Oliverio S, Amendola A, Rodolfo C, Spinedi A, Piacentini M
Department of Biology, University of Rome "Tor Vergata," 00133 Rome, Italy.
J Biol Chem. 1999 Nov 26;274(48):34123-8. doi: 10.1074/jbc.274.48.34123.
Treatment of the human promonocytic cell line U937 with all-trans-retinoic acid (RA) commits these cells to apoptosis, which can be triggered by simply increasing intracellular calcium levels by the ionophore A23187. RA treatment of U937 cells is characterized by a decrease in Bcl-2 and marked induction of "tissue" transglutaminase (tTG) gene expression. In this study, we show that the inhibition of tTG expression in U937 cells undergoing apoptosis prevents their death. In fact, U937 cell-derived clones transfected with the human tTG gene in the antisense orientation showed a pronounced decrease in apoptosis induced by several stimuli. These findings demonstrate that the Ca(2+)-dependent irreversible cross-linking of intracellular proteins catalyzed by tTG represents an important biochemical event in the gene-regulated cell death in monoblasts. In addition, our data indicate that the apoptotic program in promonocytic cells is strictly regulated by RA and that a key role is played by the free intracellular calcium concentration.
用全反式维甲酸（RA）处理人原单核细胞系U937可使这些细胞发生凋亡，而通过离子载体A23187简单地提高细胞内钙水平就能触发这种凋亡。用RA处理U937细胞的特征是Bcl-2减少以及“组织”转谷氨酰胺酶（tTG）基因表达明显诱导。在本研究中，我们表明，在经历凋亡的U937细胞中抑制tTG表达可防止其死亡。事实上，用反义方向的人tTG基因转染的U937细胞衍生克隆在几种刺激诱导的凋亡中表现出明显减少。这些发现表明，由tTG催化的细胞内蛋白质的Ca(2+)依赖性不可逆交联代表了原单核细胞基因调控细胞死亡中的一个重要生化事件。此外，我们的数据表明，原单核细胞中的凋亡程序受到RA的严格调控，并且细胞内游离钙浓度起关键作用。
