Li L, Rao J N, Bass B L, Wang J Y
Department of Surgery, University of Maryland School of Medicine, 10 North Greene St., Baltimore, MD 21201, USA.
Am J Physiol Gastrointest Liver Physiol. 2001 May;280(5):G992-G1004. doi: 10.1152/ajpgi.2001.280.5.G992.
The maintenance of intestinal mucosal integrity depends on a balance between cell renewal and cell death, including apoptosis. The natural polyamines, putrescine, spermidine, and spermine, are essential for mucosal growth, and decreasing polyamine levels cause G(1) phase growth arrest in intestinal epithelial (IEC-6) cells. The present study was done to determine changes in susceptibility of IEC-6 cells to apoptosis after depletion of cellular polyamines and to further elucidate the role of nuclear factor-kappaB (NF-kappaB) in this process. Although depletion of polyamines by alpha-difluoromethylornithine (DFMO) did not directly induce apoptosis, the susceptibility of polyamine-deficient cells to staurosporine (STS)-induced apoptosis increased significantly as measured by changes in morphological features and internucleosomal DNA fragmentation. In contrast, polyamine depletion by DFMO promoted resistance to apoptotic cell death induced by the combination of tumor necrosis factor-alpha (TNF-alpha) and cycloheximide. Depletion of cellular polyamines also increased the basal level of NF-kappaB proteins, induced NF-kappaB nuclear translocation, and activated the sequence-specific DNA binding activity. Inhibition of NF-kappaB binding activity by sulfasalazine or MG-132 not only prevented the increased susceptibility to STS-induced apoptosis but also blocked the resistance to cell death induced by TNF-alpha in combination with cycloheximide in polyamine-deficient cells. These results indicate that 1) polyamine depletion sensitizes intestinal epithelial cells to STS-induced apoptosis but promotes the resistance to TNF-alpha-induced cell death, 2) polyamine depletion induces NF-kappaB activation, and 3) disruption of NF-kappaB function is associated with altered susceptibility to apoptosis induced by STS or TNF-alpha. These findings suggest that increased NF-kappaB activity after polyamine depletion has a proapoptotic or antiapoptotic effect on intestinal epithelial cells determined by the nature of the death stimulus.
肠道黏膜完整性的维持依赖于细胞更新与细胞死亡（包括凋亡）之间的平衡。天然多胺，如腐胺、亚精胺和精胺，对黏膜生长至关重要，多胺水平降低会导致肠道上皮（IEC - 6）细胞在G1期生长停滞。本研究旨在确定细胞内多胺耗竭后IEC - 6细胞对凋亡敏感性的变化，并进一步阐明核因子-κB（NF-κB）在此过程中的作用。尽管α-二氟甲基鸟氨酸（DFMO）耗竭多胺并未直接诱导凋亡，但通过形态学特征变化和核小体间DNA片段化检测发现，多胺缺乏的细胞对星形孢菌素（STS）诱导凋亡的敏感性显著增加。相反，DFMO耗竭多胺可增强对肿瘤坏死因子-α（TNF-α）与环己酰亚胺联合诱导的凋亡性细胞死亡的抗性。细胞内多胺耗竭还会增加NF-κB蛋白的基础水平，诱导NF-κB核转位，并激活序列特异性DNA结合活性。柳氮磺胺吡啶或MG - 132抑制NF-κB结合活性不仅可防止对STS诱导凋亡敏感性的增加，还能阻断多胺缺乏细胞中TNF-α与环己酰亚胺联合诱导的细胞死亡抗性。这些结果表明：1）多胺耗竭使肠道上皮细胞对STS诱导的凋亡敏感，但增强对TNF-α诱导的细胞死亡的抗性；2）多胺耗竭诱导NF-κB激活；3）NF-κB功能破坏与对STS或TNF-α诱导凋亡的敏感性改变有关。这些发现提示，多胺耗竭后NF-κB活性增加对肠道上皮细胞具有促凋亡或抗凋亡作用，这取决于死亡刺激的性质。
