RESUMO
Nicotinic acid adenine dinucleotide phosphate (NAADP) is the most potent Ca2+ mobilizing second messenger whose formation has remained elusive. In vitro, CD38-mediated NAADP synthesis requires an acidic pH and a nonphysiological concentration of nicotinic acid (NA). We discovered that CD38 catalyzes synthesis of NAADP by exchanging the nicotinamide moiety of nicotinamide adenine dinucleotide phosphate (NADP+ ) for the NA group of nicotinic acid adenine dinucleotide (NAAD) inside endolysosomes of interleukin 8 (IL8)-treated lymphokine-activated killer (LAK) cells. Upon IL8 stimulation, cytosolic NADP+ is transported to acidified endolysosomes via connexin 43 (Cx43) and gated by cAMP-EPAC-RAP1-PP2A signaling. CD38 then performs a base-exchange reaction with the donor NA group deriving from NAAD, produced by newly described endolysosomal activities of NA phosphoribosyltransferase (NAPRT) and NMN adenyltransferase (NMNAT) 3. Thus, the membrane organization of endolysosomal CD38, a signal-mediated transport system for NADP+ and luminal NAD+ biosynthetic enzymes integrate signals from a chemokine and cAMP to specify the spatiotemporal mobilization of Ca2+ to drive cell migration.
