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

Activation of the hedgehog-signaling pathway in human cancer and the clinical implications

The hedgehog pathway, initially discovered by two Nobel laureates Drs E Wieschaus and C Nusslein-Volhard in Drosophila, is a major regulator for cell differentiation, tissue polarity and cell proliferation. Studies from many laboratories reveal activation of this pathway in a variety of human cancer, including basal cell carcinomas (BCCs), medulloblastomas, leukemia, gastrointestinal, lung, ovarian, breast and prostate cancers. It is thus believed that targeted inhibition of hedgehog signaling may be effective in treatment and prevention of human cancer. Even more exciting is the discovery and synthesis of specific signaling antagonists for the hedgehog pathway, which have significant clinical implications in novel cancer therapeutics. In this review, we will summarize major advances in the last 2 years in our understanding of hedgehog signaling activation in human cancer, interactions between hedgehog signaling and other pathways in carcinogenesis, potential antagonists for hedgehog signaling inhibition and their clinical implications for human cancer treatment.

Recent patents for Hedgehog pathway inhibitors for the treatment of malignancy

BACKGROUND

There is increasing evidence suggesting that blocking aberrant Hedgehog (Hh) signaling can be a novel therapeutic avenue for the treatment of cancer. During the past decade, efforts from academic and industrial groups have led to the discovery of a variety of Hh pathway inhibitors.

OBJECTIVE

This review covers the patent literature related to Hh pathway inhibitors for the treatment of proliferative diseases, regardless of their modes of action.

METHODS

A comprehensive survey of the patent literature since 1999 is presented.

RESULTS/CONCLUSION

Most reported Hh pathway inhibitors act on the key signaling transducer Smoothened (SMO). Screening of compound libraries using reporter and binding assays have identified a broad diversity of chemical structures that interact with SMO. These screening approaches, followed by conventional medicinal chemistry, have delivered important clinical drug candidates, such as GDC-0449 and XL-139. In addition, modification of the naturally occurring Veratrum alkaloid cyclopamine has resulted in various active analogues, including clinical drug candidate IPI-926. Although there are recent scientific literature reports of small molecules acting downstream of SMO, there is limited patent literature on this mode of Hh pathway inhibition.

GLI1 is a central mediator of EWS/FLI1 signaling in Ewing tumors

The Ewing Sarcoma Family Tumors (ESFT) consist of the classical pathologic entities of Ewing Sarcoma and peripheral Primitive Neuroectodermal Tumor. Occurring largely in the childhood through young adult years, these tumors have an unsurpassed propensity for metastasis and have no defined cell of origin. The biology of these aggressive malignancies centers around EWS/FLI1 and related EWS/ETS chimeric transcription factors, which are largely limited to this tumor class. Much progress has been made in the identification of a network of loci whose expression is modulated by EWS/FLI1 and its congeners. To date, little progress has been made in reconstructing the sequence of direct and indirect events that produce this network of modulated loci. The recent identification of GLI1 as an upregulated target of EWS/ETS transcription factors suggests a target which may be a more central mediator in the ESFT signaling network. In this paper, we further define the relationship of EWS/FLI1 expression and GLI1 upregulation in ESFT. This relationship is supported with data from primary tumor specimens. It is consistently observed across multiple ESFT cell lines and with multiple means of EWS/FLI1 inhibition. GLI1 inhibition affects tumor cell line phenotype whether shRNA or endogenous or pharmacologic inhibitors are employed. As is seen in model transformation systems, GLI1 upregulation by EWS/FLI1 appears to be independent of Hedgehog stimulation. Consistent with a more central role in ESFT pathogenesis, several known EWS/FLI1 targets appear to be targeted through GLI1. These findings further establish a central role for GLI1 in the pathogenesis of Ewing Tumors.

Tumour-initiating cells: challenges and opportunities for anticancer drug discovery

The hypothesis that cancer is driven by tumour-initiating cells (popularly known as cancer stem cells) has recently attracted a great deal of attention, owing to the promise of a novel cellular target for the treatment of haematopoietic and solid malignancies. Furthermore, it seems that tumour-initiating cells might be resistant to many conventional cancer therapies, which might explain the limitations of these agents in curing human malignancies. Although much work is still needed to identify and characterize tumour-initiating cells, efforts are now being directed towards identifying therapeutic strategies that could target these cells. This Review considers recent advances in the cancer stem cell field, focusing on the challenges and opportunities for anticancer drug discovery.

Hedgehog pathway responsiveness correlates with the presence of primary cilia on prostate stromal cells

Background

Hedgehog (Hh) signaling from the urogenital sinus (UGS) epithelium to the surrounding mesenchyme plays a critical role in regulating ductal formation and growth during prostate development. The primary cilium, a feature of most interphase vertebrate cell types, serves as a required localization domain for Hh signaling transducing proteins.

Results

Immunostaining revealed the presence of primary cilia in mesenchymal cells of the developing prostate. Cell-based assays of a urongenital sinus mesenchymal cell line (UGSM-2) revealed that proliferation-limiting (serum starvation and/or confluence) growth conditions promoted cilia formation and correlated with pathway activation associated with accumulation of Smoothened in primary cilia. The prostate cancer cell lines PC-3, LNCaP, and 22RV1, previously shown to lack demonstrable autocrine Hh signaling capacity, did not exhibit primary cilia even under proliferation-limiting growth conditions.

Conclusion

We conclude that paracrine Hedgehog signaling activity in the prostate is associated with the presence of primary cilia on stromal cells but that a role in autocrine Hh signaling remains speculative.

The Sonic Hedgehog pathway stimulates prostate tumor growth by paracrine signaling and recapitulates embryonic gene expression in tumor myofibroblasts

The Hedgehog (Hh) pathway contributes to prostate cancer growth and progression. The presence of robust Sonic Hedgehog (Shh) expression in both normal prostate and localized cancer challenged us to explain the unique growth-promoting effect in cancer. We show here that paracrine Hh signaling exerts a non-cell autonomous effect on xenograft tumor growth and that Hh pathway activation in myofibroblasts alone is sufficient to stimulate tumor growth. Nine genes regulated by Hh in the mesenchyme of the developing prostate were found to be regulated in the stroma of Hh overexpressing xenograft tumors. Correlation analysis of gene expression in matched specimens of benign and malignant human prostate tissue revealed a partial five-gene fingerprint of Hh-regulated expression in stroma of all cancers and the complete nine-gene fingerprint in the subset of tumors exhibiting a reactive stroma. No expression fingerprint was observed in benign tissues. We conclude that changes in the prostate stroma due to association with cancer result in an altered transcriptional response to Hh that mimics the growth-promoting actions of the fetal mesenchyme. Patients with an abundance of myofibroblasts in biopsy tissue may comprise a subgroup that will exhibit a particularly good response to anti-Hh therapy.

