Primers on molecular pathways GLI: more than just Hedgehog?

LMCD1 antisense RNA 1 is a newly identified long noncoding RNA

Long noncoding RNAs (lncRNAs) are one of the interesting fields in cancer researches. LncRNAs are generally dysregulated in many diseases. LMCD1 antisense RNA 1 (LMCD1-AS1) is a newly identified lncRNA with protumorigenic functions on tumor cells. LMCD1-AS1 expression is increased in hepatocellular carcinoma (HCC). LMCD1-AS1 is a sponge of miR-106b-5p activity. LMCD1-AS1 modulates the survival of osteosarcoma via targeting miR-106b-5p. LMCD1-AS1 and Sp1 are highly expressed in osteosarcoma. SP1 can bind to the promoter region of LMCD1-AS1, resulting in its overexpression in osteosarcoma. GLI2 is shown to bind to the LMCD1-AS1 promoter and is transcriptionally activated by LMCD1-AS1. LMCD1 acts as a miR-1287-5p sponge to increase GLI2 expression. LMCD1 is abundantly expressed in kidney tissue. Moreover, it is functionally involved in protein-protein interactions with transcriptional co-repressor activity, including regulation of the calcineurin-NFAT signaling cascade known to play a critical role in recovery from acute kidney injury (AKI). The E2F1/LMCD1-AS1/miR-345-5p/COL6A3 axis is a newly identified regulatory mechanism, which has a function in cholangiocarcinoma (CCA) tumorigenesis and progression and provides potential therapeutic targets for CCA. Also, LMCD1-AS1 functions in thyroid cancer (THCA) development. LMCD1-AS1 is overexpressed in THCA cells, and LMCD1-AS1 knockdown suppresses the malignant phenotypes of THCA cells. In THCA development, LMCD1-AS1 exerts protumorigenic function through sponging miR-1287-5p to increase GLI2 expression, constituting a feedback loop of LMCD1-AS1/miR-1287-5p/GLI2. In this review, the author focuses on the molecular mechanisms of newly identified long noncoding RNA LMCD1 antisense RNA 1 (LMCD1-AS1).

SUFU mediates EMT and Wnt/β-catenin signaling pathway activation promoted by miRNA-324-5p in human gastric cancer

The poor prognosis of late gastric carcinomas (GC) underscores the necessity to identify novel biomarkers for earlier diagnosis and effective therapeutic targets. MiRNA-324-5p has been shown to be over-expressed in GC, however the biological function of miRNA-324-5p implicated in gastric cancer and its downstream targets were not well understood. Wnt/β-catenin signaling pathway is aberrantly regulated in GC. We sought to explore if miRNA-324-5p promotes oncogenesis through modulating Wnt signaling and EMT. MiRNA-324-5p is highly expressed in GC based on qRT-PCR and TCGA data. In addition, in vitro cell proliferation, cell migration assays and in vivo animal exenograft were executed to show that miRNA-324-5p is an oncogenic miRNA in GC. MiRNA-324-5p activates Wnt signaling and induces EMT in GC. Further, SUFU was identified as a target of miRNA-324-5p confirmed by western blotting and luciferase assays. Spearson analysis and TCGA data indicate that the expression of SUFU is negatively associated with the expression of miRNA-324-5p. Rescue experiments were performed to determine if SUFU mediates the Wnt activation, EMT and oncogenic function of miRNA-324-5p. MiRNA-324-5p inhibitors plus SUFU siRNAs rescue partially the inhibitory effect on Wnt signaling and EMT caused by miRNA-324-5p inhibitors. Finally, the suppression of cell proliferation, migration, and colony formation ability induced by miRNA-324-5p inhibitors is alleviated by addition of SUFU siRNAs. In summary, miRNA-324-5p is overexpressed in vivo and exerts cell growth and migration-promoting effects through activating Wnt signaling and EMT by targeting SUFU in GC. It represents a potential miRNA with an oncogenic role in human gastric cancer.

Suppressor of Fused Inhibits Skin Wound Healing

Objectives: To investigate the effect of suppressor of fused (Sufu) on epidermal and dermal cellular properties and in wound healing. Approach: Transgenic (TG) mice overexpressing human Sufu (hSufu) in the epidermis were applied to investigate the effects of Sufu on epidermal and dermal cellular properties and in wound healing. Results: Histological staining revealed a reduction of epidermal and dermal thickness and an increase of hypodermal adipose tissue in homozygous K14-hSufu TG mice when compared with wild-type (WT) controls. TG mice exhibited significantly delayed skin wound healing. Moreover, the migratory and proliferative capabilities of cultured keratinocytes were decreased in K14-hSufuTG mice. Transforming growth factor-β treatment increased the expression of α-smooth muscle actin more in WT than in TG fibroblasts. Sufu overexpression significantly decreased the expression of β-catenin, glioma transcription factor 1 (Gli1), and matrix metalloproteinase-3 in wounds of K14-hSufu TG mice when compared with controls, probably indicating a delaying effect of Sufu on wound healing via blocking the hedgehog (Hh)/Gli and Wnt/β-catenin pathway. Innovation: Our results indicate a new property of Sufu in the process of skin wound healing. It provides an important basis for Sufu as a potential target for skin wound healing. Conclusion: Our findings suggest that Sufu overexpression in the epidermis impairs wound healing via dampening the Hh/Gli and Wnt/β-catenin signaling pathway. These data provide an important basis for further analyses of Sufu in skin wound healing.

