NaBC1 Boron Transporter Enables Myoblast Response to Substrate Rigidity via Fibronectin-Binding Integrins

Cells are sensitive to the physical properties of their microenvironment and transduce them into biochemical cues that trigger gene expression and alter cell behavior. Numerous proteins, including integrins, are involved in these mechanotransductive events. Here, a novel role for the boron transporter NaBC1 is identified as a mechanotransducer. It is demonstrated that soluble boron ions activate NaBC1 to enhance cell adhesion and intracellular tension in C2C12 myoblasts seeded on fibronectin-functionalized polyacrylamide (PAAm) hydrogels. Retrograde actin flow and traction forces exerted by these cells are significantly increased in vitro in response to both increased boron concentration and hydrogel stiffness. These effects are fibronectin and NaBC1-mediated as they are abrogated in hydrogels coated with laminin-111 in place of fibronectin and in esiRNA NaBC1-silenced cells. These findings thus demonstrate that NaBC1 controls boron homeostasis and also functions as a mechanosensor.