A paracrine requirement for hedgehog signalling in cancer

CXCL12/CXCR4 protein signaling axis induces sonic hedgehog expression in pancreatic cancer cells via extracellular regulated kinase- and Akt kinase-mediated activation of nuclear factor κB: implications for bidirectional tumor-stromal interactions

Recent evidence suggests a major role of tumor-stromal interactions in pancreatic cancer pathobiology. The chemokine CXCL12 (stromal cell-derived factor 1 (SDF-1)), abundantly produced by stromal cells, promotes progression, metastasis, and chemoresistance of pancreatic cancer cells. On the other hand, pancreatic tumor cell-derived sonic hedgehog (SHH) acts predominantly on stromal cells to induce desmoplasia and, thus, has a paracrine effect on tumorigenesis and therapeutic outcome. In this study, we examined the association between these two proteins of pathological significance in pancreatic cancer. Our data demonstrate that CXCL12 leads to a dose- and time-dependent up-regulation of SHH in pancreatic cancer cells. CXCL12-induced SHH up-regulation is specifically mediated through the receptor CXCR4 and is dependent on the activation of downstream Akt and ERK signaling pathways. Both Akt and ERK cooperatively promote nuclear accumulation of NF-κB by inducing the phosphorylation and destabilization of its inhibitory protein, IκB-α. Using dominant negative IκB-α, a SHH promoter (deletion mutant) reporter, and chromatin immunoprecipitation assays, we demonstrate that CXCL12 exposure enhances direct binding of NF-κB to the SHH promoter and that suppression of NF-κB activation abrogates CXCL12-induced SHH expression. Finally, our data demonstrate a strong correlative expression of CXCR4 and SHH in human pancreatic cancer tissues, whereas their expression is not observed in the normal pancreas. Altogether, our data reveal a novel mechanism underlying aberrant SHH expression in pancreatic cancer and identify a molecular link facilitating bidirectional tumor-stromal interactions.

Hedgehog pathway signaling regulates human colon carcinoma HT-29 epithelial cell line apoptosis and cytokine secretion

The Hedgehog (Hh) pathway is involved in embryogenesis and physiologic processes including cell survival and proliferation. We used the HT-29 and other human colon carcinoma cell lines to investigate Hh signaling and biological functions in colonic epithelial cells. HT-29 cells were cultured under different conditions and exposed to various stimuli. The expression of Hh pathway components and related genes and proteins were assessed by real-time PCR and immunofluorescence. Viability, apoptosis and cell proliferation were measured by the MTT assay, Annexin-V/7-AAD staining and BrdU uptake, respectively. Chemokines production was measured by ELISA in culture supernatants. Indian and Sonic Hh mRNA levels and the downstream transcription factors Gli-1 and Gli-2 increased following treatment with Hh agonists and butyrate, but decreased upon exposure to cyclopamine or GANT61. BMP4 and BMP7 expression increased after stimulation with Hh agonists. Gli-1 protein expression increased after Hh agonists and decreased following cyclopamine. Exposure to Hh agonists promoted β-catenin reduction and subcellular redistribution. Levels of IL-8 and MCP-1 decreased upon exposure to Hh agonists compared to Hh antagonists, LPS, IFN-γ or EGF. Monocyte chemotaxis decreased upon exposure to supernatants of HT-29 cells treated with Shh compared to Hh antagonists, LPS and IFN-γ. Cellular incorporation of BrdU and cell viability decreased following Hh blockade. Hh agonists abrogated the anti-CD95 induced apoptosis. Hh pathway is a key controller of colon cancer cells, as demonstrated by its effect in dampening inflammatory signals and antagonizing apoptosis. The differential expression of Hh components may underlie abnormalities in the local immune response and in epithelial barrier integrity, with potential homeostatic implications for the development of colonic inflammation and malignancies.

Unlike pancreatic cancer cells pancreatic cancer associated fibroblasts display minimal gene induction after 5-aza-2'-deoxycytidine

Purpose

Cancer associated stromal fibroblasts (CAFs) undergo transcriptional and phenotypic changes that contribute to tumor progression, but the mechanisms responsible for these changes are not well understood. Aberrant DNA methylation is an important cause of transcriptional alterations in cancer cells but it is not known how important DNA methylation alterations are to CAF behavior.

Experimental Design

We used Affymetrix exon arrays to compare genes induced by the DNA methylation inhibitor 5-aza-dC in cultured pancreatic cancer associated fibroblasts, pancreatic control fibroblasts and pancreatic cancer cell lines.

Results

We found that pancreatic CAFs and control pancreatic fibroblasts were less responsive to 5-aza-dC-mediated gene reactivation than pancreatic cancer cells (mean+/−SD of genes induced ≥5-fold was 9±10 genes in 10 pancreatic CAF cultures, 17±14 genes in 3 control pancreatic fibroblast cultures, and 134±85 genes in 4 pancreatic cancer cell lines). We examined differentially expressed genes between CAFs and control fibroblasts for candidate methylated genes and identified the disintegrin and metalloprotease, ADAM12 as hypomethylated and overexpressed in pancreatic CAF lines and overexpressed in fibroblasts adjacent to primary pancreatic adenocarcinomas.

Conclusions

Compared to pancreatic cancer cells, few genes are reactivated by DNMT1 inhibition in pancreatic CAFs suggesting these cells do not harbor many functionally important alterations in DNA methylation. CAFs may also not be very responsive to therapeutic targeting with DNA methylation inhibitors.

Sonic hedgehog pathway expression in non-small cell lung cancer

OBJECTIVE

Activation of the hedgehog pathway is an important signaling mechanism crucial in embryogenesis and has strong links to carcinogenesis. This study investigates the expression of the Sonic hedgehog pathway molecules in non-small cell lung tumors as it relates to clinical outcome of various non-small cell lung cancers.

METHODS

A tissue microarray with 81 samples from 42 patients with various non-small cell lung cancer histologies was examined without the aid of laser microdissection. All samples were stained with antibodies directed against Sonic hedgehog, Ptch-1, Smoothened, and Gli-1.

