Abstract 3929: The role of chromosome architecture in the generation of gene fusions in prostate cancer
Authors: Mani Ram S. , Tomlins Scott A. , Callahan Kaitlin , Ghosh Aparna , Nyati Mukesh K. , Varambally Sooryanarayana , Palanisamy Nallasivam , Chinnaiyan Arul M. 
Published: February 2011

The purpose of this study is to unravel the cellular mechanisms that result in oncogenic gene fusions, which are a hallmark of cancer development. Typically, these gene fusions arise from chromosomal aberrations that result in either (A) juxtapositioning of the regulatory element of a gene to a proto-oncogene, thereby activating it, or (B) fusion of two genes resulting in the production of a fusion protein with oncogenic activities. Until recently, recurrent gene fusions were predominantly associated with hematological malignancies (leukemias and lymphomas) and soft tissue tumors (sarcomas), but were rarely linked to common epithelial carcinomas. This view changed with the discovery of recurrent gene fusions involving ETS family genes in prostate cancer. Among the ETS family gene fusions, the TMPRSS2-ERG fusions involving the 5′untranslated region of androgen-regulated gene TMPRSS2 with the ERG gene are the most common and found in approximately 50% of prostate cancers. However, the mechanisms leading to the genesis and cell type specificity of gene fusions are unclear. Recent literature indicates that estrogen induces rapid interchromosomal interactions between a subset of estrogen receptor α bound genes. As estrogen and androgen signaling are intrinsically similar, we hypothesized that androgen could induce the proximity between 5′ and 3′ gene fusion partners through chromosomal movement, thereby facilitating the formation of gene fusions. We tested this hypothesis in the context of TMPRSS2-ERG gene fusions in LNCaP cells which are androgen-sensitive human prostate adenocarcinoma cells that do not harbor the TMPRSS2-ERG gene fusion. Using dual color fluorescence in situ hybridization (FISH), we observed that stimulation with dihydrotestosterone (DHT) induced proximity between TMPRSS2 and ERG genomic loci. This effect was dependent on androgen receptor (AR). Importantly, androgen did not induce proximity between the TMPRSS2 and ERG loci in DU145 human prostate cancer cells, which are androgen insensitive. Our next set of experiments were aimed to explore if DHT mediated alteration in chromosomal architecture could facilitate the formation of gene fusions. LNCaP cells were stimulated with DHT, subjected to irradiation in order to create DNA double strand breaks and were clonally expanded. TMPRSS2-ERG fusion transcripts were detected in 25% (3/12) of the clones treated with 3 Gy irradiation but in only 2.3% (1/43) of those treated with 1 Gy. Furthermore, TMPRSS2-ERG expressing clonally derived LNCaP cells showed evidence consistent with chromosomal aberrations at the ERG locus. We present strategies for genome-wide identification of androgen mediated long range chromosomal interactions. Our results suggest that androgen signaling co-localizes the 5′ and 3′ gene fusion partners, thereby increasing the probability of a gene fusion when subjected to agents that cause DNA double strand breaks.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3929.