Aagaard-Tillery K M, Jelinek D F
Department of Immunology, Mayo Clinic/Foundation, Rochester, MN 55905, USA.
J Immunol. 1995 Oct 1;155(7):3297-307.
The state of B cell maturation profoundly influences the outcome, i.e., activation, growth arrest, or programmed cell death, of a variety of stimuli, including the calcium ionophore, ionomycin. Initial studies confirmed the observation that cell lines representative of immature B cells, i.e., Burkitt lymphoma cell lines, were induced to undergo apoptosis in response to ionomycin, whereas more mature B cell lines did not, and instead underwent cell cycle arrest in the G1 interval. To understand this differential outcome, we have focused on comparing the expression and activation of an endonuclease(s) in cells induced by ionomycin to undergo programmed cell death (Ramos) with cells resistant to ionomycin-induced programmed cell death (Ly1). Our results demonstrated that a low m.w. fraction of an endogenous Ca2+/Mg(2+)-dependent endonuclease was activated in Ramos cells, but not in activated Ly1 cells, following the addition of ionomycin. Of interest, however, low m.w. endogenous endonuclease(s) activity was induced when isolated Ly1 cell nuclei were treated with exogenous calcium instead. Use of field inversion gel electrophoresis further indicated that cleavage of DNA into large m.w. (> 50 kbp) DNA fragments does not precede ionomycin-induced internucleosomal cleavage in Ramos cells or in ionomycin-resistant Ly1 cells. In summary, these data support the conclusion that ionomycin-induced apoptosis involves the activation of a latent, low m.w., calcium-responsive endonuclease and suggest that control of endonuclease depression may contribute to cell-specific regulation of calcium ionophore-induced apoptosis.
B细胞成熟状态会深刻影响多种刺激（包括钙离子载体离子霉素）所产生的结果，即激活、生长停滞或程序性细胞死亡。初步研究证实了这样的观察结果：代表未成熟B细胞的细胞系，即伯基特淋巴瘤细胞系，在离子霉素作用下会被诱导发生凋亡，而更成熟的B细胞系则不会，而是在G1期经历细胞周期停滞。为了理解这种不同的结果，我们着重比较了离子霉素诱导发生程序性细胞死亡的细胞（拉莫斯细胞）和对离子霉素诱导的程序性细胞死亡具有抗性的细胞（Ly1细胞）中核酸内切酶的表达和激活情况。我们的结果表明，添加离子霉素后，拉莫斯细胞中一种低分子量的内源性Ca2+/Mg(2+)依赖性核酸内切酶被激活，而激活的Ly1细胞中则没有。然而，有趣的是，当用外源钙处理分离出的Ly1细胞核时，会诱导低分子量内源性核酸内切酶的活性。场反转凝胶电泳的结果进一步表明，在拉莫斯细胞或对离子霉素有抗性的Ly1细胞中，DNA断裂成高分子量（>50 kbp）的DNA片段并不先于离子霉素诱导的核小体间断裂。总之，这些数据支持了离子霉素诱导的凋亡涉及一种潜在的、低分子量的、钙反应性核酸内切酶激活的结论，并表明对核酸内切酶抑制的控制可能有助于钙离子载体诱导的凋亡的细胞特异性调节。
