The role of hedgehog signalling in tumorigenesis

PDE4 inhibitor rolipram represses hedgehog signaling via ubiquitin-mediated proteolysis of GLI transcription factors to regress breast cancer

Aberrant activation of the Hedgehog (Hh) signaling pathway positively correlates with progression, invasion, and metastasis of several cancers, including breast cancer. Although numerous inhibitors of the Hh signaling pathway are available, several oncogenic mutations of key components of the pathway, including Smoothened, have limited their capability to be developed as putative anticancer drugs. In this study, we have modulated the Hh signaling pathway in breast cancer using a specific Food and Drug Administration-approved phosphodiesterase 4 inhibitor rolipram. The results indicated that increased levels of cAMP-dependent PKA, because of the treatment with rolipram on MCF-7 and MDA-MB-231 cells, induced PKA-mediated ubiquitination of glioma-associated oncogene homolog 2 full length (GLI2FL) and GLI3FL, leading to their transformation to respective repressor forms. This in turn reduced the level of GLI1 (glioma-associated oncogene homolog 1) transcription factor in a time-dependent manner. We have also shown that elevated levels of PKA reduced the level of phosphorylated glycogen synthase kinase 3β, which is known to augment PKA-mediated ubiquitination of GLI2FL and GLI3FL. Rolipram treatment also impaired wound healing and migration in both cell lines and significantly reduced tumor weight and volume in tumor-bearing mice. Histological analysis showed a reduction in multinucleated cells and cellular infiltration in the lungs of rolipram-treated mice. Moreover, rolipram decreased GLI1 levels in tumors by enhancing cAMP-PKA signaling. These findings suggest that rolipram effectively inhibits the Hh pathway downstream of Smoothened, offering potential as a therapeutic strategy for controlling breast cancer progression and metastasis, including both hormone-responsive and triple-negative subtypes.

An insight into the cancer stem cell survival pathways involved in chemoresistance in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is the most complex, aggressive and fatal subtype of breast cancer. Owing to the lack of targeted therapy and heterogenic nature of TNBC, chemotherapy remains the sole treatment option for TNBC, with taxanes and anthracyclines representing the general chemotherapeutic regimen in TNBC therapy. But unfortunately, patients develop resistance to the existing chemotherapeutic regimen, resulting in approximately 90% treatment failure. Breast cancer stem cells (BCSCs) are one of the major causes for the development of chemoresistance in TNBC patients. After surviving the chemotherapy damage, the presence of BCSCs results in relapse and recurrence of TNBC. Several pathways are known to regulate BCSCs' survival, such as the Wnt/β-catenin, Hedgehog, JAK/STAT and HIPPO pathways. Therefore it is imperative to target these pathways in the context of eliminating chemoresistance. In this review we will discuss the novel strategies and various preclinical and clinical studies to give an insight into overcoming TNBC chemoresistance. We present a detailed account of recent studies carried out that open an exciting perspective in relation to the mechanisms of chemoresistance.

Targeting Breast Cancer Stem Cells to Overcome Treatment Resistance

Despite advances in breast cancer diagnosis and treatment, many patients still fail therapy, resulting in disease progression, recurrence, and reduced overall survival. Historically, much focus has been put on the intrinsic subtyping based in the presence (or absence) of classical immunohistochemistry (IHC) markers such as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-related protein (HER2). However, it is widely understood that tumors are composed of heterogeneous populations of cells with a hierarchical organization driven by cancer stem cells (CSCs). In breast tumors, this small population of cells displaying stem cell properties is known as breast CSCs (BCSCs). This rare population exhibit a CD44⁺/CD24-/low phenotype with high ALDH activity (ALDH⁺), and possesses higher tolerability to chemotherapy, hormone therapy, and radiotherapy and is able to reproduce the bulk of the tumor after reduction of cell populations sensitive to first-line therapy leading to disease relapse. In this review, we present special attention to BCSCs with future directions in the establishment of a therapy targeting this population. Drugs targeting the main BCSCs signaling pathways undergoing clinical trials are also summarized.

Anti-Cancer Phytometabolites Targeting Cancer Stem Cells

Medicinal plants are a plentiful source of bioactive molecules with much structural diversity. In cancer treatment, molecules obtained from plants represent an attractive alternative to other treatments because several plant-derived compounds have exhibited lower toxicity and higher selectivity against cancer cells. In this review, we focus on the possible application of bioactive molecules obtained from plants against more primitive cell populations in cancers, cancer stem cells. Cancer stem cells are present in several kinds of tumors and are responsible for recurrences and metastases. Common anti-cancer drugs exhibit lower effectiveness against cancer stem cells because of their biological features. However, recently discovered natural phytometabolites exert cytotoxic effects on this rare population of cells in cancers. Therefore, this review presents the latest research on promising compounds from plants that can act as antitumor drugs and that mainly affect stem cell populations in cancers.

Efficacy of Vismodegib (Erivedge) for Basal Cell Carcinoma Involving the Orbit and Periocular Area

PURPOSE

Evaluate the effectiveness of vismodegib in the management of basal cell carcinoma with orbital extension and/or extensive periocular involvement.

METHODS

Retrospective chart review of 6 consecutive patients with biopsy-proven orbital basal cell carcinoma and 2 additional patients with extensive periocular basal cell carcinoma who were treated with oral vismodegib (150 mg/day) was performed.

RESULTS

Basal cell carcinoma extended in the orbit in 6 of 8 patients (involving orbital bones in 1 patient), and 2 of 8 patients had extensive periocular involvement (1 with basal cell nevus syndrome). Vismodegib therapy was the only treatment in 6 patients, off-label neoadjuvant in 1 patient, and adjuvant treatment in 1 patient. Orbital tumors in all 4 patients who received vismodegib as sole treatment showed partial response with a mean 83% shrinkage in tumor size after a median of 7 months of therapy. In the 2 patients receiving vismodegib as neoadjuvant or adjuvant therapies, there was complete response after a median of 7 months of therapy and no evidence of clinical recurrence after discontinuing therapy for a median of 15 months. The 2 patients with extensive periocular involvement experienced complete clinical response after a median 14 months of treatment. During treatment, the most common side effects were muscle spasm (75%) followed by alopecia (50%), dysgeusia (25%), dysosmia, and episodes of diarrhea and constipation (13%).