RESULTS

Most of the tumor samples showed negative to weak expression of the pathway proteins (Sonic hedgehog, 38% negative to 20% weak; Ptch-1, 100% negative; Smoothened, 69% negative to 7% weak; Gli-1, 57% negative to 5% weak) compared with higher expression in normal lung epithelial cells.

CONCLUSION

The same pathway expression did not correlate with clinical outcome. While our results do not provide any indication that the pathway molecules are correlated to overall patient survival possibly due to the limited sample size, our study shows minimum overexpression of Sonic hedgehog pathway in non-small cell lung cancer and this did not correlate clinically with patient outcome.

Overcoming the stromal barrier: technologies to optimize drug delivery in pancreatic cancer

Pancreatic cancer has historically proven resistant to anticancer agents. On the one hand, drugs might be more efficient if higher levels could be achieved at the tumor site rather than the normal tissues. On the other hand, the thick stroma and the relative absence of abundant vessels may account at least partially for the failure of successive clinical trials to demonstrate effective treatments in this type of malignancy. In this context, the development and testing in clinical trials of treatment strategies that aim to optimize drug delivery is an important target in improving the prognosis of patients with pancreatic cancer.

Glucocorticoid compounds modify smoothened localization and hedgehog pathway activity

The Hedgehog signaling pathway is linked to a variety of diseases, notably a range of cancers. The first generation of drug screens identified Smoothened (Smo), a membrane protein essential for signaling, as an attractive drug target. Smo localizes to the primary cilium upon pathway activation, and this transition is critical for the response to Hedgehog ligands. In a high content screen directly monitoring Smo distribution in Hedgehog-responsive cells, we identified different glucocorticoids as specific modulators of Smo ciliary accumulation. One class promoted Smo accumulation, conferring cellular hypersensitivity to Hedgehog stimulation. In contrast, a second class inhibited Smo ciliary localization and signaling activity by both wild-type Smo, and mutant forms of Smo, SmoM2, and SmoD473H, that are refractory to previously identified Smo antagonists. These findings point to the potential for developing glucocorticoid-based pharmacological modulation of Smo signaling to treat mutated drug-resistant forms of Smo, an emerging problem in long-term cancer therapy. They also raise a concern about potential crosstalk of glucocorticoid drugs in the Hedgehog pathway, if therapeutic administration exceeds levels associated with on-target transcriptional mechanisms of glucocorticoid action.

The role of stromal myofibroblast and extracellular matrix in tumor angiogenesis

Tumor angiogenesis, the building of blood vessels in an expanding tumor mass, is an elegantly coordinated process that dictates tumor growth and progression. Stromal components of the tumor microenvironment, such as myofibroblasts and the extracellular matrix, collaborate with tumor cells in regulating development. Such myofibroblasts and the extracellular matrix have ever-expanding roles in the angiogenic process as well. This review summarizes how stromal myofibroblasts and the extracellular matrix can modulate tumor angiogenesis, highlighting recent findings.

Targeting the cancer-stroma interaction: a potential approach for pancreatic cancer treatment

Recent studies have demonstrated that the interaction between the cancer and the stroma, play a key role in the development of pancreatic cancer. The desmoplasia, which consists of fibroblasts, pancreatic stellate cells, lymphatic and vascular endothelial cells, immune cells, pathologic increased nerves, and the extracellular matrix (ECM), creates a complex tumor microenvironment that promotes pancreatic cancer development, invasion, metastasis, and resistance to chemotherapy. Thus, the potential approach for targeting the components of this desmoplastic reaction or the pancreatic tumor microenvironment might represent a novel therapeutic approach to advanced pancreatic carcinoma. Novel therapies that target on the pancreatic tumor microenvironment should become one of the more effective treatments for pancreatic cancer.

Targeting Hedgehog signaling and understanding refractory response to treatment with Hedgehog pathway inhibitors

Hedgehog (Hh) signaling is a principal component of the morphogenetic code best known to direct pattern formation during embryogenesis. The Hh pathway remains active in adulthood however where it guides tissue regeneration and remodeling and Hh production in the niche plays an important role in maintaining stem cell compartment size. Deregulated Hh signaling activity is associated, depending on the context, with both cancer initiation and progression. Interestingly, the Hh pathway is remarkably druggable, raising hopes that inhibition of the pathway could support anticancer therapy. Indeed, a large body of preclinical data supports such an action, but promising clinical data are still limited to basal cell carcinoma (BSC) and medulloblastoma. Nevertheless cancer resistance against Hh targeting has already emerged as a major problem. Here we shall review the current situation with respect to targeting the Hh pathway in cancer in general and in chemotolerance in particular with a focus on the problems associated with the emergence of tumors resistant to treatment with inhibitors targeting the Hh receptor Smoothened (SMO).

The mesenchyme in malignancy: a partner in the initiation, progression and dissemination of cancer

The tumor microenvironment presents an exciting opportunity for innovative prognostic and therapeutic approaches to human cancer. The diverse cellular and extracellular contribution to tumor growth argues that prevention and cure of human cancers will result only from a multifaceted approach to cancer therapy. In this review we provide a foundation for considering the mesenchymal contribution to the tumor microenvironment. We address normal mesenchymal development, physiological interactions between the epithelium and stroma and the cellular hierarchy within these compartments. We focus on cancer-associated fibroblasts in gastrointestinal malignancy but our models have also been informed by other tumor systems. The review provides a framework for characterizing the overall biological contribution of the mesenchyme to human disease. Understanding the biological heterogeneity of specific mesenchymal cells in cancer will provide new opportunities for targeted cancer prevention and therapy.

Major signaling pathways in intestinal stem cells

BACKGROUND

The discovery of markers to identify the intestinal stem cell population and the generation of powerful transgenic mouse models to study stem cell physiology have led to seminal discoveries in stem cell biology.

