Abstract C42: Alternative splicing of FGFR3 as a mechanism for African American prostate cancer health disparities

Introduction: In this study, we investigate the role of differential expression of splicing factors and exon skipping in the receptor tyrosine kinase family on prostate cancer health disparities in African American men. Background: Prostate cancer (PCa) is the most diagnosed cancer in men and the second leading cause of male-cancer related deaths in the U.S. Dramatic ethnic disparities have been observed in PCa patients, as African American (AA) men are 60% more likely to be diagnosed with PCa and have a 2.4 fold higher mortality rate compared to European American (EA) men. Increasing evidence suggests that, after accounting for epidemiological factors, a remaining component of this disparity is due to intrinsic genetic and biological factors. Interestingly, recent exon array data from our lab suggest that differential expression of splicing factors (SFs) and differential alternative splicing may be occurring in AA PCa. We hypothesize that differential alternative splicing involving exon 14 of the FGFR3 gene is generating a shorter, more oncogenic variant in AA PCa, which is absent or weakly expressed in EA PCa. Differential splicing of FGFR3 and increased expression of SFs in AA patients may be mechanisms contributing to AA PCa health disparities. Results: Exon array data suggested FGFR3 as a candidate for differential alternative splicing. Exon profiling and RT-PCR validated enriched expression of a short variant of FGFR3 due to skipping of exon 14 in AA patient samples and cell lines. Cloning confirmed the presence of the FGFR3-L variant (containing exon 14) and the FGFR3-S variant (without exon 14) from an EA and AA PCa cell line, respectively. Enrichment of FGFR3-S resulted in increased cell proliferation in an AA cell line. RNA-seq data analysis suggests decreased survival of PCa patients with high FGFR3-S/-L expression ratios. Additionally, our exon array data predicted increased expression of seven SFs in AA patients. RT-PCR and IHC analysis validated increased expression in AA specimens. Knockdown of these SFs resulted in decreased invasion and FGFR3 splice switching in an AA cell line. Conclusions: We have identified an oncogene of interest, FGFR3, which undergoes exon skipping that is specific to AA PCa. In cell lines, this shorter isoform of FGFR3 leads to an increased oncogenic phenotype based on proliferation assays. We have shown that AA PCa patient specimens have increased expression of specific SFs compared to EA specimens and knockdown of SFs reduces AA PCa cell invasion and causes splice switching of FGFR3. Thus, differential expression of SFs and exon skipping in FGFR3 may be one mechanism contributing to the increased aggressiveness of PCa in AA patients. Citation Format: Jacqueline Olender, Bi-Dar Wang, Norman H. Lee. Alternative splicing of FGFR3 as a mechanism for African American prostate cancer health disparities. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr C42.