EVIDENCE FOR PROTEIN-TYROSINE KINASE INVOLVEMENT IN CD6-INDUCED T-CELL PROLIFERATION

Several studies have demonstrated that addition of soluble anti-CD6 mA bs to 12-O-tetradecanoyIphorbol 13-acetate (TPA)-treated naive T cells can induce cell proliferation, We showed in the present study that ce ll proliferation in TPA-treated T cell cultures can be enhanced severa l fold when the anti-CD6 mAbs are either immobilized or crosslinked wi th rabbit anti-mouse immunoglobulins (RAM Ig), Using a src family prot ein tyrosine kinase (PTK) inhibitor, herbimycin A, the cell proliferat ion induced by the anti-CD6 mAb, IOR-T1, in TPA-treated T cells were e ffectively abolished, Analysis of the cellular proteins in these cells after crosslinking the CD6 receptor with IOR-T1 (followed by RAM Ig) in the presence of TPA resulted in an increased level of tyrosine phos phorylation. Pretreatment of naive T cells with herbimycin A (0.5 and 1 mu g/ml) for 18 hr completely inhibited the tyrosine phosphorylation on cellular substrates in T cell cultures stimulated with IOR-T1/RAM Ig and TPA. Similar concentrations of herbimycin A also inhibited the increase in IL-2 mRNA expression and cell proliferation in T cell cult ures after IOR-T1/RAM Ig and TPA treatment. Furthermore, the increase in cytosolic free Ca2(+) concentration in naive T cells after crosslin king of the CD6 receptor with IOR-T1/RAM Ig was also inhibited by herb imycin A. Taken together, our results suggest that CD6-mediated T cell proliferation is IL-2 dependent, and involves tyrosine kinase activit y which is strictly dependent on protein kinase C activation. (C) 1995 Academic Press, Inc.