High-fat feeding cascade effects on components of the CAP/Cbl signaling in Sprague-Dawley rat skeletal muscle

The aim of this investigation was to determine whether the CAP (Cbl-associated protein)/Cb1 signaling cascade is present and responsive to insulin in skeletal muscle and if high-fat feeding impairs insulin-stimulated activation of this signaling cascade. Sprague-Dawley rats were assigned to either control (n = 16) or high fat-fed (n = 16) dietary groups. After a 12-week dietary period, animals were subjected to hind limb perfusions in the presence (n = 8 per group) or absence (n = 8 per group) of insulin. High-fat feeding reduced rates of insulin-stimulated skeletal muscle phosphatidylinositol 3-kinase activity and 3-O-methylglucose transport. In plasma membrane fractions, neither the high-fat diet nor insulin altered the insulin receptor P subunit (IR-beta), APS (adaptor protein containing PH and SH2 domains), c-Cb1, or TC10 protein concentration, but high-fat feeding did decrease CAP protein concentration. APS, c-Cbl, CAP, and TC10 messenger RNA were present in the skeletal muscle and reflected the protein concentration of experimental groups. Despite insulin-stimulated plasma membrane IR-beta tyrosine phosphorylation being unaffected by high-fat feeding, c-Cb1 tyrosine phosphorylation, the kinase activity of IR-fl toward APS, and glucose transporter 4 protein concentration were all significantly reduced in insulin-stimulated plasma membrane prepared from the skeletal muscle of high fat fed animals. These findings suggest that the CAP/Cb1 signaling cascade is present in skeletal muscle, activated by insulin, and impaired by high-fat feeding. (c) 2006 Elsevier Inc. All rights reserved.