Jacotot E, Callebaut C, Blanco J, Rivière Y, Krust B, Hovanessian A G
Unité de Virologie et Immunologie Cellulaire, UA CNRS 1157, Institut Pasteur, Paris, France.
Virology. 1996 Sep 15;223(2):318-30. doi: 10.1006/viro.1996.0483.
The membrane-expressed HIV-1 envelope glycoprotein complex, gp120 and gp41, has been shown to be responsible for the initiation of cell killing by apoptosis in CD4+ T cells. By using two experimental approaches we demonstrate here that CD26, also known as dipeptidyl peptidase IV (DPP IV), appears to be implicated in this function of the gp120/gp41 complex to initiate apoptosis. In the first experimental model, we used persistently HIV-1-infected H9/IIIB cells expressing the membrane-associated gp120/gp41 complex as effector cells to induce apoptosis in Jurkat CD4+ T cells: parental or transfected in order to express high levels of recombinant CD26, either wild-type or mutated at its Ser-630 which inactivates the DPP IV activity of CD26. Parental Jurkat cells and transfected control cell clones express low but reproducibly detectable levels of endogenous CD26. In coculturing experiments using H9/IIIB and Jurkat cells, the occurrence of apoptosis was found to be retarded by at least 24 hr in Jurkat cells expressing low levels of endogenous CD26, compared to cell clones expressing high levels of either wild-type or mutated catalytically inactive transfected CD26. In the second experimental model, the different Jurkat cell lines were infected with vaccinia recombinant viruses expressing HIV-1 env gene, either wild-type to generate a functional gp120/gp41 complex or mutated to generate an uncleavable membrane-expressed precursor of the envelope glycoprotein gp160. At 18 hr postinfection with such vaccinia recombinant viruses, apoptosis was observed only in Jurkat cells with enhanced levels of CD26 and expressing the gp120/gp41 complex. Apoptosis was not detected in the different Jurkat cell lines expressing the uncleavable precursor gp160. In both of the experimental models used, no significant differences were observed between the transfected cells expressing either the wild-type or the mutated form of CD26, thus suggesting that the DPP IV activity of CD26 is not essential for its function as a cofactor of CD4 in the mechanism of initiation of apoptosis by the HIV envelope gp120/gp41 complex. Taken together, these results indicate that CD26 in CD4+ T cells may determine the rate of initiation of apoptosis by the mature HIV-1 envelope glycoproteins, i.e., CD26 is being involved as a cofactor of CD4 in the mechanism of triggering apoptosis by the gp120/gp41 complex. As signaling through CD26 could lead to T cell activation, we propose that this latter might be modified following the binding of the gp120/gp41 complex to CD4 and thus leading to apoptosis.
膜表达的HIV-1包膜糖蛋白复合物gp120和gp41已被证明是CD4+T细胞中通过凋亡引发细胞死亡的起始原因。通过两种实验方法，我们在此证明，也被称为二肽基肽酶IV（DPP IV）的CD26似乎参与了gp120/gp41复合物启动凋亡的这一功能。在第一个实验模型中，我们使用持续感染HIV-1且表达膜相关gp120/gp41复合物的H9/IIIB细胞作为效应细胞，诱导Jurkat CD4+T细胞凋亡：亲本细胞或转染细胞以表达高水平的重组CD26，其可以是野生型，也可以是在其Ser-630处发生突变从而使CD26的DPP IV活性失活的形式。亲本Jurkat细胞和转染的对照细胞克隆表达低水平但可重复检测到的内源性CD26。在使用H9/IIIB细胞和Jurkat细胞的共培养实验中，与表达高水平野生型或催化失活的突变型转染CD26的细胞克隆相比，发现内源性CD26表达水平低的Jurkat细胞中凋亡的发生至少延迟了24小时。在第二个实验模型中，不同的Jurkat细胞系用表达HIV-1 env基因的痘苗重组病毒感染，该基因可以是野生型以产生功能性gp120/gp41复合物，也可以是突变型以产生包膜糖蛋白gp160的不可切割的膜表达前体。在用这种痘苗重组病毒感染后18小时，仅在CD26水平升高且表达gp120/gp41复合物的Jurkat细胞中观察到凋亡。在表达不可切割前体gp160的不同Jurkat细胞系中未检测到凋亡。在使用的两个实验模型中，表达野生型或突变型CD26的转染细胞之间均未观察到显著差异，因此表明CD26的DPP IV活性对于其作为HIV包膜gp120/gp41复合物启动凋亡机制中CD4的辅助因子的功能并非必不可少。综上所述，这些结果表明，CD4+T细胞中的CD26可能决定成熟HIV-1包膜糖蛋白引发凋亡的速率，即CD26作为CD4的辅助因子参与gp120/gp41复合物触发凋亡的机制。由于通过CD26的信号传导可导致T细胞活化，我们提出在gp120/gp41复合物与CD4结合后，后者可能会被修饰，从而导致凋亡。
