Requirement of Gαi1/3-Gab1 signaling complex for keratinocyte growth factor-induced PI3K-AKT-mTORC1 activation.

Keratinocyte growth factor (KGF), also termed as fibroblast growth factor-7, promotes proliferation, migration, and adhesion of skin keratinocytes via binding to keratinocyte growth factor receptor (KGFR) and subsequent activation of downstream signaling including the PI3K-AKT-mTORC1 pathway. Here, we found that the α-subunits of the G proteins (Gαi1/3) and growth factor receptor binding 2-associated binding protein 1 (Gab1) are required for this activation process. With KGF stimulation, Gαi1/3 formed a complex with KGFR and was required for subsequent Gab1 recruitment, phosphorylation, and following PI3K-p85 activation. In addition, Gαi1/3 short hairpin RNA knockdown largely inhibited KGF-induced cell proliferation, migration, and the accumulation of cyclin D1/fibronectin in cultured skin keratinocytes. Furthermore, we observed increased expression of Gαi1/3 in wounded human skin and keloid skin tissues, suggesting the possible involvement of Gαi1/3 in wound healing and keloid formation. Overall, we suggest that Gαi1/3 proteins lie downstream of KGFR, but upstream of Gab1-mediated activation of PI3K-AKT-mTORC1 signaling, thus revealing a role for Gαi proteins in mediating KGFR signaling, cell migration, and possible wound healing.