Effect of 1,25(OH)2-vitamin D3 on the activation of natural killer cells:: Role of protein kinase C and extracellular calcium

As a first approach for studying the implication of PKC and the steroid hormone 1,25(OH)(2)-vitamin D-3 [1,25(OH)(2)D-3] on natural killer cell (NK) activity, we analyzed in the YT NK cell lime the expression of PKC isoforms and the effects of 1,25(OH)(2)D-3 on BLT-esterase (a marker of NK lytic granules) activity. Western blot and RT-PCR showed a greater extent of PKC alpha, beta, delta, zeta, epsilon, theta, and lambda and lower levels of PKC mu and eta. In a dose-dependent manner 1,25(OH)(2)D-3 induced significant increases in BLT-esterase and PKC activities and the stimulatory effect on BLT-esterase activity was mimicked and blocked, respectively, by the PKC activator phorbol ester PMA and PKC inhibitors (H7, PKC19-36, and N-myristoylated PKC19-31 peptides). Moreover, the effects of 1,25(OH)(2)D-3 on BLT-esterase could be blocked in a Ca2+-free (+EGTA) medium and mimicked by the Ca2+ ionophore A23187. The results suggest that 1,25(OH)(2)D-3 is a stimulatory factor of NK activity acting through a mechanism involving PKC and extracellular Ca2+. (C) 1999 Academic Press.