β3 integrin-mediated spreading induced by matrix-bound BMP-2 controls Smad signaling in a stiffness-independent manner

Understanding how cells integrate multiple signaling pathways to achieve specific cell differentiation is a challenging question in cell biology. We have explored the physiological presentation of BMP-2 by using a biomaterial that harbors tunable mechanical properties to promote localized BMP-2 signaling. We show that matrix-bound BMP-2 is sufficient to induce beta 3 integrin-dependent C2C12 cell spreading by overriding the soft signal of the biomaterial and impacting actin organization and adhesion site dynamics. In turn, alpha v beta 3 integrin is required to mediate BMP-2 induced Smad signaling through a Cdc42-Src-FAK-ILK pathway. beta 3 integrin regulates a multistep process to control first BMP-2 receptor activity and second the inhibitory role of GSK3 on Smad signaling. Overall, our results show that BMP receptors and beta 3 integrin work together to control Smad signaling and tensional homeostasis, thereby coupling cell adhesion and fate commitment, two fundamental aspects of developmental biology and regenerative medicine.