, a phenomenon referred to as developmental estrogenization. We have previously shown that this response is mediated through alterations in steroid receptor expression; however, further downstream mechanisms remain unclear. Herein, we examined Sonic hedgehog (Shh)-patched (ptc)-gli in the developing rat prostate gland, its role in branching morphogenesis, and the effects of neonatal estrogens on its expression and localization to determine whether a disturbance in this signaling pathway is involved in mediating the estrogenized phenotype. Shh was expressed in epithelial cells at the distal tips of elongating ducts in discreet, heterogeneous foci, while ptc and gli1-3 were expressed in the adjacent mesenchymal cells in the developing gland. The addition of Shh protein to cultured neonatal prostates reduced ductal growth and branching, decreased Fgf10 transcript, and increased Bmp4 expression in the adjacent mesenchyme. Shh-induced growth suppression was reversed by exogenous Fgf10, but not noggin, indicating that Fgf10 suppression is the proximate cause of the growth inhibition. A model is proposed to show how highly localized Shh expression along with regulation of downstream morphogens participates in dichotomous branching during prostate morphogenesis. Neonatal exposure to high-dose estradiol suppressed Shh, ptc, gli1, and gli3 expressions and concomitantly blocked ductal branching in the dorsal and lateral prostate lobes specifically. In contrast, ventral lobe branching and Shh-ptc-gli expression were minimally affected by estrogen exposure. Organ culture studies with lateral prostates confirmed that estradiol suppressed Shh-ptc-gli expression directly at the prostatic level. Taken together, the present findings indicate that lobe-specific decreases in Shh-ptc-gli expression are involved in mediating estradiol-induced suppression of dorsal and lateral lobe ductal growth and branching during prostate morphogenesis.

Inhibition of prostate cancer proliferation by interference with SONIC HEDGEHOG-GLI1 signaling

Prostate cancer is the most common solid tumor in men, and it shares with all cancers the hallmark of elevated, nonhomeostatic cell proliferation. Here we have tested the hypothesis that the SONIC HEDGEHOG (SHH)-GLI signaling pathway is implicated in prostate cancer. We report expression of SHH-GLI pathway components in adult human prostate cancer, often with enhanced levels in tumors versus normal prostatic epithelia. Blocking the pathway with cyclopamine or anti-SHH antibodies inhibits the proliferation of GLI1+/PSA+ primary prostate tumor cultures. Inversely, SHH can potentiate tumor cell proliferation, suggesting that autocrine signaling may often sustain tumor growth. In addition, pathway blockade in three metastatic prostate cancer cell lines with cyclopamine or through GLI1 RNA interference leads to inhibition of cell proliferation, suggesting cell-autonomous pathway activation at different levels and showing an essential role for GLI1 in human cells. Our data demonstrate the dependence of prostate cancer on SHH-GLI function and suggest a novel therapeutic approach.

Hedgehog signaling promotes prostate xenograft tumor growth

During fetal prostate development, Sonic hedgehog (Shh) expression by the urogenital sinus epithelium activates Gli-1 expression in the adjacent mesenchyme and promotes outgrowth of the nascent ducts. Shh signaling is down-regulated at the conclusion of prostate ductal development. However, a survey of adult human prostate tissues reveals substantial levels of Shh signaling in normal, hyperplasic, and malignant prostate tissue. In cancer specimens, the Shh expression is localized to the tumor epithelium, whereas Gli-1 expression is localized to the tumor stroma. Tight correlation between the levels of Shh and Gli-1 expression suggests active signaling between the tissue layers. To determine whether Shh-Gli-1 signaling could be functionally important for tumor growth and progression, we performed experiments with the LNCaP xenograft tumor model and demonstrated that: 1). Shh expressed by LNCaP tumor cells activates Gli-1 expression in the tumor stroma, 2). genetically engineered Shh overexpression in LNCaP cells leads to increased tumor stromal Gli-1 expression, and 3). Shh overexpression dramatically accelerates tumor growth. These data suggest that hedgehog signaling from prostate cancer cells to the stroma can elicit the expression of paracrine signals, which promote tumor growth.

Roles for Hedgehog signaling in androgen production and prostate ductal morphogenesis

Previous studies have demonstrated that the Hedgehog (Hh) signaling pathway plays a critical role in the development and patterning of many endodermally derived tissues. We have investigated the role of Sonic hedgehog (Shh) in formation of the prostate gland by examining the urogenital phenotype of Shh mutant fetuses. Consistent with earlier work reporting an essential role for Shh in prostate induction, we have found that Shh mutant fetuses display abnormal urogenital development and fail to form prostate buds. Unexpectedly, however, we have discovered that this prostate defect could be rescued by three different methods: renal grafting, explant culture in the presence of androgens, and administration of dihydrotestosterone (DHT) to pregnant mice, indicating that the prostate defect in Shh mutants is due to insufficient levels of androgens. Furthermore, we find that the inhibition of Hh pathway signaling by treatment with cyclopamine does not block prostate formation in explant culture, but instead produces morphological defects consistent with a role for Hh signaling in ductal patterning. Taken together, our studies indicate that the initial organogenesis of the prostate proceeds independently of Shh, but that Shh or other Hh ligands may play a role in subsequent events that pattern the prostate.