CONCLUSIONS

Basal cell carcinoma with orbital extension and extensive periocular involvement responds to vismodegib therapy. The long-term prognosis remains unknown, and additional prospective studies are indicated.

Evaluation of the 'Hedgehog' signaling pathways in squamous and basal cell carcinomas of the eyelids and conjunctiva

The purpose of the present study was to assess the role of hedgehog signaling pathway in the carcinogenesis of eyelid skin and conjunctival epithelial malignant tumors. The study was conducted on specimens from 41 patients with cutaneous eyelid basal cell carcinoma, 22 with bulbar conjunctival squamous cell carcinoma, 12 with bulbar conjunctival intraepithelial neoplasia. Major molecules of Hedgehog signaling pathway (Sonic Hedgehog [Shh] and Patched-1 [Ptch-1] and Glioma-associated oncogene [Gli-1]) were evaluated in paraffin-embedded tissue specimens using immunohistochemical staining. For each specimen, the percentage (<10%, 10–50%, >50%) and the intensity of the immunohistochemical staining (graded from 0 to 3) were calculated and the scores obtained by multiplication of two values were analyzed using the Kruskall-Wallis test. Shh and Ptch-1 expression levels were statistically significantly lower in the basal cell carcinoma group compared with the squamous cell carcinoma group (P=0.043 for Shh; P=0.030 for Ptch-1). In the conjunctival squamous cell carcinoma group, the Ptch-1 score was 0 in ~25% of specimens and the Gli-1 score was ≤2 in ~45% of cases. In the conjunctival intraepithelial neoplasia group, the Ptch-1 score was ≥2 in 66% of specimens, the Gli-1 score was ≤2 in ~92% of cases. Ptch-1 mutations contribute to the development of cutaneous eyelid basal cell carcinoma. The present study provides evidence that alterations in hedgehog signaling pathways may lead to transformation of the conjunctival intraepithelial neoplasia into invasive squamous cell carcinoma.

Hedgehog Signaling in the Maintenance of Cancer Stem Cells

Cancer stem cells (CSCs) represent a rare population of cells with the capacity to self-renew and give rise to heterogeneous cell lineages within a tumour. Whilst the mechanisms underlying the regulation of CSCs are poorly defined, key developmental signaling pathways required for normal stem and progenitor functions have been strongly implicated. Hedgehog (Hh) signaling is an evolutionarily-conserved pathway essential for self-renewal and cell fate determination. Aberrant Hh signaling is associated with the development and progression of various types of cancer and is implicated in multiple aspects of tumourigenesis, including the maintenance of CSCs. Here, we discuss the mounting evidence suggestive of Hh-driven CSCs in the context of haematological malignancies and solid tumours and the novel strategies that hold the potential to block many aspects of the transformation attributed to the CSC phenotype, including chemotherapeutic resistance, relapse and metastasis.

Salinomycin exerts anticancer effects on human breast carcinoma MCF-7 cancer stem cells via modulation of Hedgehog signaling

Breast cancer tissue contains a small population of cells that have the ability to self-renew, these cells are known as breast cancer stem cells (BCSCs). The Hedgehog signal transduction pathway plays a central role in stem cell development, its aberrant activation has been shown to contribute to the development of breast cancer, making this pathway an attractive therapeutic target. Salinomycin (Sal) is a novel identified cancer stem cells (CSCs) killer, however, the molecular basis for its anticancer effects is not yet clear. In the current study, Sal's ability to modulate the activity of key elements in the Hedgehog pathway was examined in the human breast cancer cell line MCF-7, as well as in a subpopulation of cancer stem cells identified within this cancer cell line. We show here that Sal inhibits proliferation, invasion, and migration while also inducing apoptosis in MCF-7 cells. Interestingly, in a subpopulation of MCF-7 cells with the CD44(+)/CD24(-) markers and high ALDH1 levels indicative of BCSCs, modulators of Hedgehog signaling Smo and Gli1 were significantly down-regulated upon treatment with Sal. These results demonstrate that Sal also inhibits proliferation and induces apoptosis of BCSCs, further establishing it as therapeutically relevant in the context of breast cancers and also indicating that modulation of Hedgehog signaling is one potential mechanism by which it exerts these anticancer effects.

The large intracellular loop of ptch1 mediates the non-canonical Hedgehog pathway through cyclin B1 in nevoid basal cell carcinoma syndrome

Mutations in the transmembrane receptor patched homolog 1 (Homo sapiens) (ptch1) are responsible for nevoid basal cell carcinoma syndrome (NBCCS), an autosomal dominant disorder that causes developmental abnormalities and predisposes the affected individuals to cancer. Many of these mutations, including mutations in the C-terminus of the large intracellular loop (ICL) of ptch1 (p.C727VfsX745 and p.S733IfsX736), result in the premature truncation of the protein. The ptch1‑C727VfsX745 and ptch1-S733IfsX736 mutations have been identified in patients with NBCCS‑associated keratocystic odontogenic tumors (KCOTs). In the present study, we found that the molecular mechanisms regulated by the non-canonical Hedgehog (Hh) signaling pathway through cyclin B1 are involved in the pathogenesis of NBCCS-associated KCOTs. In contrast to wild-type ptch1, ptch1-C727VfsX745 and ptch1‑S733IfsX736 clearly exhibited reduced binding to cyclin B1. Moreover, the cells expressing these two mutations demonstrated an increase in cell cycle progression and these two mutation constructs failed to inhibit cell proliferation. In addition, the mutants enhanced the activity of glioma-associated oncogene family zinc finger 1 (GLI1), a downstream reporter of Hh signaling. Thus, our data suggest that the non-canonical Hh pathway mediated through ptch1 and cyclin B1 is involved in the pathogenesis of NBCCS-associated KCOTs. The C-terminus of ICL in ptch1 may also be a potential therapeutic target in the treatment of this disease.