YAP Promotes VEGFA Expression and Tumor Angiogenesis Though Gli2 in Human Renal Cell Carcinoma

BACKGROUND

High vascularization is a major characteristic of renal cell carcinoma (RCC). Thus, exploration of molecules promoting the tumor vascularization in RCC is urgent. Yes-associated Protein (YAP) is an oncogene in many cancer types, and high YAP expression was correlated with worse overall survival of RCC patients according to The Cancer Genome Atlas (TCGA) database. However, whether YAP promotes tumor angiogenesis of RCC is still unknown.

METHODS

Western blotting assay, real-time Quantitive PCR analysis, and ELISA assay were used to detect the related gene expression. The function of YAP on tumor angiogenesis was investigated by HUVEC recruitment, tube formation, and rabbit cornea assay. The clinical relevance of several genes was analyzed in a public database.

RESULTS

knockdown of YAP decreased RCC cell-inducing HUVEC recruitment and tube formation. Moreover, tumor angiogenesis ability of 786-O cells was crippled by YAP knockdown in vivo. In addition, the expression of Vascular endothelial growth factors A (VEGFA) was positively correlated with YAP expression in RCC tumor tissues, and YAP promoted expression and secretion of VEGFA in RCC cells. Mechanistically, GLI family zinc finger 2 (Gli2) knockdown in RCC cells reduced both basic and YAP-induced VEGFA expression, HUVECs recruitment, and tube formation, indicating that Gli2 is necessary for YAP to promote expression of VEGFA.

CONCLUSION

Taken together, our results demonstrate that YAP/Gli2 promotes VEGFA expression and tumor angiogenesis in RCC cells, which could provide novel therapeutic targets in RCC treatment.

Itraconazole induces apoptosis and cell cycle arrest via inhibiting Hedgehog signaling in gastric cancer cells

BACKGROUND

Itraconazole has been proved therapeutically effective against a variety of human cancers. This study assessed the effect of itraconazole on the Hedgehog (Hh) pathway and proliferation of human gastric cancer cells.

METHODS

CCK-8 assay and colony formation assay were used to assess the effects of itraconazole on proliferation of gastric cancer cells. The expression of Hh signaling components in gastric cancer cells treated with itraconazole was evaluated by reverse-transcription polymerase chain reaction, immunoblotting and dual luciferase assay. Tumor xenograft models were used to assess the inhibitory effect of itraconazole on the proliferation of gastric cancer cells in vivo.

RESULTS

Itraconazole could remarkably inhibit the proliferation of gastric cancer cells. When in combination with 5-FU, itraconazole significantly reduced the proliferation rate of cancer cells. Furthermore, itraconazole could regulate the G₁-S transition and induce apoptosis of gastric cancer cells. Hh signaling was abnormally activated in human gastric cancer samples. In vitro, studies showed that the expression of glioma-associated zinc finger transcription factor 1 (Gli1) was decreased at both transcriptional and translational levels after treatment with itraconazole. Dual luciferase assay also indicated that itraconazole could inhibit the transcription of Gli1. In vivo studies demonstrated that monotherapy with itraconazole by oral administration could inhibit the growth of xenografts, and that itraconazole could significantly enhance the antitumor efficacy of the chemotherapeutic agent 5-FU.

CONCLUSIONS

Hh signaling is activated in gastric tumor and itraconazole can inhibit the growth of gastric cancer cells by inhibiting Gli1 expression.

Gli Transcription Factors Mediate the Oncogenic Transformation of Prostate Basal Cells Induced by a Kras-Androgen Receptor Axis

Although the differentiation of oncogenically transformed basal progenitor cells is one of the key steps in prostate tumorigenesis, the mechanisms mediating this cellular process are still largely unknown. Here we demonstrate that an expanded p63⁺ and CK5⁺ basal/progenitor cell population, induced by the concomitant activation of oncogenic Kras(G12D) and androgen receptor (AR) signaling, underwent cell differentiation in vivo The differentiation process led to suppression of p63-expressing cells with a decreased number of CK5⁺ basal cells but an increase of CK8⁺ luminal tumorigenic cells and revealed a hierarchal lineage pattern consisting of p63⁺/CK5⁺ progenitor, CK5⁺/CK8⁺ transitional progenitor, and CK8⁺ differentiated luminal cells. Further analysis of the phenotype showed that Kras-AR axis-induced tumorigenesis was mediated by Gli transcription factors. Combined blocking of the activators of this family of proteins (Gli1 and Gli2) inhibited the proliferation of p63⁺ and CK5⁺ basal/progenitor cells and development of tumors. Finally, we identified that Gli1 and Gli2 exhibited different functions in the regulation of p63 expression or proliferation of p63⁺ cells in Kras-AR driven tumors. Gli2, but not Gli1, transcriptionally regulated the expression levels of p63 and prostate sphere formation. Our study provides evidence of a novel mechanism mediating pathological dysregulation of basal/progenitor cells through the differential activation of the Gli transcription factors. Also, these findings define Gli proteins as new downstream mediators of the Kras-AR axis in prostate carcinogenesis and open a potential therapeutic avenue of targeting prostate cancer progression by inhibiting Gli signaling.

