β-integrin controls IGF-1R internalization and intracellular signaling.

Cell adhesion-dependent phosphorylation of insulin-like growth factor 1 receptor (IGF-1R) on its C-terminal tail (CT) at Tyr promotes receptor internalization and Golgi accumulation. We previously proposed that this phosphorylation is associated with cell migration and cancer aggressiveness, distinguishing IGF-1R activity from that of insulin receptor, which lacks these tyrosines. Here, we further investigated how adhesion signaling influences IGF-1R location and activity in migratory cancer cells and R- fibroblasts. We observed that IGF-1R, in triple-negative breast cancer tissues, is predominantly intracellular and dispersed from the plasma membrane compared with nontumor tissue. Datasets from basal-like breast cancer patients indicated a strong, positive correlation between IGF-1R protein expression and that of β-integrin (ITGB1). In triple-negative breast cancer cells with high ITGB1 expression, suppressing ITGB1 enhanced IGF-1R stability and its retention at the plasma membrane, and reduced IGF-1R internalization during cell adhesion. In R- fibroblasts, we observed reduced IGF-1R autophosphorylation and Golgi accumulation when ITGB1 was suppressed. The stability of a TyrPhe (FF) IGF-1R mutant was less affected by ITGB1 suppression, indicating that Tyr phosphorylation is required for ITGB1-enhanced receptor internalization. Furthermore, a TyrGlu (EE) IGF-1R mutant exhibited a gain of cell migration and colony formation potential compared to WT IGF-1R or FF mutant. Tyr resides within the CT SFYYS motif, which engages the IGF-1R kinase domain. In silico, we investigated how mutation of these tyrosines may alter SFYYS conformation, dictating trajectory of the distal CT. We conclude that Tyr phosphorylation confers IGF-1R with unique protumorigenic signaling in a manner that is enhanced by ITGB1.