PHORBOL ESTER TREATMENT INHIBITS PHOSPHATIDYLINOSITOL 3-KINASE ACTIVATION BY, AND ASSOCIATION WITH, CD28, A T-LYMPHOCYTE SURFACE-RECEPTOR

CD28 is a costimulatory receptor found on the surface of most T lympho cytes. Engagement of CD28 induces interleukin 2 (IL-2) production and cell proliferation when combined with an additional signal such as tre atment with phorbol ester, an activator of protein kinase C, Recent st udies have established that after CD28 ligation, the cytoplasmic domai n of CD28 can bind to the 85-kDa subunit of phosphatidylinositol 3-kin ase (PI3 kinase), There is a concomitant increase in PI3 lipid kinase activity that may be important in CD28 signaling, Despite the requirem ent of phorbol 12-myristate 13-acetate (PMA) for effector function, we have found, however, that treatment of Jurkat T cells with the phorbo l ester PMA dramatically inhibits (i) the association of PI3 kinase wi th CD28, (ii) the ability of p85 PI3 kinase to be immunoprecipitated b y anti-phosphotyrosine antibodies, and (iii) the induction of PI3 kina se activity after stimulation of the cells with the anti-CD28 monoclon al antibody 9.3, These changes occur within minutes of PMA treatment a nd are persistent, In addition, we have found that wortmannin, a poten t inhibitor of PI3 kinase, does not interfere with the induction of IL -2 after stimulation of Jurkat T cells with anti-CD28 monoclonal antib ody and PMA, We conclude that PI3 kinase activity may not be required for CD28-dependent IL-2 production from Jurkat T cells in the presence of PMA.