INHIBITION OF PHOSPHATIDYLINOSITOL 3-KINASE BLOCKS T-CELL ANTIGEN RECEPTOR CD3-INDUCED ACTIVATION OF THE MITOGEN-ACTIVATED KINASE ERK2

The production of 3-phosphorylated inositol phospholipids is implicate d in regulation of cell growth and transformation. To explore the role of these lipids in T cell antigen receptor (TCR)/CD3-induced signalin g, we have examined the effects of a specific phosphatidylinesitol 3-k inase (PtdIns3K) inhibitor, wortmannin, and overexpression of two PtdI ns3K constructs on the activation of down-stream effecters in anti-CD3 treated T cells. We report that treatment of cells with wortmannin bl ocked anti-CD3-induced activation of the mitogen-activated kinase Erk2 while not affecting phorbol-ester-induced Erk2 activation. An inactiv e analog of wortmannin, WM12, did not affect TCR/CD3-induced Erk2 acti vation, and wortmannin had no effect on the activity of Erk2 when adde d directly to the in vitro assays. Expression of a disruptive PtdIns3K construct also reduced Erk2 activation, while a construct that stimul ates PtdIns3K enhanced the activation of Erk2. Receptor-induced activa tion of other Ser/Thr kinases, such as c-Raf, B-Raf, Mek1, Mek2, Mekk, was not affected by wortmannin. Our results suggest that the producti on of 3-phosphorylated inositol phospholipids is involved in the activ ation of Erk2, but does not regulate the enzymes that are thought to b e upstream of Erk2.