Sonic hedgehog in normal and neoplastic proliferation: insight gained from human tumors and animal models

Transcriptomic Analysis Provides Insights into Candidate Genes and Molecular Pathways Involved in Growth of Mytilus coruscus Larvae

Growth is a fundamental aspect of aquaculture breeding programs, pivotal for successful cultivation. Understanding the mechanisms that govern growth and development differences across various stages can significantly boost seedling production of economically valuable species, thereby enhancing aquaculture efficiency and advancing the aquaculture industry. Mytilus coruscus, a commercially vital marine bivalve, underscores this importance. To decipher the intricate molecular mechanisms dictating growth and developmental disparities in marine shellfish, we conducted transcriptome sequencing and meticulously analyzed gene expression variations and molecular pathways linked to growth traits in M. coruscus. This study delved into the molecular and gene expression variations across five larval development stages, with a specific focus on scrutinizing the differential expression patterns of growth-associated genes using RNA sequencing and quantitative real-time PCR analysis. A substantial number of genes-36,044 differentially expressed genes (DEGs)-exhibited significant differential expression between consecutive developmental stages. These DEGs were then categorized into multiple pathways (Q value < 0.05), including crucial pathways such as the spliceosome, vascular smooth muscle contraction, DNA replication, and apoptosis, among others. In addition, we identified two pivotal signaling pathways-the Hedgehog (Hh) signaling pathway and the TGF-beta (TGF-β) signaling pathway-associated with the growth and development of M. coruscus larvae. Ten key growth-related genes were pinpointed, each playing crucial roles in molecular function and the regulation of growth traits in M. coruscus. These genes and pathways associated with growth provide deep insights into the molecular basis of physiological adaptation, metabolic processes, and growth variability in marine bivalves.

Homeostatic control of stearoyl desaturase expression via patched-like receptor PTR-23 ensures the survival of C. elegans during heat stress

Organismal responses to temperature fluctuations include an evolutionarily conserved cytosolic chaperone machinery as well as adaptive alterations in lipid constituents of cellular membranes. Using C. elegans as a model system, we asked whether adaptable lipid homeostasis is required for survival during physiologically relevant heat stress. By systematic analyses of lipid composition in worms during and before heat stress, we found that unsaturated fatty acids are reduced in heat-stressed animals. This is accompanied by the transcriptional downregulation of fatty acid desaturase enzymes encoded by fat-1, fat-3, fat-4, fat-5, fat-6, and fat-7 genes. Conversely, overexpression of the Δ9 desaturase FAT-7, responsible for the synthesis of PUFA precursor oleic acid, and supplementation of oleic acid causes accelerated death of worms during heat stress. Interestingly, heat stress causes permeability defects in the worm's cuticle. We show that fat-7 expression is reduced in the permeability defective collagen (PDC) mutant, dpy-10, known to have enhanced heat stress resistance (HSR). Further, we show that the HSR of dpy-10 animals is dependent on the upregulation of PTR-23, a patched-like receptor in the epidermis, and that PTR-23 downregulates the expression of fat-7. Consequently, abrogation of ptr-23 in wild type animals affects its survival during heat stress. This study provides evidence for the negative regulation of fatty acid desaturase expression in the soma of C. elegans via the non-canonical role of a patched receptor signaling component. Taken together, this constitutes a skin-gut axis for the regulation of lipid desaturation to promote the survival of worms during heat stress.

Shh activation restores interneurons and cognitive function in newborns with intraventricular haemorrhage

Premature infants with germinal matrix haemorrhage-intraventricular haemorrhage (GMH-IVH) suffer from neurobehavioural deficits as they enter childhood and adolescence. Yet the underlying mechanisms remain unclear. Impaired development and function of interneurons contribute to neuropsychiatric disorders. Therefore, we hypothesized that the occurrence of IVH would reduce interneuron neurogenesis in the medial ganglionic eminence and diminish the population of parvalbumin+ and somatostatin+ cortical interneurons. Because Sonic Hedgehog promotes the production of cortical interneurons, we also postulated that the activation of Sonic Hedgehog signalling might restore neurogenesis, cortical interneuron population, and neurobehavioural function in premature newborns with IVH. These hypotheses were tested in a preterm rabbit model of IVH and autopsy samples from human preterm infants. We compared premature newborns with and without IVH for intraneuronal progenitors, cortical interneurons, transcription factors regulating neurogenesis, single-cell transcriptome of medial ganglionic eminence and neurobehavioural functions. We treated premature rabbit kits with adenovirus expressing Sonic Hedgehog (Ad-Shh) or green fluorescence protein gene to determine the effect of Sonic Hedgehog activation on the interneuron production, cortical interneuron population and neurobehaviour. We discovered that IVH reduced the number of Nkx2.1+ and Dlx2+ progenitors in the medial ganglionic eminence of both humans and rabbits by attenuating their proliferation and inducing apoptosis. Moreover, IVH decreased the population of parvalbumin+ and somatostatin+ neurons in the frontal cortex of both preterm infants and kits relative to controls. Sonic Hedgehog expression and the downstream transcription factors, including Nkx2.1, Mash1, Lhx6 and Sox6, were also reduced in kits with IVH. Consistent with these findings, single-cell transcriptomic analyses of medial ganglionic eminence identified a distinct subpopulation of cells exhibiting perturbation in genes regulating neurogenesis, ciliogenesis, mitochondrial function and MAPK signalling in rabbits with IVH. More importantly, restoration of Sonic Hedgehog level by Ad-Shh treatment ameliorated neurogenesis, cortical interneuron population and neurobehavioural function in kits with IVH. Additionally, Sonic Hedgehog activation alleviated IVH-induced inflammation and several transcriptomic changes in the medial ganglionic eminence. Taken together, IVH reduced intraneuronal production and cortical interneuron population by downregulating Sonic Hedgehog signalling in both preterm rabbits and humans. Notably, activation of Sonic Hedgehog signalling restored interneuron neurogenesis, cortical interneurons and cognitive function in rabbit kits with IVH. These findings highlight disruption in cortical interneurons in IVH and identify a novel therapeutic strategy to restore cortical interneurons and cognitive function in infants with IVH. These studies can accelerate the development of new therapies to enhance the neurodevelopmental outcome of survivors with IVH.

Combined treatments with AZD5363, AZD8542, curcumin or resveratrol induce death of human glioblastoma cells by suppressing the PI3K/AKT and SHH signaling pathways

Glioblastoma (GBM) is a very aggressive tumor that presents vascularization, necrosis and is resistant to chemotherapy and radiotherapy. Current treatments are not effective eradicating GBM, thus, there is an urgent need to develop novel therapeutic strategies against GBM. AZD5363, AZD8542, curcumin and resveratrol, are widely studied for the treatment of cancer and in the present study we explored the effects of the administration of combined treatments with AZD5363, AZD8542, curcumin or resveratrol on human GBM cells. We found that the combined treatments with AZD5363+AZD8542+Curcumin and AZD8542+Curcumin+Resveratrol inhibit the PI3K/AKT and SHH survival pathways by decreasing the activity of AKT, the reduction of the expression of SMO, pP70S6k, pS6k, GLI1, p21 and p27, and the activation of caspase-3 as a marker of apoptosis. These results provide evidence that the combined treatments AZD5363+AZD8542+Curcumin and AZD8542+Curcumin+Resveratrol have the potential to be an interesting option against GBM.

Understanding stem cells and its pivotal role in regenerative medicine

Stem cells (SCs) are clonogenic cells that develop into the specialized cells which later responsible for making up various types of tissue in the human body. SCs are not only the appropriate source of information for cell division, molecular and cellular processes, and tissue homeostasis but also one of the major putative biological aids to diagnose and cure various degenerative diseases. This study emphasises on various research outputs that occurred in the past two decades. This will give brief information on classification, differentiation, detection, and various isolation techniques of SCs. Here, the various signalling pathways which includes WNT, Sonic hedgehog, Notch, BMI1 and C-met pathways and how does it effect on the regeneration of various classes of SCs and factors that regulates the potency of the SCs are also been discussed. We also focused on the application of SCs in the area of regenerative medicine along with the cellular markers that are useful as salient diagnostic or curative tools or in both, by the process of reprogramming, which includes diabetes, cancer, cardiovascular disorders and neurological disorders. The biomarkers that are mentioned in various literatures and experiments include PDX1, FOXA2, HNF6, and NKX6-1 (for diabetes); CD33, CD24, CD133 (for cancer); c-Kit, SCA-1, Wilm's tumor 1 (for cardiovascular disorders); and OCT4, SOX2, c-MYC, EN1, DAT and VMAT2 (for neurological disorders). In this review, we come to know the advancements and scopes of potential SC-based therapies, its diverse applications in clinical fields that can be helpful in the near future.

