Abstract B59: Race-related differential splicing of the insulin receptor: A novel target underlying prostate cancer disparities

Background: Age-adjusted incidence and mortality rates for prostate cancer (PCa) among African American (AA) men are significantly greater than among white men. Much of this disparity remains after controlling for behavioral, social, and neighborhood determinants of health, which is consistent with a biologic contribution. Evidence suggests that the genetic etiology and molecular progression of PCa are different in AAs versus whites. Our laboratory has identified novel alternatively spliced genes in AA versus white PCa biopsy tissue that track with population-based prostate tumor aggressiveness. This work addresses the urgent need to interrogate novel molecular mechanisms driving more aggressive PCa in AAs to aid in development of new biomarkers and therapeutic targets for improved prognosis and treatment of aggressive disease. Methods: We have analyzed RNA from human PCa biopsy tissue from 20 AA and 15 white patients using exon arrays. From these data, we prioritized targets for further study by identifying those associated with androgen signaling and PCa and those that have also been shown to be alternatively spliced in breast, lung, and liver cancer. To validate race-related alternative splicing of the insulin receptor (INSR) gene, we have used qPCR and targeted sequencing of RNA from population-specific PCa cell lines and patient-derived explants. In addition, we have knocked down the INSR splice variants in population-specific PCa cell lines using isoform-specific siRNAs and assessed resulting alterations in proliferation using a WST-1 proliferation assay. Current studies include assessing additional resulting alterations in expression of selected key targets in INSR signaling using Western blot analysis. In addition, studies are under way to treat population-specific PCa cell lines with INSR signaling inhibitors and assess resulting alterations in PCa cell biology. Results: Exon array analysis of RNA from AA and white PCa biopsy tissue revealed 934 differentially expressed exons in 861 corresponding genes. Thirty-nine targets have been prioritized for further study. We have validated race-related alternative splicing of INSR, involving differential exon inclusion/skipping of exon 11, in population-specific PCa cell lines and patient-derived explants, with the exclusion of exon 11 occurring more often in preclinical models of white PCa. Knockdown of INSR splice variants in population-specific PCa cell lines has shown that decreased expression of the isoform excluding exon 11 inhibits proliferation while decreased expression of the isoform including exon 11 has no effect on proliferation. Further studies to assess additional resulting alterations in expression of selected key targets in INSR signaling are under way. In addition, studies are under way to treat population-specific PCa cell lines with INSR signaling inhibitors and assess resulting alterations in PCa cell biology. Conclusions: These studies identify differential splicing of INSR in AA and white PCa and the INSR isoform excluding exon 11 as contributors to prostate tumor aggressiveness. Further interrogation of this mechanism underlying PCa disparities and its effect on targeted therapeutics has the potential to reduce PCa disparities for AA men and improve outcomes for men of all races with aggressive disease driven by this mechanism. Citation Format: April Deveaux, Bi-Dar Wang, Bonnie Lacroix, Brendon Patierno, Dadong Zhang, Kouros Owzar, Norman Lee, Daniel George, Jennifer Freedman, Steven Patierno. Race-related differential splicing of the insulin receptor: A novel target underlying prostate cancer disparities [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr B59.