A novel pro-oncogenic mutated form of VEGFR2 modulates the activity of co-expressed wild-type receptor in melanoma

Melanoma is an aggressive cancer which partially responds to existing therapies. Recent evidences showed that the tyrosine kinase receptor (RTK) VEGFR2 is expressed in melanoma cells, it regulates cell proliferation and it is often mutated. In this study, we identified a new mutation of VEGFR2, namely R1051Q, which occurs with low frequency in cancer patients. Notably, R-Q substitution in position 255 of the tyrosine kinase domain (corresponding to residue 1051 in VEGFR2) is conserved in other RTKs, including FGFR1, FGFR3, FGFR4, PDGFRB, FLT4 and TIE1, in cancer samples, suggesting that mutation of this residue in RTKs may have a pro-tumoral activity. Functional characterization demonstrated that VEGFR2R1051Q is active also in the absence of VEGF ligand and, as a consequence, it has a reduced membrane lateral diffusion when compared to VEGFR2WT, similarly to the mobility of VEGF-activated wild-type receptor. When co-expressed with endogenous VEGFR2WT to mimic heterozygosity, mutated VEGFR2R1051Q increases the prooncogenic capacity of melanoma SK-MEL-31 cells. The expression of VEGFR2R1015Q upregulates the phosphorylation levels of proteins of the Akt/mTOR pathway, a master regulator of cell metabolism. In keeping, SK-MEL-31 cells expressing VEGFR2R1051Q show a higher metabolic activity when compared to cells expressing VEGFR2WT, which also reflects in a higher rate of ATP production. FLIM/FRET experiments showed that mutated VEGFR2R1051Q hetero-dimerizes with VEGFR2WT with a higher FRET efficiency than the one observed for homodimeric-VEGFR2WT. When coexpressed, mutated VEGFR2 slows down the membrane mobility (and supposedly modify the behavior/activity) of wild-type receptor. Our results point to the possibility that mutated VEGFR2 may be capable of boosting the activation of co-expressed wild-type VEGFR2 eventually resulting in faster tumor growth. Here we demonstrate that mutated VEGFR2 increases the oncogenic capacity of melanoma cells in vitro an in vivo by modulating the activity of co-expressed (heterozygosity) wild-type VEGFR2. Our study suggests that screening for somatic VEGFR2 mutations could help to predict interindividual differences in terms of tumor growth and response to therapy.