Selective Activation of cAMP-dependent Protein Kinase Type I Inhibits Rat Natural Killer Cell Cytotoxicity

Abstract

The present study examines the expression and involvement of cAMP-dependent protein kinase (PKA) isozymes in cAMP-induced inhibition of natural killer (NK) cell-mediated cytotoxicity. Rat interleukin-2-activated NK cells express the PKA ␣-isoforms RI␣, RII␣, and C␣ and contain both PKA type I and type II. Prostaglandin E 2 , forskolin, and cAMP analogs all inhibit NK cell lysis of major histocompatibility complex class I mismatched allogeneic lymphocytes as well as of standard tumor target cells. Specific involvement of PKA in the cAMP-induced inhibition of NK cell cytotoxicity is demonstrated by the ability of a cAMP antagonist, (R p )-8-Br-adenosine 3 ,5 -cyclic monophosphorothioate, to reverse the inhibitory effect of complementary cAMP agonist (S p )-8-Br-adenosine 3 ,5 -cyclic monophosphorothioate. Furthermore, the use of cAMP analog pairs selective for either PKA isozyme (PKA type I or PKA type II), shows a preferential involvement of the PKA type I isozyme, indicating that PKA type I is necessary and sufficient to completely abolish killer activatory signaling leading to NK cell cytotoxicity. Finally, combined treatment with phorbol ester and ionomycin maintains NK cell cytotoxicity and eliminates the cAMP-mediated inhibition, demonstrating that protein kinase C and Ca 2؉ -dependent events stimulate the cytolytic activity of NK cells at a site distal to the site of cAMP/PKA action.Natural killer (NK) 1 cells constitute a distinct lineage of lymphocytes (1) with the innate ability to specifically recognize and kill certain normal allogeneic leukocytes (2, 3), tumor cells, and virally infected cells (4, 5) by direct cell-mediated cytotoxicity. The presence of both activating and inhibitory NK cell receptors have been implicated in regulation of NK cytolysis. As formulated in the "missing self" hypothesis (6), a no-kill signal is induced by specific interaction of "self" MHC class I molecules with inhibitory NK receptors. Therefore, the presence of intracellular signaling pathways down-regulating or inhibiting the cytotoxic response may be important in preventing killing of normal autologous cells. In contrast to the "self" MHC class I-induced inhibition of natural killing, activating receptors have not been characterized to the same extent. However, both foreign MHC antigens on normal allogeneic cells and non-MHC antigens expressed on tumor cells have been demonstrated to interact with yet not fully characterized activating NK cell receptors (7-10). The present view is that NK cytotoxicity is a result of a fine balance between negative and positive signals induced through distinct sets of receptors inhibiting or activating the cytolytic activity (11).The second messenger cAMP regulates a number of cellular processes (12, 13). With the exception of certain ion channels, directly regulated by cAMP (14, 15), all known effects of cAMP are mediated via activation of cAMP-dependent protein kinase (PKA). The inactive PKA holoenzyme is a tetramer consisting of two regulatory (R) and two catalytic (C) subunits (16)....

Method of transfection affects the cAMP-mediated induction of the RIIbeta subunit of protein kinase A in Sertoli cells: inhibition of response by increase in intracellullar calcium

“…3). Half-maximal induction was obtained with 20-30 mmol/l 8-CPTcAMP and maximal induction was obtained at approximately 100 mmol/l which is in agreement with that observed for other cAMP-regulated processes both in Sertoli cells as well as other cell systems (25)(26)(27).…”

Perioperative Use of β-blockers and COX-2 Inhibitors May Improve Immune Competence and Reduce the Risk of Tumor Metastasis

“…This synergism may be attributed to the fact that both CAs and PGs can independently suppress NKCA by activating their respective membrane receptors on NK cells, [27][28][29][30][31] causing intracellular elevation of cAMP levels. 28,32,33 Thus, when both CAs and PGs are in excess, only their simultaneous blockade can prevent NK suppression through this mechanism.…”

Adenosine-Mediated Inhibition of the Cytotoxic Activity and Cytokine Production by Activated Natural Killer Cells

“…Abnormally high levels of RIIh expression are found in T cells of patients with systemic lupus erythematosus, and RIIh directly interacts and suppresses CREB transcriptional activity in activated T cells (20). Activation of PKA I by specific cAMP-elevated agents (S p -8-Br) inhibits the cytotoxic activity of rat NK cells (37).…”