Ryu S J, Oh Y S, Park S C
Department of Biochemistry and Molecular Biology, The Aging and Apoptosis Research Center, Seoul National University College of Medicine, Seoul, Korea.
Cell Death Differ. 2007 May;14(5):1020-8. doi: 10.1038/sj.cdd.4402091. Epub 2007 Feb 9.
We previously reported that senescent human diploid fibroblasts (HDFs) are resistant to apoptosis induced by H(2)O(2) and staurosporine. We report here that senescent HDFs are resistant to thapsigargin-induced apoptosis as well. These agonists caused the reductions in mitochondrial membrane potential (MMP) and in the apoptosis inhibitory protein (B-cell lymphoma) only in young HDFs but not in senescent HDFs. In addition, downregulation of Bcl-2 increased the sensitivity of senescent HDFs to apoptosis induction, suggesting the significant role of Bcl-2 in apoptosis resistance of the senescent HDFs. We further found that P-cAMP response element-binding protein (CREB), a positive regulator of Bcl-2, decreased in stress-induced apoptosis of young HDFs but not in senescent HDFs, and that Bcl-2 was markedly reduced in CREB small interfering RNA (siRNA), transfected senescent HDFs. In addition, activity of protein phosphatase 2A (PP2A), which dephosphorylates p-CREB, significantly increased in young HDFs but not in senescent HDFs treated with H(2)O(2), staurosporine or thapsigargin. Taken together, these results suggest that failure of stress-induced downregulation of Bcl-2 underlies resistance of senescent HDFs to apoptosis.
我们之前报道过，衰老的人二倍体成纤维细胞（HDFs）对过氧化氢（H₂O₂）和星形孢菌素诱导的凋亡具有抗性。我们在此报告，衰老的HDFs对毒胡萝卜素诱导的凋亡也具有抗性。这些激动剂仅在年轻的HDFs中导致线粒体膜电位（MMP）降低以及凋亡抑制蛋白（B细胞淋巴瘤）减少，而在衰老的HDFs中则不然。此外，Bcl-2的下调增加了衰老的HDFs对凋亡诱导的敏感性，表明Bcl-2在衰老的HDFs的凋亡抗性中起重要作用。我们进一步发现，Bcl-2的正向调节因子磷酸化环磷酸腺苷反应元件结合蛋白（P-cAMP response element-binding protein，P-CREB）在应激诱导的年轻HDFs凋亡中减少，但在衰老的HDFs中未减少，并且在转染了CREB小干扰RNA（siRNA）的衰老HDFs中Bcl-2明显减少。此外，使p-CREB去磷酸化的蛋白磷酸酶2A（PP2A）的活性在年轻的HDFs中显著增加，但在用H₂O₂、星形孢菌素或毒胡萝卜素处理的衰老HDFs中未增加。综上所述，这些结果表明应激诱导Bcl-2下调失败是衰老的HDFs对凋亡具有抗性的基础。