Hedgehog signaling is a potent regulator of liver lipid metabolism and reveals a GLI-code associated with steatosis

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in industrialized countries and is increasing in prevalence. The pathomechanisms, however, are poorly understood. This study assessed the unexpected role of the Hedgehog pathway in adult liver lipid metabolism. Using transgenic mice with conditional hepatocyte-specific deletion of Smoothened in adult mice, we showed that hepatocellular inhibition of Hedgehog signaling leads to steatosis by altering the abundance of the transcription factors GLI1 and GLI3. This steatotic 'Gli-code' caused the modulation of a complex network of lipogenic transcription factors and enzymes, including SREBP1 and PNPLA3, as demonstrated by microarray analysis and siRNA experiments and could be confirmed in other steatotic mouse models as well as in steatotic human livers. Conversely, activation of the Hedgehog pathway reversed the "Gli-code" and mitigated hepatic steatosis. Collectively, our results reveal that dysfunctions in the Hedgehog pathway play an important role in hepatic steatosis and beyond.

DOI:http://dx.doi.org/10.7554/eLife.13308.001

The liver is one of the main organs responsible for processing everything that mammals eat and drink. Nutrients absorbed by the gut like sugars and lipids (fats) are processed by the liver and are stored or distributed to provide energy to other organs. Sometimes these metabolic processes become unbalanced. This can lead to lipids accumulating in the liver – a process known as steatosis, which is a feature of human non-alcoholic fatty liver disease.

In organs like the liver, cells are instructed how to behave via signaling pathways. A protein outside the cell signals to specific proteins inside, which switch on a set of target genes. One such pathway is the Hedgehog pathway, which primarily regulates tissue regeneration and the development of embryos. A component of this pathway is the Smoothened gene, which indirectly switches on proteins called GLI factors that regulate metabolic genes, including those involved in lipid metabolism. The Hedgehog pathway has been found to control the metabolism of lipids in fat tissue but it is not known whether it is important for lipid metabolism in the liver.

Matz-Soja et al. investigated this possible role of the Hedgehog pathway in the liver using mice with a Smoothened gene that could be deleted specifically in that organ. This deletion disrupted Hedgehog signaling and led to lipids accumulating in the liver and eventually to steatosis. These changes were associated with an increase in the amounts and activityof several enzymes (and the proteins that regulate these enzymes) that help to synthesize lipids. Steatosis was also associated with low amounts of two of the three GLI factors; indeed, this seems to be key for triggering problems with lipid metabolism. Human livers with steatosis showed the same changes in levels of the GLI factors.

Increasing the amount of GLI factors in liver cells taken from mice with steatosis reduced the accumulation of lipids and brought lipid metabolism back to its normal balance. A focus of future studies will be to understand how the Hedgehog signaling pathway interacts with other signaling pathways known to regulate liver lipid metabolism, such as insulin signaling. This knowledge will help clinicians to design new treatments for lipid-associated diseases like non-alcoholic fatty liver disease.

DOI:http://dx.doi.org/10.7554/eLife.13308.002

Nuclear Factor of Activated T Cells-dependent Down-regulation of the Transcription Factor Glioma-associated Protein 1 (GLI1) Underlies the Growth Inhibitory Properties of Arachidonic Acid

Numerous reports have demonstrated a tumor inhibitory effect of polyunsaturated fatty acids (PUFAs). However, the molecular mechanisms modulating this phenomenon are in part poorly understood. Here, we provide evidence of a novel antitumoral mechanism of the PUFA arachidonic acid (AA). In vivo and in vitro experiments showed that AA treatment decreased tumor growth and metastasis and increased apoptosis. Molecular analysis of this effect showed significantly reduced expression of a subset of antiapoptotic proteins, including BCL2, BFL1/A1, and 4-1BB, in AA-treated cells. We demonstrated that down-regulation of the transcription factor glioma-associated protein 1 (GLI1) in AA-treated cells is the underlying mechanism controlling BCL2, BFL1/A1, and 4-1BB expression. Using luciferase reporters, chromatin immunoprecipitation, and expression studies, we found that GLI1 binds to the promoter of these antiapoptotic molecules and regulates their expression and promoter activity. We provide evidence that AA-induced apoptosis and down-regulation of antiapoptotic genes can be inhibited by overexpressing GLI1 in AA-sensitive cells. Conversely, inhibition of GLI1 mimics AA treatments, leading to decreased tumor growth, cell viability, and expression of antiapoptotic molecules. Further characterization showed that AA represses GLI1 expression by stimulating nuclear translocation of NFATc1, which then binds the GLI1 promoter and represses its transcription. AA was shown to increase reactive oxygen species. Treatment with antioxidants impaired the AA-induced apoptosis and down-regulation of GLI1 and NFATc1 activation, indicating that NFATc1 activation and GLI1 repression require the generation of reactive oxygen species. Collectively, these results define a novel mechanism underlying AA antitumoral functions that may serve as a foundation for future PUFA-based therapeutic approaches.

