TMPRSS2-ERG gene fusion causing ERG overexpression precedes chromosome copy number changes in prostate carcinomas and paired HGPIN lesions

Abstract

TMPRSS2-ETS gene fusions have been found recurrently in prostate carcinomas, but not in the presumed precursor lesion, high-grade prostatic intraepithelial neoplasia (HGPIN). However, HGPIN lesions may share chromosomal changes with prostate cancer. To determine the relative order of genetic events in prostate carcinogenesis, we have analyzed 34 prostate carcinomas, 19 paired HGPIN lesions, 14 benign prostate hyperplasias, and 11 morphologically normal prostatic tissues for TMPRSS2-ERG and TMPRSS2-ETV1 rearrangements and genomic imbalances. TMPRSS2 exon 1 was fused in-frame with ERG exon 4 in 17 of 34 (50%) prostate carcinomas and in 4 of 19 (21%) HGPIN lesions, but in none of controls. The findings were further validated by sequencing analysis and by the real-time polymerase chain reaction quantification of TMPRSS2-ERG fusion transcript and the ERG exons 5/6:exons 1/2 expression ratio. Chromosome copy number changes were detected by comparative genomic hybridization in 42% of clinically confined carcinomas and in none of the 16 HGPIN lesions analyzed. We demonstrate for the first time that the TMPRSS2-ERG fusion gene can be detected in a proportion of HGPIN lesions and that this molecular rearrangement is an early event that may precede chromosome-level alterations in prostate carcinogenesis.

Figure 1

Detection and analysis of type A TMPRSS2-ERG fusion transcript in prostate carcinoma and HGPIN samples. (A) RT-PCR analysis with a sense primer located in TMPRSS2 exon 1 and an antisense primer located in ERG exon 6 in PCa (PCa 55, PCa 114, PCa 134, and PCa 152 in lanes 2–5, respectively) and HGPIN (HGPIN 60, HGPIN 83, and HGPIN 42 in lanes 7–9, respectively) samples. The expected size of the type A TMPRSS2-ERG fusion transcript is indicated. Lanes 1, 6, and 10 = 100-bp molecular marker. (B) Partial sequence of the junction of type A TMPRSS2-ERG chimeric mRNA showing the nucleotide sequence of the fusion transcript. The arrow shows in-frame fusion between TMPRSS2 exon 1 and ERG exon 4.

Figure 2

Representative images of four HGPIN lesions harboring the TMPRSS2-ERG fusion gene. (A) HGPIN 42. (B) HGPIN 58. (C) HGPIN 60. (D) HGPIN 83 (hematoxylin-eosin stain; original magnification, x25).