Range of SHH signaling in adrenal gland is limited by membrane contact to cells with primary cilia

The signaling protein Sonic Hedgehog (SHH) is crucial for the development and function of many vertebrate tissues. It remains largely unclear, however, what defines the range and specificity of pathway activation. The adrenal gland represents a useful model to address this question, where the SHH pathway is activated in a very specific subset of cells lying near the SHH-producing cells, even though there is an abundance of lipoproteins that would allow SHH to travel and signal long-range. We determine that, whereas adrenal cells can secrete SHH on lipoproteins, this form of SHH is inactive due to the presence of cosecreted inhibitors, potentially explaining the absence of long-range signaling. Instead, we find that SHH-producing cells signal at short range via membrane-bound SHH, only to receiving cells with primary cilia. Finally, our data from NCI-H295R adrenocortical carcinoma cells suggest that adrenocortical tumors may evade these regulatory control mechanisms by acquiring the ability to activate SHH target genes in response to TGF-β.

Dbx2 exhibits a tumor-promoting function in hepatocellular carcinoma cell lines via regulating Shh-Gli1 signaling

BACKGROUND

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide. HCC patients suffer from a high mortality-to-incidence ratio and low cure rate since we still have no specific and effective treatment. Although tremendous advances have been made in the investigation of HCC, the specific mechanisms of the progression of this disease are still only partially established. Hence, more research is needed to elucidate the underlying potential mechanisms to develop effective strategies for HCC.

AIM

To determine the role of developing brain homeobox 2 (Dbx2) gene in promoting the development of HCC.

METHODS

Dbx2 expression in clinical specimens and HCC cell lines was detected by Western blot (WB) and immunohistochemistry. Gain and loss of Dbx2 function assays were performed in vitro and in vivo. Cell viability assays were used to investigate cell growth, flow cytometry was employed to assess cell cycle and apoptosis, and trans-well assays were conducted to evaluate cell migration, invasion, and metastasis. The expression of key molecules in the sonic hedgehog (Shh) signaling was determined by WB.

RESULTS

Compared to matched adjacent non-tumorous tissues, Dbx2 was overexpressed in 5 HCC cell lines and 76 surgically resected HCC tissues. Dbx2 overexpression was correlated with large tumor size. Both gain and loss of function assays indicated that Dbx2 promoted HCC cell proliferation by facilitating the transition from G1 to S phase, attenuating apoptosis and promoted HCC proliferation, migration, and invasion in vitro and in vivo. Mechanistically, Dbx2 modulated Shh signaling by enhancing FTCH1 and GLi1 expression in HCC cells that overexpressed Dbx2, which was reversed in HCC cells with Dbx2 knockdown.

CONCLUSION

Our results indicate that Dbx2 is significantly upregulated in HCC tissues and plays significant roles in proliferation and metastasis of HCC cells by activating the Shh pathway.

Effect of the sonic hedgehog inhibitor GDC-0449 on an in vitro isogenic cellular model simulating odontogenic keratocysts

Odontogenic keratocysts (OKCs) are common cystic lesions of odontogenic epithelial origin that can occur sporadically or in association with naevoid basal cell carcinoma syndrome (NBCCS). OKCs are locally aggressive, cause marked destruction of the jaw bones and have a propensity to recur. PTCH1 mutations (at ∼80%) are frequently detected in the epithelia of both NBCCS-related and sporadic OKCs, suggesting that PTCH1 inactivation might constitutively activate sonic hedgehog (SHH) signalling and play a major role in disease pathogenesis. Thus, small molecule inhibitors of SHH signalling might represent a new treatment strategy for OKCs. However, studies on the molecular mechanisms associated with OKCs have been hampered by limited epithelial cell yields during OKC explant culture. Here, we constructed an isogenic PTCH1^R135X/+ cellular model of PTCH1 inactivation by introducing a heterozygous mutation, namely, c.403C>T (p.R135X), which has been identified in OKC patients, into a human embryonic stem cell line using the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9) system. This was followed by the induction of epithelial differentiation. Using this in vitro isogenic cellular model, we verified that the PTCH1^R135X/+ heterozygous mutation causes ligand-independent activation of SHH signalling due to PTCH1 haploinsufficiency. This activation was found to be downregulated in a dose-dependent manner by the SHH pathway inhibitor GDC-0449. In addition, through inhibition of activated SHH signalling, the enhanced proliferation observed in these induced cells was suppressed, suggesting that GDC-0449 might represent an effective inhibitor of the SHH pathway for use during OKC treatment.

Using gene-edited cell cultures, Chinese researchers have gathered useful insights into the genetic origins and treatment of benign oral tumours called odontogenic keratocysts (OKCs). A total of 80% of OKCs are associated with mutations in the gene PTCH1, which are thought to activate a signalling pathway that drives OKC tumour growth. However, research is hindered by OKC cell culturing limitations. Tiejun Li, from the Peking University School and Hospital of Stomatology, and colleagues created an OKC cell culture model that uses CRISPR gene editing to introduce a PTCH1 gene mutation into human stem cells before differentiating them into epithelial cells. Using their model, the team confirm that PTCH1 mutation activates tumour-associated signalling, which the basal cell carcinoma drug vismodegib greatly reduces. Vismodegib also reduces the overproliferation of mutant cells and offers a potential treatment option for OKC patients.

Clinical and pre-clinical utility of genomics in medulloblastoma

INTRODUCTION

Integrated genomics has significantly advanced our understanding of medulloblastoma heterogeneity. It is now clear that it actually comprises at least four distinct molecular subgroups termed Wnt/Wingless (WNT), Sonic Hedgehog (SHH), Group 3, and Group 4 with stark clinical and biological differences. Areas covered: This paper reviews advances in the classification and risk stratification of medulloblastoma, specifically integrating subgroup with clinical and cytogenetic risk factors, with a summary of the potential to lead to more precise therapies. Moreover, the current state of preclinical modeling is summarized with respect to their utility in generating new treatments and correlation with genomic discoveries. Opportunities and challenges in developing new treatment paradigms are summarized and discussed, specifically new therapies for very high-risk metastatic/MYC-amplified Group 3 and TP53-mutant SHH and reductions in therapy for lower risk groups. Expert commentary: Survival across medulloblastoma has been stagnant for over 30 years, and new treatment paradigms are urgently required. Current therapy significantly over treats a high proportion of patients leaving them with lifelong side effects; while many patients still succumb to their disease. Applying biological advances could improve quality of life for a significant proportion of patients while offering new upfront approaches to the highest risk patients.

The different pathogeneses of sporadic adenoma and adenocarcinoma in non-ampullary lesions of the proximal and distal duodenum

Non-ampullary duodenal adenoma with activation of Wnt/β-catenin signalling is common in familial adenomatous polyposis (FAP) patients, whereas sporadic non-ampullary adenoma is uncommon. The adenoma-carcinoma sequence similar to colon cancer is associated with duodenal tumors in FAP, but not always in sporadic tumors. We obtained 37 non-ampullary duodenal tumors, including 25 adenomas and 12 adenocarcinomas, were obtained from biopsies and endoscopic resections. We performed immunohistochemistry for β-catenin, the hallmark of Wnt activation, and aldehyde dehydrogenase 1 (ALDH1), a putative cancer stem cell marker. In non-ampullary lesions, abnormal nuclear localization of β-catenin was observed in 21 (84.0%) of 25 adenomas and 4 (33.3%) of 12 adenocarcinomas. In the proximal duodenum, nuclear β-catenin was less frequent in both adenomas and adenocarcinomas. Gastric duodenal metaplasia (GDM) was observed only in the proximal duodenum. All adenomas with GDM were the gastric foveolar and pyloric gland types, and showed only membranous β-catenin. The intestinal-type adenomas had nuclear β-catenin in the proximal and distal duodenum. ALDH1-positive cells were more frequent in adenocarcinomas than adenomas. Nuclear β-catenin accumulation frequently occurred in ALDH1-positive cells in adenoma, but not in adenocarcinoma. In the non-ampullary proximal duodenum, Wnt/β-catenin pathway activation was more closely associated with adenomas than adenocarcinomas, and while it might cooperate with ALDH1 in adenoma, it does not in adenocarcinoma. The pathogenesis thus may differ between sporadic adenoma and adenocarcinoma of non-ampullary duodenal lesions, especially in the proximal and distal duodenum.