Profile of vismodegib and its potential in the treatment of advanced basal cell carcinoma

Basal cell carcinoma (BCC) is the most common human malignancy. Recent advances in our understanding of the critical biologic pathways implicated in the development and progression of BCC have led to the development of the first molecular targeted therapy for this disease. The hedgehog pathway is mutated in virtually all patients with BCC and recent trials with vismodegib, an inhibitor of this pathway, have shown significant responses. This review will discuss the importance of the hedgehog pathway in the pathogenesis of BCC and describe in detail the pharmacology of vismodegib in relation to its activity in advanced BCC.

Basal Cell Carcinoma Aggressiveness, Molecular Factors And Therapy: A Clinician Perspective

Basal cell carcinoma represents the most common skin and epithelial cancer. Most of the patients are cured by surgery. However, some cases display fullblown aggressiveness which has a dual connotation. The tumour may reach an impressive size being locally destructive while in rare cases, basal cell carcinomas may metastasize. If this agressivetumour is located on the face or neck, the surgeon is confronted with a clinical dilemma since total removal of the lesion with clear margins is impossible. Therefore, nonsurgical approaches need to be adopted in these cases. A better understand of the molecular pathways could theoretically lead to new improved therapeutic treatments. The current paper presents an update on the molecular factors with clinical importance for the treatment of basal cell carcinoma in parallel with presentation of an aggressive case as well as a review of the current therapeutic methods.

Scube activity is necessary for Hedgehog signal transduction in vivo

The Hedgehog (HH) signaling pathway is a central regulator of embryonic development, controlling the pattern and proliferation of a wide variety of organs. Previous studies have implicated the secreted protein, Scube2, in HH signal transduction in the zebrafish embryo (Hollway et al., 2006; Kawakami et al., 2005; Woods and Talbot, 2005) although the nature of the molecular function of Scube2 in this process has remained undefined. This analysis has been compounded by the fact that removal of Scube2 activity in the zebrafish embryo leads to only subtle defects in HH signal transduction in vivo (Barresi et al., 2000; Hollway et al., 2006; Ochi and Westerfield, 2007; van Eeden et al., 1996; Wolff et al., 2003). Here we present the discovery of two additional scube genes in zebrafish, scube1 and scube3, and demonstrate their roles in facilitating HH signal transduction. Knocking down the function of all three scube genes simultaneously phenocopies a complete loss of HH signal transduction in the embryo, revealing that Scube signaling is essential for HH signal transduction in vivo. We further define the molecular role of scube2 in HH signaling.

Hedgehog pathway as a drug target: Smoothened inhibitors in development

Emerging laboratory and clinical investigations demonstrate that Hedgehog signaling (Hh) represents a novel therapeutic target in various human cancers. This conserved signaling pathway precisely regulates self-renewal and terminal differentiation in embryonic development, but is typically silenced in adult tissues, with reactivation usually only during tissue repair. Aberrant Hh pathway signaling has been implicated in the pathogenesis, self-renewal, and chemotherapy resistance of a growing number of solid and hematologic malignancies. Major components of the Hh pathway include the Hh ligands (Sonic, Desert, and Indian), the transmembrane receptor Patched, the signal transducer Smoothened (Smo), and transcription factors Gli1–3 which regulate the transcription of Hh target genes. Mutations in Hh pathway genes, increased Hh signaling in tumor stroma, and Hh overexpression in self-renewing cells (cancer stem cells) have been described, and these different modes of Hh signaling have implications for the design of Hh pathway inhibitors and their integration into conventional treatment regimens. Discovery of a naturally-occurring Smo inhibitor, cyclopamine, and the identification of Hh pathway mutations and over expression in cancer cells prompted the development of several cyclopamine derivatives. Encouraging laboratory and in vivo data has resulted in Phase I and II clinical trials of Smo inhibitors. In this review, we will discuss the current understanding of Hh pathway signaling in malignancy and Smo antagonists in development. Recent data with these agents shows that they are well-tolerated and may be effective for subsets of patients. Challenges remain for appropriate patient selection and the optimal combination and sequence of these targeted therapies into current treatment paradigms.

Combination of hedgehog signaling blockage and chemotherapy leads to tumor reduction in pancreatic adenocarcinomas

OBJECTIVES

Activation of the hedgehog signal transduction pathway, triggered by hedgehog binding to the transmembrane receptor patched 1 (PTCH1) or by mutations in the PTCH1 gene, plays an important role in the development of various tumors.

METHODS

To investigate whether the Hedgehog signaling pathway is also active in human pancreatic adenocarcinomas, we determined the expression levels of the known Hedgehog target genes PTCH1 and GLI-1 in pancreatic tumors. To determine whether alterations in the PTCH1 gene are responsible for this pathway activation, we screened pancreatic carcinomas for mutations in PTCH. To investigate the contribution of hedgehog signaling to the tumorigenicity of pancreatic tumor cells, we blocked the Hedgehog pathway in cultured tumor cells and xenografts using the steroidal alkaloid cyclopamine and the small-molecule Hedgehog inhibitor Hh-Antag.

RESULTS

We identified single nucleotide polymorphisms (SNPs) within the PTCH1 gene but no somatic PTCH1 mutations. Pathway-blockage resulted in a significant dose-dependent reduction of tumor cell growth in vitro and in vivo. Moreover, combined treatment with cyclopamine and the conventional antimetabolite gemcitabine revealed a synergistic effect on the reduction of tumor growth in pancreatic adenocarcinoma xenografts.

CONCLUSIONS

Inhibition of Hedgehog signaling could be a promising approach for the treatment of pancreatic adenocarcinomas.

Computational analysis of expression of human embryonic stem cell-associated signatures in tumors

Background

The cancer stem cell model has been proposed based on the linkage between human embryonic stem cells and human cancer cells. However, the evidences supporting the cancer stem cell model remain to be collected. In this study, we extensively examined the expression of human embryonic stem cell-associated signatures including core genes, transcription factors, pathways and microRNAs in various cancers using the computational biology approach.