Exploration of Shh and BMP paracrine signaling in a prostate cancer xenograft

Stromal-epithelial signaling is a critical regulator of normal prostate development and has been speculated to play an equally important role in the development and progression of prostate cancer. Sonic hedgehog (Shh) and bone morphogenetic proteins (BMP-4, BMP-7), expressed by the urogenital sinus epithelium and mesenchyme, exert reciprocal and coordinate effects on outgrowth of nascent prostate ducts. Over-expression of Shh in the LNCaP xenograft was shown previously to accelerate tumor growth by a paracrine mechanism. A survey of BMP regulators expressed in the developing prostate revealed increased Noggin and BMP-7 mRNA in the stromal component of Shh over-expressing xenografts. In vitro studies demonstrated that treatment of LNCaP cells with BMP-4 and BMP-s7 induced Id-1 expression and inhibited tumor cell proliferation. The activity of BMP-4 was abrogated by co-addition of Noggin; the activity of BMP-7 was not. Quantitative analysis of BMP signaling revealed ambivalent results: decreased tumor cell expression of the BMP response gene Id-1 but increased staining for phospho-SMAD 1,5, 8. To directly test whether increased xenograft tumor growth could be explained by Noggin-mediated blockade of BMP-2/4 effects on tumor cell proliferation, we generated LNCaP xenografts containing stromal cells over-expressing Noggin. Tumor cells in these xenografts exhibited decreased Id-1 and reduced SMAD phosphorylation, but tumor growth was not altered. We conclude that tumor cell Shh expression can induce significant changes in expression of BMP ligands and inhibitors in the stromal microenvironment but that acceleration of LNCaP xenograft tumor growth by Shh over-expression cannot be attributed solely to increased Noggin expression in the tumor stroma.

Small-molecule modulators of the Sonic Hedgehog signaling pathway

Sonic hedgehog (Shh) is the most widely characterized of the three vertebrate Hedgehog homologs, and is essential for proper embryonic development. Shh binds to its receptor, Patched (Ptch1), resulting in the de-repression of Smoothened (Smo). This leads to the activation of Gli2, which regulates the transcription of target genes that include Gli1 and Ptch1. Several synthetic and naturally occurring small-molecule modulators of Smo have been discovered. Shh-signaling antagonists that bind to Smo include cyclopamine, SANT1, and Cur-61414. Shh signaling agonists that bind to Smo include the synthetic small molecules purmorphamine and SAG. Small molecules that inhibit Shh signaling downstream of Smo, GANT58 and GANT61 have also been reported. Robotnikinin inhibits the Shh pathway by directly targeting Shh. Although progress has been made in understanding and modulating Shh signaling, fundamental aspects of Shh signal transduction remain obscure, including the mechanism(s) whereby Ptch1 regulates Smo activity. Small-molecule modulators of Shh signaling provide a means to regulate the activity of a pathway implicated in medulloblastoma, basal cell carcinoma (BCC), pancreatic cancer, prostate cancer and developmental disorders. Several Shh inhibitors have not succeeded in the clinic for unknown reasons, but clinical trials in BCC and pancreatic cancer with the promising Smo antagonists GDC-0449 and IPI-926 are currently underway.

Discovery of a potent and orally active hedgehog pathway antagonist (IPI-926)

Recent evidence suggests that blocking aberrant hedgehog pathway signaling may be a promising therapeutic strategy for the treatment of several types of cancer. Cyclopamine, a plant Veratrum alkaloid, is a natural product antagonist of the hedgehog pathway. In a previous report, a seven-membered D-ring semisynthetic analogue of cyclopamine, IPI-269609 (2), was shown to have greater acid stability and better aqueous solubility compared to cyclopamine. Further modifications of the A-ring system generated three series of analogues with improved potency and/or solubility. Lead compounds from each series were characterized in vitro and evaluated in vivo for biological activity and pharmacokinetic properties. These studies led to the discovery of IPI-926 (compound 28), a novel semisynthetic cyclopamine analogue with substantially improved pharmaceutical properties and potency and a favorable pharmacokinetic profile relative to cyclopamine and compound 2. As a result, complete tumor regression was observed in a Hh-dependent medulloblastoma allograft model after daily oral administration of 40 mg/kg of compound 28.

Emerging drugs in the treatment of pancreatic cancer

BACKGROUND

Pancreatic cancer is the fourth leading cause of cancer-related death in the US. However, there is a growing belief that novel biological agents could improve survival of patients with this cancer. Gemcitabine-based chemotherapy remains the cornerstone treatment for advanced pancreatic cancers. So far, the current targeted agents that have been used in combination with gemcitabine have failed to improve clinical outcomes. This failure may stem from the heterogeneous molecular pathogenesis of pancreatic cancers, which involves several oncogenic pathways and defined genetic mutations.

OBJECTIVE

The aims of this review are: i) to define the existing treatments available at present for patients with pancreatic cancers in the neo-adjuvant, adjuvant, locally advanced and metastatic settings; ii) to highlight the molecular heterogeneity of the cancers and the rationale for targeting specific oncogenic pathways; iii) to give an overview of targeted agents that may potentially have an impact in the treatment of pancreatic cancers.

CONCLUSIONS

Molecular pathogenesis of pancreatic cancer involves several pathways and defined genetic mutations. Targeting these complex molecular pathways with a combination of novel biological and chemotherapeutic agents could potentially improve patient outcome.

Structure-activity relationships and cancer-cell selective toxicity of novel inhibitors of glioma-associated oncogene homologue 1 (Gli1) mediated transcription

We report novel inhibitors of Gli1-mediated transcription as potential anticancer agents. Focused chemical libraries were designed and assessed for inhibition of functional cell-based Gli1-mediated transcription and selective toxicity toward cancer cells. The SAR was revealed, and the selectivity of the lead compounds' inhibition of Gli1-mediated transcription over that of Gli2 was determined. Compound 63 (NMDA298-1), which inhibited Gli1-mediated transcription in C3H10T1/2 cells with an IC(50) of 6.9 muM, showed 3-fold selectivity for inhibiting transcription mediated by Gli1 over that by Gli2. Cell-viability assays were performed to evaluate the chemical library in a normal cell line and a panel of cancer cell lines with or without up-regulated expression of the Gli1 gene. These compounds decreased the viability of several cancer cell lines but were less active in the noncancerous BJ-hTERT cells.