Notch1-expressing cells are indispensable for prostatic branching morphogenesis during development and re-growth following castration and androgen replacement

Notch expression is frequently associated with progenitor cells, and its function is crucial for development. Our recent work showing that Notch1 is selectively expressed in basal epithelial cells of the prostate and higher Notch1 expression during development suggests that Notch1-expressing cells may define progenitor cells in the prostate. To test this hypothesis, we have generated a transgenic mouse line in which the Notch1-expressing cells can be ablated in a controlled manner. Specific targeting was achieved by expressing the bacterial nitroreductase, an enzyme that catalyzes its substrate into a cytotoxin capable of inducing apoptosis, under the Notch1 promoter. Cell death in transgenic prostate was confirmed by histological analyses including terminal dUTP nick-end labeling and caspase 3 immunocytochemical staining. We evaluated the consequences of ablation of Notch1-expressing cells in two systems, organ culture of early postnatal prostates and re-growth of prostate in castrated mice triggered by hormone replacement. Our data show that elimination of Notch1-expressing cells inhibited the branching morphogenesis, growth, and differentiation of early postnatal prostate in culture and impaired prostate re-growth triggered by hormone replacement in castrated mice. Furthermore, we found that Notch1 expression following castration and hormone replacement was concomitant with known basal cell markers p63 and cytokeratin 14 and was high in the proliferative human prostate epithelial cells. Taken together, these data suggest that Notch1-expressing cells define the progenitor cells in the prostatic epithelial cell lineage, which are indispensable for prostatic development and re-growth.

Sonic hedgehog signaling plays an essential role during embryonic salivary gland epithelial branching morphogenesis

Gene targeting studies indicate that sonic hedgehog (Shh) signaling plays an essential role during craniofacial development. Because numerous mandibular derivatives (e.g., teeth, tongue, Meckel's cartilage) are absent in Shh null mice and the embryonic submandibular salivary gland (SMG) develops from the mandibular arch, we postulated that Shh signaling is important for embryonic SMG development. To address this question, we first determined the spatiotemporal distribution of Shh; two transmembrane proteins, patched 1 (Ptc) and Smoothened (Smo), which act as a negative or a positive regulator of the Shh signal, respectively; and the Gli 3 transcription factor, which is downstream of the Shh signal. The epithelial localization of Shh, Ptc, Smo, and Gli 3 suggests that Shh signaling may act within the epithelium in a juxtacrine manner. The SMG phenotype in our embryonic day (E) 18.5 Shh null mice can be characterized as "paedomorphic," that is, it fails to progress to ontogenic stages beyond the Early Pseudoglandular ( approximately E14). In a complementary set of experiments, we used organ culture to evaluate the effect of enhanced or abrogated Shh signaling on embryonic SMG development in vitro. Paired E13 (Late Initial Bud stage) or E14 (Pseudoglandular stage) SMGs were cultured in the presence or absence of exogenous Shh peptide supplementation; Shh-supplemented explants exhibit a significant stage-dependent increase in branching morphogenesis compared with control explants. Furthermore, by using cyclopamine, a steroidal alkaloid that specifically disrupts the Shh pathway, to abrogate endogenous Shh signaling in vitro, we found a significant decrease in branching in cyclopamine-treated explants compared with controls, as well as a significant decrease in epithelial cell proliferation. Our results indicate that Shh signaling plays an essential role during embryonic SMG branching morphogenesis. Exogenous FGF8 peptide supplementation in vitro rescues the abnormal SMG phenotype seen in cyclopamine-treated explants, demonstrating that overexpression of a parallel, but related, downstream signaling pathway can compensate for diminished Shh signaling and restore embryonic SMG branching morphogenesis.

Sonic hedgehog regulates prostatic growth and epithelial differentiation

The Sonic hedgehog (SHH)-signalling pathway mediates epithelial-mesenchymal interactions in several tissues during development and disease, and we have investigated its role in rat ventral prostate (VP) development. We have demonstrated that Shh and Ptc expression correlates with growth and development of the prostate and that their expression is not regulated by androgens in the VP. Prostatic budding was induced in response to testosterone in Shh null mouse urogenital sinus (UGS) explants grown in vitro and in rat UGS explants cultured with cyclopamine, suggesting that SHH-signalling is not critical for prostatic induction. SHH-signalling was disrupted at later stages of VP development (in vitro), resulting in a reduction in organ size, an increase in ductal tip number, and reduced proliferation of ductal tip epithelia. The addition of recombinant SHH to VPs grown in vitro caused a decrease in ductal tip number and expansion of the mesenchyme. In the presence of testosterone, inhibition of SHH-signalling accelerated the canalisation of prostatic epithelial ducts and resulted in ducts that showed morphological similarities to cribiform prostatic intraepithelial neoplasia (PIN). The epithelia of these ducts also demonstrated precocious and aberrant differentiation, when examined by immunohistochemistry for p63 and cytokeratin 14. In conclusion, we show that SHH-signalling is not essential for prostatic induction, but is important for prostatic growth, branching, and proliferation, and that androgen-stimulated growth in the absence of signalling from the SHH pathway results in aberrant epithelial differentiation.