Results

We used the class comparison analysis and survival analysis algorithms to identify differentially expressed genes and their associated transcription factors, pathways and microRNAs among normal vs. tumor or good prognosis vs. poor prognosis phenotypes classes based on numerous human cancer gene expression data. We found that most of the human embryonic stem cell- associated signatures were frequently identified in the analysis, suggesting a strong linkage between human embryonic stem cells and cancer cells.

Conclusions

The present study revealed the close linkage between the human embryonic stem cell associated gene expression profiles and cancer-associated gene expression profiles, and therefore offered an indirect support for the cancer stem cell theory. However, many interest issues remain to be addressed further.

Topical treatment of Basal cell carcinomas in nevoid Basal cell carcinoma syndrome with a smoothened inhibitor

Basal cell carcinoma (BCC) is a distinctive manifestation in nevoid basal cell carcinoma syndrome (NBCCS) patients. Both inherited and acquired mutations of patched 1 (PTCH1), a tumor-suppressor gene controlling the activity of Smoothened (SMO), are the primary cause of the constitutive activation of the Hedgehog (HH) pathway, leading to the emergence of BCCs in NBCCS. LDE225, a distinct, selective antagonist of SMO, showed potent inhibition of basaloid tumor nest formation and mediated regression of preformed basaloid tumors in organ cultures of skin derived from Ptch1 heterozygous knockout mice. In a double-blind, randomized, vehicle-controlled, intraindividual study, a total of 8 NBCCS patients presenting 27 BCCs were treated twice daily with 0.75% LDE225 cream or vehicle for 4 weeks. Application of 0.75% LDE225 cream was well tolerated and showed no skin irritation. Of 13 LDE225-treated BCCs, 3 showed a complete, 9 a partial, and only 1 no clinical response. Except for one partial response, the vehicle produced no clinical response in any of the 14 treated BCCs. Treatment with 0.75% LDE225 cream in NBCCS patients was very well tolerated and caused BCC regression, thus potentially offering an attractive therapeutic alternative to currently available therapies for this indication.JID JOURNAL CLUB ARTICLE: For questions, answers, and open discussion about this article, please go to http://www.nature.com/jid/journalclub.

Organogenesis and tumorigenesis: insight from the JAK/STAT pathway in the Drosophila eye

The Janus kinase (JAK) signal transducer and activator of transcription (STAT) pathway is one of the main signaling pathways in eukaryotic cells. This pathway is used during diverse growth and developmental processes in multiple tissues to control cell proliferation, differentiation, survival, and apoptosis. In addition to its role during development, the JAK/STAT pathway has also been implicated in tumorigenesis. Drosophila melanogaster is a powerful genetic tool, and its eyes have been used extensively as a platform to study signaling pathways. Many reports have demonstrated that the JAK/STAT pathway plays pleiotropic roles in Drosophila eye development. Its functions and activation are decided by its interplay with other signal pathways and the epigenetic status. In this review, we focus on the functions and regulation of the JAK/STAT pathway during eye development and provide some insights into the study of this pathway in tumorigenesis. Developmental Dynamics 239:2522–2533, 2010. © 2010 Wiley-Liss, Inc.

The molecular genetics underlying basal cell carcinoma pathogenesis and links to targeted therapeutics

Mutations in the sonic hedgehog signaling pathway play a key role in the development of basal cell carcinomas. Specifically, mutations in the PTCH1 (also known as PTCH or PTC1) and SMO genes cause tumor formation through constitutive activation of the pathway. Misregulation of the pathway has also been implicated in the nevoid basal cell carcinoma syndrome and other tumors. Understanding the function of the sonic hedgehog pathway has led to novel strategies for treatment. In this review we highlight the role of the pathway in the pathogenesis of basal cell carcinoma and review potential targeted therapies.

Infundibulocystic basal cell carcinoma of the eyelid in basal cell nevus syndrome

PURPOSE

To describe the histopathologic findings in a series of eyelid basal cell carcinomas removed from patients with basal cell nevus syndrome.

METHODS

Retrospective case series of 5 patients with basal cell nevus syndrome identified from our oculoplastics service. The systemic and ophthalmic features were reviewed, and a retrospective histopathologic analysis of all available previously excised eyelid lesions was performed. The pertinent published literature on basal cell nevus syndrome and eyelid basal cell carcinoma was reviewed.

RESULTS

A total of 26 eyelid lesions were examined histopathologically. Twenty-three of these lesions were basal cell carcinomas. The infundibulocystic variant of basal cell carcinoma was identified most commonly (57%).

CONCLUSIONS

Eyelid basal cell carcinomas in patients with basal cell nevus syndrome were commonly of the infundibulocystic variety in our series. Infundibulocystic basal cell carcinomas, which can be clinically indistinguishable from the more common forms, are thought to be less aggressive than other types of basal cell carcinoma and are a reassuring histopathologic diagnosis. It is important for the ophthalmologist and pathologist to be aware of infundibulocystic basal cell carcinomas, as they are more common in patients with basal cell nevus syndrome and may be a clue to the diagnosis of this autosomal dominant cancer-predisposition syndrome or other associated syndromes. To our knowledge, this variant of basal cell carcinoma has not been previously discussed in the ophthalmic literature.

Mouse hitchhiker mutants have spina bifida, dorso-ventral patterning defects and polydactyly: identification of Tulp3 as a novel negative regulator of the Sonic hedgehog pathway

The mammalian Sonic hedgehog (Shh) signalling pathway is essential for embryonic development and the patterning of multiple organs. Disruption or activation of Shh signalling leads to multiple birth defects, including holoprosencephaly, neural tube defects and polydactyly, and in adults results in tumours of the skin or central nervous system. Genetic approaches with model organisms continue to identify novel components of the pathway, including key molecules that function as positive or negative regulators of Shh signalling. Data presented here define Tulp3 as a novel negative regulator of the Shh pathway. We have identified a new mouse mutant that is a strongly hypomorphic allele of Tulp3 and which exhibits expansion of ventral markers in the caudal spinal cord, as well as neural tube defects and preaxial polydactyly, consistent with increased Shh signalling. We demonstrate that Tulp3 acts genetically downstream of Shh and Smoothened (Smo) in neural tube patterning and exhibits a genetic interaction with Gli3 in limb development. We show that Tulp3 does not appear to alter expression or processing of Gli3, and we demonstrate that transcriptional regulation of other negative regulators (Rab23, Fkbp8, Thm1, Sufu and PKA) is not affected. We discuss the possible mechanism of action of Tulp3 in Shh-mediated signalling in light of these new data.

