Activators of protein kinase C up-regulate the cell surface expression of CD2 and CD5 T cell glycoproteins.

Activation of human T cells through the CD3-T cell receptor complex caused an augmentation in the cell surface expression of CD2 and CD5 glycoproteins. Evidence that protein kinase C is involved in the up-regulatory mechanism of these cell surface molecules has been obtained by three different approaches: (a) the changes in antigen expression were observed with activators of protein kinase C such as phorbol esters but not with activators of kinases dependent on calcium/calmodulin or cAMP; (b) the overexpression of CD2 and CD5 is also observed in cells treated with 1,2-dioctanoyl-rac-glycerol, an analogue of the physiological activator of protein kinase C; and (c) 1-(5-isoquinolinyl)-2-methylpiperazine, an inhibitor of protein kinase C but not N-(2-guanidinoethyl)-5-isoquinolinesulfonamide dihydrochloride, an inhibitor of the cAMP-dependent kinase, impairs CD2 and CD5 up-regulation. These changes in cell surface antigen expression appear to be caused by the concomitant increase in the mRNA levels for CD2 and CD5. Phosphorylation studies of the CD2 and CD5 glycoproteins indicated that the overexpression of these molecules was not associated with a specific pattern of phosphorylation since it was observed independently of their hyperphosphorylated or nonphosphorylated state.