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Delineation of TMPRSS2-ERG Splice Variants in Prostate Cancer

Authors' Affiliations: ¹ Center for Prostate Disease Research, Department of Surgery, Uniformed Services University of the Health Sciences, Rockville, Maryland; ² Armed Forces Institute of Pathology, Department of Genitourinary Pathology and ³ Urology Service, Department of Surgery, Walter Reed Army Medical Center, Washington, District of Columbia; and ⁴ U.S. Military Cancer Institute, Uniformed Services University of the Health Sciences, Bethesda, Maryland

Requests for reprints: Shiv Srivastava or Gyorgy Petrovics, Center for Prostate Disease Research, Department of Surgery, Uniformed Services University of the Health Sciences, Rockville, MD 20852. E-mail: ssrivastava{at}cpdr.org or gpetrovics{at}cpdr.org.

Purpose: The expression of the ETS-related gene (ERG) is low or undetectable in benign prostate epithelial cells. High prevalence of ERG overexpression in prostate cancer cells due to TMPRSS2-ERG fusions suggest for causal roles of ERG protein in the neoplastic process. TMPRSS2-ERG fusion junctions have been extensively studied in prostate cancer. However, virtually nothing is known about the nature of full-length transcripts and encoded proteins. This study focuses on qualitative and quantitative features of full-length TMPRSS2-ERG transcripts in prostate cancer.

Experimental Design: Full-length TMPRSS2-ERG transcripts were cloned and sequenced from a cDNA library generated from pooled RNA of six TMPRSS2-ERG fusion–positive prostate tumors. The encoded ERG proteins were analyzed in HEK293 cells. Copy numbers of TMPRSS2-ERG splice variants were determined by quantitative reverse transcription-PCR in laser capture microdissected prostate cancer cells.

Results: Two types of TMPRSS2-ERG cDNAs were identified: type I, which encodes full-length prototypical ERG protein (ERG1, ERG2, ERG3), and type II, encoding truncated ERG proteins lacking the ETS domain (ERG8 and a new variant, TEPC). In microdissected prostate tumor cells from 122 patients, relative abundance of these variants was in the following order: ERG8 > TEPC > ERG 3 > ERG1/2 with combined overexpression rate of 62.3% in prostate cancer. Increased ratio of type I over type II splice forms showed a trend of correlation with less favorable pathology and outcome.

Conclusions: Qualitative and quantitative features of specific ERG splice variants defined here promise to enhance the utility of ERG as a biomarker and therapeutic target in prostate cancer.