A concise and diversity-oriented approach to the synthesis of SAG derivatives

An efficient and rapid solution-phase combinatorial synthesis of the SAG library was developed. The salient features for this library synthesis is the application of carbothioamide-derived palladacycle-catalyzed Suzuki coupling reactions for the parallel synthesis of a series of pyridine-based biaryl aldehydes under aerobic conditions and a direct N-alkylation of carbamates using NaH as base in DMF in the presence of catalytic amount of water. The resultant library has been submitted to biological screening to evaluate their potential role in the regulation of Hedgehog pathway.

G-protein-coupled receptor GPR49 is up-regulated in basal cell carcinoma and promotes cell proliferation and tumor formation

The significance of Hedgehog (HH) signaling in the development of basal cell carcinoma (BCC) has been established. Although several target genes of HH signaling have been described previously, their precise role in tumorigenesis and cell proliferation is not yet known. To identify genes responsible for tumor formation in BCC, we screened a DNA microarray database of human BCC cases; the orphan G-protein-coupled receptor GPR49 was found to be up-regulated in all cases. GPR49 is a novel gene reported to be a marker of follicular and other tissue stem cells. Using real-time quantitative RT-PCR analysis, significant expression of GPR49 mRNA was observed in 19 of 20 BCC cases (95%) compared with controls. Up-regulation of GPR49 was confirmed by in situ hybridization. Moreover, knockdown of mouse Gpr49 showed suppression of cell proliferation in a mouse BCC cell line, and overexpression of GPR49 in human immortalized keratinocyte HaCaT cells induced proliferation. Furthermore, HaCaT cells overexpressing GPR49 showed tumor formation when transplanted into immunodeficient mice. In addition, inhibition of the HH signaling pathway in a mouse BCC cell line down-regulated endogenous Gpr49, whereas activation of HH signaling in mouse NIH3T3 cells up-regulated endogenous GPR49. These results suggest that GPR49 is expressed downstream of HH signaling and promotes cell proliferation and tumor formation in cases of BCC.

A molecular expression signature distinguishing follicular lesions in thyroid carcinoma using preamplification RT-PCR in archival samples

Follicular variant of papillary thyroid carcinoma is a lesion that frequently causes difficulties from a diagnostic perspective in the laboratory. The purpose of this study was to interrogate a cohort of archival thyroid lesions using gene expression analysis of a panel of markers proposed to have utility as adjunctive markers in the diagnosis of thyroid neoplasia and follicular variant of papillary thyroid carcinoma in particular. Laser Capture Microdissection was used to procure pure cell populations for extraction. In addition a novel, multiplex preamplification technique was used to facilitate analysis of multiple targets. The panel comprised: HLA-DMA, HLA-DBQ1, CD74, CSNK1G2, IRF3, KRAS2, LYN, MT1K, MT1X, RAB23, TGFB1 and TOP2A, with CDKN1B as an endogenous control. Expression profiles for each target were generated using TaqMan Real-Time PCR. HLA-DMA, HLA-DQB1, MT1X, CSNK1G2 and RAB23 were found to be differentially expressed (P<0.05) when comparing follicular adenoma and follicular variant of papillary thyroid carcinoma. Comparison of follicular adenoma and follicular thyroid carcinoma groups showed significant differential expression for MT1K, MT1X and RAB23 (P<0.05). Comparison of the papillary thyroid carcinoma group (classic and follicular variants) and the follicular adenoma group showed differential expression for CSNK1G2, HLA-DQB1, MT1X and RAB23 (P<0.05). Finally, KRAS2 was found to be differentially expressed (P<0.05) when comparing the papillary thyroid carcinoma and follicular thyroid carcinoma groups. This panel of molecular targets discriminates between follicular adenoma, papillary thyroid carcinoma, follicular variant of papillary thyroid carcinoma and follicular thyroid carcinoma by their expression repertoires. It may have utility for broader use in the setting of fine-needle aspiration cytology and could improve the definitive diagnosis of certain categories of thyroid malignancy.

Small-molecule modulators of Hh and Wnt signaling pathways

Hedgehog (Hh) and Wnt signaling pathways play key roles in growth and patterning during embryonic development and in the postembryonic regulation of stem cell number in the epithelia. Numerous studies link aberrant modulation of these pathways to specific human diseases. This article focuses on general aspects of Hh and Wnt signal transduction and biologic molecules involved in the respective signaling cascades. Specifically, the authors summarize small-molecule modulators of both pathways that show promise as therapeutic modalities.

Cholesterol, statins and cancer

1. The link between cholesterol and cardiovascular disease is well-established. Emerging evidence is now forging a tantalizing link between cholesterol and cancer. 2. Results from a number of case-control studies have indicated that the commonly prescribed cholesterol-lowering drugs, the statins, may reduce the risk of certain cancers, although this area certainly remains controversial. 3. Herein, the recent literature examining statins and cancer is reviewed briefly and the relationship between a key cholesterol homeostatic pathway and signalling pathways that are involved in carcinogenesis is discussed. In particular, how the sterol-regulatory element binding protein, Akt and Hedgehog pathways may converge in cancer is reviewed.

Patched mutations and hairy skin patches: a new sign in Gorlin syndrome

We report on the occurrence of discrete patches of unusually long pigmented hair on the skin of three patients with Gorlin syndrome from two unrelated families with confirmed heterozygous mutations in the Patched (PTCH) gene. The PTCH protein is a negative regulator of Hedgehog signaling, and the Sonic Hedgehog (SHH)-PTCH pathway is known to play an important role in the formation and cycling of the hair follicle. We believe that the patches represent a genuine physical sign associated with Gorlin syndrome, and discuss molecular mechanisms by which they might arise.

