Analysis of New 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。我们之前证明了CD38的细胞外结构域具有NAD^+糖水解酶（NADase）活性，并且HL-60细胞中全反式维甲酸（RA）诱导的外链NADase活性是由于CD38。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. 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。其中一个重要的磷酸化蛋白被鉴定为c-cbl原癌基因产物p120^<c-cbl>.2。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。3. 这些刺激蛋白酪氨酸磷酸化的拮抗识别的表位都被定位在CD38的相同羧基末端序列上，并且其外链nadase活性也需要相同的序列。4. Fcgamma-II受体似乎参与了通过抗cd38单抗诱导的细胞蛋白酪氨酸磷酸化介导的信号转导途径。5. CD38 mRNA的表达通过核RA受体介导；在CD38基因的第一个内含子中存在RA受体应答元件。

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. 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. Stimulation of RA-differentiated HL-60 cells with anti-CD38 monoclonal antibodies (mAbs) induced rapid tyrosine phosphorylation of cellular proteins with the molecular weights 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>.2. Superoxide formation in response to formyl-Met-Leu-Phe was markedly enhanced by the anti-CD38 mAbs in the differentiated HL-60 cells. 3. The epitopes recognized by these agonistic mAbs stimulating protein tyrosine phosphorylation were all mapped on the same carboxyl-terminal sequence of CD38, and the same sequence was also required for its ecto-NADase activity. 4. Fcgamma-II receptors appeared to be involved in the signal transduction pathway mediated through the agonistic anti-CD38 mAb-induced tyrosine phosphorylation of cellular proteins. 5. The expression of CD38 mRNA was mediated through nuclear RA receptors ; a RA receptor-responsive element was present in the first intron of CD38 gene.