Alternative activation of hedgehog pathway induced by ultraviolet B radiation: preliminary study

BACKGROUND

There is still much ambiguity in studies of Sonic hedgehog (Shh) pathways and its dysregulation. Some studies concerning the role of the Shh pathway in basal cell carcinoma (BCC) have been conducted, but there is a lack of studies about Shh pathway dysregulation under the influence of ultraviolet (UV)B radiation.

AIM

To evaluate skin expression of Shh, Ptch1, Ptch2, Smo and Gli1 proteins in BCCs with and without the influence of UVB radiation.

METHODS

In total, 34 healthy controls (HCs) and 42 patients with nodular BCC were recruited into the study. Patients were divided into five groups (A-E), depending on UVB dose received and BCC status. In all skin specimens, expression of Shh, Ptch1, Ptch2, Smo and Gli1 protein was evaluated.

RESULTS

Comparing the BCC group with the HC group, there was significantly higher expression of Shh, Ptch1, Ptch2, Smo and Gli1 proteins. Expression of Ptch2, Smo and Gli1 was increased in response to UVB doses of 3 MED (minimal erythema dose), whereas expression of Ptch1 and Shh was unaffected.

CONCLUSION

The lack of change in expression of Shh and Ptch1 after exposure to UVB suggests that the Shh pathway may be activated through a noncanonical pathway under the influence of strong UVB doses.

The Hippo pathway in intestinal regeneration and disease

The Hippo pathway is a signalling cascade conserved from Drosophila melanogaster to mammals. The mammalian core kinase components comprise MST1 and MST2, SAV1, LATS1 and LATS2 and MOB1A and MOB1B. The transcriptional co-activators YAP1 and TAZ are the downstream effectors of the Hippo pathway and regulate target gene expression. Hippo signalling has crucial roles in the control of organ size, tissue homeostasis and regeneration, and dysregulation of the Hippo pathway can lead to uncontrolled cell growth and malignant transformation. Mammalian intestine consists of a stem cell compartment as well as differentiated cells, and its ability to regenerate rapidly after injury makes it an excellent model system to study tissue homeostasis, regeneration and tumorigenesis. Several studies have established the important role of the Hippo pathway in these processes. In addition, crosstalk between Hippo and other signalling pathways provides tight, yet versatile, regulation of tissue homeostasis. In this Review, we summarize studies on the role of the Hippo pathway in the intestine on these physiological processes and the underlying mechanisms responsible, and discuss future research directions and potential therapeutic strategies targeting Hippo signalling in intestinal disease.

Role of GLI1 and NDRG1 in Increased Resistance to Apoptosis Induction

We examined the effects of GLI1 expression in PW mouse embryo fibroblasts and H441 lung carcinoma cells. Ectopic expression of GLI1 in PW cells induced anchorage-independent growth and increased resistance to staurosporine-induced apoptosis, and overexpression of GLI1 in H441 cells caused resistance to apoptosis induced by staurosporine and etoposide. GLI1 expression in both H441 and PW cells was associated with increased expression of NDRG1, a gene known to be downregulated by the MYC family of proteins, indicating that upregulation of NDRG1 by GLI1 is not cell-type specific. Consistent with suppression of NDRG1 by c-MYC and N-MYC, increased NDRG1 expression correlated with decreased expression of c-MYC and N-MYC in GLI1-expressing H441 and GLI1-expressing PW cells, respectively. Downregulation of GLI1 expression in A549 cells by siRNA transfection increased sensitivity to etoposide-induced apoptosis, and downregulation of NDRG1 expression in H441 cells by siRNA transfection increased sensitivity to etoposide-induced apoptosis. Of clinical significance, inhibition of GLI1 and NDRG1 expression may increase sensitivity of cancer cells to chemotherapeutic drugs. Strategies that aim to inhibit GLI1 function and NDRG1 expression may be useful for targeted therapy of cancers induced by the SHH-GLI signaling pathway.

Relation between sonic hedgehog pathway gene polymorphisms and basal cell carcinoma development in the Polish population

In recent decades, increases have been observed in the incidence of nonmelanoma skin cancers, including basal cell carcinoma (BCC) and squamous cell carcinoma. BCC is the most common neoplasm in Caucasian populations. Sonic hedgehog (Shh) pathway impairment plays a key role in BCC pathogenesis, and there is evidence that Shh pathway genetic variations may predispose to BCC development. We genotyped 22 single-nucleotide polymorphisms (SNPs) in 4 Shh pathway genes: SHH, GLI, SMO, and PTCH. The study group consisted of 142 BCC patients and 142 age-matched, sex-matched healthy subjects (controls). SNPs were assessed using the PCR-RFLP method. The genotype distribution for the polymorphisms in the rs104894049 331 A/T SHH, rs104894040 349 T/C SHH, and rs41303402 385 G/A SMO genes differed significantly between the BCC patients and the controls. The presence of CC genotype in the SHH rs104894040 349 T/C polymorphism was linked to the highest risk of BCC development (OR 87.9, p < 0.001). Other genotypes, such as the TT in SHH rs104894049 331 A/T and the GG in SMO rs41303402 385 G/A also statistically raised the risk of BCC, but these associations were weaker. Other investigated polymorphisms showed no statistical differences between patients and controls. The results obtained testify to the importance of the SHH and SMO gene polymorphisms in skin cancerogenesis. These results mainly underline the potential role of SHH3 rs104894040 349 T/C gene polymorphism in the development of skin basal cell carcinomas in patients of Polish origin.

A critical role of autocrine sonic hedgehog signaling in human CD138+ myeloma cell survival and drug resistance

Hedgehog (Hh) signaling plays an important role in the oncogenesis of B-cell malignancies such as multiple myeloma (MM). However, the source of Hh ligand sonic hedgehog (SHH) and its target cells remains controversial. Previous studies showed that stromally induced Hh signaling is essential for the tumor cells and that CD19(+)CD138(-) MM stem cells are the target cells of Hh signaling. Here we demonstrate that SHH was mainly secreted by human myeloma cells but not by stromal cells in MM bone marrow. Autocrine SHH enhanced CD138(+) myeloma cell proliferation and protected myeloma cells from spontaneous and stress-induced apoptosis. More importantly, autocrine SHH protected myeloma cells against chemotherapy-induced apoptosis in vitro and in vivo. Combinational treatment with chemotherapy and SHH-neutralizing antibody displayed synergistic antimyeloma effects. Mechanistic studies showed that SHH signaling activated the SHH/GLI1/BCL-2 axis, leading to the inhibition of myeloma cell apoptosis. Thus, this study identifies the myeloma autocrine Hh signaling pathway as a potential target for the treatment of MM. Targeting this pathway may improve the efficacy of chemotherapy in MM patients.

Transcriptional profiles of SHH pathway genes in keratocystic odontogenic tumor and ameloblastoma

BACKGROUND

Sonic hedgehog (SHH) pathway activation has been identified as a key factor in the development of many types of tumors, including odontogenic tumors. Our study examined the expression of genes in the SHH pathway to characterize their roles in the pathogenesis of keratocystic odontogenic tumors (KOT) and ameloblastomas (AB).

METHODS

We quantified the expression of SHH, SMO, PTCH1, SUFU, GLI1, CCND1, and BCL2 genes by qPCR in a total of 23 KOT, 11 AB, and three non-neoplastic oral mucosa (NNM). We also measured the expression of proteins related to this pathway (CCND1 and BCL2) by immunohistochemistry.

RESULTS

We observed overexpression of SMO, PTCH1, GLI1, and CCND1 genes in both KOT (23/23) and AB (11/11). However, we did not detect expression of the SHH gene in 21/23 KOT and 10/11 AB tumors. Low levels of the SUFU gene were expressed in KOT (P = 0.0199) and AB (P = 0.0127) relative to the NNM. Recurrent KOT exhibited high levels of SMO (P = 0.035), PTCH1 (P = 0.048), CCND1 (P = 0.048), and BCL2 (P = 0.045) transcripts. Using immunolabeling of CCND1, we observed no statistical difference between primary and recurrent KOT (P = 0.8815), sporadic and NBCCS-KOT (P = 0.7688), and unicystic and solid AB (P = 0.7521).

CONCLUSIONS

Overexpression of upstream (PTCH1 and SMO) and downstream (GLI1, CCND1 and BCL2) genes in the SHH pathway leads to the constitutive activation of this pathway in KOT and AB and may suggest a mechanism for the development of these types of tumors.

