Analysis of NAD-cleavage Enzymes Involved in Signal Transduction System

人细胞表面抗原CD38是一种具有单跨膜结构域的46 kda的II型糖蛋白，其氨基酸序列与葡聚糖adp -核糖基环化酶同源。我们之前已经证明，CD38的细胞外结构域具有NAD^+糖水解酶（NADase）活性，而HL-60细胞中全反式维甲酸（RA）诱导的外链NADase活性是由于CD38 （Kontani， K.et al.， J.Biol.Chem）。[j]。CD38不仅可以催化NAD^+的水解，还可以催化环状adp核糖的形成和水解，这是一种新的候选物质，可以介导细胞内Ca^<2+>储存释放Ca^<2+>。在本研究中，我们得到了以下发现。1. 除了这些酶的活性外，CD38还具有结合透明质酸的能力。2. 抗cd38单克隆抗体（mAb）刺激ra分化的HL-60细胞，可诱导分子量为120,000、87,000和77,000的细胞蛋白快速酪氨酸磷酸化。其中一个显著的磷酸化蛋白被鉴定为c-cbl原癌基因产物p120^<c-cbl>.3。在分化的HL-60细胞中，抗cd38单抗显著增强了甲酰基met -亮氨酸反应的超氧化物形成。4. Zn^<2+>直接与CD38相互作用，将其催化性质从nad酶转化为adp -核糖基环化酶，可能是由于阻止水分子进入酶-底物复合物的中间体。5. 虽然CD38 mRNA的表达是通过核RA受体介导的，但CD38基因第一个内含子中的负调控元件似乎参与了RA诱导的HL-60细胞中CD38 mRNA的表达。

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.