Zocchi E, Daga A, Usai C, Franco L, Guida L, Bruzzone S, Costa A, Marchetti C, De Flora A
Institute of Biochemistry, University of Genova, Viale Benedetto XV No. 1, 16132 Genova, Italy.
J Biol Chem. 1998 Apr 3;273(14):8017-24. doi: 10.1074/jbc.273.14.8017.
CD38 is a bifunctional ectoenzyme, predominantly expressed on hematopoietic cells during differentiation, that catalyzes the synthesis (cyclase) and the degradation (hydrolase) of cyclic ADP-ribose (cADPR), a powerful calcium mobilizer from intracellular stores. Due to the well established role of calcium levels in the regulation of apoptosis, proliferation, and differentiation, the CD38/cADPR system seems to be a likely candidate involved in the control of these fundamental processes. The ectocellular localization of the cyclase activity, however, contrasts with the intracellular site of action of cADPR. Here we demonstrate that ectocellular expression of human CD38 in CD38(-) HeLa and 3T3 cells results in intracellular CD38 substrate (NAD+ + NADH) consumption and product (cADPR) accumulation. Furthermore, a causal relationship is established between presence of intracellular cADPR, partial depletion of thapsigargin-sensitive calcium stores, increase in basal free cytoplasmic calcium concentration, and decrease of cell doubling time. The significant shortening of the S phase in CD38(+) HeLa cells, as compared with controls, demonstrates an effect of intracellular cADPR on the mammalian cell cycle.
CD38是一种双功能胞外酶，在分化过程中主要表达于造血细胞上，它催化环磷酸腺苷核糖（cADPR）的合成（环化酶）和降解（水解酶），cADPR是一种从细胞内储存库中动员钙的强效物质。由于钙水平在细胞凋亡、增殖和分化调控中已确立的作用，CD38/cADPR系统似乎是参与控制这些基本过程的一个可能候选者。然而，环化酶活性的胞外定位与cADPR的细胞内作用位点形成对比。在这里，我们证明在CD38(-)的HeLa细胞和3T3细胞中人类CD38的胞外表达导致细胞内CD38底物（NAD+ + NADH）的消耗和产物（cADPR）的积累。此外，在细胞内cADPR的存在、毒胡萝卜素敏感钙储存的部分耗尽、基础游离细胞质钙浓度的增加以及细胞倍增时间的减少之间建立了因果关系。与对照相比，CD38(+) HeLa细胞中S期的显著缩短证明了细胞内cADPR对哺乳动物细胞周期的影响。