Cyclosporine A up-regulates Sonic hedgehog in gingiva: role of the up-regulation on gingival cell proliferation

BACKGROUND AND OBJECTIVE

Sonic hedgehog protein (SHH) is a mitogen that stimulates cell proliferation. Cyclosporine A enhances the proliferation of gingival cells; however, the relationships of SHH to cyclosporine A or to cyclosporine A-enhanced gingival cell proliferation have not been described.

MATERIAL AND METHODS

Here, we investigated SHH expression in gingiva in vitro and in vivo after cyclosporine A treatment and tested the effect of SHH inhibition on cyclosporine A-enhanced gingival fibroblast proliferation in vitro.

RESULTS

In human gingival fibroblasts, cyclosporine A treatment increased the expression of SHH transcripts and SHH protein, and stimulated cell proliferation; the addition of cyclopamine, an SHH signaling inhibitor, suppressed cyclosporine A-enhanced cell proliferation. Up-regulated expression of SHH and up-regulation of proliferating cell nuclear antigen transcripts and protein were observed in the edentulous gingiva of cyclosporine A-treated rats.

CONCLUSION

Cyclosporine A up-regulates gingival SHH expression in vitro and in vivo, and the inhibition of the SHH pathway counteracts the stimulatory effect of cyclosporine A on gingival fibroblast proliferation. Therefore, we suggest that SHH mediates a novel molecular mechanism for cyclosporine A-induced gingival complications.

Blocking signaling at the level of GLI regulates downstream gene expression and inhibits proliferation of canine osteosarcoma cells

The Hedgehog-GLI signaling pathway is active in a variety of human malignancies and is known to contribute to the growth and survival of human osteosarcoma cells. In this study, we examined the expression and regulation of GLI transcription factors in multiple canine osteosarcoma cell lines and analyzed the effects of inhibiting GLI with GANT61, a GLI-specific inhibitor. Compared with normal canine osteoblasts, real-time PCR showed that GLI1 and GLI2 were highly expressed in two out of three cell lines and correlated with downstream target gene expression of PTCH1and PAX6. Treatment of canine osteosarcoma cells with GANT61 resulted in decreased expression of GLI1, GLI2, PTCH1, and PAX6. Furthermore, GANT61 inhibited proliferation and colony formation in all three canine osteosarcoma cell lines. The finding that GLI signaling activity is present and active in canine osteosarcoma cells suggests that spontaneously arising osteosarcoma in dogs might serve as a good model for future preclinical testing of GLI inhibitors.

Activation of hedgehog signaling pathway in human non-small cell lung cancers

The activation of the hedgehog pathway, which is an important signaling mechanism crucial in embryogenesis, has strong links to carcinogenesis. Aberrant regulation of this pathway can result in the development of tumors. The present study was designed to investigate Hh related protein expression in non-small cell lung cancers. Fifty five non-small cell lung cancers samples were used in the study. By reverse transcription-polymerase chain reaction (RT-PCR), the expression of Shh, Ptch-1, and Gli-1 in tumor and adjacent normal tissues was examined and associated to clinical pathologic features. The expression levels of Shh, Ptch-1, Gli-1 in non-small cell lung cancer tissues were 63.64, 69.09, 43.64 %, respectively, higher than that in the adjacent normal tissues. Survival analysis showed that both Ptch-1 and Gli-1 expression were associated with poor survival (both P <0.05, log-rank test). Shh and Ptch-1 expression were correlated with lymph node metastasis. These results suggest that dysregulation of Hh signaling pathway plays an important role in the development of human NSCLCs. The expression of Ptch-1 and Gli-1 is possibly involved in NSCLCs progression, which may be a useful prognostic indicator of NSCLCs.

A new role for Hedgehogs in juxtacrine signaling

The Hedgehog pathway plays important roles in embryonic development, adult stem cell maintenance and tumorigenesis. In mammals these effects are mediated by Sonic, Desert and Indian Hedgehog (Shh, Dhh and Ihh). Shh undergoes autocatalytic cleavage and dual lipidation prior to secretion and forming a response gradient. Post-translational processing and secretion of Dhh and Ihh ligands has not previously been investigated. This study reports on the synthesis, processing, secretion and signaling activities of SHH, IHH and DHH preproteins expressed in cultured cells, providing unexpected evidence that DHH does not undergo substantial autoprocessing or secretion, and does not function in paracrine signaling. Rather, DHH functions as a juxtacrine signaling ligand to activate a cell contact-mediated HH signaling response, consistent with its localised signaling in vivo. Further, the LnCAP prostate cancer cell, when induced to express endogenous DHH and SHH, is active only in juxtacrine signaling. Domain swap studies reveal that the C-terminal domain of HH regulates its processing and secretion. These findings establish a new regulatory role for HHs in cell-mediated juxtacrine signaling in development and cancer.

Hedgehog signaling induces osteosarcoma development through Yap1 and H19 overexpression

Osteosarcoma is one of the most common bone tumors. However, the genetic basis for its pathogenesis remains elusive. Here, we investigated the roles of Hedgehog (Hh) signaling in osteosarcoma development. Genetically-engineered mice with ubiquitous upregulated Hh signaling specifically in mature osteoblasts develop focal bone overgrowth, which greatly resembles the early stage of osteosarcoma. However, these mice die within three months, which prohibits further analysis of tumor progression. We therefore generated a mouse model with partial upregulated Hh signaling in mature osteoblasts and crossed it into a p53 heterozygous background to potentiate tumor development. We found that these mutant mice developed malignant osteosarcoma with high penetrance. Isolated primary tumor cells were mainly osteoblastic and highly proliferative with many characteristics of human osteosarcomas. Allograft transplantation into immunocompromised mice displayed high tumorigenic potential. More importantly, both human and mouse tumor tissues express high level of yes-associated protein 1 (Yap1), a potent oncogene that is amplified in various cancers. We show that inhibition of Hh signaling reduces Yap1 expression and knockdown of Yap1 significantly inhibits tumor progression. Moreover, long non-coding RNA H19 is aberrantly expressed and induced by upregulated Hh signaling and Yap1 overexpression. Our results demonstrate that aberrant Hh signaling in mature osteoblasts is responsible for the pathogenesis of osteoblastic osteosarcoma through Yap1 and H19 overexpression.

Modulation of lipid metabolic defects rescues cleft palate in Tgfbr2 mutant mice

Mutations in transforming growth factor beta (TGFβ) receptor type II (TGFBR2) cause Loeys-Dietz syndrome, characterized by craniofacial and cardiovascular abnormalities. Mice with a deletion of Tgfbr2 in cranial neural crest cells (Tgfbr2(fl/fl);Wnt1-Cre mice) develop cleft palate as the result of abnormal TGFβ signaling activation. However, little is known about metabolic processes downstream of TGFβ signaling during palatogenesis. Here, we show that Tgfbr2 mutant palatal mesenchymal cells spontaneously accumulate lipid droplets, resulting from reduced lipolysis activity. Tgfbr2 mutant palatal mesenchymal cells failed to respond to the cell proliferation stimulator sonic hedgehog, derived from the palatal epithelium. Treatment with p38 mitogen-activated protein kinase (MAPK) inhibitor or telmisartan, a modulator of p38 MAPK activation and lipid metabolism, blocked abnormal TGFβ-mediated p38 MAPK activation, restoring lipid metabolism and cell proliferation activity both in vitro and in vivo. Our results highlight the influence of alternative TGFβ signaling on lipid metabolic activities, as well as how lipid metabolic defects can affect cell proliferation and adversely impact palatogenesis. This discovery has broader implications for the understanding of metabolic defects and potential prevention of congenital birth defects.

Inactivation of Patched1 in mice leads to development of gastrointestinal stromal-like tumors that express Pdgfrα but not kit

BACKGROUND & AIMS

A fraction of gastrointestinal stromal tumor (GIST) cells overexpress the platelet-derived growth factor receptor (PDGFR)A, although most overexpress KIT. It is not known if this is because these receptor tyrosine kinases have complementary oncogenic potential, or because of heterogeneity in the cellular origin of GIST. Little also is known about why Hedgehog (HH) signaling is activated in some GIST. HH binds to and inactivates the receptor protein patched homolog (PTCH).

METHODS

Ptch was conditionally inactivated in mice (to achieve constitutive HH signaling) using a Cre recombinase regulated by the lysozyme M promoter. Cre-expressing cells were traced using R26R-LacZ reporter mice. Tumors were characterized by in situ hybridization, immunohistochemistry, immunoblot, and quantitative reverse-transcriptase polymerase chain reaction analyses. Cell transformation was assessed by soft agar assay.

