Modulation of K_v1.3 channels by protein kinase A I in T lymphocytes is mediated by the disc large 1-tyrosine kinase Lck complex

The cAMP/PKA signaling system constitutes an inhibitory pathway in T cells and, although its biochemistry has been thoroughly investigated, its possible effects on ion channels are still not fully understood. K_v1.3 channels play an important role in T-cell activation, and their inhibition suppresses T-cell function. It has been reported that PKA modulates K_v1.3 activity. Two PKA isoforms are expressed in human T cells: PKAI and PKAII. PKAI has been shown to inhibit T-cell activation via suppression of the tyrosine kinase Lck. The aim of this study was to determine the PKA isoform modulating K_v1.3 and the signaling pathway underneath. 8-Bromoadenosine 3′,5′-cyclic monophosphate (8-BrcAMP), a nonselective activator of PKA, inhibited K_v1.3 currents both in primary human T and in Jurkat cells. This inhibition was prevented by the PKA blocker PKI₆-22. Selective knockdown of PKAI, but not PKAII, with siRNAs abolished the response to 8-BrcAMP. Additional studies were performed to determine the signaling pathway mediating PKAI effect on K_v1.3. Overexpression of a constitutively active mutant of Lck reduced the response of K_v1.3 to 8-Br-cAMP. Moreover, knockdown of the scaffolding protein disc large 1 (Dlg1), which binds K_v1.3 to Lck, abolished PKA modulation of K_v1.3 channels. Immunohistochemistry studies showed that PKAI, but not PKAII, colocalizes with K_v1.3 and Dlg1 indicating a close proximity between these proteins. These results indicate that PKAI selectively regulates K_v1.3 channels in human T lymphocytes. This effect is mediated by Lck and Dlg1. We thus propose that the K_v1.3/Dlg1/Lck complex is part of the membrane pathway that cAMP utilizes to regulate T-cell function.