Early steps of insulin action in the skin of intact rats

Insulin is an important regulator of growth and initiates its action by bin ding to its receptor, which undergoes tyrosyl autophosphorylation and furth er enhances its tyrosine kinase activity towards other intermediate molecul es, including insulin receptor substrate 1, insulin receptor substrate 2, a nd Shc. Insulin receptor substrate proteins can dock various src-homology-2 -domain-containing signaling proteins, such as the 85 kDa subunit of phosph atidylinositol 3 kinase and growth-factor-receptor-bound protein 2. The ser ine-threonine kinase is activated downstream to phosphatidylinositol 3 kina se. Shc protein has been shown to directly induce the association with grow th-factor-receptor-bound protein 2 and downstream the activation of the mit ogen-activated protein kinase. In this study we investigated insulin signal transduction pathways in skin of intact rats by immunoprecipitation and im munoblotting with specific antibodies, and also by immunohistochemistry wit h anti-insulin-receptor antibody. Our results showed that skin fragments cl early demonstrated the presence of insulin receptor in cell bodies of the e pidermis and hair follicles and some faint staining was also detected in fi broblasts of the dermis. It was also observed that acute stimulation with i nsulin can induce tyrosyl phosphorylation of insulin receptor, that the ins ulin receptor substrates and Shc proteins serve as signaling molecules for insulin in skin of rats, and that insulin is able to induce association of insulin receptor substrate 1/phosphatidylinositol 3 kinase and Shc/growth-f actor-receptor-bound protein 2 in this tissue, as well as phosphorylation o f mitogen-activated protein kinase and serine-threonine kinase, demonstrati ng that proteins involved in early steps of insulin action are expressed in skin of intact rats and are quickly activated after insulin stimulation.