CD38 is a signaling enzyme responsible for catalyzing the synthesis of cyclic ADP ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate; both are universal Ca(2+) messenger molecules. Ablation of the CD38 gene in mice causes multiple physiological defects, including impaired oxytocin release, that result in altered social behavior. A series of catalysis-based inhibitors of CD38 were designed and synthesized, starting with arabinosyl-2'-fluoro-2'-deoxynicotinamide mononucleotide. Structure-function relationships were analyzed to assess the structural determinants important for inhibiting the NADase activity of CD38. X-ray crystallography was used to reveal the covalent intermediates that were formed with the catalytic residue, Glu226. Metabolically stable analogues that were resistant to inactivation by phosphatase and esterase were synthesized and shown to be effective in inhibiting intracellular cADPR production in human HL-60 cells during induction of differentiation by retinoic acid. The inhibition was species-independent, and the analogues were similarly effective in blocking the cyclization reaction of CD38 in rat ventricular tissue extracts, as well as inhibiting the α-agonist-induced constriction in rat mesentery arteries. These compounds thus represent the first generally applicable and catalysis-based inhibitors of the Ca(2+) signaling function of CD38.

Background: The role and mechanism of cADPR, an endogenous Ca2+-mobilizing nucleotide, in cardiomyogenesis remain to be determined.Results: We found that inhibition of the cADPR cascade facilitated cardiomyocyte differentiation of mouse ES cells.Conclusion: The CD38-cADPR-Ca2+ signaling pathway antagonizes the cardiomyocyte differentiation of mouse ES cells.Significance: Inhibition of cADPR signaling should provide a good approach to enrich functional cardiomyocytes from ES cells.

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Cyclic ADP-ribose (cADPR) mobilizes intracellular Ca 21 stores and activates Ca 21 influx to regulate a wide range of physiological processes. It is one of the products produced from the catalysis of NAD 1 by the multifunctional CD38/ADP-ribosyl cyclase superfamily. After elimination of the nicotinamide ring by the enzyme, the reaction intermediate of NAD 1 can either be hydrolyzed to form linear ADPR or cyclized to form cADPR. We have previously shown that human CD38 exhibits a higher preference towards the hydrolysis of NAD 1 to form linear ADPR while Aplysia ADP-ribosyl cyclase prefers cyclizing NAD 1 to form cADPR. In this study, we characterized the enzymatic properties of porcine CD38 and revealed that it has a prominent secondary NAD 1 cyclase activity producing cADPR. We also determined the X-ray crystallographic structures of porcine CD38 and were able to observe conformational flexibility at the base of the active site of the enzyme which allow the NAD 1 reaction intermediate to adopt conformations resulting in both hydrolysis and cyclization forming linear ADPR and cADPR respectively.