Activation of CD38 by interleukin-8 signaling regulates intracellular Ca²⁺ level and motility of lymphokine-activated killer cells

CD38 is an ADP-ribosyl cyclase, producing a potent Ca²⁺ mobilizer cyclic ADP-ribose (cADPR). In this study, we have investigated a role of CD38 and its regulation through interleukin-8 (IL8) signaling in lymphokine-activated killer (LAK) cells. Incubation of LAK cells with IL8 resulted in an increase of cellular cADPR level and a rapid rise of intracellular Ca²⁺ concentration ([Ca²⁺]_i), which was sustained for a long period of time (>10 min). Preincubation of an antagonistic cADPR analog, 8-Br-cADPR (8-bromo-cyclic adenosine diphosphate ribose), abolished the sustained Ca²⁺ signal only but not the initial Ca²⁺ rise. An inositol 1,4,5-trisphosphate (IP₃) receptor antagonist blocked both Ca²⁺ signals. Interestingly, the sustained Ca²⁺ rise was not observed in the absence of extracellular Ca ²⁺. Functional CD38-null (CD38^-) LAK cells showed the initial rapid increase of [Ca²⁺]_i but not the sustained Ca²⁺ rise in response to IL8 treatment. An increase of cellular cADPR level by cGMP analog, 8-pCPT-cGMP (8-(4-chlorophenylthio)-guanosine-3′, 5′-cyclic monophosphate), but not cAMP analog or phorbol 12-myristate 13-acetate was observed. IL8 treatment resulted in the increase of cGMP level that was inhibited by the IP₃ receptor blocker but not a protein kinase C inhibitor. cGMP-mediated Ca²⁺ rise was blocked by 8-Br-cADPR. In addition, IL8-mediated LAK cell migration was inhibited by 8-Br-cADPR and a protein kinase G inhibitor. Consistent with these observations, IL8-induced migration of CD38^- LAK cells was not observed. However, direct application of cADPR or 8-pCPT-cGMP stimulated migration of CB38 ^- cells. These results demonstrate that CD38 is stimulated by sequential activation of IL8 receptor, IP₃-mediated Ca²⁺ rise, and cGMP/protein kinase G and that CD38 plays an essential role in IL8-induced migration of LAK cells.