Analysis of signal transduction of insulin with special reference to protein kinase FA

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Protein kinase FA(PKFA) is a serine/threonine kinase, which was originally discovered as the factor necessary to convert inactive phoshatase 1 to active form. Binding of insulin to its receptor stimulates the tyrosine kinase activity of the insulin receptor and leads to increased serine/threonine phosphorylation of many cellular proteins and decreased phosphorylation of other proteins. In order to clarify the mechanism of signal transduction of insulin, I studied PKFA, expecting that PKFA is a key enzyme which connects the activation of tyrosine kinase with increased serine/threonine phosphorylation and dephosphorylation of proteins in the cells stimulated by insulin. First, I tried to establish an assay system for PKFA activity and then, examined activation of PKFA and translocation of the enzyme from the plasma membrane to the cytosol after stimulation by insulin. However, I could not observe activation of the enzyme nor translocation of the enzyme in all systems that I examined. Thu … More s, I changed the target from PKFA to mitogen activated protein (MAP) kinase which is converted to active from by phosphorylation of tyrosine and threonine, and studied the mechanism of signal transduction leading to the activation of MAP kinase in Swiss 3T3 cells.Treatment of quiescent Swiss 3T3 cells with EGF resulted in the increase in the protein kinase activity that phosphorylated myelin basic protein, making a peak 2.5 min after the treatment. This kinase activity was identified as MAP kinase by FPLC Mono Q column chromatography. The increase in MAP kinase activity was also observed with phorbolester, thrombin, and bradykinin, and the increase in the kinase activity correlated well with the induction of DNA synthesis. I examined the mechanism of signal transduction from treatment of thrombin to the activation of MAP kinase in detail and confirmed the involvement of GTP binding protein, PI-3 kinase, and C kinase in the pathway to the activation of MAP kinase, In addition, the phosphorylation of DNA topoisomerase II was studied as one of final target of phosphorylation cascade. Less