C3G downregulation induces the acquisition of a mesenchymal phenotype that enhances aggressiveness of glioblastoma cells

© The Author(s) 2021.Glioblastoma (GBM) is the most aggressive tumor from the central nervous system (CNS). The current lack of efficient therapies makes essential to find new treatment strategies. C3G, a guanine nucleotide exchange factor for some Ras proteins, plays a dual role in cancer, but its function in GBM remains unknown. Database analyses revealed a reduced C3G mRNA expression in GBM patient samples. C3G protein levels were also decreased in a panel of human GBM cell lines as compared to astrocytes. Based on this, we characterized C3G function in GBM using in vitro and in vivo human GBM models. We report here that C3G downregulation promoted the acquisition of a more mesenchymal phenotype that enhanced the migratory and invasive capacity of GBM cells. This facilitates foci formation in anchorage-dependent and -independent growth assays and the generation of larger tumors in xenografts and chick chorioallantoic membrane (CAM) assays, but with a lower cell density, as proliferation was reduced. Mechanistically, C3G knock-down impairs EGFR signaling by reducing cell surface EGFR through recycling inhibition, while upregulating the activation of several other receptor tyrosine kinases (RTKs) that might promote invasion. In particular, FGF2, likely acting through FGFR1, promoted invasion of C3G-silenced GBM cells. Moreover, ERKs mediate this invasiveness, both in response to FGF2- and serum-induced chemoattraction. In conclusion, our data show the distinct dependency of GBM tumors on C3G for EGF/EGFR signaling versus other RTKs, suggesting that assessing C3G levels may discriminate GBM patient responders to different RTK inhibition protocols. Hence, patients with a low C3G expression might not respond to EGFR inhibitors.This work was supported by grants from the Spanish Ministry of Economy and Competitiveness [SAF2016-76588-C2-1-R and PID2019-104143RB-C22 to AP; and SAF2016-76588-C2-2-R and PID2019-104143RB-C21 to CG], and by two grants from the Council of Education of Junta de Castilla y León, Spain [SA017U16 and SA078P20 to CG]. All funding was cosponsored by the European FEDER Program. SM and OH are recipients of FPU fellowships from Spanish Ministry of Education. CS was supported by a fellowship from Complutense University from Madrid. A G-U and MRF are supported by Madrid Community Program for Talent Attraction (MRF 2017-T1/BMD-5468). P. B. received support from BBVA (Becas Leonardo 2018, BBM-TRA-0041)