The presence of primary cilia in cancer cells does not predict responsiveness to modulation of smoothened activity

Primary cilia are microtubule-based organelles that regulate smoothened-dependent activation of the GLI transcription factors in canonical hedgehog signaling. In many cancers, primary cilia are markedly decreased or absent. The lack of primary cilia may inhibit or alter canonical hedgehog signaling and, thereby, interfere in the cellular responsiveness to modulators of smoothened activity. Clinical trials of smoothened antagonists for cancer treatment have shown the best response in basal cell carcinomas, with limited response in other solid tumors. To determine whether the presence or absence of primary cilia in cancer cells will predict their responsiveness to modulation of smoothened activity, we compared the ability of an agonist and/or inhibitor of smoothened (SAG and SANT1, respectively) to modulate GLI-mediated transcription, as measured by GLI1 mRNA level or GLI-luciferase reporter activity, in non-cancer cells with primary cilia (ovarian surface epithelial cells and breast fibroblasts), in cancer cells that cannot assemble primary cilia (MCF7, MDA-MB-231 cell lines), and in cancer cells with primary cilia (SKOV3, PANC1 cell lines). As expected, SAG and SANT1 resulted in appropriate modulation of GLI transcriptional activity in ciliated non-cancer cells, and failed to modulate GLI transcriptional activity in cancer cells without primary cilia. However, there was also no modulation of GLI transcriptional activity in either ciliated cancer cell line. SAG treatment of SKOV3 induced localization of smoothened to primary cilia, as assessed by immunofluorescence, even though there was no increase in GLI transcriptional activity, suggesting a defect in activation of SMO in the primary cilia or in steps later in the hedgehog pathway. In contrast to SKOV3, SAG treatment of PANC1 did not cause the localization of smoothened to primary cilia. Our data demonstrate that the presence of primary cilia in the cancer epithelial cells lines tested does not indicate their responsiveness to smoothened activation or inhibition.

Expression of Gli1 and Wnt2B correlates with progression and clinical outcome of pancreatic cancer

OBJECTIVE

The aim of this study was to investigate the expression and clinical significance of Gli1 and Wnt2B in pancreatic cancer.

METHODS

We have constructed a formalin-fixed paraffin embedded pancreatic tissue microarrays 180 cylindrical tissue cores of human pancreatic cancer and its paracancerous nonmalignant pancreatic specimens (NMPs) from 90 patients. Levels of Gli1 and Wnt2B were measured by immunohistochemistry. We analyzed the correlations between the expression of these factors and clinicopathological parameters including prognosis.

RESULTS

The expressions of both Gli1 and Wnt2B in human pancreatic cancer tissues were significantly higher than those of normal pancreatic tissues (P=0.000, P=0.004 respectively). The analysis showed that the high cytoplasmic expression levels of Gli1 in pancreatic cancer tissues had significant correlation with lymph node metastasis (P=0.036) and Wnt2B had significant correlation with perineural invasion (P=0.045). Gli1 and Wnt2B have no positive correlation. Survival analysis by Kaplan-Meier demonstrated that elevated Wnt2B expression in cancer tissue predicted worse overall survival (OS) compared with group in lower expression (P=0.024). No correlation was found between the expression of Gli1 and overall survival of pancreatic cancer patients (P>0.05).

CONCLUSIONS

In conclusion, these results indicate that the high-expression levels of Gli1 and Wnt2B might play a pivotal role during tumorigenesis of pancreatic cancer, and the high expression of Wnt2B might be associated with poor prognosis.

The clinicopathological significance and relationship of Gli1, MDM2 and p53 expression in resectable pancreatic cancer

AIMS

To study the expression of Gli1, MDM2 and p53 for clinical significance in pancreatic cancer (PC), and their functional relationship in regulating the biological behaviour of PC cells.

METHODS AND RESULTS

Immunohistochemistry showed that the expression of Gli1, MDM2 and p53 was much higher in 57 cases of PC than in paired normal pancreatic tissues, and was positively associated with tumour UICC stage and T stage (P < 0.05). Patients with expression of Gli1 only or coexpression of Gli1 and MDM2 had significantly worse overall survival than patients with negative expression (P < 0.05). RNA interference showed that p53 knockdown increased the protein level of Gli1 but decreased the level of MDM2, and enhanced cell invasion and migration in wild-type p53 Capan-2 cells; whereas Gli1 or MDM2 knockdown did not change p53 expression, but decreased the protein level of MDM2 or Gli1, respectively, and inhibited cell invasion and migration in mutant p53 PANC-1 cells.