Inhibition of p70S6K2 down-regulates Hedgehog/GLI pathway in non-small cell lung cancer cell lines

Background

The Hedgehog (HH) pathway promotes tumorigenesis in a diversity of cancers. Activation of the HH signaling pathway is caused by overexpression of HH ligands or mutations in the components of the HH/GLI1 cascade, which lead to increased transactivation of GLI transcription factors. Although negative kinase regulators that antagonize the activity of GLI transcription factors have been reported, including GSK3β, PKA and CK1s, little is known regarding positive kinase regulators that are suitable for use on cancer therapeutic targets. The present study attempted to identify kinases whose silencing inhibits HH/GLI signalling in non-small cell lung cancer (NSCLC).

Results

To find positive kinase regulators in the HH pathway, kinome-wide siRNA screening was performed in a NSCLC cell line, A549, harboring the GLI regulatory reporter gene. This showed that p70S6K2-silencing remarkably reduced GLI reporter gene activity. The decrease in the activity of the HH pathway caused by p70S6K2-inhibition was accompanied by significant reduction in cell viability. We next investigated the mechanism for p70S6K2-mediated inhibition of GLI1 transcription by hypothesizing that GSK3β, a negative regulator of the HH pathway, is activated upon p70S6K2-silencing. We found that phosphorylated-GSK3β (Ser9) was reduced by p70S6K2-silencing, causing a decreased level of GLI1 protein. Finally, to further confirm the involvement of p70S6K2 in GLI1 signaling, down-regulation in GLI-mediated transcription by PI3KCA-inhibition was confirmed, establishing the pivotal role of the PI3K/p70S6K2 pathway in GLI1 cascade regulation.

Conclusion

We report herein that inhibition of p70S6K2, known as a downstream effector of the PI3K pathway, remarkably decreases GLI-mediated transactivation in NSCLC by reducing phosphorylated-GSK3β followed by GLI1 degradation. These results infer that p70S6K2 is a potential therapeutic target for NSCLC with hyperactivated HH/GLI pathway.

Late reactivation of sonic hedgehog by Helicobacter pylori results in population of gastric epithelial cells that are resistant to apoptosis: implication for gastric carcinogenesis

As much as that a disturbance of tissue homeostasis through dysregulated apoptosis is generally associated with carcinogenesis, gastric carcinogenesis after Helicobacter pylori infection could be the accumulated consequence of imbalances between apoptosis and proliferation. Since sonic hedgehog (Shh) has been reported to play versatile roles in various tumorigenesis, we hypothesized that late reactivation of sonic hedgehog by H. pylori infection results in population of gastric epithelial cells that are resistant to apoptosis. The Resistant Clones against H. pylori-induced Apoptosis (RCHA) were established and maintained up to 19th cell passages, during which the serial changes of Shh expression were measured. Apoptosis was measured in N-Shh over-expressed stable cell lines and compared with parent cell line after either infected with H. pylori or treated with cyclopamine. For clinical relevance, the expressions of Shh were compared in tissues from gastric adenoma or adenocarcinoma according to H. pylori infection. Longer passages of RCHA after H. pylori infection, the higher expressions of Shh, suggesting RCHA was associated with the reactivation of Shh. Significant decrement in subG1 phase of cell cycle and attenuated executions of apoptosis after H. pylori infection in cells of Shh overexpression, whereas either Shh siRNA or cyclopamine increased the H. pylori-induced cytotoxicity and significantly abrogated anti-apoptotic actions imposed by Shh. Significantly higher expressions of Shh were seen in H. pylori-associated gastric cancers than H. pylori-not associated gastric cancer. Late reactivation of sonic hedgehog by H. pylori infection results in population of gastric epithelial cells that are resistant to apoptosis and imposes proliferative changes under the background of atrophic gastritis, providing the carcinogenic basis.

Aberrant activation of hedgehog signaling pathway contributes to endometrial carcinogenesis through beta-catenin

The hedgehog and Wnt signaling pathways play important roles in human cancers with possible interaction. This study aimed at analysis and correlation of the expression of Gli1, a transcriptional factor and target gene of hedgehog signaling pathway, with clinicopathological parameters and expression of beta-catenin, an important member of the Wnt pathway, in normal, hyperplastic and malignant endometrium. Immunohistochemical study on 15 normal endometrium, 14 simple and complex hyperplasia without atypia, 37 atypical complex hyperplasia and 80 endometrial cancers showed significant Gli1 overexpression and beta-catenin nuclear immunoreactivity in endometrial cancers and atypical endometrial hyperplasia when compared with normal endometrium (P<0.05). Overexpression of Gli1 in endometrial cancers correlated with well-differentiated histological grade (P<0.001), non-myometrial invasion (P=0.004) and superficial myometrial invasion (P=0.041). beta-Catenin nuclear immunoreactivity was also associated with well-differentiated histology (P=0.013). Gli1 overexpression positively correlated with beta-catenin nuclear immunoreactivity in atypical complex hyperplasia (P=0.013) and endometrial carcinoma (P=0.017). Similar Gli1 and beta-catenin protein expression pattern was observed in normal and endometrial cancer cell lines by western blotting. We further showed a complex formation between Gli1 and beta-catenin protein in endometrial cancer cell lines in an immunoprecipitation study. Ectopic overexpression of Gli1 into endometrial cancer cells led to reduced expression of beta-catenin in cell cytoplasm and increased expression of beta-catenin in the nuclei. In summary, overexpression of Gli1 was an early event in endometrial carcinogenesis. Aberrant activation of hedgehog pathway may play important roles in endometrial cancer through beta-catenin nuclear accumulation.

Evolution and functional diversification of the GLI family of transcription factors in vertebrates

Background

In vertebrates the “SONIC HEDGEHOG” signalling pathway has been implicated in cell-fate determination, proliferation and the patterning of many different cell types and organs. As the GLI family members (GLI1, GLI2 and GLI3) are key mediators of hedgehog morphogenetic signals, over the past couple of decades they have been extensively scrutinized by genetic, molecular and biochemical means. Thus, a great deal of information is currently available about the functional aspects of GLI proteins in various vertebrate species. To address the roles of GLI genes in diversifying the repertoire of the Hh signalling and deploying them for the vertebrate specifications, in this study we have examined the evolutionary patterns of vertebrate GLI sequences within and between species.

