PROTEIN-KINASE A-MEDIATED PHOSPHORYLATION OF THE T-CELL SURFACE-ANTIGEN CD27

CD27 is a T-cell surface antigen expressed on the majority of peripher al T cells and belongs to a newly defined receptor family including th e low-affinity nerve growth factor receptor, tumour necrosis factor (T NF) receptors, the B-cell activation antigen CD40, and the Fas antigen . Although the function of CD27 has not been defined, several experime ntal observations support the notion that this molecule plays an impor tant role in the process of T-cell activation. In this paper, we have demonstrated that a rapid hyperphosphorylation of CD27 is induced by a cyclic AMP-inducing agent, forskolin, and a membrane-permeable cAMP a nalogue, 8-bromo-cAMP, as well as phorbol 12-myristate 13-acetate (PMA ). In addition, increased phosphorylation of CD27 in T-cell activation either via CD2 or CD3 pathways was strongly suppressed by a cyclic nu cleotide-dependent kinase inhibitor, H-8, but only slightly by a prote in kinase C inhibitor, staurosporine. These results suggest that prote in kinase A might be a key kinase responsible for CD27 phosphorylation in the process of T-cell activation. CD27 is the first T-cell surface antigen demonstrated to be phosphorylated by the cyclic AMP-protein k inase A-mediated pathway.