Abstract 3913: Fibroblast growth factor receptor 1 isoforms in prostate cancer bone metastases
Authors: Labanca Estefania , Wan Xinhai , Yang Jun , Iyer Matthew , Logothetis Christopher , Chinnaiyan Arul , Navone Nora 
Published: August 2015

Abstract
Bone metastases dominate the clinical picture of men with advanced prostate cancer (PCa). The fibroblast growth factor (FGF)/FGF receptor (FGFR) complex is commonly altered during PCa progression. Four highly conserved genes (FGFR1, FGFR2, FGFR3, and FGFR4) encode a repertoire of alternatively spliced variants of FGFRs that vary in the extracellular ligand-binding and intracellular kinase domains. A previous study from our group implicated FGFR1 as a therapy target for PCa bone metastases (Sci Transl Med 2014; 6:252ra122). One of the most important mechanisms by which FGFRs determine specificity for different FGFs is by alternative exon usage of the immunoglobulin-like (Ig-like) motif of the extracellular domain. We analyzed FGFR1 transcripts in 183 human PCa samples and in PCa patient-derived xenografts (PDXs) assessed by RNA sequencing. We identified eight different protein coding transcript to be the most abundantly expressed, namely ENST00000326324; ENST00000356207; ENST00000397103 (with a predicted protein length of 731 to 733 aa) and ENST00000397091; ENST00000397108; ENST00000397113; ENST00000425967; ENST00000532791 (with a predicted protein length of 820 to 853aa). Probably reflecting FGFR1alpha/beta isoforms: FGFR1alpha, containing three Ig-like domains and FGFR1beta, containing only two Ig-like domains. Interestingly, different PCa tissue samples expressed different isoforms.
We subsequently assessed, by real-time reverse transcription polymerase chain reaction, the expression of FGFR1alpha and beta in three PCa cell lines (PC3, DU145 and C4-2B) and seven PCa PDXs (MDA PCa 2b, MDA PCa 118b, MDA PCa 155-12; MDA PCa 146-10; MDA PCa 146-12; MDA PCa 150-3 and MDA PCa 183) derived from primary PCa, bone metastases and brain metastases and reflecting the typical adenocarcinoma as well as, adenocarcinomas with neuroendrocrine differentiation and small cell carcinomas of PCa. We found that all PDXs express primarily FGFR1alpha isoform while PCa cell lines express FGFR1beta.
We stably transfected PC3 cells with FGFR1alpha (NM_023110.2) and FGFR1beta (NM_023105.2) isoforms. After clones were established, we placed the cells for 10 days in culture and found that tissue culture plates containing PC3 expressing FGFR1alpha had significantly more cells compared with dishes containing PC3 expressing FGF1beta isoform as assessed by direct cell counting in a phase contrast microscope. Furthermore, PC3 cells transfected with FGFR1 alpha display a more adhesive phenotype than cells transfected with FGFR1beta or empty vector as assessed by cell attachment in a 24-well plate.
We conclude that FGFR1 isoforms are involved in the pathogenesis of PCa and can be used to develop markers of response to FGFR1 blockade. These results warrant further studies to fully understand the biological implications of FGFR1 isoforms in the pathogenesis of PCa.
Citation Format: Estefania Labanca, Xinhai Wan, Jun Yang, Matthew Iyer, Christopher Logothetis, Arul Chinnaiyan, Nora Navone. Fibroblast growth factor receptor 1 isoforms in prostate cancer bone metastases. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3913. doi:10.1158/1538-7445.AM2015-3913