Abstract 1101: A novel role for FGFR in breast cancer

Abstract

Abstract FGF-10 and its two receptors, FGFR1 and FGFR2, have been implicated in breast cancer susceptibility and/or progression, suggesting that, as with several other cancers, FGF signalling may be co-opted by breast cancer cells to give them a growth advantage. We aim to elucidate the role of FGF signalling in breast cancer progression and behaviour. We determined the expression levels of FGFs and FGFRs in a number of breast cancer cell lines, identifying a positive correlation of FGF-10 and FGFR1 expression with ER status. This is particularly interesting, given the correlation between amplification of FGFR1 and poor prognosis in ER positive breast cancer. To investigate the effects of FGFR signalling, we treated both weakly and highly metastatic human breast cancer cell lines (MCF-7 and MDA-MB-231, respectively), with recombinant FGF-10. This elicited rapid ERK phosphorylation, which was abrogated by pre-treatment with an FGFR inhibitor, PD173074. Interestingly, the signalling pathways downstream of FGF-10 stimulation differed between the two cell lines, with MCF-7 cells signalling via FGF Receptor Substrate 2 (FRS2), whereas MDA-MB-231 cells did not. FGF-10 treatment stimulated cell proliferation only in MCF-7 cells, suggesting that its mitogenic effect acts via P-FRS2, whereas it drove survival and migration equally in both cell lines. Using a breast cancer organotypic model we observed, specifically in cells that had invaded into the stroma, FGFR1 was localised to the nucleus. Using immunocytochemistry we have also identified nuclear FGFR1 in invasive lobular carcinoma. In 2D culture, immunofluorescence and subcellular fractionation of breast cancer cells revealed that FGF-10 treatment stimulated nuclear localisation of a C-terminal fragment of FGFR1, an effect peaking after 1 hour and dependent on active FGF signalling. Using specific inhibitors and RNAi, we identified granzyme B (GrB) as the protease responsible for FGFR1 cleavage. Importantly, inhibition of GrB blocked accumulation of nuclear FGFR1 upon FGF-10 treatment and increased total levels of full length FGFR1. Furthermore, GrB inhibition enhanced the effect FGF-10 stimulation had on phosphorylation of FRS2 and ERK. Functionally, GrB inhibition blocked the pro-migratory effect of FGF-10 treatment suggesting that nuclear localisation of the receptor may be critical for cell migration. To elucidate the role of nuclear FGFR1, we performed ChIP on chip studies, identifying a number of putative target genes. Modulating of FGFR1 levels showed that FGFR1 can activate or suppress expression of these target genes, perhaps reflecting an invasive signature. Our studies identify an entirely novel mechanism by which FGF signalling may regulate cancer cell behaviour. Establishing the functional, prognostic and therapeutic relevance of FGF signalling in breast cancer is critical for the development of new targeting strategies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1101. doi:10.1158/1538-7445.AM2011-1101