Analysis of NAD-cleavage Enzymes Involved in Signal Transduction System

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The human cell surface antigen CD38, which has an amino acid sequence homologous to Aplysia ADP-ribosyl cyclase, is a 46-kDa type II glycoprotein with a single-transmembrane domain. We previously demonstrated that the extracellular domain of CD38 exhibits NAD^+ glycohydrolase (NADase) activity and that the ecto-form NADase activity induced by all-trans retinoic acid (RA) in HL-60 cells is due to CD38 (Kontani, K.et al., J.Biol.Chem.268 : 16895,1993). CD38 catalyzes not only the hydrolysis of NAD^+, but also the formation and hydrolysis of cyclic ADP-ribose, which is a novel candidate that mediates Ca^<2+> release from intracellular Ca^<2+> stores. In the present study, we obtained the following findings. 1. Besides these enzyme activities, CD38 had the ability to bind hyaluronate. 2. Stimulation of RA-differentiated HL-60 cells with anti-CD38 monoclonal antibody (mAb) induced rapid tyrosine phosphorylation of cellular proteins with the molecular weight of 120,000,87,000 and 77,000. One of the prominent phosphorylated proteins was identified as the c-cbl proto-oncogene product, p120^<c-cbl>.3. Superoxide formation in response to formyl-Met-Leu-Phe was markedly enhanced by the anti-CD38 mAb in the differentiated HL-60 cells. 4. Zn^<2+> directly interacted with CD38 to convert its catalytic properties from NADase to ADP-ribosyl cyclase, probably due to prevention of the access of water molecule to an intermediate of the enzyme-substrate complex. 5. Although the expression of CD38 mRNA was mediated through nuclear RA receptors, a negative regulatory element present in the first intron of CD38 gene appeared to be involved in the RA-induced expression of CD38 mRNA in HL-60 cells.