Whitekus M J, Santini R P, Rosenspire A J, McCabe M J
Institute of Chemical Toxicology, Detroit, MI 48201, USA.
J Immunol. 1999 Jun 15;162(12):7162-70.
Dysregulation of CD95/Fas-mediated apoptosis has been implicated as a contributing factor in autoimmune disorders. Animal studies clearly have established a connection between mercury exposure and autoimmune disease in rodents, while case reports have suggested a link between accidental mercury contamination and autoimmune disease in humans. The mechanism(s) for these associations are poorly understood. Using the Jurkat cell model, we have found that low levels (</=10 microM) of inorganic mercury (i.e., HgCl2) attenuated anti-CD95-mediated growth arrest and markedly enhanced cell survival. Several biochemical assays for apoptosis, including DNA degradation, poly(ADP-ribose) polymerase degradation, and phosphatidylserine externalization, directly verified that HgCl2 attenuated anti-CD95-mediated apoptosis. In an attempt to further characterize the effect of mercury on CD95-mediated apoptosis, several signaling components of the CD95 death pathway were analyzed to determine whether HgCl2 could modulate them. HgCl2 did not modulate CD95 expression; however, it did block CD95-induced caspase-3 activation. HgCl2 was not able to attenuate TNF-alpha-mediated apoptosis in U-937 cells, or ceramide-C6-mediated apoptosis in Jurkat cells, suggesting that mercury acts upstream of, or does not involve, these signals. Thus, inorganic mercury specifically attenuates CD95-mediated apoptosis likely by targeting a signaling component that is upstream of caspase-3 activation and downstream of CD95.
CD95/Fas介导的细胞凋亡失调被认为是自身免疫性疾病的一个促成因素。动物研究明确证实了啮齿动物接触汞与自身免疫性疾病之间的联系，而病例报告则提示了人类意外汞污染与自身免疫性疾病之间的关联。这些关联的机制尚不清楚。利用Jurkat细胞模型，我们发现低水平（≤10 microM）的无机汞（即HgCl2）可减弱抗CD95介导的生长停滞并显著提高细胞存活率。几种细胞凋亡的生化检测方法，包括DNA降解、聚（ADP - 核糖）聚合酶降解和磷脂酰丝氨酸外化，直接证实了HgCl2可减弱抗CD95介导的细胞凋亡。为了进一步表征汞对CD95介导的细胞凋亡的影响，我们分析了CD95死亡途径的几个信号成分，以确定HgCl2是否能对其进行调节。HgCl2并未调节CD95的表达；然而，它确实阻断了CD95诱导的半胱天冬酶 - 3激活。HgCl2无法减弱U - 937细胞中TNF - α介导的细胞凋亡，也无法减弱Jurkat细胞中神经酰胺 - C6介导的细胞凋亡，这表明汞作用于这些信号的上游或与之无关。因此，无机汞可能通过靶向半胱天冬酶 - 3激活上游且CD95下游的一个信号成分，特异性地减弱CD95介导的细胞凋亡。