CONCLUSIONS

Overexpression of Gli1, MDM2 and mutant p53 contributes to the development and progression of PC, and plays an important role in predicting PC patients' prognosis. Moreover, we report a positive association between Gli1 and MDM2 in PC cells, but their relationship with p53 is dependent on wild-type or mutant p53 status.

Targeted inactivation and identification of targets of the Gli2a transcription factor in the zebrafish

Hedgehog (Hh) signaling is mediated by the Gli transcription factors and, in the zebrafish, plays an important role in patterning both the neural tube and myotome. Using a null allele of the gli2a gene induced by targeted mutagenesis, we show that Gli2a is completely dispensable in the fish but acts redundantly with Gli1 to regulate expression of known Hh targets, such as ptch2, prdm1a and eng2a, in the myotome and neural tube. To identify novel targets of Hh signaling, we performed chromatin immunoprecipitation sequencing (ChIP-seq) of whole embryo extracts. Samples were significantly enriched for 192 genomic regions, some of which are associated with four known Hh target genes, ptch1, ptch2, gli1 and olig2. Sequence analysis of these regions reveals a high level of conservation of Gli-binding sites from fish to mammals in some, but not all, cases. Expression analysis of other transcription units that are closely associated with peaks identified several putative targets not previously implicated as Hh targets, including myl10, hnmt, lrp4, efemp2, fras1, quo, and lamc1. Each of these genes shows loss of, or reduced expression in, embryos homozygous for an antimorphic allele of gli2a, you-too (yot), consistent with their being direct targets of Gli2a.

Role of the Hedgehog pathway in hepatocellular carcinoma (review)

The Hedgehog (Hh) pathway is an evolutionarily conserved signaling mechanism that controls many aspects of cell differentiation and the development of tissues and organs during embryogenesis. Early investigations have focused on the effects of Hh activity on the development of organs including skin, gut, the nervous system and bone. However, in addition to normal developmental processes, these investigations also found that Hh signaling is involved in aberrant proliferation and malignant transformation. Consequently, the role of Hh in cancer pathology, and its modulation by environmental factors is the subject of many investigations. Numerous environmental toxins, alcohol, and hepatitis viruses can cause hepatocellular carcinoma (HCC), which is the most common form of liver cancer. Significant hyperactivation of Hh signaling has been observed in liver injury and cirrhosis which often leads to the development of HCC lesions. Moreover, Hh activity plays an important role in the progression of HCC. Here, we review findings relevant to our understanding of the role of Hh signaling in HCC pathogenesis.

Inhibition of Hedgehog signaling in the gastrointestinal tract: targeting the cancer microenvironment

This review summarizes emerging information regarding the Hedgehog (Hh) signaling pathway during neoplastic transformation in the gastrointestinal tract. Although there is a role for the well-established canonical pathway in which Hedgehog ligands interact with their receptor Patched, there is sufficient evidence that downstream components of the Hh pathway, e.g., Gli1, are hijacked by non-Hh signaling pathways to promote the conversion of the epithelium to dysplasia and carcinoma. We review the canonical pathway and involvement of primary cilia, and then focus on current evidence for Hh signaling in luminal bowel cancers as well as accessory organs, i.e., liver, pancreas and biliary ducts. We conclude that targeting the Hh pathway with small molecules, nutriceuticals and other mechanisms will likely require a combination of inhibitors that target Gli transcription factors in addition to canonical modulators such as Smoothened.

New prospects for drug development: the hedgehog pathway revealed. Focus on hematologic malignancies

The hedgehog (Hh) pathway is a critical regulator of vertebrate embryonic development and is involved in the function of processes such as stem cell maintenance and differentiation, tissue polarity and cell proliferation. Given how critical these functions are, it is not surprising that mutations in Hh pathway components are often implicated in the tumorigenesis of a variety of human cancers. Promotion of tumor growth has recently been shown by activated Hh signaling in the tumor itself, as well as by pathway activation within surrounding cells comprising the tumor microenvironment. Targeted disruption of various Hh pathway proteins has been successfully employed as an anticancer strategy with several synthetic Hh antagonists now available. Here, the molecular basis of Hh signaling, the therapeutic rationales for targeting this pathway and the current status of Hh pathway inhibitors in the clinic are reviewed.

GLI2 regulates TGF-β1 in human CD4+ T cells: implications in cancer and HIV pathogenesis

Elevated levels of the immunoregulatory cytokine TGF-β1 in cancer and HIV infection have been linked to the suppression of protective immune responses. The transcriptional regulation of TGF-β1 is complex and still not completely understood. We report here for the first time that the transcription factor GLI2 regulates the expression of TGF-β1 in human CD4⁺ T cells. In silico screening revealed five novel putative GLI binding sites in the human TGF-β1 promoter. At least two of these sites within the human TGF-β1 promoter are regulated by the GLI2 activator as knockdown of GLI2 in regulatory CD4⁺CD25^hi T cells, high producers of TGF-β1, significantly decreased TGF-β1 transcription. Additionally, naïve CD4⁺ T cells, low producers of TGF-β1, increased their basal level of TGF-β1 mRNA following lentiviral infection with GLI2. The transcriptional regulation of TGF-β1 by GLI2 is a new extension to Sonic Hedgehog (SHH) and TGF-β1 cross-regulation and may provide insight into the detrimental elevation of TGF-β1 leading to pathogenesis in cancer and HIV infection.

