Tiam1 mediates Rac1 activation and contraction‐induced glucose uptake in skeletal muscle cells

Contraction‐stimulated glucose uptake in skeletal muscle requires Rac1, but the molecular mechanism of its activation is not fully understood. Treadmill running was applied to induce C57BL/6 mouse hind limb skeletal muscle contraction in vivo and electrical pulse stimulation contracted C2C12 myotube cultures in vitro. The protein levels or activities of AMPK or the Rac1‐specific GEF, Tiam1, were manipulated by activators, inhibitors, siRNA‐mediated knockdown, and adenovirus‐mediated expression. Activated Rac1 was detected by a pull‐down assay and immunoblotting. Glucose uptake was measured using the 2‐NBD‐glucose fluorescent analog. Electrical pulse stimulated contraction or treadmill exercise upregulated the expression of Tiam1 in skeletal muscle in an AMPK‐dependent manner. Axin1 siRNA‐mediated knockdown diminished AMPK activation and upregulation of Tiam1 protein expression by contraction. Tiam1 siRNA‐mediated knockdown diminished contraction‐induced Rac1 activation, GLUT4 translocation, and glucose uptake. Contraction increased Tiam1 gene expression and serine phosphorylation of Tiam1 protein via AMPK. These findings suggest Tiam1 is part of an AMPK‐Tiam1‐Rac1 signaling pathway that mediates contraction‐stimulated glucose uptake in skeletal muscle cells and tissue.