Regulatory role for Krüppel-like zinc-finger protein Gli-similar 1 (Glis1) in PMA-treated and psoriatic epidermis

In this study, we analyze the expression and potential function of the Krüppel-like zinc-finger protein Gli-similar protein 1 (Glis1) in normal and inflammatory skin and in the differentiation of epidermal keratinocytes. Glis1 mRNA is not expressed in normal human epidermis, but is significantly induced in psoriatic epidermis and in mouse skin upon treatment with the tumor promoter phorbol-12-myristate-13-acetate (PMA). The expression of Glis1 is restricted to the suprabasal layers. These observations suggest that Glis1 expression is associated with hyperplastic, inflammatory epidermis. Consistent with these findings, Glis1 mRNA is not expressed in undifferentiated or differentiated normal human epidermal keratinocytes (NHEK) in culture, but is dramatically induced after the addition of PMA or interferon gamma. A similar induction of Glis1 mRNA by PMA treatment was observed in the immortalized epidermal keratinocyte cell line NHEK-HPV, whereas PMA did not induce Glis1 in HaCaT cells or in several squamous cell carcinoma cell lines. To obtain insight into its function, Glis1 and a C-terminal deletion mutant Glis1DeltaC were expressed in NHEK-HPV cells and changes in epidermal differentiation and gene expression examined. Microarray analysis revealed that Glis1DeltaC promoted PMA-induced epidermal differentiation, as indicated by increased expression of many differentiation-specific genes. This, in association with its induction in psoriasis, suggests that transcriptional factor Glis1 is involved in the regulation of aberrant differentiation observed in psoriatic epidermis.

Cytogenetic alterations in nonmelanoma skin cancer: a review

Since the advent of cytogenetic analysis, knowledge about fundamental aspects of cancer biology has increased, allowing the processes of cancer development and progression to be more fully understood and appreciated. Classical cytogenetic analysis of solid tumors had been considered difficult, but new advances in culturing techniques and the addition of new cytogenetic technologies have enabled a more comprehensive analysis of chromosomal aberrations associated with solid tumors. Our purpose in this review is to discuss the cytogenetic findings on a number of nonmelanoma skin cancers, including squamous- and basal cell carcinomas, keratoacanthoma, squamous cell carcinoma in situ (Bowen's disease), and solar keratosis. Through classical cytogenetic techniques, as well as fluorescence-based techniques such as fluorescence in situ hybridization and comparative genomic hybridization, numerous chromosomal alterations have been identified. These aberrations may aid in further defining the stages and classifications of nonmelanoma skin cancer and also may implicate chromosomal regions involved in progression and metastatic potential. This information, along with the development of newer technologies (including laser capture microdissection and comparative genomic hybridization arrays) that allow for more refined analysis, will continue to increase our knowledge about the role of chromosomal events at all stages of cancer development and progression and, more specifically, about how they are associated with nonmelanoma skin cancer.

Molecular aetiology and pathogenesis of basal cell carcinoma

Recent insights into the cell biology of the epidermis and its appendages are transforming our understanding of the pathogenesis of basal cell carcinoma (BCC). The significant progress that has been made warrants a comprehensive review of the molecular and cellular pathology of BCC. The items addressed include environmental and genetic risk factors, the biology of the putative precursor cell(s), and the contribution of aberrations in processes such as apoptosis, cell proliferation, differentiation and signalling to carcinogenesis. Furthermore, established and novel treatment modalities are discussed with particular attention to future biological approaches.

Constitutive activation of the shh-ptc1 pathway by a patched1 mutation identified in BCC

Mutations in the transmembrane receptor patched1 (ptc1) are responsible for the majority of basal cell carcinoma (BCC) cases. Many of these mutations, including ptc1-Q688X, result in premature truncation of the ptc1 protein. ptc1-Q688X has been identified in patients with both BCC and nevoid basal cell carcinoma syndrome, an inheritable disorder causing a predisposition to cancer susceptibility. Here we describe a mechanism by which ptc1-Q688X causes constitutive cellular signaling. Cells expressing ptc1-Q688X demonstrate an increase in cell cycle progression and induce cell transformation. The ptc1-Q688X mutant enhances Gli1 activity, a downstream reporter of sonic hedgehog (shh)-ptc1 signaling, independent of shh stimulation. In contrast to wild-type ptc1, ptc1-Q688X fails to associate with endogenous cyclin B1. Expression of nuclear-targeted cyclin B1 derivatives promotes Gli1-dependent transcription, which correlates temporally with cyclin B1-cdk1 kinase activity. Coexpression of wild-type ptc1 with a nuclear-targeted cyclin B1 derivative, mutated to mimic constitutive phosphorylation, dramatically decreases Gli1 activity. In addition, the coexpression of this constitutively nuclear cyclin B1 derivative with ptc1-Q688X substantially enhances foci formation. These studies therefore describe a molecular mechanism for the aberrant activity of ptc1-Q688X that includes the premature activation of the transcription factor Gli1.

Basal cell nevus syndrome

PURPOSE OF REVIEW

Basal cell nevus syndrome (BCNS), is a hereditary condition transmitted as an autosomal dominant trait exhibiting high penetrance and variable expressivity. Inherited or spontaneous mutations in the human homologue of the Drosophila patched gene underlie the disorder and in addition to tumor predisposition, are associated with a range of 'patterning' defects. Recent advances, with glimpses of possible therapies are emerging, but because of the wide-ranging nature of phenotypic expression and overlap with other syndromes, there is difficulty. Finally, because of the importance of PTCH and paralogous genes in many species other than humans, reports appear in a correspondingly wide range of journals, which makes 'keeping abreast' difficult.

