Molecular Mechanism of ß-Catenin Signaling Pathway Inactivation in ETV1-Positive Prostate Cancers.

In the United States of America, prostate cancer is the second most common age-related cancer among men. African-American men have the highest incidence of, and mortality rate from this disease in the United States. According to the American Cancer Society, 29% of all cancer cases and 9% of all cancer deaths are a result of prostate cancer. Individuals who are at highest risk include African-American men, men over 60 years of age, and those with a family history of the disease. African-Americans also have twice the risk of developing prostate cancer as compared to Caucasians. Erythroblastosis virus E26 transformation-specific (ETS) factors play an important role in human cancers. ETS Variant 1 (ETV1), an ETS factor, is notable for its association in prostate cancers, where truncated ETV1 (dETV1) or its full length counterpart is overexpressed in approximately 10% of the prostate cancer patients. Prostate cancer tumorigenesis may be initiated by deregulation of the Wnt/ß-catenin pathway. Mutations that stabilize ß-catenin were shown to contribute to the loss of cell-growth control in tumorigenesis. We hypothesized that ETV1's interaction with components of the Wnt/ß-catenin pathway may alter ß-catenin's interaction with downstream tumor-suppressor genes, which are critical in regulating apoptosis and cell-growth properties of prostate cells. Our results demonstrate for the first time that ETV1 alters ß-catenin activity by activating kinases that regulate Wnt/ß-catenin activity through post-translational modification in prostate cancer cells. We further demonstrate that therapeutic agents such as PD98059, that reverse effect of ETV1 on Wnt/ß-catenin signaling pathway, can be used to target ETV1-positive prostate cancer cells. These therapeutic agents could have a profound impact on prevention and treatment of prostate cancer which may help to reduce health disparity seen in minority patients. Understanding the role of ETV1 in Wnt/ß-catenin pathway will also allow us to develop better diagnostic tools, which can be used as a biomarker for ETV1-positive prostate cancers.

Anti-Epileptic Drug Targets Ewing Sarcoma.

Ewing Sarcoma (ES) is a rare form of bone cancer that most commonly affects children and adolescents. Chromosomal translocations are fundamental to the development of Ewing Sarcoma, linked to the changes in gene expression affecting transcription factors. Histone acetyl transferases (HATs) and histone deacetylases (HDACs) regulate transcription by modifying acetylation of both histones and transcription factors. Despite the use of multimodal therapeutic approaches current therapies are associated with significant short and long-term side effects. Hence, new therapeutic approaches are needed. In this study, we show that ERG/EWS-ERG, inhibits transcriptional activation properties of RXRα. These results suggest that ERG/EWS-ERG/EWS-Fli-1 may target transcriptional co-activators and transcriptional repressors and thereby regulate RXRα transcriptional activity. To understand the molecular mechanism of action, how the fusion protein targets nuclear receptor function, and to provide a clue for the cancer health disparity seen in Ewing Sarcoma, we hypothesized that the aberrant fusion protein, EWS-ERG/EWS-Fli-1 regulates HDACs-mediated repressor complex and inhibits the binding of transcriptional activator complex causing transcriptional repression of RXRα activity. Since it is known that HDACs regulate nuclear receptors, we proposed that HDAC inhibitor, valproic acid (VPA), an anti-epileptic drug, may reverse the inhibitory properties of EWS-ERG/EWS-Fli-1 oncoprotein on RXRα transcriptional activity and might therefore be used as therapeutic agent in ES. We demonstrate that VPA reverses the inhibitory effect of EWSERG/EWS-Fli-1 on RXRα transcriptional activity and also inhibits the cell growth. Furthermore, VPA induces apoptosis and restored the expression of RXRα target genes RARß, CRABPII and p21 activity and repressed the expression of aberrant fusion proteins, EWS-ERG and EWS-Fli-1 in Ewing Sarcoma cells. Thus, therapeutic regulation of transcriptional repressor properties of EWS-ERG/EWS-Fli-1 with an anti-epileptic drug with a promising new potential might have a profound impact on prevention, management and treatment of Ewing Sarcoma. Therapeutic use of VPA in minority patients may help reduce the health disparity.

Ets Related Gene and Smad3 Proteins Collaborate to Activate Transforming Growth Factor-Beta Mediated Signaling Pathway in ETS Related Gene-Positive Prostate Cancer Cells.

TGF-ß/Smads signaling plays a significant role in the regulation of growth of normal and prostate cancer cells. Smad proteins function as important mediators of intracellular signal transduction of transforming growth factor-ß (TGF-ß). TGF-ß signaling pathway is known to regulate cell proliferation, differentiation, apoptosis and play a major role in some human diseases and cancers. Following their phosphorylation by TGF-ß receptor-I, Receptor-regulated Smads (including Smad2 and Smad3 proteins) form a heteromeric complex with co-Smad (Smad4) and then translocate into the nucleus where they bind and regulate the expression of target genes. ERG (Ets Related Gene) belongs to the ETS family of transcriptional factors. Chromosomal rearrangement of TMPRSS2 gene and ERG gene has been found in majority of prostate cancers. Over-expression of full length or truncated ERG proteins have been shown to associate with a higher rate of recurrent and unfavorable prognosis of prostate cancer. In order to understand how ERG oncoprotein regulates TGF-ß/Smads signaling pathway, we have studied the effect of ERG on TGF-ß/Smad3 signaling pathway. In this study, we demonstrate that ERG oncoprotein physically interacts with Smad3 protein and stabilizes phospho-Smad3 protein and thereby enhance TGF-ß/Smad3 signaling pathway in prostate cells. Thus, ERG oncoprotein plays an important role in prostate tumorigenesis by using a novel mechanism to activate TGF-ß/Smad3 signaling pathway.

Histone deacetylase inhibitors, valproic acid and trichostatin-A induce apoptosis and affect acetylation status of p53 in ERG-positive prostate cancer cells.

An ETS family member, ETS Related Gene (ERG) is involved in the Ewing family of tumors as well as leukemias. Rearrangement of the ERG gene with the TMPRSS2 gene has been identified in the majority of prostate cancer patients. Additionally, overexpression of ERG is associated with unfavorable prognosis in prostate cancer patients similar to leukemia patients. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) regulate transcription as well as epigenetic status of genes through acetylation of both histones and transcription factors. Deregulation of HATs and HDACs is frequently seen in various cancers, including prostate cancer. Many cellular oncogenes as well as tumor viral proteins are known to target either or both HATs and HDACs. Several studies have demonstrated that there are alterations of HDAC activity in prostate cancer cells. Recently, we found that ERG binds and inhibits HATs, which suggests that ERG is involved in deregulation of protein acetylation. Additionally, it has been shown that ERG is associated with a higher expression of HDACs. In this study, we tested the effect of the HDAC inhibitors valproic acid (VPA) and trichostatin-A (TSA) on ERG-positive prostate cancer cells (VCaP). We found that VPA and TSA induce apoptosis, upregulate p21/Waf1/CIP1, repress TMPRSS2-ERG expression and affect acetylation status of p53 in VCaP cells. These results suggest that HDAC inhibitors might restore HAT activity through two different ways: by inhibiting HDAC activity and by repressing HAT targeting oncoproteins such as ERG.