SCOPE OF REVIEW

In this review we give an overview of the current knowledge in the field of intestinal stem cells (ISCs) highlighting the most recent progress on markers defining the ISC population and pathways governing intestinal stem cell maintenance and differentiation. Furthermore we review their interaction with other stem cell related pathways. Finally we give an overview of alteration of these pathways in human inflammatory gastrointestinal diseases.

MAJOR CONCLUSIONS

We highlight the complex network of interactions occurring among different pathways and put in perspective the many layers of regulation that occur in maintaining the intestinal homeostasis.

GENERAL SIGNIFICANCE

Understanding the involvement of ISCs in inflammatory diseases can potentially lead to new therapeutic approaches to treat inflammatory GI pathologies such as IBD and celiac disease and could reveal the molecular mechanisms leading to the pathogenesis of dysplasia and cancer in inflammatory chronic conditions. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

Cancer stem cell targeting: the next generation of cancer therapy and molecular imaging

Cancer stem cells (CSCs) have the capacity to generate the heterogeneous lineages of all cancer cells comprising a tumor and these populations of cells are likely to be more relevant in determining prognosis. However, these cells do not operate in isolation, but instead rely upon signals co-opted from their microenvironment, making the targeting and imaging of CSCs within a cancer mass a daunting task. A better understanding of the molecular cell biology underlying CSC pathology will facilitate the development of new therapeutic targets and novel strategies for the successful eradication of cancer. In addition, the continued investigation of sensitive molecular-imaging modalities will enable more accurate staging, treatment planning and the ability to monitor the effectiveness of CSC-targeted therapies in vivo. In this review, we explore the possibilities and limitations of CSC-directed therapies and molecular imaging modalities.

Prevailing importance of the hedgehog signaling pathway and the potential for treatment advancement in sarcoma

The hedgehog signaling pathway is important in embryogenesis and post natal development. Constitutive activation of the pathway due to mutation of pathway components occurs in ~25% of medulloblastomas and also in basal cell carcinomas. In many other malignancies the therapeutic role for hedgehog inhibition though intriguing, based on preclinical data, is far from assured. Hedgehog inhibition is not an established part of the treatment paradigm of sarcoma but the scientific rationale for a possible benefit is compelling. In chondrosarcoma there is evidence of hedgehog pathway activation and an ontologic comparison between growth plate chondrocyte differentiation and different chondrosarcoma subtypes. Immunostaining epiphyseal growth plate for Indian hedgehog is particularly positive in the zone of pre-hypertrophic chondrocytes which correlates ontologically with conventional chondrosarcoma. In Ewing sarcoma/PNET tumors the Gli1 transcription factor is a direct target of the EWS-FLI1 oncoprotein present in 85% of cases. In many cases of rhabdomyosarcomas there is increased expression of Gli1 (Ragazzini et al., 2004). Additionally, a third of embryonal rhabdomyosarcomas have loss of Chr.9q22 that encompasses the patched locus (Bridge et al., 2000). The potential to treat osteosarcoma by inhibition of Gli2 and the role of the pathway in ovarian fibromas and other connective tissue tumors is also discussed (Nagao et al., 2011; Hirotsu et al., 2010). Emergence of acquired secondary resistance to targeted therapeutics is an important issue that is also relevant to hedgehog inhibition. In this context secondary resistance of medulloblastomas to treatment with a smoothened antagonist in two tumor mouse models is examined.

Signaling in colon cancer stem cells

: Colorectal cancer is the fourth most common form of cancer worldwide and ranks third among the cancer-related deaths in the US and other Western countries. It occurs with equal frequency in men and women, constituting 10% of new cancer cases in men and 11% in women. Despite recent advancement in therapeutics, the survival rates from metastatic are less than 5%. Growing evidence supports the contention that epithelial cancers including colorectal cancer, the incidence of which increases with aging, are diseases driven by the pluripotent, self-renewing cancer stem cells (CSCs). Dysregulation of Wnt, Notch, Hedgehog and/or TGF-β signaling pathways that are involved in proliferation and maintenance of CSCs leads to the development of CRC. This review focuses on the signaling pathways relevant for CRC to understand the mechanisms leading to tumor progression and therapy resistance, which may help in the development of therapeutic strategies for CRC.

Shh maintains dermal papilla identity and hair morphogenesis via a Noggin-Shh regulatory loop

During hair follicle morphogenesis, dermal papillae (DPs) function as mesenchymal signaling centers that cross-talk with overlying epithelium to regulate morphogenesis. While the DP regulates hair follicle formation, relatively little is known about the molecular basis of DP formation. The morphogen Sonic hedgehog (Shh) is known for regulating hair follicle epithelial growth, with excessive signaling resulting in basal cell carcinomas. Here, we investigate how dermal-specific Shh signaling contributes to DP formation and hair growth. Using a Cre-lox genetic model and RNAi in hair follicle reconstitution assays, we demonstrate that dermal Smoothened (Smo) loss of function results in the loss of the DP precursor, the dermal condensate, and a stage 2 hair follicle arrest phenotype reminiscent of Shh(-/-) skin. Surprisingly, dermal Smo does not regulate cell survival or epithelial proliferation. Rather, molecular screening and immunostaining studies reveal that dermal Shh signaling controls the expression of a subset of DP-specific signature genes. Using a hairpin/cDNA lentiviral system, we show that overexpression of the Shh-dependent gene Noggin, but not Sox2 or Sox18, can partially rescue the dermal Smo knockdown hair follicle phenotype by increasing the expression of epithelial Shh. Our findings suggest that dermal Shh signaling regulates specific DP signatures to maintain DP maturation while maintaining a reciprocal Shh-Noggin signaling loop to drive hair follicle morphogenesis.

Inhibition of the hedgehog pathway targets the tumor-associated stroma in pancreatic cancer

PURPOSE

The Hedgehog (Hh) pathway has emerged as an important pathway in multiple tumor types and is thought to be dependent on a paracrine signaling mechanism. The purpose of this study was to determine the role of pancreatic cancer-associated fibroblasts (human pancreatic stellate cells, HPSCs) in Hh signaling. In addition, we evaluated the efficacy of a novel Hh antagonist, AZD8542, on tumor progression with an emphasis on the role of the stroma compartment.