RESULTS

Loss of Ptch from lysozyme M-expressing cells resulted in the development of tumors of GIST-like localization and histology; these were reduced when mice were given imatinib, a drug that targets KIT and PDGFRA. The Hh signaling pathway was activated in the tumor cells, and Pdgfrα, but not Kit, was overexpressed and activated. Lineage tracing revealed that Cre-expressing intestinal cells were Kit-negative. These cells sometimes expressed Pdgfrα and were located near Kit-positive interstitial cells of Cajal. In contrast to KIT, activation of PDGFRA increased anchorage-independent proliferation and was required for tumor formation in mice by cells with activated HH signaling.

CONCLUSIONS

Inactivation of Ptch in mice leads to formation of GIST-like tumors that express Pdgfrα, but not Kit. Activation of Pdgfrα signaling appears to facilitate tumorigenesis.

Molecular signatures of basal cell carcinoma susceptibility and pathogenesis: a genomic approach

Gene expression profiling can be useful for phenotypic classification, investigation of functional pathways, and to facilitate the search for disease risk genes through the integration of transcriptional data with available genomic information. To enhance our understanding of the genetic and molecular basis of basal cell carcinoma (BCC) we performed global gene expression analysis to generate a disease-associated transcriptional profile. A gene signature composed of 331 differentially expressed genes (DEGs) was generated from comparing 4 lesional and 4 site-matched control samples using Affymetrix Human Genome U95A microarrays. Hierarchical clustering based on the obtained gene signature separated the samples into their corresponding phenotype. Pathway analysis identified several significantly overrepresented pathways including PPAR-γ signaling, TGF-β signaling and lipid metabolism, as well as confirmed the importance of SHH and p53 in the pathogenesis of BCC. Comparison of our microarray data with previous microarray studies revealed 13 DEGs overlapping in 3 studies. Several of these overlapping genes function in lipid metabolism or are components of the extracellular matrix, suggesting the importance of these and related pathways in BCC pathogenesis. BCC-associated DEGs were mapped to previously reported BCC susceptibility loci including 1p36, 1q42, 5p13.3, 5p15 and 12q11-13. Our analysis also revealed transcriptional 'hot spots' on chromosome 5 which help to confirm (5p13 and 5p15) and suggest novel (5q11.2-14.3, 5q22.1-23.3 and 5q31-35.3) disease susceptibility loci/regions. Integrating microarray analyses with reported genetic information helps to confirm and suggest novel disease susceptibility loci/regions. Identification of these specific genomic and/or transcriptional targets may lead to novel diagnostic and therapeutic modalities.

Dehydroepiandrosterone biosynthesis, role, and mechanism of action in the developing neural tube

Dehydroepiandrosterone (DHEA) is synthesized from cholesterol by activity of P450scc and P450c17, enzymes that we previously characterized in the developing nervous system. We describe the localization of P450c17 in the differentiated field of the ventral spinal cord in different motor neuron subtypes. We show that, during organogenesis, P450c17 activity is regulated along the antero/posterior axis of the spinal cord concomitantly with the gradient of neurogenesis. To examine whether DHEA may modulate this process, we measured proliferation and differentiation of ventral neural precursors in primary and explant cultures. Our results showed that DHEA-induced the expression of class II protein Nkx6.1, motor neuron precursor Olig-2, and definitive motor neuron marker Isl-1/2. DHEA also promoted proliferation of ventrally committed precursors in isolated spinal cord precursor cultures and in whole spinal cord explants. Both the proliferative and inductive effects of DHEA were dependent on sonic hedgehog signaling. The possibilities that the effects observed with DHEA were due to its metabolism into androgens or to activation of NMDA receptors were excluded. These results support the hypothesis that the tight regulation of DHEA biosynthesis may be a biologic clock restricting the period of ventral neuronal-precursor proliferation, thus controlling the number of pre-committed neurons in the developing neural tube.

Targeting of the tumor suppressor GRHL3 by a miR-21-dependent proto-oncogenic network results in PTEN loss and tumorigenesis

Despite its prevalence, the molecular basis of squamous cell carcinoma (SCC) remains poorly understood. Here, we identify the developmental transcription factor Grhl3 as a potent tumor suppressor of SCC in mice, and demonstrate that targeting of Grhl3 by a miR-21-dependent proto-oncogenic network underpins SCC in humans. Deletion of Grhl3 in adult epidermis evokes loss of expression of PTEN, a direct GRHL3 target, resulting in aggressive SCC induced by activation of PI3K/AKT/mTOR signaling. Restoration of Pten expression completely abrogates SCC formation. Reduced levels of GRHL3 and PTEN are evident in human skin, and head and neck SCC, associated with increased expression of miR-21, which targets both tumor suppressors. Our data define the GRHL3-PTEN axis as a critical tumor suppressor pathway in SCC.

Sequential activation of Snail1 and N-Myc modulates sonic hedgehog-induced transformation of neural cells

Activation of the Sonic hedgehog (Shh) pathway and increased expression of Gli1 play an important role in proliferation and transformation of granule cell progenitors (GCP) in the developing cerebellum. Medulloblastomas arising from cerebellar GCPs are frequently driven by Shh pathway-activating mutations; however, molecular mechanisms of Shh pathway dysregulation and transformation of neural progenitors remain poorly defined. We report that the transcription factor and oncogene Snail1 (Sna1) is directly induced by Shh pathway activity in GCPs, murine medulloblastomas, and human medulloblastoma cells. Enforced expression of Sna1 was sufficient to induce GCPs and medulloblastoma cell proliferation in the absence of Shh/Gli1 exposure. In addition, enforced expression of Sna1 increased transformation of medulloblastoma cells in vitro and in vivo. Analysis of potential Sna1 targets in neural cells revealed a novel Sna1 target, N-Myc, a transcription factor known to play a role in Shh-mediated GCP proliferation and medulloblastoma formation. We found that Sna1 directly induced transcription of N-Myc in human medulloblastoma cells and that depletion of N-Myc ablated the Sna1-induced proliferation and transformation. Taken together, these results provide further insight into the mechanism of Shh-induced transformation of neural progenitor cells and suggest that induction of Sna1 may serve to amplify the oncogenic potential of Shh pathway activation through N-Myc induction.

Activation of sonic hedgehog signaling in oral squamous cell carcinomas: a preliminary study

Sonic hedgehog signaling is important for human development, and aberrant regulation of this pathway can result in the development of tumors. The aim of this study was to examine the expression of sonic hedgehog signaling molecules in oral squamous cell carcinoma. By quantitative real-time polymerase chain reaction, the expression of SHH, SMO, PTCH-1, and GLI-1 was analyzed in 30 oral squamous cell carcinoma cases and 8 samples of nonneoplastic oral mucosa and associated to clinical pathologic features. The expression of β-catenin, cyclin D1, Wnt-1, and Egfr was evaluated by immunohistochemistry in 26 available cases of oral squamous cell carcinoma. Normal oral mucosa from healthy individuals was negative for all genes that were evaluated. SHH, PTCH-1, SMO, and GLI-1 were not expressed in nonneoplastic oral mucosa, and low levels of GLI-1 were observed in nonneoplastic oral mucosa that was adjacent to the tumor. All oral squamous cell carcinoma cases expressed high levels of PTCH-1, SMO, and GLI-1 and were devoid of SHH. The expression of SMO was associated with clinical stage (P = .022) and a borderline association in cervical lymph node metastasis (P = .053). PTCH-1 expression showed a strong correlation with SMO (rs = 0.64; P < .001) and GL-1 (rs = 0.70; P < .001); SMO and GLI-1 also correlated with each other (rs, 0.55; P < .001). All proteins evaluated were expressed as cyclin D1 (92% of samples), β-catenin (73%), Egfr (46%), or Wnt-1 (32%). Our data demonstrate that sonic hedgehog signaling is activated in oral squamous cell carcinoma and suggest that this pathway mediates its tumorigenesis.