Results

Phylogenetic tree analysis suggests that the vertebrate GLI1, GLI2 and GLI3 genes diverged after the separation of urochordates from vertebrates and before the tetrapods-bony fishes split. Lineage specific duplication events were also detected. Estimation of mode and strength of selection acting on GLI orthologs demonstrated that all members of the GLI gene family experienced more relaxed selection in teleost fish than in the mammalian lineage. Furthermore, the GLI1 gene appeared to have been exposed to different functional constraints in fish and tetrapod lineages, whilst a similar level of functional constraints on GLI2 and GLI3 was suggested by comparable average non-synonymous (Ka) substitutions across the lineages. A relative rate test suggested that the majority of the paralogous copies of the GLI family analyzed evolved with similar evolutionary rates except GLI1 which evolved at a significantly faster rate than its paralogous counterparts in tetrapods.

Conclusions

Our analysis shows that sequence evolutionary patterns of GLI family members are largely correlated with the reported similarities and differences in the functionality of GLI proteins within and between the various vertebrate species. We propose that duplication and divergence of GLI genes has increased in the complexity of vertebrate body plan by recruiting the hedgehog signalling for the novel developmental tasks.

Mechanisms of Hedgehog pathway activation in cancer and implications for therapy

The Hedgehog (Hh) signaling pathway regulates body patterning and organ development during embryogenesis. In adults the Hh pathway is mainly quiescent, with the exception of roles in tissue maintenance and repair, and its inappropriate reactivation has been linked to several disparate human cancers. In addition to cancers with mutations in components of the Hh pathway, Hh ligand-dependent cancers have been proposed to respond to Hh in an autocrine manner. More recent findings that Hh might instead signal in a paracrine manner from the tumor to the surrounding stroma or in cancer stem cells alter our understanding of Hh mechanisms in cancer, with important implications for choice of preclinical tumor models, drug screening, patient selection and therapeutic intervention. We review here the roles of the Hh pathway in cancer, Hh pathway inhibitors (HPIs) and early clinical trial results using a novel small molecule HPI, GDC-0449.

Paracrine sonic hedgehog signalling by prostate cancer cells induces osteoblast differentiation

BACKGROUND

Sonic hedgehog (Shh) and components of its signalling pathway have been identified in human prostate carcinoma and increased levels of their expression appear to correlate with disease progression and metastasis. The mechanism through which Shh signalling could promote metastasis in bone, the most common site for prostate carcinoma metastasis, has not yet been investigated. The present study determined the effect of Shh signalling between prostate cancer cells and pre-osteoblasts on osteoblast differentiation, a requisite process for new bone formation that characterizes prostate carcinoma metastasis.

RESULTS

LNCaP human prostate cancer cells modified to overexpress Shh (designated LNShh cells) and MC3T3 mouse pre-osteoblasts were maintained as mixed populations within the same culture chamber. In this non-conventional mixed culture system, LNShh cells upregulated the expression of Shh target genes Gli1 and Patched 1 (Ptc1) in MC3T3 cells and this was inhibited by cyclopamine, a specific chemical inhibitor of hedgehog signalling. Concomitantly, MC3T3 cells exhibited time-dependent decreased cell proliferation, upregulated alkaline phosphatase Akp2 gene expression, and increased alkaline phosphatase activity indicative of early phase osteoblast differentiation. LNShh cell-induced differentiation was inhibited in MC3T3 cells stably transfected with a dominant negative form of Gli1, a transcription factor that mediates Shh signalling. Interestingly, LNShh cells did not significantly increase the endogenous expression of the osteoblast differentiation transcription factor Runx2 and its target genes osteocalcin and osteopontin. Consistent with these results, exogenous Shh peptide did not upregulate Runx2 expression in MC3T3 cells. However, Runx2 levels were increased in MC3T3 cells by ascorbic acid, a known stimulator of osteoblast differentiation.

CONCLUSION

Altogether, these data demonstrate that Shh-expressing prostate cancer cells can directly and specifically induce differentiation in pre-osteoblasts via a Gli1-dependent mechanism that does not require transcriptional upregulation of Runx2. Paracrine activation of the Shh pathway in osteoblast progenitors and subsequent induction of osteoblast differentiation could be a mechanism through which high levels of Shh expression in prostate carcinoma contribute to bone metastasis. Targeting of paracrine Shh signalling may provide an effective therapeutic strategy against prostate carcinoma metastasis in bone.

Androgenic regulation of hedgehog signaling pathway components in prostate cancer cells

Hedgehog signaling is thought to play a role in several human cancers including prostate cancer. Although prostate cancer cells express many of the gene products involved in hedgehog signaling, these cells are refractory to the canonical signaling effects of exogenous hedgehog ligands or to activated Smoothened, the hedgehog-regulated mediator of Gli transcriptional activation. Here, we show that the expression of hedgehog ligands and some hedgehog target genes are regulated by androgen in the human prostate cancer cell line, LNCaP and its more metastatic variants (C4-2 and C4-2B). Androgen (R1881) strongly suppressed the expression of hedgehog ligands in these cells and their prolonged maintenance in androgen-deficient medium upregulated Sonic and Indian hedgehog mRNA and protein levels by up to 30,000-fold. Hedgehogs were released into the conditioned medium of androgen-deprived LNCaP cells and this medium was able to increase hedgehog target gene expression in hedgehog-responsive mouse fibroblasts (MC3T3-E1). Moreover, this activity was accompanied by increased expression of Gli target genes, Patched 1 and Gli2, in LNCaP that could be suppressed by cyclopamine, indicating that chronic androgen-deprivation also re-awakens the autocrine responsiveness of the cancer cells to hedgehog. In contrast to the suppressive effects of R1881 on hedgehog ligand and Gli2 expression, we found that Gli1 expression in LNCaP cells was induced by R1881. Given the ability of androgen to modulate the expression and release of hedgehog ligands and the activity of the autocrine hedgehog signaling pathway in these prostate cancer cells, our results imply that chronic androgen deprivation therapy (ADT) for prostate cancer might create a hedgehog signaling environment in the region of the tumor that could ultimately impact on the long term effectiveness of this treatment. This consideration supports the idea of clinically testing hedgehog-blocking drugs in conjunction with ADT in patients with advanced prostate cancer.

A GLI1-p53 inhibitory loop controls neural stem cell and tumour cell numbers

How cell numbers are determined is not understood. Hedgehog-Gli activity is involved in precursor cell proliferation and stem cell self-renewal, and its deregulation sustains the growth of many human tumours. However, it is not known whether GLI1, the final mediator of Hh signals, controls stem cell numbers, and how its activity is restricted to curtail tumourigenesis. Here we have altered the levels of GLI1 and p53, the major tumour suppressor, in multiple systems. We show that GLI1 expression in Nestin+ neural progenitors increases precursor and clonogenic stem cell numbers in vivo and in vitro. In contrast, p53 inhibits GLI1-driven neural stem cell self-renewal, tumour growth and proliferation. Mechanistically, p53 inhibits the activity, nuclear localisation and levels of GLI1 and in turn, GLI1 represses p53, establishing an inhibitory loop. We also find that p53 regulates the phosphorylation of a novel N' truncated putative activator isoform of GLI1 in human cells. The balance of GLI1 and p53 functions, thus, determines cell numbers, and prevalence of p53 restricts GLI1-driven stem cell expansion and tumourigenesis.

