Abstract 2476: The oncogenic role of p63 in altered-FGFR3 bladder tumors

Abstract

Abstract Recently, a new classification of muscle-invasive bladder cancer (MIBCs) has been proposed (Kamoun, 2020). There are 6 classes of MIBC: the over-expression or activating mutations in Fibroblast Growth Factor Receptor 3 (FGFR3) are associated with luminal subtypes. As typically expected, basal tumors exhibit increased TP63 activity, but interestingly, this is also observed in luminal-papillary (LumP) tumors. LumP are enriched in both, FGFR3 mutations and p63 activation. The regulatory gene pathways and p63 functional role in these tumors remains poorly characterized. Therefore, this is our main objective, together with the study of the link with FGFR3 mutations. We hypothesize that p63 drives a protumoral program in bladder cancer (BC) commanded by the regulation of altered FGFR3. We used human BC cell lines bearing FGFR3 mutations with inducible silencing for p63 in order to identify the functional role of p63 in this context. Loss of p63 led to a decreased 2D and 3D growth (p<0.001). Gelatin degradation and migration ability were significantly lower in p63 depleted cells compared to CRL (p<0,01). In vivo assays showed that tumor volume was significantly lower in p63 depleted tumors compared to CRL (p<0.01), accompanied by a reduction of proliferating cell nuclear antigen (PCNA) expression, indicating that p63 is an essential protein through which the cell mediates its proliferative and migratory mechanism. In order to study the link between both, FGFR3 alterations and p63 activity, we used FGFR3 Knocked down cells and pharmacological inhibitors. FGFR3 inhibition decreased p63 expression associated with a reduction in TP63 activity. It reduced proliferation and cell migration in similar level to those observed by directly silencing p63 in FGFR3 altered cells. Conversely, FGFR3 wt cells were not affected by the inhibitor. Overall, these results show that FGFR3 inhibition blunted the carcinogenic program carried out by p63, suggesting there is a regulation of FGFR3 over p63. Supporting the regulation of p63 by FGFR3, analysis of mRNA levels in human bladder tumors showed that p63 expression was significantly higher in FGFR3 mutated tumors in two different sets of samples. In summary, we experimentally demonstrated the regulation of FGFR3 over the protumoral transcription factor p63 that induces proliferation, migration and tumor growth in bladder cancer. Citation Format: Macarena Zambrano, Aura I. Moreno-Vega, Florent Dufour, Marianela Sciacca, Yanina V. Langle, François Radvanyi, Ana M. Eiján, Isabelle Bernard-Pierrot, Catalina Lodillinsky. The oncogenic role of p63 in altered-FGFR3 bladder tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2476.