Hedgehog signalling in gut development, physiology and cancer

The Hedgehog pathway is one of the most common signal transduction pathways used by mammalian cells. Most studies have focused on its role during development, primarily of the nervous system, skin, bone and pancreas. Due to the activation of this pathway during proliferation and neoplastic transformation, more recent studies have examined its role in adult tissues. Significant levels of sonic hedgehog are expressed in the gastric mucosa, which has served to direct analysis of its role during organogenesis, gastric acid secretion and neoplastic transformation. Therefore the goal of this review is to apply current knowledge of this pathway to further our understanding of gastrointestinal physiology and neoplasia, using the stomach as a prototype.

The alpha subunit of the G protein G13 regulates activity of one or more Gli transcription factors independently of smoothened

Smoothened (Smo) is a seven-transmembrane (7-TM) receptor that is essential to most actions of the Hedgehog family of morphogens. We found previously that Smo couples to members of the G(i) family of heterotrimeric G proteins, which in some cases are integral although alone insufficient in the activation of Gli transcription factors through Hedgehog signaling. In response to a report that the G(12/13) family is relevant to Hedgehog signaling as well, we re-evaluated the coupling of Smo to one member of this family, G(13), and investigated the capacity of this and other G proteins to activate one or more of forms of Gli. We found no evidence that Smo couples directly to G(13). We found nonetheless that Gα(13) and to some extent Gα(q) and Gα(12) are able to effect activation of Gli(s). This capacity is realized in some cells, e.g. C3H10T1/2, MC3T3, and pancreatic cancer cells, but not all cells. The mechanism employed is distinct from that achieved through canonical Hedgehog signaling, as the activation does not involve autocrine signaling or in any other way require active Smo and does not necessarily involve enhanced transcription of Gli1. The activation by Gα(13) can be replicated through a G(q)/G(12/13)-coupled receptor, CCK(A), and is attenuated by inhibitors of p38 mitogen-activated protein kinase and Tec tyrosine kinases. We posit that G proteins, and perhaps G(13) in particular, provide access to Gli that is independent of Smo and that they thus establish a basis for control of at least some forms of Gli-mediated transcription apart from Hedgehogs.

Role of transcription factors in neurogenesis after cerebral ischemia

Studies have revealed that the adult mammalian brain has the capacity to regenerate some neurons after cerebral ischemia. And this perspective on neurogenesis adds to the conceptual framework for strategies for the repair of ischemia-induced brain injury, that is, if the effect of ischemia-induced neurogenesis is enhanced, then the recovery of brain function after stroke can be promoted. Neurogenesis is a multistep process that requires the proliferation of neural stem/progenitor cells, migration and that new cells differentiate, survive and integrate into existing neural networks. For that to occur, the same concerted action of various factors is needed, especially transcription factors which regulate the expression of many moleculars and interact with them to promote neurogenesis. This review article gives a brief overview of some transcription factors (NF-κB, Hes, STAT3, AP-1, CREB, HIF1, Pax6, Tcf/Lef, Gli, Sox2, Olig2, Dlx2, TLX, Bmi-1) in ischemia-induced neurogenesis.

HH/GLI signalling as a new therapeutic target for patients with oral squamous cell carcinoma

Aberrant activation of HH/GLI has recently been reported in multiple cancer types, yet its role in oral squamous cell carcinoma (OSCC) has not been investigated. In this study, we aimed to determine the role of HH/GLI in OSCC. Expression of GLI1 and GLI2 was examined in OSCC samples from 136 patients by immunohistochemistry and correlated with clinicopathology parameters and clinical outcomes of the patients. Two HH/GLI specific small molecule inhibitors cyclopamine and GANT61, were used to test the potential role of HH/GLI in OSCC. We found that GLI2, one of the main transcriptional activators of HH/GLI signalling, was expressed in 60 (44%) of the 136 OSCC samples and the expression was significantly associated with poor clinical outcomes. Only 44% of the patients whose tumours expressed GLI2 survived at 5years after surgery compared to 77% of those whose tumours lacked the GLI2 expression (P<0.0001). Both cyclopamine and GANT61 effectively inhibited GLI expression, slowed cell growth, promoted G1 arrest, increased apoptosis and inhibited migration of OSCC cells. Our results demonstrate that activation of HH/GLI pathway plays an important role in OSCC progression. Together with the finding that expression of GLI2 is strongly associated with a poor clinic outcome of OSCC patients, the data suggest that a subset of OSCC patients may benefit from anti-HH/GLI therapies.