EXPERIMENTAL DESIGN

Expression of Hh pathway members and activation of the Hh pathway were analyzed in both HPSCs and pancreatic cancer cells. We tested the effects of Smoothened (SMO) inhibition with AZD8542 on tumor growth in vivo using an orthotopic model of pancreatic cancer containing varying amounts of stroma.

RESULTS

HPSCs expressed high levels of SMO receptor and low levels of Hh ligands, whereas cancer cells showed the converse expression pattern. HPSC proliferation was stimulated by Sonic Hedgehog with upregulation of downstream GLI1 mRNA. These effects were abrogated by AZD8542 treatment. In an orthotopic model of pancreatic cancer, AZD8542 inhibited tumor growth only when HPSCs were present, implicating a paracrine signaling mechanism dependent on stroma. Further evidence of paracrine signaling of the Hh pathway in prostate and colon cancer models is provided, demonstrating the broader applicability of our findings.

CONCLUSION

Based on the use of our novel human-derived pancreatic cancer stellate cells, our results suggest that Hh-targeted therapies primarily affect the tumor-associated stroma, rather than the epithelial compartment.

Palmitoylation of Hedgehog proteins

Hedgehog (Hh) proteins are secreted signaling proteins that contain amide-linked palmitate at the N-terminus and cholesterol at the C-terminus. Palmitoylation of Hh proteins is critical for effective long- and short-range signaling. The palmitoylation reaction occurs during transit of Hh through the secretory pathway, most likely in the lumen of the ER. Attachment of palmitate to Hh proteins is independent of cholesterol modification and autoprocessing and is catalyzed by Hhat (Hedgehog acyltransferase). Hhat is a member of the membrane bound O-acyltransferase (MBOAT) family, a subgroup of multipass membrane proteins that catalyze transfer of fatty acyl groups to lipids and proteins. Several classes of secreted proteins have recently been shown to be substrates for MBOAT acyltransferases, including Hh proteins and Spitz (palmitoylated by Hhat), Wg/Wnt proteins (modified with palmitate and/or palmitoleate by Porcupine) and ghrelin (octanoylated by ghrelin O-acyltransferase). These findings highlight protein fatty acylation as a mechanism that not only influences membrane binding of intracellular proteins but also regulates the signaling range and efficacy of secreted proteins.

Identification of novel pathways involved in the pathogenesis of human adamantinomatous craniopharyngioma

Activating mutations in the gene encoding β-catenin have been identified in the paediatric form of human craniopharyngioma (adamantinomatous craniopharyngioma, ACP), a histologically benign but aggressive pituitary tumour accounting for up to 10% of paediatric intracranial tumours. Recently, we generated an ACP mouse model and revealed that, as in human ACP, nucleocytoplasmic accumulation of β-catenin (β-cat(nc)) and over-activation of the Wnt/β-catenin pathway occurs only in a very small proportion of cells, which form clusters. Here, combining mouse genetics, fluorescence labelling and flow-sorting techniques, we have isolated these cells from tumorigenic mouse pituitaries and shown that the β-cat(nc) cells are enriched for colony-forming cells when cultured in stem cell-promoting media, and have longer telomeres, indicating shared properties with normal pituitary progenitors/stem cells (PSCs). Global gene profiling analysis has revealed that these β-cat(nc) cells express high levels of secreted mitogenic signals, such as members of the SHH, BMP and FGF family, in addition to several chemokines and their receptors, suggesting an important autocrine/paracrine role of these cells in the pathogenesis of ACP and a reciprocal communication with their environment. Finally, we highlight the clinical relevance of these findings by showing that these pathways are also up-regulated in the β-cat(nc) cell clusters identified in human ACP. As well as providing further support to the concept that pituitary stem cells may play an important role in the oncogenesis of human ACP, our data reveal novel disease biomarkers and potential pharmacological targets for the treatment of these devastating childhood tumours.

The role of stroma in pancreatic cancer: diagnostic and therapeutic implications

Pancreatic ductal adenocarcinoma (PDAC) is one of the five most lethal malignancies worldwide and survival has not improved substantially in the past 30 years. Desmoplasia (abundant fibrotic stroma) is a typical feature of PDAC in humans, and stromal activation commonly starts around precancerous lesions. It is becoming clear that this stromal tissue is not a bystander in disease progression. Cancer-stroma interactions effect tumorigenesis, angiogenesis, therapy resistance and possibly the metastatic spread of tumour cells. Therefore, targeting the tumour stroma, in combination with chemotherapy, is a promising new option for the treatment of PDAC. In this Review, we focus on four issues. First, how can stromal activity be used to detect early steps of pancreatic carcinogenesis? Second, what is the effect of perpetual pancreatic stellate cell activity on angiogenesis and tissue perfusion? Third, what are the (experimental) antifibrotic therapy options in PDAC? Fourth, what lessons can be learned from Langton's Ant (a simple mathematical model) regarding the unpredictability of genetically engineered mouse models?

Advances in the treatment of Basal cell carcinoma: Hedgehog inhibitors

Basal cell carcinoma (BCC) is the most common tumor of the skin and can result in significant morbidity as well as costs. The discovery of aberrant Hedgehog (HH) signaling in patients with genetic propensity to develop BCCs has resulted in a better understanding of the genetic abnormalities leading to the development of BCC. The current state of knowledge with regard to the genetics of BCC is discussed. Existing therapies are reviewed, in particular new targeted therapies to the HH signaling pathway that have resulted in a landmark breakthrough for patients with refractory BCC. Data from recent and ongoing trials are presented.