The Caenorhabditis elegans mucin-like protein OSM-8 negatively regulates osmosensitive physiology via the transmembrane protein PTR-23

The molecular mechanisms of animal cell osmoregulation are poorly understood. Genetic studies of osmoregulation in yeast have identified mucin-like proteins as critical regulators of osmosensitive signaling and gene expression. Whether mucins play similar roles in higher organisms is not known. Here, we show that mutations in the Caenorhabditis elegans mucin-like gene osm-8 specifically disrupt osmoregulatory physiological processes. In osm-8 mutants, normal physiological responses to hypertonic stress, such as the accumulation of organic osmolytes and activation of osmoresponsive gene expression, are constitutively activated. As a result, osm-8 mutants exhibit resistance to normally lethal levels of hypertonic stress and have an osmotic stress resistance (Osr) phenotype. To identify genes required for Osm-8 phenotypes, we performed a genome-wide RNAi osm-8 suppressor screen. After screening ∼18,000 gene knockdowns, we identified 27 suppressors that specifically affect the constitutive osmosensitive gene expression and Osr phenotypes of osm-8 mutants. We found that one suppressor, the transmembrane protein PTR-23, is co-expressed with osm-8 in the hypodermis and strongly suppresses several Osm-8 phenotypes, including the transcriptional activation of many osmosensitive mRNAs, constitutive glycerol accumulation, and osmotic stress resistance. Our studies are the first to show that an extracellular mucin-like protein plays an important role in animal osmoregulation in a manner that requires the activity of a novel transmembrane protein. Given that mucins and transmembrane proteins play similar roles in yeast osmoregulation, our findings suggest a possible evolutionarily conserved role for the mucin-plasma membrane interface in eukaryotic osmoregulation.

The ability to sense and respond to changes in cell volume is a process termed osmoregulation and is an essential prerequisite for cellular life. While the molecular details of this physiological process are well described in unicellular organisms such as yeast and bacteria, the mechanisms that govern osmoregulation in animals are poorly understood. Using a genetic approach in the nematode C. elegans, we identified the mucin-like protein OSM-8 as a critical regulator of osmoregulation. Disruption of the osm-8 gene results in the activation of physiological responses that are normally only activated in response to hyperosmotic stress, suggesting that osm-8 is a negative regulator of C. elegans osmoregulatory physiology. Through a genome-wide RNAi suppressor screen, we also identified a transmembrane protein, PTR-23, that is required for osm-8 mutants to activate osmoregulatory physiological responses. Together with previous findings from yeast, our data define an important and possibly evolutionarily conserved role for the plasma membrane-mucin matrix interface in eukaryotic osmoregulation. Our findings also illustrate the value of studying cell physiological processes such as osmoregulation in a live animal model, in which complex and dynamic extracellular matrix structures are preserved.

Cross-signaling among phosphinositide-3 kinase, mitogen-activated protein kinase and sonic hedgehog pathways exists in esophageal cancer

The hedgehog (Hh) signaling pathway is essential for the development of tissues and organs. Hyperactive Hh signaling has been implicated in many gastric cancers, including esophageal cancer. However, the interaction between the Hh pathway and other potential signaling pathways in primary esophageal tumorigenesis has not been well investigated. In our study, we found that esophageal cancer cells expressed Hh signaling molecules and that the hyperexpression of Hh target genes was related to protein kinase B (AKT) activation but not extracellular signal-regulated kinase activation. We analyzed the relationship between Gli1 or p-AKT expression and clinicopathological features in esophageal carcinoma samples and found that Gli1 expression was associated with lymph vessel invasion (p = 0.016), blood vessel invasion (p = 0.006) and a poor prognosis (p = 0.003), and p-AKT expression was associated with blood vessel invasion (p = 0.031) and a poor prognosis (p = 0.031). We also studied the relationship between Hh and phosphinositide-3 kinase (PI3K)/AKT or mitogen-activated protein kinase (MAPK) signaling pathways in both TE-1 and TE-10 cell lines. We found that the PI3K/AKT pathway played a critical role in Hh signaling after stimulation with epidermal growth factor, Gβγ and N-Shh. Conversely, PI3K/AKT and MAPK signaling cooperated with the Shh pathway to promote esophageal cancer cell survival and proliferation. The results from esophageal cancer cells shed light on the significance of Hh signaling in esophageal tumor formation and the crosstalk of the Hh pathway with other basic signaling pathways, which is consistent with that observed in human tumor samples.

Mitogenic Sonic hedgehog signaling drives E2F1-dependent lipogenesis in progenitor cells and medulloblastoma

Deregulation of the Rb/E2F tumor suppressor complex and aberrantion of Sonic hedgehog (Shh) signaling are documented across the spectrum of human malignancies. Exaggerated de novo lipid synthesis is also found in certain highly proliferative, aggressive tumors. Here, we show that in Shh-driven medulloblastomas, Rb is inactivated and E2F1 is upregulated, promoting lipogenesis. Extensive lipid accumulation and elevated levels of the lipogenic enzyme fatty acid synthase (FASN) mark those tumors. In primary cerebellar granule neuron precursors (CGNPs), proposed Shh-associated medulloblastoma cells-of-origin, Shh signaling triggers E2F1 and FASN expression, whereas suppressing fatty acid oxidation (FAO), in a smoothened-dependent manner. In the developing cerebellum, E2F1 and FASN co-localize in proliferating CGNPs. in vivo and in vitro, E2F1 is required for FASN expression and CGNP proliferation, and E2F1 knockdown impairs Shh-mediated FAO inhibition. Pharmacological blockade of Rb inactivation and/or lipogenesis inhibits CGNP proliferation, drives medulloblastoma cell death and extends survival of medulloblastoma-bearing animals In vivo. These findings identify a novel mechanism through which Shh signaling links cell cycle progression to lipid synthesis, through E2F1-dependent regulation of lipogenic enzymes. These findings pertinent to the etiology of tumor metabolism also underscore the key role of the Shh→E2F1→FASN axis in regulating de novo lipid synthesis in cancers, and as such its value as a global therapeutic target in hedgehog-dependent and/or Rb-inactivated tumors.

Differential expression of Shh and BMP signaling in the potential conversion of human adipose tissue stem cells into neuron-like cells in vitro

The nervous system (NS) has a limited self-repair capability and adult neurogenesis is limited to certain regions of the brain. This generates a great interest in using stem cells to repair the NS. Previous reports have shown the differentiation of adipose tissue-derived mesenchymal stem cells (ASCs) in neuron-like cells when cultures are enriched with growth factors participating in embryonic and adult neurogenesis. Therefore, it could be thought that there exists a functional parallelism between neurogenesis and neuronal differentiation of ASCs. For this reason, the goal of this work was to study the differential gene expression of Shh and BMP genetic pathways involved in cell fate determination and proliferation. In this study we demonstrated that hASCs are endowed with active Hedgehog and BMP signaling pathways through the expression of genes of both cascades and that their expressions are downregulated after neuronal induction. This idea is in accordance with the facts that Shh and BMP signaling is involved in the maintenance of cells with stem cells properties and that proliferation decreases during the process of differentiation. Furthermore, Noggin expression was detected in induced hASCs whereas there was no expression in noninduced cells, which indicates that these cells are probably adopting a neuronal fate because noggin diverts neural stem cells from glial to neuronal fate. We also detected FM1-43 and synaptophisin staining, which is evidence of the presence of putative functional presynaptic terminals, a neuron-specific property. These results could partially contribute to the elucidation of the molecular mechanisms involved in neuronal differentiation of adult human nonneural tissues.

YAP1 is amplified and up-regulated in hedgehog-associated medulloblastomas and mediates Sonic hedgehog-driven neural precursor proliferation

Medulloblastoma is the most common solid malignancy of childhood, with treatment side effects reducing survivors' quality of life and lethality being associated with tumor recurrence. Activation of the Sonic hedgehog (Shh) signaling pathway is implicated in human medulloblastomas. Cerebellar granule neuron precursors (CGNPs) depend on signaling by the morphogen Shh for expansion during development, and have been suggested as a cell of origin for certain medulloblastomas. Mechanisms contributing to Shh pathway-mediated proliferation and transformation remain poorly understood. We investigated interactions between Shh signaling and the recently described tumor-suppressive Hippo pathway in the developing brain and medulloblastomas. We report up-regulation of the oncogenic transcriptional coactivator yes-associated protein 1 (YAP1), which is negatively regulated by the Hippo pathway, in human medulloblastomas with aberrant Shh signaling. Consistent with conserved mechanisms between brain tumorigenesis and development, Shh induces YAP1 expression in CGNPs. Shh also promotes YAP1 nuclear localization in CGNPs, and YAP1 can drive CGNP proliferation. Furthermore, YAP1 is found in cells of the perivascular niche, where proposed tumor-repopulating cells reside. Post-irradiation, YAP1 was found in newly growing tumor cells. These findings implicate YAP1 as a new Shh effector that may be targeted by medulloblastoma therapies aimed at eliminating medulloblastoma recurrence.

Neuronal differentiation in basal cell carcinoma: possible relationship to Hedgehog pathway activation?

