8.A.87 The TBC1 Domain (TBC1) Family
The 160 kDa protein (designated AS160, for Akt substrate of 160 kDa) with a predicted Rab GAP (GTPase-activating protein) domain is phosphorylated on multiple sites by the protein kinase, Akt. Phosphorylation of AS160 in adipocytes is required for insulin-stimulated translocation of the glucose transporter GLUT4 from an intracellular site to the plasma membrane (Mîinea et al. 2005). Several Isoforms promote insulin-induced glucose transporter SLC2A4/GLUT4 translocation to the plasma membrane, thus increasing glucose uptake (Baus et al. 2008; Chen et al. 2012).
AS160 is a crucial mediator of insulin-stimulated glucose transport, and skeletal muscle is the major tissue for insulin-mediated glucose disposal. Insulin increases muscle membrane localization of AKT2, but not AKT1; insulin increased AKT2 phosphorylation in the cytosol and membrane fractions. Insulin also increased AS160 localization to the cytosol and membranes but it increased AS160 phosphorylation only in the cytosol, not in the membranes (Zheng and Cartee 2016).