Fibrosis-dependent mechanisms of hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is a rising worldwide cause of cancer mortality, making the elucidation of its underlying mechanisms an urgent priority. The liver is unique in its response to injury, simultaneously undergoing regeneration and fibrosis. HCC occurs in the context of these two divergent responses, leading to distinctive pathways of carcinogenesis. In this review we highlight pathways of liver tumorigenesis that depend on, or are enhanced by, fibrosis. Activated hepatic stellate cells drive fibrogenesis, changing the composition of the extracellular matrix. Matrix quantity and stiffness also increase, providing a reservoir for bound growth factors. In addition to promoting angiogenesis, these factors may enhance the survival of both preneoplastic hepatocytes and activated hepatic stellate cells. Fibrotic changes also modulate the activity of inflammatory cells in the liver, reducing the activity of natural killer and natural killer T cells that normally contribute to tumor surveillance. These pathways synergize with inflammatory signals, including telomerase reactivation and reactive oxygen species release, ultimately resulting in cancer. Clarifying fibrosis-dependent tumorigenic mechanisms will help rationalize antifibrotic therapies as a strategy to prevent and treat HCC.

The utility of hedgehog signaling pathway inhibition for cancer

The Hedgehog (Hh) signaling pathway has been implicated in tumor initiation and metastasis across different malignancies. Major mechanisms by which the Hh pathway is aberrantly activated can be attributed to mutations of members of Hh pathway or excessive/inappropriate expression of Hh pathway ligands. The Hh signaling pathway also affects the regulation of cancer stem cells, leading to their capabilities in tumor formation, disease progression, and metastasis. Preliminary results of early phase clinical trials of Hh inhibitors administered as monotherapy demonstrated promising results in patients with basal cell carcinoma and medulloblastoma, but clinically meaningful anticancer efficacy across other tumor types seems to be lacking. Additionally, cases of resistance have been already observed. Mutations of SMO, activation of Hh pathway components downstream to SMO, and upregulation of alternative signaling pathways are possible mechanisms of resistance development. Determination of effective Hh inhibitor-based combination regimens and development of correlative biomarkers relevant to this pathway should remain as clear priorities for future research.

Novel AKT1-GLI3-VMP1 pathway mediates KRAS oncogene-induced autophagy in cancer cells

Autophagy is an evolutionarily conserved degradation process of cytoplasmic cellular constituents. It has been suggested that autophagy plays a role in tumor promotion and progression downstream oncogenic pathways; however, the molecular mechanisms underlying this phenomenon have not been elucidated. Here, we provide both in vitro and in vivo evidence of a novel signaling pathway whereby the oncogene KRAS induces the expression of VMP1, a molecule needed for the formation of the authophagosome and capable of inducing autophagy, even under nutrient-replete conditions. RNAi experiments demonstrated that KRAS requires VMP1 to induce autophagy. Analysis of the mechanisms identified GLI3, a transcription factor regulated by the Hedgehog pathway, as an effector of KRAS signaling. GLI3 regulates autophagy as well as the expression and promoter activity of VMP1 in a Hedgehog-independent manner. Chromatin immunoprecipitation assays demonstrated that GLI3 binds to the VMP1 promoter and complexes with the histone acetyltransferase p300 to regulate promoter activity. Knockdown of p300 impaired KRAS- and GLI3-induced activation of this promoter. Finally, we identified the PI3K-AKT1 pathway as the signaling pathway mediating the expression and promoter activity of VMP1 upstream of the GLI3-p300 complex. Together, these data provide evidence of a new regulatory mechanism involved in autophagy that integrates this cellular process into the molecular network of events regulating oncogene-induced autophagy.

The stem cell niche in regenerative medicine

Stem cells are fundamental units for achieving regenerative therapies, which leads naturally to a theoretical and experimental focus on these cells for therapeutic screening and intervention. A growing body of data in many tissue systems indicates that stem cell function is critically influenced by extrinsic signals derived from the microenvironment, or "niche." In this vein, the stem cell niche represents a significant, and largely untapped, entry point for therapeutic modulation of stem cell behavior. This Perspective will discuss how the niche influences stem cells in homeostasis, in the progression of degenerative and malignant diseases, and in therapeutic strategies for tissue repair.

Role of hedgehog signaling in malignant pleural mesothelioma

PURPOSE

The aim of this study was to assess the activity of hedgehog signaling pathway in malignant pleural mesothelioma (MPM).

EXPERIMENTAL DESIGN

The expression of hedgehog signaling components was assessed by quantitative PCR and in situ hybridization in 45 clinical samples. Primary MPM cultures were developed in serum-free condition in 3% oxygen and were used to investigate the effects of smoothened (SMO) inhibitors or GLI1 silencing on cell growth and hedgehog signaling. In vivo effects of SMO antagonists were determined in an MPM xenograft growing in nude mice.

RESULTS

A significant increase in GLI1, sonic hedgehog, and human hedgehog interacting protein gene expression was observed in MPM tumors compared with nontumoral pleural tissue. SMO antagonists inhibited GLI1 expression and cell growth in sensitive primary cultures. This effect was mimicked by GLI1 silencing. Reduced survivin and YAP protein levels were also observed. Survivin protein levels were rescued by overexpression of GLI1 or constitutively active YAP1. Treatment of tumor-bearing mice with the SMO inhibitor HhAntag led to a significant inhibition of tumor growth in vivo accompanied by decreased Ki-67 and nuclear YAP immunostaining and a significant difference in selected gene expression profile in tumors.

CONCLUSIONS

An aberrant hedgehog signaling is present in MPM, and inhibition of hedgehog signaling decreases tumor growth indicating potential new therapeutic approach.