Although deregulated Hedgehog signalling and elevated Gli transcription factor expression are known to promote the development of basal cell carcinoma (BCC), little is known about molecular mechanisms driving the development of specific growth pattern subtypes. Using gene array analysis, we have previously observed that over-expression of GLI1 in human keratinocytes promotes increased expression of the neuronal differentiation markers ARC and ULK1. We asked whether neuronal differentiation is a characteristic of BCC and whether there is any correlation with BCC subtype. Using RT-PCR and immunohistochemistry, we confirmed that the neuronal markers ARC, beta-tubulin III, GAP-43 and Neurofilament are expressed in human BCC but not in normal epidermis. Moreover, we found that expression of these neuronal differentiation markers showed strong correlation to BCC subtype, with more aggressive infiltrative and morphoeic BCC showing low levels or lack of expression compared to nodular, superficial and micronodular subtypes. Primary human keratinocytes retrovirally expressing GLI1(-) and GLI2(-) showed elevated levels of beta-tubulin III and ARC but not Neurofilament or GAP-43, suggesting that beta-tubulin III and Arc may be early targets of aberrant Gli expression in BCC, whereas expression of Neurofilament and GAP-43 are either later, downstream targets or under control of alternative pathways. We propose that neuronal differentiation is a feature of BCC and that expression of these markers is in part due to aberrant Hedgehog signalling. Moreover, we suggest that correlation between loss of expression of neuronal markers in infiltrative and morphoeic BCC subtypes reflects dedifferentiation of more aggressive BCC subtypes.

Tuberous sclerosis complex suppression in cerebellar development and medulloblastoma: separate regulation of mammalian target of rapamycin activity and p27 Kip1 localization

During development, proliferation of cerebellar granule neuron precursors (CGNP), candidate cells-of-origin for the pediatric brain tumor medulloblastoma, requires signaling by Sonic hedgehog (Shh) and insulin-like growth factor (IGF), the pathways of which are also implicated in medulloblastoma. One of the consequences of IGF signaling is inactivation of the mammalian target of rapamycin (mTOR)-suppressing tuberous sclerosis complex (TSC), comprised of TSC1 and TSC2, leading to increased mRNA translation. We show that mice, in which TSC function is impaired, display increased mTOR pathway activation, enhanced CGNP proliferation, glycogen synthase kinase-3 alpha/beta (GSK-3 alpha/beta) inactivation, and cytoplasmic localization of the cyclin-dependent kinase inhibitor p27(Kip1), which has been proposed to cause its inactivation or gain of oncogenic functions. We observed the same characteristics in wild-type primary cultures of CGNPs in which TSC1 and/or TSC2 were knocked down, and in mouse medulloblastomas induced by ectopic Shh pathway activation. Moreover, Shh-induced mouse medulloblastomas manifested Akt-mediated TSC2 inactivation, and the mutant TSC2 allele synergized with aberrant Shh signaling to increase medulloblastoma incidence in mice. Driving exogenous TSC2 expression in Shh-induced medulloblastoma cells corrected p27(Kip1) localization and reduced proliferation. GSK-3 alpha/beta inactivation in the tumors in vivo and in primary CGNP cultures was mTOR-dependent, whereas p27(Kip1) cytoplasmic localization was regulated upstream of mTOR by TSC2. These results indicate that a balance between Shh mitogenic signaling and TSC function regulating new protein synthesis and cyclin-dependent kinase inhibition is essential for the normal development and prevention of tumor formation or expansion.

Expression of sonic hedgehog signaling molecules in normal, hyperplastic and carcinomatous endometrium

The aim of the present study was to determine the expression profile of the hedgehog (Hh) signaling molecules in normal, hyperplastic, and carcinomatous uterine endometrium. For this purpose, 271 endometrial tissue samples, (62 of normal endometrium, 127 of endometrial hyperplasias, and 82 endometrial adenocarcinomas) were studied using antibodies recognizing Hh-related signaling proteins, such as, sonic hedgehog (Shh), Patched (PTCH), Smoothened (Smo), Suppressor of fused [Su(Fu)], Gli-1, Gli-2, and Gli-3 by immunohistochemistry. The mRNA expression of these molecules was also assessed on reverse transcription-polymerase chain reaction. In the normal endometrium, the expression of Hh signaling molecules was generally downregulated except for Su(Fu), Gli-2, and Shh. In particular, the expression of both PTCH and Smo was very low or almost absent. Overall expression of Hh signaling molecules increased in hyperplastic endometrium; in particular, PTCH and Smo were significantly highly expressed in complex and atypical hyperplasia. In carcinoma samples extensive alterations were observed in the expression pattern of the signaling molecules. Nuclear Gli-2, cytoplasmic Gli-3, and Su(Fu) were overexpressed, whereas Shh, PTCH, and Smo expression were significantly reduced compared with the hyperplastic endometrium. The results suggest that the alteration of Hh signaling may be implicated in tumorigenesis of the endometrium.

Quantitative analysis of mRNA transcripts of Hox, SHH, PTCH, Wnt, and Fzd genes in canine hematopoietic progenitor cells and various in vitro colonies differentiated from the cells

Homeobox (Hox), Sonic hedgehog (SHH), and Wingless-type MMTV integration site family (Wnt) are known to modulate the self-renewal and expansion of hematopoietic progenitor/stem cells in humans and mice. Frizzled (Fzd) and Patched1 (PTCH1) represent the receptors of Wnt and SHH, respectively. In this study, the amounts of mRNA transcripts of the genes associated with the self-renewal of hematopoietic stem cells, HoxB3, HoxB4, HoxA10, Wnt5a, Wnt2b, Fzd1, Fzd6, SHH, and PTCH1, were measured in canine unfractionated bone marrow cells, CD34-enriched cells, and various colony-forming units in culture (CFU-C). Partial cDNA sequences of these 9 canine genes were determined in this study. Quantitative real-time polymerase chain reaction was employed to indicate their relative amounts of mRNA transcripts. Amounts of mRNA transcripts of HoxB3, HoxA10, PTCH1, and Wnt5a genes in canine CD34-enriched cell fraction were significantly larger than those in the CD34-depleted cell fraction. Amounts of mRNA transcripts of HoxB3, HoxA10, PTCH1, Wnt5a, and Wnt2b genes in various CFU-C cells were significantly smaller than those in the seeded CD34-enriched cell fraction. These results suggested important roles of the products of these genes in self-renewal, expansion, and survival of hematopoietic progenitor cells in dogs as shown in humans and rodents.

A genome-wide shRNA screen identifies GAS1 as a novel melanoma metastasis suppressor gene

Metastasis suppressor genes inhibit one or more steps required for metastasis without affecting primary tumor formation. Due to the complexity of the metastatic process, the development of experimental approaches for identifying genes involved in metastasis prevention has been challenging. Here we describe a genome-wide RNAi screening strategy to identify candidate metastasis suppressor genes. Following expression in weakly metastatic B16-F0 mouse melanoma cells, shRNAs were selected based upon enhanced satellite colony formation in a three-dimensional cell culture system and confirmed in a mouse experimental metastasis assay. Using this approach we discovered 22 genes whose knockdown increased metastasis without affecting primary tumor growth. We focused on one of these genes, Gas1 (Growth arrest-specific 1), because we found that it was substantially down-regulated in highly metastatic B16-F10 melanoma cells, which contributed to the high metastatic potential of this mouse cell line. We further demonstrated that Gas1 has all the expected properties of a melanoma tumor suppressor including: suppression of metastasis in a spontaneous metastasis assay, promotion of apoptosis following dissemination of cells to secondary sites, and frequent down-regulation in human melanoma metastasis-derived cell lines and metastatic tumor samples. Thus, we developed a genome-wide shRNA screening strategy that enables the discovery of new metastasis suppressor genes.

Structure, expression, and biological function of INSM1 transcription factor in neuroendocrine differentiation

Zinc-finger transcription factors are DNA-binding proteins that are implicated in many diverse biological functions. INSM1 (formerly IA-1) contains five zinc-finger motifs and functions as a transcription factor. INSM1 protein structure is highly conserved in homologues of different species. It is predominantly expressed in developing neuroendocrine tissues and the nervous system in mammals. INSM1 represents an important player in early embryonic neurogenesis. In pancreatic endocrine cell differentiation, Ngn3 first activates INSM1 and subsequently NeuroD/beta2. Conversely, INSM1 exerts a feedback mechanism to suppress NeuroD/beta2 and its own gene expression. INSM1 gene ablation in the mouse results in the impairment of pancreatic endocrine cell maturation. Further, deletion of INSM1 severely impairs catecholamine biosynthesis and secretion from the adrenal gland that results in early embryonic lethality. Genetically, INSM1 acts as a downstream factor of Mash 1 and Phox2b in the differentiation of the sympatho-adrenal lineage. In the developing neocortex, mouse embryos lacking INSM1 expression contain half the number of basal progenitors and show a reduction in cortical plate radial thickness. Cell signaling studies reveal that INSM1 contributes to the induction of cell cycle arrest/exit necessary to facilitate cellular differentiation. INSM1 is highly expressed in tumors of neuroendocrine origin. Hence, its promoter could serve as a tumor-specific promoter that drives a specific targeted cancer gene therapy for the treatment of neuroendocrine tumors. Taken together, all of these features of INSM1 strongly support its role as an important regulator during neuroendocrine differentiation.

