NaBC1 Acts as a Mechanosensitive Co-regulator of Fibronectin-binding Integrins Adhesion and Myoblast Polarization

Cell adhesion and polarization are fundamental processes in tissue organization and mechanosensitive signaling. Here, we demonstrate that activation of the borate transporter NaBC1 enhances myoblast adhesion and polarization by modulating integrin expression and actin cytoskeleton dynamics. Using C2C12 myoblasts cultured on fibronectin-functionalized substrates, we show that NaBC1 stimulation induces the formation of more and larger focal adhesions, promotes early cell spreading, and reduces retrograde actin flow, indicative of molecular clutch engagement. This enhanced adhesive state is accompanied by the transcriptional and protein-level upregulation of fibronectin-binding integrins (α ₅ β ₁ , α _v β ₃ ), and by their spatial colocalization with NaBC1 at the cell membrane. Furthermore, FITC-labelled boron accumulates in focal adhesions and intracellular compartments such as mitochondria, lysosomes, and the ER, suggesting a role for boron in both adhesion and subcellular signaling. These effects are fibronectin-specific and are abrogated in cells exposed to mutant fibronectins and laminin-111 (unable to activate the molecular clutch). Altogether, our results identify the boron transporter NaBC1 as a modulator of myoblast adhesion and mechanotransduction acting in close cooperation with fibronectin-binding integrins.