Purpose: Incidence and mortality rates for renal cell carcinoma (RCC) have been rising for decades. Unfortunately, the molecular events that support RCC carcinogenesis remain poorly understood. In an effort to gain a better understanding of signaling events in clear cell RCC (cRCC), we investigated the antitumor activity of secreted frizzled-related protein 1 (sFRP1), a negative regulator of Wnt signaling. Experimental Design: Genomic profiling of cRCC tumors and patient-matched normal tissues was done and confirmed using quantitative PCR and immunohistochemistry. Methylation-specific PCR was done on patient samples to evaluate the mechanism responsible for sFRP1loss. sFRP1 expression was restored in cRCC cells and the effects on tumor phenotype were characterized. Results: Genomic profiling, quantitative PCR, and immunohistochemistry indicated that loss of sFRP1occurred in cRCC and papillary RCC patient tissues. Twelve Wnt-regulated genes were up-regulated in cRCC tissues, including c-myc and cyclin D1, potentiators of cell proliferation and survival. Methylation of the sFRP1 gene was one mechanism identified for attenuation of sFRP1 mRNA. Stable reexpression of sFRP1in cRCC cells resulted in decreased expression of Wnt target genes, decreased growth in cell culture, inhibition of anchorage-independent growth, and decreased tumor growth in athymic nude mice. Conclusions: To our knowledge, this is the first report to show that stable restoration of sFRP1 expression in cRCC cells attenuates the cRCC tumor phenotype. Our data support a role for sFRP1as a tumor suppressor in cRCC and that perhaps loss of sFRP1is an early, aberrant molecular event in renal cell carcinogenesis.

p120 catenin is a cadherin-associated protein that regulates Rho GTPases and promotes the invasiveness of E-cadherin-deficient cancer cells. Multiple p120 isoforms are expressed in cells via alternative splicing, and all of them are essential for HGF signaling to Rac1. However, only full-length p120 (isoform 1) promotes invasiveness. This selective ability of p120 isoform 1 is mediated by reduced RhoA activity, both under basal conditions and following HGF treatment. All p120 isoforms can bind RhoA in vitro, via a central RhoA binding site. However, only the cooperative binding of RhoA to the central p120 domain and to the alternatively spliced p120 N terminus stabilizes RhoA binding and inhibits RhoA activity. Consistent with this, increased expression of p120 isoform 1, when compared with other p120 isoforms, is predictive of renal tumor micrometastasis and systemic progression, following nephrectomy. Furthermore, ectopic expression of the RhoA-binding, N-terminal domain of p120 is sufficient to block the ability of p120 isoform 1 to inhibit RhoA and to promote invasiveness. The data indicate that the increased expression of p120 isoform 1 during tumor progression contributes to the invasive phenotype of cadherin-deficient carcinomas and that the N-terminal domain of p120 is a valid therapeutic target.During epithelial tumor progression, tumor cells acquire the ability to invade surrounding tissues and eventually metastasize. A number of pathways have been uncovered to date that promote local invasiveness and metastatic tumor spread, and recent evidence argues that most of these converge on the loss of E-cadherin expression or function (1, 2). E-cadherin is the main epithelial cell-cell adhesion molecule, and its loss in most of these tumors coincides with an epithelial to mesenchymal transition (EMT), 2 where cells shed their epithelial characteristics and acquire a more mesenchymal phenotype. EMT is associated with normal development and wound healing, but its aberrant regulation contributes to cancer progression and metastasis (3). External cues, such as growth factors, can promote EMT via signaling pathways that are not well characterized but may involve the function of Snail family transcriptional repressors. The best characterized function of these transcription factors (i.e. Snail, Slug, and SIP1) is down-regulation of E-cadherin expression (4 -7). Consistent with this, experiments in transgenic mice strongly suggest that loss of E-cadherin directly promotes the transition of a benign adenoma into a carcinoma (8). Furthermore, reestablishing E-cadherin function in cadherin-deficient cell lines can reverse the invasive phenotype, suggesting that E-cadherin acts as a suppressor of cell invasion (9). The mechanism by which E-cadherin promotes suppression of invasiveness is still unclear. However, the adhesive function, which is mediated by its extracellular domain, is not thought to be involved in this effect (10). The intracellular domain of E-cadherin interacts directly with ␤-catenin and p120 catenin (p...

BackgroundClear cell renal cell carcinoma (ccRCC) is the most common kidney cancer. The purpose of this study is to define a biological pathway signature and a cellular differentiation program in ccRCC.MethodologyWe performed gene expression profiling of early-stage ccRCC and patient-matched normal renal tissue using Affymetrix HG-U133a and HG-U133b GeneChips combined with a comprehensive bioinformatic analyses, including pathway analysis. The results were validated by real time PCR and IHC on two independent sample sets. Cellular differentiation experiments were performed on ccRCC cell lines and their matched normal renal epithelial cells, in differentiation media, to determine their mesenchymal differentiation potential.Principal FindingsWe identified a unique pathway signature with three major biological alterations—loss of normal renal function, down-regulated metabolism, and immune activation–which revealed an adipogenic gene expression signature linked to the hallmark lipid-laden clear cell morphology of ccRCC. Culturing normal renal and ccRCC cells in differentiation media showed that only ccRCC cells were induced to undergo adipogenic and, surprisingly, osteogenic differentiation. A gene expression signature consistent with epithelial mesenchymal transition (EMT) was identified for ccRCC. We revealed significant down-regulation of four developmental transcription factors (GATA3, TFCP2L1, TFAP2B, DMRT2) that are important for normal renal development.ConclusionsccRCC is characterized by a lack of epithelial differentiation, mesenchymal/adipogenic transdifferentiation, and pluripotent mesenchymal stem cell-like differentiation capacity in vitro. We suggest that down-regulation of developmental transcription factors may mediate the aberrant differentiation in ccRCC. We propose a model in which normal renal epithelial cells undergo dedifferentiation, EMT, and adipogenic transdifferentiation, resulting in ccRCC. Because ccRCC cells grown in adipogenic media regain the characteristic ccRCC phenotype, we have indentified a new in vitro ccRCC cell model more resembling ccRCC tumor morphology.

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Peroxisomeproliferator-activated receptor gamma (PPARc) agonists demonstrate antitumor activity likely through transactivating genes that regulate cell proliferation, apoptosis, and differentiation. The PAX8/PPARc fusion oncogene, which is common in human follicular thyroid carcinomas appears to act via dominant negative suppression of wild-type PPARc, suggesting that it may be a tumor suppressor gene in thyroid cells. We have identified a novel high-affinity PPARc agonist (RS5444) that is dependent upon PPARc for its biological activity. This is the first report of this molecule and its antitumor activity. In vitro, the IC 50 for growth inhibition is B0.8 nM while anaplastic thyroid carcinoma (ATC) tumor growth was inhibited threeto fourfold in nude mice. siRNA against PPARc and a pharmacological antagonist demonstrated that functional PPARc was required for growth inhibitory activity of RS5444. RS5444 upregulated the cell cycle kinase inhibitor, p21 WAF1/CIP1 . Silencing p21 WAF1/CIP1 rendered cells insensitive to RS5444. RS5444 plus paclitaxel demonstrated additive antiproliferative activity in cell culture and minimal ATC tumor growth in vivo. RS5444 did not induce apoptosis but combined with paclitaxel, doubled the apoptotic index compared to that of paclitaxel. Our data indicate that functional PPARc is a molecular target for therapy in ATC. We demonstrated that RS5444, a thiazolidinedione (Tzd) derivative, alone or in combination with paclitaxel, may provide therapeutic benefit to patients diagnosed with ATC.