Targeting GLI1 expression in human inflammatory breast cancer cells enhances apoptosis and attenuates migration

Background:

Inflammatory breast cancer (IBC) is an aggressive subtype of breast cancer with distinct molecular profiles. Gene expression profiling previously identified sonic hedgehog (SHH) as part of a gene signature that is differentially regulated in IBC patients.

Methods:

The effects of reducing GLI1 levels on protein expression, cell proliferation, apoptosis and migration were determined by immunoblots, MTT assay, Annexin-V/PI assay and conventional and automated cell migration assays.

Results:

Evaluation of a panel of breast cancer cell lines revealed elevated GLI1 expression, typically a marker for hedgehog-pathway activation, in a triple-negative, highly invasive IBC cell line, SUM149 and its isogenic-derived counterpart rSUM149 that has acquired resistance to ErbB1/2 targeting strategies. Downregulation of GLI1 expression in SUM149 and rSUM149 by small interfering RNA or a small molecule GLI1 inhibitor resulted in decreased proliferation and increased apoptosis. Further, GLI1 suppression in these cell lines significantly inhibited cell migration as assessed by a wound-healing assay compared with MCF-7, a non-invasive cell line with low GLI1 expression. A novel high-content migration assay allowed us to quantify multiple effects of GLI1 silencing including significant decreases in cell distance travelled and linearity of movement.

Conclusion:

Our data reveal a role for GLI1 in IBC cell proliferation, survival and migration, which supports the feasibility of targeting GLI1 as a novel therapeutic strategy for IBC patients.

Gli1 enhances migration and invasion via up-regulation of MMP-11 and promotes metastasis in ERα negative breast cancer cell lines

Gli1 is an established oncogene and its expression in Estrogen Receptor (ER) α negative and triple negative breast cancers is predictive of a poor prognosis; however, the biological functions regulated by Gli1 in breast cancer have not been extensively evaluated. Herein, Gli1 was over-expressed or down-regulated (by RNA interference and by expression of the repressor form of Gli3) in the ERα negative, human breast cancer cell lines MDA-MB-231 and SUM1315. Reduced expression of Gli1 in these two cell lines resulted in a decrease in migration and invasion. Gli1 over-expression increased the migration and invasion of MDA-MB-231 cells with a corresponding increase in expression of MMP-11. Silencing MMP-11 in MDA-MB-231 cells that over-expressed Gli1 abrogated the Gli1-induced enhancement of migration and invasion. Sustained suppression of Gli1 expression decreased growth of MDA-MB-231 in vitro by increasing apoptosis and decreasing proliferation. In addition, silencing of Gli1 reduced the numbers and sizes of pulmonary metastases of MDA-MB-231 in an in vivo experimental metastasis assay. In summary, Gli1 promotes the growth, survival, migration, invasion and metastasis of ERα negative breast cancer. Additionally, MMP-11 is up-regulated by Gli1 and mediates the migration and invasion induced by Gli1 in MDA-MB-231.

Disturbed expression of splicing factors in renal cancer affects alternative splicing of apoptosis regulators, oncogenes, and tumor suppressors

Background

Clear cell renal cell carcinoma (ccRCC) is the most common type of renal cancer. One of the processes disturbed in this cancer type is alternative splicing, although phenomena underlying these disturbances remain unknown. Alternative splicing consists of selective removal of introns and joining of residual exons of the primary transcript, to produce mRNA molecules of different sequence. Splicing aberrations may lead to tumoral transformation due to synthesis of impaired splice variants with oncogenic potential. In this paper we hypothesized that disturbed alternative splicing in ccRCC may result from improper expression of splicing factors, mediators of splicing reactions.

Methodology/Principal Findings

Using real-time PCR and Western-blot analysis we analyzed expression of seven splicing factors belonging to SR proteins family (SF2/ASF, SC35, SRp20, SRp75, SRp40, SRp55 and 9G8), and one non-SR factor, hnRNP A1 (heterogeneous nuclear ribonucleoprotein A1) in 38 pairs of tumor-control ccRCC samples. Moreover, we analyzed splicing patterns of five genes involved in carcinogenesis and partially regulated by analyzed splicing factors: RON, CEACAM1, Rac1, Caspase-9, and GLI1.

Conclusions/Significance

We found that the mRNA expression of splicing factors was disturbed in tumors when compared to paired controls, similarly as levels of SF2/ASF and hnRNP A1 proteins. The correlation coefficients between expression levels of specific splicing factors were increased in tumor samples. Moreover, alternative splicing of five analyzed genes was also disturbed in ccRCC samples and splicing pattern of two of them, Caspase-9 and CEACAM1 correlated with expression of SF2/ASF in tumors. We conclude that disturbed expression of splicing factors in ccRCC may possibly lead to impaired alternative splicing of genes regulating tumor growth and this way contribute to the process of carcinogenesis.