RECENT FINDINGS

Progress has been achieved in understanding the role of Gli-1, 2, & 3 in development of 'sporadic' BCCs and BCNS. Expression of PTCH1 is now known to be regulated by alternative promoters and a single functional Gli-binding site. Expression of FOXE1 as a new transcriptional target of Gli2 has been demonstrated in human epidermis and BCCs. Finally, the discovery of Shh pathway inhibitors such as cyclopamine, a naturally occurring alkaloid and ornithine decarboxylase inhibition suggest possible interventional therapies.

SUMMARY

In BCNS, phenotype does not correlate with position of mutations within Patched, suggesting genetic makeup and environment modulate effects of premature protein truncation induced by PTCH mutation. These developmental abnormalities occur as a result of haplo-insufficiency in heterozygotes for the mutated gene, whereas neoplastic complications arise from a classical two-hit tumor suppressor gene model. Attention is therefore turning toward TP53 and PTCH associations.

Characterization of Rab23, a negative regulator of sonic hedgehog signaling

The hedgehog signaling pathway is indispensable in embryogenesis, being responsible for the development of a wide array of vertebrate organs. Given its importance in embryogenesis, the precise regulation of hedgehog signaling is crucial. Aberrant activation of this pathway in postnatal life has been associated with a number of tumor types, reinforcing the role of developmental signaling pathways in tumorigenesis. The small GTPase Rab23 acts as a negative regulator of the hedgehog signaling pathway, most notably in the vertebrate neural system. By analogy with studies of other Rab proteins, analysis of the localization of wild-type and constitutively active and inactive forms of Rab23 provides the potential to shed light on the role of Rab23 at the cellular level. We previously produced expression constructs encoding these proteins for analysis in mammalian cell cultures at both the light and the electron microscopy level. This revealed that both wild-type and active Rab23 localizes to the plasma membrane and to endocytic vesicles (T. M. Evans et al. [2003] Traffic4, 869-884). We describe the methods used to design and make the Rab23 expression constructs, and to assess their localization relative to key hedgehog pathways and endocytic markers in both transiently and stably transfected cell cultures.

Insight into the pathogenesis of sporadic basal cell carcinoma

Sporadic basal cell carcinoma (BCC) is the commonest human cancer. Although its aggressiveness is low and metastatic potential negligible, the increasing incidence of the tumor in the Western world drives attention to its pathogenesis. In 1996, germ-line mutations in the patched receptor of the Sonic hedgehog (Shh) signaling pathway were described in the Gorlin-Goltz syndrome in association with multiple nevoid BCCs. Later, the aberrant activation of the Shh was identified in sporadic BCCs as well. Recently, the role of other tumor suppressors and DNA repair gene mutations and their relationship with UV radiation-induced DNA damage have been elucidated.

Hh pathway expression in human gut tissues and in inflammatory gut diseases

Sonic hedgehog (Shh) directs early gut patterning via epithelial-mesenchymal signaling and remains expressed in endoderm-derived tissues into the adult period. In human adult gut epithelium SHH/SHH expression is strongest in basal layers, which suggests that SHH may function in the maintenance of gut epithelial stem or progenitor cells. Recent publications suggest a role for aberrant SHH/SHH expression in gut epithelial neoplasias. We hypothesized that the regenerating gut epithelium in inflammatory gut disorders would show an upregulation of SHH/SHH signaling and this abnormal signal may explain the increased incidence of neoplasia in these diseases. Archived healthy gut and inflammatory gut diseased tissues were analyzed by RNA in situ hybridization and immunohistochemistry to describe location and levels of SHH signaling. We show that SHH/SHH and its receptor PTCH1/PTCH1 expression is restricted to the glandular epithelium of the gut, in an antiluminal pattern (strongest in basal layers and weak to absent in luminal epithelium). Inflammatory diseases of the gut show dramatic increases in epithelial SHH signaling. Expression increases in inflamed glandular epithelium (including metaplastic glandular epithelium), losing its radial (crypt-villous) polarity, and expression appears upregulated and present in all epithelial cells. We also describe strong SHH/SHH and PTCH1/PTCH1 expression in intraepithelial and mucosal inflammatory cells. We suggest that SHH signaling in inflammatory diseases of the gut acts to ensure stem cell restitution of damaged mucosal epithelium. However, such signaling may also present a risk for neoplastic transformation.

Expression of Sonic hedgehog pathway genes is altered in colonic neoplasia

The Hedgehog (Hh) signalling pathway is crucial for normal development and patterning of numerous human organs including the gut. Hh proteins are also expressed during gastric gland development and gastric epithelial differentiation in adults. Recently, dysregulation of these developmentally important genes has been implicated in cancer, leading to the present study of the expression of Hh signalling proteins in colon cancer. In this study, normal colon and colonic lesions (hyperplastic polyp, adenoma, and colonic adenocarcinoma) were examined by immunohistochemistry using antibodies against Hh signalling molecules: the secreted protein Sonic hedgehog (SHH), its receptor Patched (PTCH), and the PTCH-associated transmembrane protein Smoothened (SMOH). The study shows that Hh signalling pathway members are expressed in normal colonic epithelium. SHH was expressed at the top of the crypts and in a few basally located cells, while PTCH was detected in the neuroendocrine cells and SMOH at the brush border of superficial epithelium. RT-PCR analysis of laser-microdissected crypts from normal human colon confirmed that mRNAs encoding these proteins were expressed in colonic epithelium. Expression of SHH, PTCH, and SMOH was up-regulated in hyperplastic polyps, adenomas, and adenocarcinomas of the colon, and SHH expression correlated with increased expression of the proliferation marker Ki-67 in all lesions examined. To address whether the Hh signalling pathway is functional in the gut, the effect of Shh on epithelial cells in vitro was explored by treating primary murine colonocytes with either Shh peptide or neutralizing anti-Shh antibody. The proportion of cells in the S-phase was assessed by bromodeoxyuridine (BrdU) incorporation. It was found that exogenous Shh promotes cell proliferation in colonocytes, while anti-Shh inhibits proliferation, suggesting that Shh is required during proliferation of epithelial cells in vitro. It is suggested that SHH is required during epithelial proliferation in the colon and that there is a possible role for Hh signalling in epithelial colon tumour progression in vivo.