SHH pathway and cerebellar development

The morphogenetic factor Sonic hedgehog (SHH) has been discovered as one of the masterplayers in cerebellar patterning and was subjected to intensive investigation during the last decade. During early postnatal development, this continuously secreted cholesterol-modified protein drives the expansion of the largest neuronal population of the brain, the granular cells. Moreover, it acts on Bergmann glia differentiation and would potentially affect Purkinje cells homeostasis at adult age. The cerebellar cortex constituted an ideal developmental model to dissect out the upstream mechanisms and downstream targets of this complex pathway. Its deep understanding discloses some of the mechanistic disorders underlying pediatric tumorigenesis, congenital ataxia, and mental retardation. Therapeutical use of its regulators has been consolidated on murine transgenic models and is now considered as a realistic human clinical application. Here, we will review the most recent advances made in the comprehensive understanding of SHH involvement in cerebellar development and pathology.

Epidermal growth factor receptor signaling synergizes with Hedgehog/GLI in oncogenic transformation via activation of the MEK/ERK/JUN pathway

Persistent activation of the Hedgehog (HH)/GLI signaling pathway has been implicated in the development of a number of human cancers. The GLI zinc finger transcription factors act at the end of the HH signaling cascade to control gene expression, and recent studies have shown that the activity of GLI proteins can be additionally modified by integration of distinct signals, such as the MEK/extracellular signal-regulated kinase (ERK) and phosphinositide-3 kinase (PI3K)/AKT pathway. However, little is known about the identity of the upstream activators of these HH/GLI interacting signaling pathways in cancer. Here, we provide evidence that integration of the HH/GLI and epidermal growth factor receptor (EGFR) pathway synergistically induces oncogenic transformation, which depends on EGFR-mediated activation of the RAS/RAF/MEK/ERK but not of the PI3K/AKT pathway. EGFR/MEK/ERK signaling induces JUN/activator protein 1 activation, which is essential for oncogenic transformation, in combination with the GLI activator forms GLI1 and GLI2. Furthermore, pharmacologic inhibition of EGFR and HH/GLI efficiently reduces growth of basal cell carcinoma (BCC) cell lines derived from mice with activated HH/GLI signaling. The results identify the synergistic integration of GLI activator function and EGFR signaling as a critical step in oncogenic transformation and provide a molecular basis for therapeutic opportunities relying on combined inhibition of the HH/GLI and EGFR/MEK/ERK/JUN pathway in BCC.

Antitumor effects of a combined 5-aza-2'deoxycytidine and valproic acid treatment on rhabdomyosarcoma and medulloblastoma in Ptch mutant mice

Patched (Ptch) heterozygous mice develop medulloblastoma (MB) and rhabdomyosarcoma (RMS) resembling the corresponding human tumors. We have previously shown that epigenetic silencing of the intact Ptch allele contributes to tumor formation in this model. Here, we investigated whether targeting of epigenetic silencing mechanisms could be useful in the treatment of Ptch-associated cancers. A reduction of endogenous DNA methyltransferase1 (Dnmt1) activity significantly reduced tumor incidence in heterozygous Ptch knockout mice. A combined treatment with the Dnmt inhibitor 5-aza-2'deoxycytidine (5-aza-dC) and the histone deacetlyase (HDAC) inhibitor valproic acid (VPA) efficiently prevented MB and RMS formation, whereas monotherapies with either drug were less effective. Wild-type Ptch expression was efficiently reactivated in tumors by 5-aza-dC/VPA combination therapy. This was associated with reduced methylation of the Ptch promoter and induction of histone hyperacetylation suggesting inhibition of HDACs in vivo. However, the treatment was not effective in clinically overt, advanced stage tumors. This is a first in vivo demonstration that targeting of Dnmt and HDAC activities is highly effective in preventing formation of Ptch-associated tumors. The results suggest a novel clinical strategy for consolidation therapy of corresponding tumors in humans after completion of conventional treatment. Our data also suggest that epigenetic therapy may be less effective in treating advanced stages of tumors, at least in this tumor model.

Brain tumor stem cells

The dogma that solid tumors are composed of tumor cells that all share the same ability to produce proliferating daughter cells has been challenged in recent years. There is growing evidence that many adult tissues contain a set of tissue stem cells, which might undergo malignant transformation while retaining their stem cell characteristics. These include the ability of indefinite self-renewal and the capability to differentiate into daughter cells of tissue-specific lineages. Brain tumors such as medulloblastomas or glioblastomas often contain areas of divergent differentiation, which raises the intriguing question of whether these tumors could derive from neural stem cells (NSCs).This chapter reviews the current knowledge of NSCs and relates them to brain tumor pathology. Current therapy protocols for malignant brain tumors are targeted toward the reduction of bulk tumor mass. The concept of brain-tumor stem cells could provide new insights for future therapies, if the capacity for self-renewal of tumor cells and growth of the tumor mass would reside within a small subset of cancer cells.

Insulin receptor substrate 1 is an effector of sonic hedgehog mitogenic signaling in cerebellar neural precursors

Sonic hedgehog (SHH) and insulin-like growth factor (IGF) signaling are essential for development of many tissues and are implicated in medulloblastoma, the most common solid pediatric malignancy. Cerebellar granule neuron precursors (CGNPs), proposed cells-of-origin for specific classes of medulloblastomas, require SHH and IGF signaling for proliferation and survival during development of the cerebellum. We asked whether SHH regulates IGF pathway components in proliferating CGNPs. We report that SHH-treated CGNPs showed increased levels of insulin receptor substrate 1 (IRS1) protein, which was also present in the germinal layer of the developing mouse cerebellum and in mouse SHH-induced medulloblastomas. Previous roles for IRS1, an oncogenic protein that is essential for IGF-mediated proliferation in other cell types, have not been described in SHH-mediated CGNP proliferation. We found that IRS1 overexpression can maintain CGNP proliferation in the absence of SHH. Furthermore, lentivirus-mediated knock down experiments have shown that IRS1 activity is required for CGNP proliferation in slice explants and dissociated cultures. Contrary to traditional models for SHH signaling that focus on gene transcription, SHH stimulation does not regulate Irs1 transcription but rather stabilizes IRS1 protein by interfering with mTOR-dependent IRS1 turnover and possibly affects Irs1 mRNA translation. Thus, we have identified IRS1 as a novel effector of SHH mitogenic signaling that may serve as a future target for medulloblastoma therapies. Our findings also indicate a previously unreported interaction between the SHH and mTOR pathways, and provide an example of a non-classical means for SHH-mediated protein regulation during development.

Expression pattern of sonic hedgehog and effect of topical mitomycin C on its expression in human ocular surface neoplasms

PURPOSE

To examine if the cells of human ocular surface neoplasms express sonic hedgehog (Shh) and the effects of topical mitomycin C on its expression.

METHODS

Conjunctival tissues obtained from two normal subjects, two patients with squamous cell carcinoma of the ocular surface (conjunctiva), and one patient with ocular epithelial dysplasia were used in this study. Histological sections were processed for light microscopic immunohistochemical analysis for Shh.

RESULTS

Faint immunoreactivity for Shh was detected in basal epithelial cells of limbus, bulbar, and palpebral conjunctival epithelial cells. On the other hand, squamous cell carcinoma cells markedly expressed Shh with positive staining for Patched 1(Ptc), the cell surface receptor of Shh. Similar marked expression of Shh was detected in the patient with ocular epithelial dysplasia, and this Shh expression was almost eliminated following topical mitomycin C treatment. A cell culture experiment was conducted to examine the effect of mitomycin C on Shh expression in a cultured squamous cell carcinoma cell line.

CONCLUSIONS

Conjunctival epithelium constitutively expresses a low level of Shh, and its expression increases during malignant conversion of epithelial cells. Reduction of Shh expression might be involved in the therapeutic efficacy of topical mitomycin C for ocular surface epithelial neoplasms.