Sonic hedgehog in gastric physiology and neoplastic transformation: friend or foe?

PURPOSE OF REVIEW

To understand the role of sonic hedgehog (Shh) in normal gastric physiology and neoplastic transformation.

RECENT FINDINGS

Emerging evidence shows that gastric epithelial cells produce Shh ligand, which subsequently targets the mesenchyme. This paracrine signaling event is recapitulated by Shh-producing tumors that signal to the supporting stroma to encourage growth. Primary cilia contain components of the hedgehog signaling apparatus, and thus are typically found on responding stromal cells.

SUMMARY

In the stomach, Shh is produced in epithelial cells and received by responding cells in the mesenchyme. In vitro, Shh enhances gastric acid secretion and induces mucin expression. It remains to be determined whether the canonical signaling pathway mediates the observed epithelial effects. Shh expression and signaling is reduced in chronic gastritis, and Shh(-/-) embryos exhibit hyperplasia and metaplastic changes in the gastric mucosa. After its loss in the corpus, Shh is re-expressed in some gastric carcinomas typically arising in the distal stomach or antrum, suggesting that it promotes tumor growth.

Does prostate cancer co-opt the developmental program?

The hypothesis that cancer is a caricature of normal development and tissue renewal was originally based on descriptive studies of normal tissues and cancers. The concepts that arose from these studies were that both normal tissues and tumors are sustained by a self-renewing population of stem cells that initially gives rise to undifferentiated and highly proliferative progeny. Eventually, derivatives of these proliferating cells become growth quiescent and express differentiation markers characteristic of the organs within which they reside. A major difference between normal tissues and tumors is the impairment of differentiation in tumors such that undifferentiated, mitotically active cells accumulate in tumors. An important feature of the model is the idea that the biology of the undifferentiated and proliferating cell populations in tumors is governed by the same pathways that regulate normal development and tissue renewal. At the time these ideas were formulated, we lacked sufficient understanding of the molecular and cellular basis of prostate development and cancer progression to evaluate the validity of these ideas for understanding prostate cancer. Research in recent years has validated the prediction that cells with stem cell-like properties are a critical source of new cells both during prostate development and during prostate cancer progression. It is also the case that many of the genes that regulate prostatic development re-appear during prostate cancer progression. A closer examination of the best understood of these developmental regulatory pathways, the androgen-signaling pathway, reveals important differences between normal development and tumors. This pathway is co-opted in prostate cancer by genetic and epigenetic changes that alter the molecular details of how signaling is initiated and alter the transcriptional outcome of signaling by silencing key targets of androgen signaling and fusing androgen-responsive promoters to new genes to create new targets for androgen signaling. Future research is needed to understand if other developmental regulatory pathways are altered during prostate progression in a manner analogous to the androgen signaling pathway.

Synthetic microRNA targeting glioma-associated antigen-1 protein

The transcription factor glioma-associated antigen-1 (Gli-1) mediates activation of the sonic hedgehog (Shh) pathway, a process that precedes the transformation of tissue stem cells into cancerous stem cells and that is involved in early and late epithelial tumorigenesis. Hypothesizing that targeting the 3'-untranslated region (3'-UTR) of Gli-1 mRNA would effectively inhibit epithelial tumor cell proliferation, we evaluated several complementary miRNA molecules for their ability to do so. The synthetic miRNAs and corresponding duplex/small temporal RNAs were introduced as 3-nucleotide (nt) loops into GU-rich portions of the 3'UTR Gli-1 sequence. One particular miRNA (miRNA Gli-1-3548) and its corresponding duplex (Duplex 3548) significantly inhibited proliferation of Gli-1+ ovarian (SK-OV-3) and pancreatic (MiaPaCa-2) tumor cells by delaying cell division and activating late apoptosis in MiaPaCa-2 cells. Here, we describe the design of effective miRNA sequences and their applications as anti-gene agents.

Comparative expression of Hedgehog ligands at different stages of prostate carcinoma progression

Recent studies have revealed the potential involvement of Hedgehog (Hh) signalling in proliferation and invasive behaviour of prostate carcinoma (PCa). The aim of this study was to specify the role of Sonic Hh (Shh), Desert Hh (Dhh) and Indian Hh (Ihh) in the natural history of PCa. Hh ligands expression was compared in primary hormone-naive PCa (HNPC), hormone-treated PCa (HTPC) and hormone-refractory PCa (HRPC), using immunohistochemistry. Shh and Dhh were expressed by both epithelial and stromal cells of prostate tissues. Ihh was only expressed by stromal cells. For the three ligands, mRNA and immunostaining were not correlated. In HNPC, Shh epithelial expression was significantly associated with high Gleason scores (p = 0.03), metastatic lymph nodes (p = 0.004) and Dhh epithelial staining was associated with high pT stages (p = 0.003), seminal vesicle invasion (p = 0.03) and bladder neck invasion (p = 0.0008). Negative Shh staining in stromal cells was associated with high Gleason scores (p = 0.015), high pT stages (p = 0.01) and bladder neck invasion (p = 0.04). Concomitant absence of Shh and Dhh expression in stromal cells was an independent prognostic parameter for biological recurrence on multivariate analysis (p = 0.01). Epithelial expression of Shh and Dhh was increased in HTPC compared to HNPC (p = 0.02 and p = 0.04). Interestingly, in vitro, transcript analysis also showed increased expression of these 2 Hh ligands when androgen-sensitive LNCaP cells were maintained in androgen-free medium mimicking hormonal therapy. Epithelial expression of Dhh was increased (p < 0.0001) in HRPC compared to HNPC, while stromal expression of Shh and Dhh was decreased (p < 0.0001). In conclusion, the Hh signalling pathway is associated with pejorative pathological parameters in HNPC and is up-regulated in epithelial cells of HTPC and HRPC. Moreover, the lack of Hh molecules in stromal cells seems to be associated with invasive and hormone-refractory behaviours and suggests specific changes in stromal-epithelial crosstalks during PCa progression.

