Li W, Tait J F
Department of Laboratory Medicine, University of Washington, Seattle 98195-7110, USA.
Arch Biochem Biophys. 1998 Mar 1;351(1):89-95. doi: 10.1006/abbi.1997.0535.
Alteration in membrane-phosphatidylserine (PS) asymmetry occurs during lymphocyte apoptosis, but the mechanism and regulation of this process are not well understood. We investigated the possible involvement of CD9, a member of the tetraspan family of membrane proteins, in the PS-exposure process in Jurkat T cells; flow cytometry with FITC-annexin V was used to detect the PS-positive cells. We found that antibody to CD9 inhibited the prompt (within 5 min) PS exposure stimulated by calcium ionophore A23187, whereas it had no effect on resting cells. Antibodies against other control antigens (CD7, CD56, CD57, CD59, CD63, and CD71) had no effect on PS exposure in either resting or calcium-ionophore-treated cells. The inhibitory effect of anti-CD9 was dose dependent. The observed inhibitory effect appeared to be "all or none" at the cellular level: increasing antibody doses decreased the percentage of PS-positive cells, whereas the number of PS molecules exposed per positive cell was constant. The inhibitory effect was not blocked by co-incubation with other antibodies of the same isotype, arguing against a nonspecific effect via Fc receptors. The anti-CD9, however, did not block the delayed (8- to 24-h) PS exposure induced by apoptotic treatments such as ultraviolet light, cycloheximide, and actinomycin D, indicating that CD9 might act selectively on only some pathways leading to PS exposure. Our results suggest that lymphocyte PS exposure is regulated by multiple pathways and that signals regulating PS exposure can be delivered through cell-surface antigen CD9.
淋巴细胞凋亡过程中会发生膜磷脂酰丝氨酸（PS）不对称性的改变，但这一过程的机制和调控尚未完全明确。我们研究了四跨膜蛋白家族成员CD9在Jurkat T细胞PS暴露过程中的可能作用；采用FITC-膜联蛋白V流式细胞术检测PS阳性细胞。我们发现，抗CD9抗体可抑制钙离子载体A23187刺激的快速（5分钟内）PS暴露，而对静息细胞无影响。针对其他对照抗原（CD7、CD56、CD57、CD59、CD63和CD71）的抗体对静息或钙离子载体处理细胞的PS暴露均无影响。抗CD9的抑制作用呈剂量依赖性。在细胞水平上，观察到的抑制作用似乎是“全或无”的：增加抗体剂量会降低PS阳性细胞的百分比，而每个阳性细胞暴露的PS分子数量是恒定的。与同型的其他抗体共同孵育并不能阻断这种抑制作用，这表明不是通过Fc受体产生的非特异性效应。然而，抗CD9并不阻断紫外线、环己酰亚胺和放线菌素D等凋亡处理诱导的延迟（8至24小时）PS暴露，这表明CD9可能仅选择性地作用于某些导致PS暴露的途径。我们的结果表明，淋巴细胞PS暴露受多种途径调控，并且调控PS暴露的信号可通过细胞表面抗原CD9传递。
