Tracing the origins of chromosomal translocations in prostate cancer

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Abstract Chromosomal translocations are a hallmark of cancer progression. These translocations often result in gene fusions, a common mechanism for oncogene activation. 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. The development of next generation sequencing based approaches like RNA-Seq and paired-end whole-genome sequencing have accelerated the discoveries of gene fusions in prostate cancer. However, the mechanisms underlying the formation and cell type specificities of chromosomal translocations are far from clear. Our proposal aims to bridge the gap between the rapid discovery of chromosomal translocations and our limited understanding of the mechanisms leading to their formation. In our recent study, we demonstrate that androgen signaling induces chromosomal proximity between TMPRSS2 and ERG loci, and facilitates the formation of the TMPRSS2-ERG gene fusion when subjected to an agent that causes DNA double strand breaks. These results provide a conceptual framework for the genesis of gene fusions in human prostate cancer. In specific aim 1, we propose to employ next-generation sequencing to identify genome-wide chromosomal interactions mediated by androgen signaling. The mentor’s expertise in throughput technologies will help the candidate acquire the necessary skill-set to accomplish aim 1. Interestingly, we identified novel recurrent mutations in the androgen receptor AR collaborating factor FOXA1, which is mutated in 5 of 147 (3.4%) prostate cancers. Preliminary functional studies on one representative mutation revealed that mutated FOXA1 disrupts androgen signaling and increases proliferation. In specific aim 2, we propose to study the effect of FOXA1 mutations in regulating AR signaling and interactome. Aim 2, a logical extension of aim 1 will be pursued during the independent phase (R00). Accomplishment of these two aims will provide us with a comprehensive understanding of the three dimensional genomic architecture of prostatic cells, how AR regulates this architecture, the influence mutations in AR collaborating factors, and importantly how this impacts the formation of gene fusions. While spatial proximity is necessary for chromosomal translocations, it is not sufficient. DNA breaks synergize with spatial proximity to fuel chromosomal translocations. In specific aim 3, we will study the role of inflammation mediated activation of NF-κB pathway in the formation of DNA breaks and ETS gene fusions in prostate cancer. Successful completion of the aims outlined in this proposal will improve our understanding of the origins of chromosomal translocations in prostate cancer, may have broader implications for understanding and treating cancer and may provide suggestions as to the general etiology of human prostate cancer. These projects have been conceived based on my original ideas. Dr. Chinnaiyan has extended his full support towards my career goals and has encouraged me to take these projects to my independent lab in the future.