SIGNAL TRANSDUCTION BY PROTEIN PHOSPHORYLATION

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We propose to continue our studies on the structure and function of two types of protein-phosphatases involved in the regulation of cellular processes in relation to hormone action or other types of intracellular signalling. Specifically, we are interested in: 1) The mechanism of regulation of phosphorylase phosphatase by Mn2+ ions and phosphorylation of its regulatory subunit (inhibitor-2) known to bring about changes in conformation in the catalytic subunit. 2) The possible involvement of this enzyme in the control of carbohydrate metabolisms in 3T3 cells in response to hormones or growth factors. While insulin and EGF trigger changes in the activity of enzymes directly involved in the synthesis or breakdown of glycogen, the chain of events by which this is brought about is not known. The possibility that the hormones cause the activation of specific protein kinases that act on different phosphorylation sites that may interact with one another will be further investigated. 3) Our main effort will be directed toward the structure and regulation of particulate and cytosolic protein tyrosine phosphatases that have been purified to homogeneity from human placenta. While both enzyme species appear structurally identical, something must account for their different localization. Aside from determining their usual structural and enzymatic properties, sequence information will be obtained for oligonucleotide probes (for cloning), and synthesis of peptides for antibody production (for subcellular and tissue distribution). As of now, essentially nothing is known about the regulation of these enzymes. The possibility that it might be exercised by modifying their subcellular localization, or through specific activators and/or inhibitors will be investigated. Attempts will be made to overexpress the phosphatases in appropriate cell types in order to study their responsiveness to growth factors and oncogenes, and determine what effect this might have on cell functions.