Aberrant activation of hedgehog signaling pathway in ovarian cancers: effect on prognosis, cell invasion and differentiation

Aberrant activation of hedgehog (HH) pathway has been implicated in the development of human malignancies. This study aimed at investigating the role of HH molecules in human ovarian carcinogenesis. The expression profiles of HH molecules were examined in ovarian tumor samples and ovarian cancer cell lines and the in vitro effects of HH molecules on cell proliferation, apoptosis, migration, invasion and cell differentiation as well as related downstream target genes were assessed. Overexpression of Patched and Gli1 protein in ovarian cancers correlated with poor survival of the patients (P = 0.008; P = 0.004). Significantly elevated expression of Sonic hedgehog messenger RNA was observed in ovarian cancers compared with normal tissues and benign ovarian tumors and such differential expression was specific to histological types (P < 0.05). Ectopic Gli1 overexpression in ovarian cancer cells conferred increased cell proliferation, cell mobility, invasiveness and change in differentiation in association with increased expression of E-cadherin, vimentin, Bcl-2, caspases as well as beta1 integrin, membrane type 1 matrix metalloproteinase (MT1-MMP) and vascular endothelial growth factor (VEGF). Treatment with 3-keto-N-(aminoethyl-aminocaproyl-dihydrocinnamoyl)-cyclopamine induced cancer cell apoptosis, suppressed cell growth, mobility and invasiveness and induced cancer cell dedifferentiation with decreased expression of E-cadherin, cytokeratin 7, Snail, calretinin, vimentin, Bcl-2, caspases, beta1 integrin, MT1-MMP and VEGF. Our data suggested that abnormal HH signaling activation plays important roles in the development and progression of ovarian cancers. Gli1 expression is an independent prognostic marker. Inhibition of the HH pathway molecules might be a valid therapeutic strategy for ovarian cancers.

Hedgehog: functions and mechanisms

The Hedgehog (Hh) family of proteins control cell growth, survival, and fate, and pattern almost every aspect of the vertebrate body plan. The use of a single morphogen for such a wide variety of functions is possible because cellular responses to Hh depend on the type of responding cell, the dose of Hh received, and the time cells are exposed to Hh. The Hh gradient is shaped by several proteins that are specifically required for Hh processing, secretion, and transport through tissues. The mechanism of cellular response, in turn, incorporates multiple feedback loops that fine-tune the level of signal sensed by the responding cells. Germline mutations that subtly affect Hh pathway activity are associated with developmental disorders, whereas somatic mutations activating the pathway have been linked to multiple forms of human cancer. This review focuses broadly on our current understanding of Hh signaling, from mechanisms of action to cellular and developmental functions. In addition, we review the role of Hh in the pathogenesis of human disease and the possibilities for therapeutic intervention.

GLI2 knockdown using an antisense oligonucleotide induces apoptosis and chemosensitizes cells to paclitaxel in androgen-independent prostate cancer

PURPOSE

GLI transcription factors mediate hedgehog signaling and have been implicated in several human malignancies, including prostate cancer. The objectives of this study were to characterize GLI2 expression levels in human prostate cancer cell lines and tissues to test the effect of antisense oligonucleotide (ASO) targeting GLI2 on androgen-independent (AI) prostate cancer cell lines.

EXPERIMENTAL DESIGN

A tissue microarray was used to characterize differences in GLI2 expression in benign prostate hyperplasia, prostate cancer treated by neoadjuvant hormonal therapy and AI prostate cancer. The effects of GLI2 ASO on PC-3 cell growth and paclitaxel chemosensitivity were assessed in vitro and in vivo. Oligonucleotide spotted microarray analysis was used to determine alteration in GLI2 coregulated genes after ASO treatment.

RESULTS

The expression of GLI2 was significantly higher in prostate cancer than in benign prostate hyperplasia, decreased after androgen ablation in a time-dependent fashion, but became highly expressed again in AI prostate cancer. GLI2 ASO treatment of PC-3 cells reduced GLI2 mRNA and protein levels in a dose-dependent manner. GLI2 knockdown increased PC-3 cell apoptotic rates and significantly decreased cell growth and modulated levels of apoptosis-related genes, such as Bcl2, Bcl-xL, and clusterin. GLI2 knockdown also changed levels of several cell cycle regulators, such as cyclin D1, p27, and PKC-eta. Systematic administration of GLI2 ASO in athymic mice significantly delayed PC-3 tumor progression and enhanced paclitaxel chemosensitivity.

CONCLUSIONS

These findings suggest that increased levels of GLI2 correlates with AI progression and that GLI2 may be a therapeutic target in castrate-resistant prostate cancer.

Therapeutic inhibition of Hedgehog-GLI signaling in cancer: epithelial, stromal, or stem cell targets?

Hedgehog (HH)-GLI signaling is a developmental patterning pathway used by many tumors for bulk proliferation that has been shown also to regulate cancer stem cell self-renewal and survival. Surprisingly, a recent study by Yauch et al. (2008) proposes that HH-GLI signaling acts only on the tumor stroma. The mode of action of HH-GLI signaling in cancer may shape the development of therapeutic antagonists.

Hedgehog signaling regulates brain tumor-initiating cell proliferation and portends shorter survival for patients with PTEN-coexpressing glioblastomas

The identification of brain tumor stem-like cells (BTSCs) has implicated a role of biological self-renewal mechanisms in clinical brain tumor initiation and propagation. The molecular mechanisms underlying the tumor-forming capacity of BTSCs, however, remain unknown. Here, we have generated molecular signatures of glioblastoma multiforme (GBM) using gene expression profiles of BTSCs and have identified both Sonic Hedgehog (SHH) signaling-dependent and -independent BTSCs and their respective glioblastoma surgical specimens. BTSC proliferation could be abrogated in a pathway-dependent fashion in vitro and in an intracranial tumor model in athymic mice. Both SHH-dependent and -independent brain tumor growth required phosphoinositide 3-kinase-mammalian target of rapamycin signaling. In human GBMs, the levels of SHH and PTCH1 expression were significantly higher in PTEN-expressing tumors than in PTEN-deficient tumors. In addition, we show that hyperactive SHH-GLI signaling in PTEN-coexpressing human GBM is associated with reduced survival time. Thus, distinct proliferation signaling dependence may underpin glioblastoma propagation by BTSCs. Modeling these BTSC proliferation mechanisms may provide a rationale for individualized glioblastoma treatment.

Prostate cancer and metastasis initiating stem cells

Androgen refractory prostate cancer metastasis is a major clinical challenge. Mechanism-based approaches to treating prostate cancer metastasis require an understanding of the developmental origin of the metastasis-initiating cell. Properties of prostate cancer metastases such as plasticity with respect to differentiated phenotype and androgen independence are consistent with the transformation of a prostate epithelial progenitor or stem cell leading to metastasis. This review focuses upon current evidence and concepts addressing the identification and properties of normal prostate stem or progenitor cells and their transformed counterparts.