The hedgehog processing pathway is required for NSCLC growth and survival

Considerable interest has been generated from the results of recent clinical trials using smoothened (SMO) antagonists to inhibit the growth of hedgehog (HH) signaling-dependent tumors. This interest is tempered by the discovery of SMO mutations mediating resistance, underscoring the rationale for developing therapeutic strategies that interrupt HH signaling at levels distinct from those inhibiting SMO function. Here, we demonstrate that HH-dependent non-small cell lung carcinoma (NSCLC) growth is sensitive to blockade of the HH pathway upstream of SMO, at the level of HH ligand processing. Individually, the use of different lentivirally delivered shRNA constructs targeting two functionally distinct HH-processing proteins, skinny hedgehog (SKN) or dispatched-1 (DISP-1), in NSCLC cell lines produced similar decreases in cell proliferation and increased cell death. Further, providing either an exogenous source of processed HH or a SMO agonist reverses these effects. The attenuation of HH processing, by knocking down either of these gene products, also abrogated tumor growth in mouse xenografts. Finally, we extended these findings to primary clinical specimens, showing that SKN is frequently overexpressed in NSCLC and that higher DISP-1 expression is associated with an unfavorable clinical outcome. Our results show a critical role for HH processing in HH-dependent tumors, identifies two potential druggable targets in the HH pathway, and suggest that similar therapeutic strategies could be explored to treat patients harboring HH ligand-dependent cancers.

Changes in connexin43 expression and localization during pancreatic cancer progression

Gap junctions and gap junction communication have long been recognized to play roles in tissue organization and remodeling through both cell autonomous and intercellular means. We hypothesized that these processes become dysregulated during pancreas cancer progression. Molecular and histological characterization of the gap junction protein, connexin43, during progression of pancreatic ductal adenocarcinoma could yield insight into how these events may contribute to or be modulated during carcinogenesis. In a mouse model of pancreatic ductal adenocarcinoma generated through targeted endogenous expression of Kras(G12D) in the murine pancreas, we examined the evolving expression and localization of connexin43. Overall, connexin43 expression increased over time, and its localization became more widespread. At early stages, connexin43 is found almost exclusively in association with the basolateral membrane of duct cells found in invasive lesions. Connexin43 became increasingly associated with the surrounding stroma over time. Connexin43 phosphorylation was also altered during tumorigenesis, as assessed by migrational changes of the protein in immunoblots. These data suggest a potential role for gap junctions and connexin43 in mediating interactions between and amongst the stromal and epithelial cells in pancreatic ductal adenocarcinoma.

Molecular pathways: the hedgehog signaling pathway in cancer

The Hedgehog (Hh) signaling pathway regulates embryonic development and may be aberrantly activated in a wide variety of human cancers. Efforts to target pathogenic Hh signaling have steadily progressed from the laboratory to the clinic, and the recent approval of the Hh pathway inhibitor vismodegib for patients with advanced basal cell carcinoma represents an important milestone. On the other hand, Hh pathway antagonists have failed to show significant clinical activity in other solid tumors. The reasons for these negative results are not precisely understood, but it is possible that the impact of Hh pathway inhibition has not been adequately measured by the clinical endpoints used thus far or that aberrancies in Hh signal transduction limits the activity of currently available pathway antagonists. Further basic and correlative studies to better understand Hh signaling in human tumors and validate putative antitumor mechanisms in the clinical setting may ultimately improve the success of Hh pathway inhibition to other tumor types.

Selective identification of hedgehog pathway antagonists by direct analysis of smoothened ciliary translocation

Hedgehog (Hh) signaling promotes tumorigenesis. The accumulation of the membrane protein Smoothened (Smo) within the primary cilium (PC) is a key event in Hh signal transduction, and many pharmacological inhibitors identified to date target Smo's actions. Smo ciliary translocation is inhibited by some pathway antagonists, while others promote ciliary accumulation, an outcome that can lead to a hypersensitive state on renewal of Hh signaling. To identify novel inhibitory compounds acting on the critical mechanistic transition of Smo accumulation, we established a high content screen to directly analyze Smo ciliary translocation. Screening thousands of compounds from annotated libraries of approved drugs and other agents, we identified several new classes of compounds that block Sonic hedgehog-driven Smo localization within the PC. Selective analysis was conducted on two classes of Smo antagonists. One of these, DY131, appears to inhibit Smo signaling through a common binding site shared by previously reported Smo agonists and antagonists. Antagonism by this class of compound is competed by high doses of Smo-binding agonists such as SAG and impaired by a mutation that generates a ligand-independent, oncogenic form of Smo (SmoM2). In contrast, a second antagonist of Smo accumulation within the PC, SMANT, was less sensitive to SAG-mediated competition and inhibited SmoM2 at concentrations similar to those that inhibit wild-type Smo. Our observations identify important differences among Hh antagonists and the potential for development of novel therapeutic approaches against mutant forms of Smo that are resistant to current therapeutic strategies.

Synthesis and characterization of Sant-75 derivatives as Hedgehog-pathway inhibitors

Sant-75 is a newly identified potent inhibitor of the hedgehog pathway. We designed a diversity-oriented synthesis program, and synthesized a series of Sant-75 analogues, which lays the foundation for further investigation of the structure–activity relationship of this important class of hedgehog-pathway inhibitors.

Paracrine Hedgehog increases the steroidogenic potential of prostate stromal cells in a Gli-dependent manner

Acquired intratumoral steroidogenesis is involved in progression of prostate cancer to castration resistant disease (CRPC) and a target for improved therapeutics. Recent work has shown that prostate cancer cells can acquire steroidogenic activity as they progress to a therapeutic-resistant state. However, benign prostate stromal cells (PrSCs) also have steroidogenic potential though they are often overlooked as a source of intratumoral androgens. Here, we present preliminary studies showing that the steroidogenic activity of primary human PrSCs is significantly increased by exposure to a Hedgehog agonist (SAG) or by transduction of PrSCs with lentiviruses that expresses active Gli2 (Gli2ΔN), a transcription factor that is triggered by Hh signaling. Comparative gene expression profiling on Chips, that was confirmed by quantitative real-time PCR, revealed that hedgehog agonist treatment induced in these cells expressions of hedgehog target genes (Gli1, Ptch1, and SCUBE1) plus a specific cadre of genes involved in cholesterol/steroid biosynthesis, metabolism, and transport. Genes involved downstream in steroid hormone generation, including CYP17A1 and CYP19A1 were also induced. Both the hedgehog agonist and the Gli2-expressing lentivirus significantly increased the output of testosterone (T) from PrSCs that were supplemented with dihydroepiandrosterone (DHEA), an adrenal precursor of T. Finally, knockdown of Gli2 by siRNA suppressed the ability of SAG to induce this response. Collectively, our data indicate that hedgehog/Gli signaling may be a factor in acquired intratumoral steroidogenesis of a prostate tumor through its actions on stromal cells in the tumor microenvironment and an influence for the development of CRPC.

