Abstract
Background: Cytoskeletal reorganization is important for a wide variety of insulin‐mediated biological actions, including cell growth, migration and metabolism, but the intracellular signalling pathways leading to insulin‐induced cytoskeletal reorganization have largely been unknown. We therefore investigated the involvement of Grb2/Ash‐Ras and phosphatidylinositol (PI) 3‐kinase in the insulin‐induced morphological changes in fibroblasts over‐expressing human insulin receptors (HIRcB cells).
Results: I nsulin, as well as 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) and 8‐bromo‐cAMP, induced a unique morphological change associated with actin cytoskeletal reorganization characterized by the disruption of actin stress fibres and thicker actin bundle formation. Microinjection of an anti‐Grb2/Ash antibody, but not control IgG, inhibited the insulin‐induced actin reorganization, whereas the TPA‐ and 8‐bromo‐cAMP‐induced morphological changes were not inhibited by microinjection of the anti‐Grb2/Ash antibody. In addition, microinjection of dominant negative ras p21 protein, but not the heat‐treated protein, inhibited insulin‐induced cytoskeletal reorganization. Microinjection of activated p21^ras^ protein resulted in very similar cytoskeletal reorganization with actin bundle formation in the cytoplasm. The PI3‐kinase inhibitor wortmannin inhibited insulin‐induced cytoskeletal reorganization, but not the TPA‐ nor 8‐bromo‐cAMP‐induced reorganization. Interestingly, wortmannin also inhibited the activated p21^ras^‐induced morphological change.
Conclusions: We concluded that Grb2/Ash‐Ras activation and probably Ras‐associated PI3‐kinase activation are involved in the insulin‐induced morphological change.