Naturally occurring small-molecule inhibitors of hedgehog/GLI-mediated transcription

The aberrant hedgehog (Hh)/GLI signaling pathway causes the formation and progression of a variety of tumors. To search for Hh/GLI inhibitors, we screened for naturally occurring inhibitors of the transcriptional activator GLI1 by using a cell-based assay. We identified zerumbone (1), zerumbone epoxide (2), staurosporinone (9), 6-hydroxystaurosporinone (10), arcyriaflavin C (11) and 5,6-dihydroxyarcyriaflavin A (12) as inhibitors of GLI-mediated transcription. In addition, we isolated physalins F (17) and B (18) from Physalis minima, which are also potent inhibitors. These compounds also inhibited GLI2-mediated transactivation. Semiquantitative RT-PCR and Western blotting analysis further revealed that 1, 9, 17, and 18 decreased Hh-related component expressions. We also show that inhibitors of GLI-mediated transactivation reduce the level of the antiapoptosis Bcl2 expression. Finally, these identified compounds were cytotoxic to PANC1 pancreatic cancer cells, which express Hh/GLI components. These results strongly suggest that the cytotoxicity of the compounds to PANC1 cells correlates with their inhibition of GLI-mediated transcription.

Implications of hedgehog signaling antagonists for cancer therapy

The hedgehog (Hh) pathway, initially discovered in Drosophila by two Nobel laureates, Dr. Eric Wieschaus and Dr. Christiane Nusslein-Volhard, is a major regulator for cell differentiation, tissue polarity and cell proliferation. Studies from many laboratories, including ours, reveal activation of this pathway in most basal cell carcinomas and in approximately 30% of extracutaneous human cancers, including medulloblastomas, gastrointestinal, lung, breast and prostate cancers. Thus, it is believed that targeted inhibition of Hh signaling may be effective in treating and preventing many types of human cancers. Even more exciting is the discovery and synthesis of specific signaling antagonists for the Hh pathway, which have significant clinical implications in novel cancer therapeutics. This review discusses the major advances in the current understanding of Hh signaling activation in different types of human cancers, the molecular basis of Hh signaling activation, the major antagonists for Hh signaling inhibition and their potential clinical application in human cancer therapy.

Autonomous Hedgehog signalling is undetectable in PC-3 prostate cancer cells

The Hedgehog signalling pathway has been implicated in the development of prostate cancer, although this area remains controversial. Some but not all studies have noted relatively high Hedgehog pathway activity in commonly used prostate cancer cell lines. We aimed to evaluate the widely used PC-3 cell line as a model to investigate Hedgehog signalling in a prostate cancer setting. Using a sensitive Hedgehog inducible luciferase reporter assay, we found no evidence of autonomous Hedgehog signalling in PC-3 cells, irrespective of passage number. In addition, manipulations that should either increase (an oxysterol) or decrease (cyclopamine) Hedgehog pathway activity had no effect on reporter activity, and cyclopamine treatment did not affect PC-3 cell viability. Therefore, our findings contradict some earlier reports and caution against the use of PC-3 cells to investigate the Hedgehog pathway in a prostate cancer setting.

Novel human glioma-associated oncogene 1 (GLI1) splice variants reveal distinct mechanisms in the terminal transduction of the hedgehog signal

Hedgehog (HH) signaling is one of the key pathways with major significance for embryogenesis, tumorigenesis, and stem cell maintenance. Glioma-associated oncogene 1 (GLI1) is a transcription factor that acts as the terminal signaling effector but also represents a pathway target gene. Here we report the identification and functional properties of novel GLI1 splice variants generated by skipping exons 2 and 3 and encoding an N-terminal truncated GLI1 protein (GLI1DeltaN). Analysis of the GLI1DeltaN mRNAs in adult human tissues revealed comparable expression levels to the full-length GLI1 (GLI1FL), whereas in tumor cell lines a generally lower and more variable expression pattern was observed. Furthermore, GLI1DeltaN is up-regulated by HH signaling to the same extent as GLI1FL but has a weaker capacity to activate transcription. However, in specific cellular contexts GLI1DeltaN may be more potent than GLI1FL in activating endogenous gene expression. Moreover, the dual-specificity tyrosine phosphorylation-regulated kinase 1 (Dyrk1) potentiates the transcriptional activity of GLI1FL but not GLI1DeltaN. Interestingly, GLI1FL, in contrast to GLI1DeltaN, is localized solely at the nucleus, in line with its increased transcriptional capacity. The negative regulator of the pathway, Suppressor of Fused (SUFU), elicits a cytoplasmic retention of the GLI1 isoforms, which is more pronounced for GLI1FL, as this contains an N-terminal SUFU binding domain. Collectively, our findings reveal that the activation mechanism of the terminal transducer of the pathway, GLI1, is mediated not only by GLI1FL but also by the GLI1DeltaN variant.

Prostate epithelial cell fate

Androgen receptor (AR) within prostatic mesenchymal cells, with the absence of AR in the epithelium, is still sufficient to induce prostate development. AR in the luminal epithelium is required to express the secretory markers associated with differentiation. Nkx3.1 is expressed in the epithelium in early prostatic embryonic development and expression is maintained in the adult. Induction of the mouse prostate gland by the embryonic mesenchymal cells results in the organization of a sparse basal layer below the luminal epithelium with rare neuroendocrine cells that are interdispersed within this basal layer. The human prostate shows similar glandular organization; however, the basal layer is continuous. The strong inductive nature of embryonic prostatic and bladder mesenchymal cells is demonstrated in grafts where embryonic stem (ES) cells are induced to differentiate and organize as a prostate and bladder, respectively. Further, the ES cells can be driven by the correct embryonic mesenchymal cells to form epithelium that differentiates into secretory prostate glands and differentiated bladders that produce uroplakin. This requires the ES cells to mature into endoderm that gives rise to differentiated epithelium. This process is control by transcription factors in both the inductive mesenchymal cells (AR) and the responding epithelium (FoxA1 and Nkx3.1) that allows for organ development and differentiation. In this review, we explore a molecular mechanism where the pattern of transcription factor expression controls cell determination, where the cell is assigned a developmental fate and subsequently cell differentiation, and where the assigned cell now emerges with it's own unique character.