Multifaceted tumor stromal fibroblasts

Tumors are highly complex tissues composed of neoplastic cells and different kinds of stromal cells. Tumor stromal cells, especially fibroblasts, play important roles during the multistep development of tumors. In this review, the two-faced characteristics of tumor stromal fibroblasts are discussed in the light of our current knowledge. For one thing, fibroblasts act as an "inflammation regulator" by secretion of cytokines and regulation of tumor immunity; for another, they act as a "damage healer" for cure of wounds by remodeling extracellular matrix or taking a part in the "foreign body reaction". Since the properties of fibroblasts are complicated, both aspects of fibroblasts for tumor development should be considered carefully in clinical studies to target cancer-associated fibroblasts.

Crosstalk between TGF-β and hedgehog signaling in cancer

Hedgehog (HH) and TGF-β signals control various aspects of embryonic development and cancer progression. While their canonical signal transduction cascades have been well characterized, there is increasing evidence that these pathways are able to exert overlapping activities that challenge efficient therapeutic targeting. We herein review the current knowledge on HH signaling and summarize the recent findings on the crosstalks between the HH and TGF-β pathways in cancer.

A piperidine chiron for the Veratrum alkaloids

A Veratrum piperidine chiron was prepared over 11 steps (7.9% yield) from (-)-citronellal. Three methods for the installation of the propargylic side chain onto a cyclic enamide are presented.

Emerging roles of the tumor-associated stroma in promoting tumor metastasis

The stroma in human carcinomas consists of extracellular matrix and various types of non-carcinoma cells, mainly leukocytes, endothelial cells, fibroblasts, myofibroblasts and bone marrow-derived progenitors. The tumor-associated stroma actively supports tumor growth by stimulating neo-angiogenesis, as well as proliferation and invasion of apposed carcinoma cells. It has long been accepted that alterations within carcinoma cells mediate metastasis in a cell-autonomous fashion. Recent studies have, however, suggested an additional notion that cancer cells instigate local and systemic changes in the tumor microenvironment and contribute to niche formation for metastasis. Research, aiming to establish the roles of the tumor-associated stroma in facilitating the spread of carcinoma cells into distant organs, has provided an abundance of data and greater knowledge of the biology of metastatic carcinoma cells and associated stromal cells. This has stimulated further advances in the development of novel therapeutic approaches targeting tumor metastasis.

Stroma and pancreatic ductal adenocarcinoma: an interaction loop

Pancreatic ductal adenocarcinoma (PDA) has two exceptional features. First, it is a highly lethal disease, with a median survival of less than 6 months and a 5-year survival rate less than 5%. Second, PDA tumor cells are surrounded by an extensive stroma, which accounts for up to 90% of the tumor volume. It is well recognized that stromal microenvironment can accelerate malignant transformation, tumor growth and progression. More importantly, the interaction loop between PDA and its stroma greatly contributes to tumor growth and progression. We propose that the extensive stroma of PDA is closely linked to its poor prognosis. An improved understanding of the mechanisms that contribute to pancreatic tumor growth and progression is therefore urgently needed. Targeting the stroma may thus provide novel prevention, earlier detection and therapeutic options to this deadly malignancy. Accordingly, in this review, we will summarize the mechanism of PDA stroma formation, the role of the stroma in tumor progression and therapy resistance and the potential of stroma-targeted therapeutics strategies.

The activity of Gli transcription factors is essential for Kras-induced pancreatic tumorigenesis

Pancreatic ductal adenocarcinoma (PDAC), one of the most aggressive human malignancies, is thought to be initiated by KRAS activation. Here we find that transcriptional activation mediated by the Gli family of transcription factors, although dispensable for pancreatic development, is required for Kras-induced proliferation and survival in primary pancreatic epithelial cells in culture and for Kras-driven pancreatic intraepithelial neoplasia and PDAC formation in vivo. Further, ectopic Gli1 activation in the mouse pancreas accelerates Kras-driven tumor formation, underscoring the importance of Gli transcription factors in pancreatic tumorigenesis. Interestingly, we demonstrate Gli-regulated I-kappa-B kinase epsilon (IKBKE) and NF-κB activity in pancreatic cancer cells and show that this activity is a critical downstream mediator for Gli-dependent PDAC cell transformation and survival. Together, these studies demonstrate the requirement for Gli in Kras-dependent pancreatic epithelial transformation, suggest a mechanism of Gli-NF-κB oncogenic activation, and provide genetic evidence supporting the therapeutic targeting of Gli activity in pancreatic cancer.

Activation of the Sonic Hedgehog pathway in thyroid neoplasms and its potential role in tumor cell proliferation

The sonic hedgehog (SHH) pathway is activated in several types of malignancy and plays an important role in tumor cell proliferation and tumorigenesis. SHH binding to a 12-pass transmembrane receptor, Patched (PTCH), leads to freeing of Smoothened (SMO) and subsequent activation of GLI transcription factors. In the present study, we analyzed the expression of SHH, PTCH, SMO, and GLI1 in 31 follicular thyroid adenomas (FTA), 8 anaplastic thyroid carcinomas (ATC), and 51 papillary thyroid carcinomas (PTC) by immunohistochemical staining. More than 65% of FTA, PTC, and ATC specimens stained positive for SHH, PTCH, SMO, and GLI. However, the expression of the genes encoding these four molecules did not correlate with any clinicopathologic parameters, including the age, gender, the status of BRAF gene mutation, tumor stage, local invasion, and metastasis. Three thyroid tumor cell lines (KAT-18, WRO82, and SW1736) all expressed the genes encoding these four molecules. 5-Bromo-2-deoxyuridine labeling and MTT cell proliferation assays revealed that cyclopamine (CP), an inhibitor of the SHH pathway, was able to inhibit the proliferation of KAT-18 and WRO82 cells more effectively than SW1736 cells. CP led to the arrest of cell cycle or apoptosis. Knockdown of SHH and GLI expression by miRNA constructs that target SHH or GLI mRNA in KAT-18 and SW1736 cells led to the inhibition of cell proliferation. Our results suggest that the SHH pathway is widely activated in thyroid neoplasms and may have potential as an early marker of thyroid cancer or as a potential therapeutic target for thyroid cancer treatment.