Gli1 promotes cell survival and is predictive of a poor outcome in ERalpha-negative breast cancer

Gli1 is a transcription factor and oncogene with documented roles in the progression of several cancer types, including cancers of the skin and pancreas. The contribution of Gli1 to the progression of breast cancer is less established. In order to investigate the functional impact of Gli1 in breast cancer, expression of Gli1 and its contribution to cell growth was assessed in breast cancer cell lines. These in vitro results were compared to expression of Gli1, determined by immunohistochemistry, in 171 breast cancers. In these cancers, the association of Gli1 with expression of estrogen receptor alpha (ERalpha) and progesterone receptor (PR), ErbB2, p53, the rate of proliferation, and clinicopathologic parameters and outcome was assessed. Expression of Gli1 and ERalpha mRNA was strongly correlated in ERalpha-positive cell lines (r = 0.999). Treatment with estrogen increased expression of Gli1 in 2 of 3 ERalpha-positive cell lines; this increase was prevented by treatment with the ERalpha-specific antagonist MPP. Silencing of Gli1 by shRNA markedly reduced the survival of two ERalpha-negative cell lines, but caused only a modest reduction in ERalpha-positive cell lines. In breast cancer tissues, cancers with nuclear localization of Gli1 had a higher ERalpha (P=0.027) and lower p53 expression (P=0.017) than those without nuclear localization of Gli1. However, nuclear localization of Gli1 was predictive of a poorer cancer-specific survival in ERalpha-negative, including triple negative, cancers (P = 0.005), but not ERalpha-positive cancers. In conclusion, we demonstrate a positive association between expression of Gli1 and ERalpha; however, our data indicate a greater functional effect of Gli1 in ERalpha-negative cancers.

Mechanisms of Hedgehog pathway activation in cancer and implications for therapy

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

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

The expression pattern of PDX-1, SHH, Patched and Gli-1 is associated with pathological and clinical features in human pancreatic cancer

BACKGROUND AND AIMS

Pancreatic cancer cells have been shown to possess stem-cell-like properties, especially by reactivating embryonic transcription factors involved in tissue differentiation. We therefore investigated if and to what extent developmental genes of the human pancreas are expressed in pancreatic ductal adenocarcinomas and precursor lesions, pancreatic intraepithelial neoplasia (PanIN), and if this correlates or predicts response to treatment and overall survival.

MATERIAL AND METHODS

Invasive ductal adenocarcinomas of the pancreas [UICC pT3pN0 (n = 13) vs. pT3pN1 (n = 25)] and tumors after neoadjuvant chemotherapy [5-fluorouracil (FU)/folic-acid and gemcitabine; UICC ypN0 (n = 7) vs. ypN1 (n = 6)] resected between 1997 and 2003 were characterized histochemically and immunohistochemically [pancreas duodenum homeobox 1 (PDX-1), Sonic hedgehog protein (SHH), Patched (Ptc) and Gli-1]. Gene distribution was compared with morphological patterns of the pancreatic carcinoma and PanIN as well as with peritumorous reactions of normal pancreas.

RESULTS

The overall expression of PDX-1, SHH, Ptc and Gli-1 was low, but showed a distinctive and topographic linkage inside pancreatic carcinomas as well as inside PanINs. Additionally, a topographic and significant association of these markers with nodal status (PDX-1, Ptc, Gli-1), tumor size (PDX-1, Gli-1) and R status (PDX-1) was found. After stratification with the strongest outcome predictor, grading, survival analysis revealed that Ptc expression in grade 2 and PDX-1 expression in grade 3 carcinomas are independent survival factors.

CONCLUSIONS

Markers of pancreas development are reexpressed in invasive ductal adenocarcinomas and their expression is essentially associated with general clinical and pathological features such as survival or nodal status.

The Hedgehog protein family

The Hedgehog (Hh) pathway is one of the fundamental signal transduction pathways in animal development and is also involved in stem-cell maintenance and carcinogenesis. The hedgehog (hh) gene was first discovered in Drosophila, and members of the family have since been found in most metazoa. Hh proteins are composed of two domains, an amino-terminal domain HhN, which has the biological signal activity, and a carboxy-terminal autocatalytic domain HhC, which cleaves Hh into two parts in an intramolecular reaction and adds a cholesterol moiety to HhN. HhC has sequence similarity to the self-splicing inteins, and the shared region is termed Hint. New classes of proteins containing the Hint domain have been discovered recently in bacteria and eukaryotes, and the Hog class, of which Hh proteins comprise one family, is widespread throughout eukaryotes. The non-Hh Hog proteins have carboxy-terminal domains (the Hog domain) highly similar to HhC, although they lack the HhN domain, and instead have other amino-terminal domains. Hog proteins are found in many protists, but the Hh family emerged only in early metazoan evolution. HhN is modified by cholesterol at its carboxyl terminus and by palmitate at its amino terminus in both flies and mammals. The modified HhN is released from the cell and travels through the extracellular space. On binding its receptor Patched, it relieves the inhibition that Patched exerts on Smoothened, a G-protein-coupled receptor. The resulting signaling cascade converges on the transcription factor Cubitus interruptus (Ci), or its mammalian counterparts, the Gli proteins, which activate or repress target genes.