Functions of normal and malignant prostatic stem/progenitor cells in tissue regeneration and cancer progression and novel targeting therapies

This review summarizes the recent advancements that have improved our understanding of the functions of prostatic stem/progenitor cells in maintaining homeostasis of the prostate gland. We also describe the oncogenic events that may contribute to their malignant transformation into prostatic cancer stem/progenitor cells during cancer initiation and progression to metastatic disease stages. The molecular mechanisms that may contribute to the intrinsic or the acquisition of a resistant phenotype by the prostatic cancer stem/progenitor cells and their differentiated progenies with a luminal phenotype to the current therapies and disease relapse are also reviewed. The emphasis is on the critical functions of distinct tumorigenic signaling cascades induced through the epidermal growth factor system, hedgehog, Wnt/beta-catenin, and/or stromal cell-derived factor-1/CXC chemokine receptor-4 pathways as well as the deregulated apoptotic signaling elements and ATP-binding cassette multidrug transporter. Of particular therapeutic interest, we also discuss the potential beneficial effects associated with the targeting of these signaling elements to overcome the resistance to current treatments and prostate cancer recurrence. The combined targeted strategies toward distinct oncogenic signaling cascades in prostatic cancer stem/progenitor cells and their progenies as well as their local microenvironment, which could improve the efficacy of current clinical chemotherapeutic treatments against incurable, androgen-independent, and metastatic prostate cancers, are also described.

Transient inhibition of the Hedgehog pathway in young mice causes permanent defects in bone structure

The Hedgehog (Hh) pathway plays critical roles in normal development and in tumorigenesis. We generated Gli-luciferase transgenic mice to evaluate the Smo inhibitor, HhAntag, by whole animal functional imaging. HhAntag rapidly reduced systemic luciferase activity in 10- to 14-day-old mice following oral dosing. Although pathway activity was restored 2 days after drug removal, brief inhibition caused permanent defects in bone growth. HhAntag inhibited proliferation and promoted differentiation of chondrocytes, leading to dramatic expansion of the hypertrophic zone. After drug removal, osteoblasts invaded the cartilage plate, mineralization occurred, and there was premature fusion of the growth plate resulting in permanent disruption of bone epiphyses.

Cancer metastasis facilitated by developmental pathways: Sonic hedgehog, Notch, and bone morphogenic proteins

This review will highlight the significance of three critical pathways in developmental biology and our emerging understanding of their roles in regulating tumor metastasis: Bone morphogenic protein (BMP), Notch and Sonic hedgehog (SHH). We will discuss parallels between their known roles in development and how these processes can be used by tumor cells to create microenvironments that enhance tumor metastasis. That tumor cells usurp pathways critical to the developing embryo is not surprising, as many of the normal developmental programs include processes that are also seen during tumor progression to a metastatic phenotype, including epithelial to mesenchymal transition (EMT), tissue specific morphogenesis, cellular motility and invasion. BMPs are involved in EMT, contribute to tissue specific morphogenesis, and are expressed in highly-metastatic tumor cells. BMPs have also been hypothesized to have a role in the establishment of a pre-neoplastic niche. Notch and SHH facilitate neovascularization, angiogenesis, EMT and can contribute to the maintenance of highly-metastatic tumor stem cells.

Targeting hedgehog in cancer stem cells: how a paradigm shift can improve treatment response

The integration of developmental biology and cancer therapeutics has revolutionized the understanding of tumor proliferation. Cell-signaling pathways first recognized for their importance in embryogenesis have begun to inspire the scientific community to investigate new avenues in cancer initiation and growth. Other ground-breaking discoveries provided evidence for a revisit to the theory of cancer stem cells, which has long-term implications for the efficient and lasting elimination of cancer. This paradigm shift involves a change from viewing the malignant tumor as a perpetually mutating mass of clonogenic cells to seeing it as an organ mistakenly created by mutations that disrupt cell-signaling pathways in stem cells. As researchers find more evidence of the essential involvement of these signaling pathways in cancer formation and maintenance, the link between tumorigenesis and aberrant stem cell activation can be more clearly drawn. One such pathway is the hedgehog (Hh)-signaling pathway, which is important in growth and differentiation during embryogenesis and for proper functioning in many adult tissues. Investigation of this pathway and its involvement in cancer has already led to drug development that could eradicate basal cell carcinoma, the most common type of cancer in humans. Future research focused on Hh and related signaling pathways involved in cancer might improve treatment response in malignancies resistant to traditional therapy.

Gli-1 siRNA induced apoptosis in Huh7 cells

AIM: To investigate the effects of Gli-1 small interference RNA (siRNA) on Huh7 cells, and the change of Bcl-2 expression in Huh7 cells.

METHODS: Human hepatocellular carcinoma cells Huh7 were used. Cell viability was analyzed by 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay. The expressions of Gli-1 and Bcl-2 family members were detected by RT-PCR and Western blot. Apoptosis was detected by Flow cytometry using propidium iodide, measured by Hoechst 33258 staining using Advanced Fluorescence Microscopy and caspase-3 enzymatic assay. Cell growth was analyzed after treatment with Gli-1 siRNA and 5-fluorouracil (5-Fu).

RESULTS: Inhibition of Gli-1 mRNA in Huh7 cells through Gli-1 siRNA reduced cell viability. Gli-1 siRNA treatment also induced apoptosis by three criteria, increase in the sub-G1 cell cycle fraction, nuclear condensation, a morphologic change typical of apoptosis, and activation of caspase-3. Gli-1 siRNA was also able to down-regulate Bcl-2. However, Gli-1 siRNA resulted in no significant changes in Bcl-xl, Bax, Bad, and Bid. Furthermore, Gli-1 siRNA increased the cytotoxic effect of 5-Fu on Huh7 cell.

CONCLUSION: Down-regulation of Bcl-2 plays an important role in apoptosis induced by Gli-1 siRNA in HCC cells. Combination Gli-1 siRNA with chemotherapeutic drug could represent a more promising strategy against HCC. The effects of the strategies need further investigation

in vivo and may have potential clinical application.

Role of GLI2 transcription factor in growth and tumorigenicity of prostate cells

Aberrant activation of the Hedgehog (Hh) signaling pathway has been reported in various cancer types including prostate cancer. The GLI2 transcription factor is a primary mediator of Hh signaling. However, its relative contribution to development of prostate tumors is poorly understood. To establish the role of GLI2 in maintaining the tumorigenic properties of prostate cancer cells, we developed GLI2-specific small hairpin RNA. Knockdown of GLI2 in these cells resulted in significant down-regulation of the Hh signaling pathway, followed by inhibition of colony formation, anchorage-independent growth, and growth of xenografts in vivo. Conversely, ectopic expression of Gli2 in nontumorigenic prostate epithelial cells resulted in accelerated cell cycle progression, especially transition through G(2)-M, and augmented proliferation. Altogether, our findings suggest that GLI2 plays a critical role in the malignant phenotype of prostate cancer cells, and GLI2 may potentially become an attractive therapeutic target for the treatment of prostate cancer.