The association of type 1, type 2A and type 2B phosphatases with the human T lymphocyte plasma membrane.
Several putative plasma-membrane-associated components of the T-lymphocyte signal-transduction pathway are phosphorylated during the initial events of cellular activation. Little is known about the control of dephosphorylation of these components. We have shown by immunoblotting that the type 1 phosphatase, the type 2A phosphatase and type 2B phosphatase (calcineurin) are associated with the plasma membrane of normal human T lymphoblasts and the human T leukaemic cell line Jurkat 6. The type 1 phosphorylase phosphatase activity is present in a latent form which can be stimulated synergistically by deinhibitor and p-nitrophenyl phosphate. The PCSH form of the type 2A phosphatase appears to be the predominant oligomer in the plasma-membrane fraction. All three phosphatases can be extracted from membranes with Nonidet P40, but whereas the type 1c and type 2Ac phosphatases separate into the detergent-poor phase of Triton X-114, calcineurin separates into both detergent-rich and -poor phases. It is probable that one or more of these three plasma-membrane-associated phosphatases play regulatory roles in determining the phosphorylation state of membrane-bound proteins involved in human T-cell activation.
Alexander
D R
DR
Imperial Cancer Research Fund, London, U.K.
Hexham
J M
JM
Crumpton
M J
MJ
D019703:Calcineurin; D002148:Calmodulin-Binding Proteins / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology; D006801:Humans; D015151:Immunoblotting; D010748:Phosphopeptides / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010765:Phosphorylase Phosphatase / Q000378:metabolism; D013601:T-Lymphocytes / Q000201:enzymology* / Q000648:ultrastructure
D002148:Calmodulin-Binding Proteins; D010748:Phosphopeptides; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D010765:Phosphorylase Phosphatase