Induced chromosomal proximity and gene fusions in prostate cancer

Abstract

Gene fusions play a critical role in cancer progression. The mechanisms underlying their genesis and cell type specificity are not well understood. About 50% of human prostate cancers display a gene fusion involving the 5' untranslated region of TMPRSS2, an androgen-regulated gene, and the protein-coding sequences of ERG, which encodes an erythroblast transformation-specific (ETS) transcription factor. By studying human prostate cancer cells with fluorescence in situ hybridization, we show that androgen signaling induces proximity of the TMPRSS2 and ERG genomic loci, both located on chromosome 21q22.2. Subsequent exposure of the cells to gamma irradiation, which causes DNA double-strand breaks, facilitates the formation of the TMPRSS2-ERG gene fusion. These results may help explain why TMPRSS2-ERG fusions are restricted to the prostate, which is dependent on androgen signaling.

Figure 1

(A) FISH based evaluation of induced proximity between TMPRSS2 (green) and ERG (red) on stimulation with 100 nM DHT in LNCaP cells. Colocalization is indicated by yellow arrows. Scale bar indicate 2 µm. (B) Induced proximity between TMPRSS2 and ERG in DU145 and LNCaP cells is quantified and represented as the percentage of nuclei exhibiting colocalization signals. GAPDH, glyceraldehydes-3-phosphate dehydrogenase. (C) SYBR Green (Moleculr Probes, Eugene, Orgeon) and TaqMan (applied Biosystems, Foster City, California) quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis of the TMPRSS2-ERG fusion transcript. (D) Gel based RT-PCR analysis with primers spanning the first exon of TMPRSS2 and sixth exon of ERG for representative clones. (E) FISH analysis of the ERG locus. Split signals representing ERG rearrangement are highlighted by arrows.