Dependence receptors: between life and death

The recently described family of dependence receptors is a new family of functionally related receptors. These proteins have little sequence similarity but display the common feature of inducing two completely opposite intracellular signals depending on ligand availability: in the presence of ligand, these receptors transduce a positive signal leading to survival, differentiation or migration, while in the absence of ligand, the receptors initiate or amplify a negative signal for apoptosis. Thus, cells that express these proteins manifest a state of dependence on their respective ligands. The mechanisms that trigger cell death induction in the absence of ligand are in large part unknown, but typically require cleavage by specific caspases. In this review we will present the proposed mechanisms for cell death induction by these receptors and their potential function in nervous system development and regulation of tumorigenesis.

Hedgehog signalling in colorectal tumour cells: induction of apoptosis with cyclopamine treatment

Hedgehog (Hh) signalling controls many aspects of development. It also regulates cell growth and differentiation in adult tissues and is activated in a number of human malignancies. Hh and Wnt signalling frequently act together in controlling cell growth and tissue morphogenesis. Despite the fact that the majority of colorectal tumours have a constitutively activated canonical Wnt pathway, few previous studies have investigated the expression of Hh signalling components in colorectal tumours. We describe here epithelial cell lines derived from both nonmalignant colorectal adenomas and colorectal adenocarcinomas that express both Sonic and Indian Hh. Interestingly, these cells also express the Hh receptor Patched and the downstream signalling components Smoothened and Gli1, suggesting autocrine Hh signalling in these cells. To test whether autocrine Hh signalling contributes to cell survival, we treated colorectal tumour cells with cyclopamine, a known inhibitor of Hh signalling. Cyclopamine treatment induced apoptosis in both adenoma- and carcinoma-derived cell lines, which could be partially rescued by further stimulation of Hh signalling. These data suggest that autocrine Hh signalling can increase aberrant cell survival in colorectal tumour cells and may be a novel target for colon cancer therapy using drugs such as cyclopamine.

Next stop, the twilight zone: hedgehog network regulation of mammary gland development

The hedgehog signal transduction network is a critical mediator of cell-cell communication during embryonic development. Evidence also suggests that properly regulated hedgehog network function is required in some adult organs for stem cell maintenance or renewal. Mutation, or misexpression, of network genes is implicated in the development of several different types of cancer, particularly that of skin, brain, lung, and pancreas. Recent studies in the mouse mammary gland have demonstrated roles for hedgehog network genes at virtually every phase of mammary gland development where it regulates such diverse processes as embryonic mammary gland induction, establishment of ductal histoarchitecture, and functional differentiation in lactation. Further, studies suggest a role for misregulated network function in the progression of breast cancer.

Meeting report: cellular dependence--old concept, new mechanisms

Programmed cell death occurs in response to both the presence of various extracellular factors and the lack of specific factors. Receptors that can mediate cell death in the absence of ligand binding are called dependence receptors, and they were the topic of the meeting held during the summer of 2003 in Fondation des Treilles, France. Not only is progress being made in the identification of new dependence receptors, but the partners that carry out this "negative" signal are also coming to light. With several of the receptors implicated in various human developmental disorders or disease states, gaining an understanding of the molecular mechanisms controlling dependence receptor-mediated cell death has clear clinical relevance.

Inhibition of neuroepithelial patched-induced apoptosis by sonic hedgehog

During early development in vertebrates, Sonic hedgehog (Shh) is produced by the notochord and the floor plate. A ventrodorsal gradient of Shh directs ventrodorsal patterning of the neural tube. However, Shh is also required for the survival of neuroepithelial cells. We show that Patched (Ptc) induces apoptotic cell death unless its ligand Shh is present to block the signal. Moreover, the blockade of Ptc-induced cell death partly rescues the chick spinal cord defect provoked by Shh deprivation. Thus, the proapoptotic activity of unbound Ptc and the positive effect of Shh-bound Ptc on cell differentiation probably cooperate to achieve the appropriate spinal cord development.

Inhibition of Hedgehog signaling by direct binding of cyclopamine to Smoothened

The steroidal alkaloid cyclopamine has both teratogenic and antitumor activities arising from its ability to specifically block cellular responses to vertebrate Hedgehog signaling. We show here, using photoaffinity and fluorescent derivatives, that this inhibitory effect is mediated by direct binding of cyclopamine to the heptahelical bundle of Smoothened (Smo). Cyclopamine also can reverse the retention of partially misfolded Smo in the endoplasmic reticulum, presumably through binding-mediated effects on protein conformation. These observations reveal the mechanism of cyclopamine's teratogenic and antitumor activities and further suggest a role for small molecules in the physiological regulation of Smo.

Comparison of the expression of p53, p21, Bax and the induction of apoptosis between patients with basal cell carcinoma and normal controls in response to ultraviolet irradiation

AIM

Ultraviolet light (UV) is known to cause DNA damage in the epidermis. The damaged DNA is repaired or deleted by apoptosis to prevent the generation of cancer. It has been suggested that a deficient apoptotic mechanism may predispose individuals to skin cancer. Therefore, the response of normal controls and patients with basal cell carcinoma (BCC) to UV irradiation was investigated.

METHODS

The buttock skin from normal volunteers and patients with BCC was irradiated using solar simulated radiation (SSR). SSR mimics the effect of natural sunlight. Skin biopsies were excised and examined for p53, p21, and Bax protein expression and for the induction of apoptosis.

RESULTS

At 33 hours after UV irradiation, the induction of apoptosis was significantly higher (p = 0.04) in patients with BCC than in normal volunteers (Mann Whitney test). A trend towards higher p21 expression was found at 33 hours in patients with BCC (mean, 18.69 positive cells/field) than in normal volunteers (mean, 9.89), although this difference was not significant (p = 0.05 positive cells/field).

CONCLUSION

These results may imply that patients with BCC have enhanced sensitivity to UV irradiation or that there is some defect in the cell arrest or repair pathways, which results in damaged cells been pushed into apoptosis rather than repair.