BMPs and their clinical potentials

Bone morphogenetic protein (BMP) signaling in diseases is the subject of an overwhelming array of studies. BMPs are excellent targets for treatment of various clinical disorders. Several BMPs have already been shown to be clinically beneficial in the treatment of a variety of conditions, including BMP-2 and BMP-7 that have been approved for clinical application in nonunion bone fractures and spinal fusions. With the use of BMPs increasingly accepted in spinal fusion surgeries, other therapeutic approaches targeting BMP signaling are emerging beyond applications to skeletal disorders. These approaches can further utilize next-generation therapeutic tools such as engineered BMPs and ex vivo- conditioned cell therapies. In this review, we focused to provide insights into such clinical potentials of BMPs in metabolic and vascular diseases, and in cancer. [BMB reports 2011; 44(10): 619-634].

Ectopic overexpression of Sonic Hedgehog (Shh) induces stromal expansion and metaplasia in the adult murine pancreas

Ligand-dependent activation of the Hedgehog (Hh) signaling pathway has been implicated in both tumor initiation and metastasis of pancreatic ductal adenocarcinoma (PDAC). Prior studies in genetically engineered mouse models (GEMMs) have assessed the role of Hh signaling by cell autonomous expression of a constitutively active Gli2 within epithelial cells. On the contrary, aberrant pathway reactivation in the human exocrine pancreas occurs principally as a consequence of Sonic Hh ligand (Shh) overexpression from epithelial cells. To recapitulate the cognate pathophysiology of Hh signaling observed in the human pancreas, we examined GEMM where Hh ligand is conditionally overexpressed within the mature exocrine pancreas using a tamoxifen-inducible Elastase-Cre promoter (Ela-CreERT2;LSL-mShh). We also facilitated potential cell autonomous epithelial responsiveness to secreted Hh ligand by generating compound transgenic mice with concomitant expression of the Hh receptor Smoothened (Ela-CreERT2;LSL-mShh;LSL-mSmo). Of interest, none of these mice developed intraductal precursor lesions or PDAC during the follow-up period of up to 12 months after tamoxifen induction. Instead, all animals demonstrated marked expansion of stromal cells, consistent with the previously described epithelial-to-stromal paracrine Hh signaling. Hh responsiveness was mirrored by the expression of primary cilia within the expanded mesenchymal compartment and the absence within mature acinar cells. In the absence of cooperating mutations, Hh ligand overexpression in the mature exocrine pancreas is insufficient to induce neoplasia, even when epithelial cells coexpress the Smo receptor. This autochthonous model serves as a platform for studying epithelial stromal interactions in pancreatic carcinogenesis.

Pathways involved in Drosophila and human cancer development: the Notch, Hedgehog, Wingless, Runt, and Trithorax pathway

Animal models are established tools to study basic questions of biology in a systematic way. They have greatly facilitated our understanding of the mechanisms by which nature forms and maintains organisms. Much of the knowledge on molecular changes underlying the development of organisms originates from research in the fruit fly model Drosophila melanogaster. Vertebrate models including the mouse and zebrafish model, but also other animal models coming from different corners of the animal kingdom have shown that much of the basic machinery of development is essentially identical, not just in all vertebrates but in all major phyla of invertebrates too. Moreover, key elements of this machinery have been demonstrated to be involved in recurrent molecular abnormalities detected in tumor-tissue from patients, indicating their implication in the genesis of human cancer. Thus, research in this field has become a common topic for both biologists and hemato-oncologists. In this review, we summarize current knowledge on some of these key elements and molecular pathways such as Notch, Hedgehog, Wingless, Runt, and Trithorax that have been originally described and studied in animal models and which seem to play a major role in the pathophysiology and targeted management of human cancer.

Hedgehog pathway activation in human transitional cell carcinoma of the bladder

BACKGROUND

The Hedgehog (Hh) signalling pathway functions as an organiser in embryonic development. Recent studies have shown constitutive activation of this pathway in various malignancies, but its role in bladder cancer remains poorly studied.

METHODS

Expression levels of 31 genes and 9 microRNAs (miRNAs) involved in the Hh pathway were determined by quantitative real-time RT-PCR in 71 bladder tumour samples (21 muscle-invasive (MIBC) and 50 non-muscle-invasive (NMIBC) bladder cancers), as well as in 6 bladder cancer cell lines.

RESULTS

The SHH ligand gene and Gli-inducible target genes (FOXM1, IGF2, OSF2, H19, and SPP1) were overexpressed in tumour samples as compared with normal bladder tissue. SHH overexpression was found in 96% of NMIBC and 52% of MIBC samples, as well as in two bladder cancer cell lines. Altered expression of miRNAs supported their oncogene or tumour-suppressor gene status. In univariate analysis, high expression levels of PTCH2, miRNA-92A, miRNA-19A, and miRNA-20A were associated with poorer overall survival in MIBC (P=0.02, P=0.012, P=0.047, and P=0.036, respectively).

CONCLUSION

We observed constitutive activation of the Hh pathway in most NMIBC and about 50% of MIBC. We also found that some protein-coding genes and miRNAs involved in the Hh pathway may have prognostic value at the individual level.

Hedgehog pathway as a drug target: Smoothened inhibitors in development

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