Sreenivasan Yashin, Sarkar Abira, Manna Sunil K
Laboratory of Immunology, Centre for DNA Fingerprinting & Diagnostics, Nacharam, Hyderabad 500 076, India.
Oncogene. 2003 Jul 10;22(28):4356-69. doi: 10.1038/sj.onc.1206486.
Nuclear transcription factor kappa B (NF-kappaB) has been shown both to block apoptosis and to promote cell proliferation, and hence has been considered an important target for anticancer drug development. The pyrimidine analogue cytosine arabinoside (araC) is among the most effective agents used in the treatment of acute leukemia, and we demonstrate in this study that its chemotherapeutic activity may be mediated by its inhibition of NF-kappaB. We found that in Jurkat cells, although tumor necrosis factor (TNF), araC, or ceramide induced NF-kappaB, the induction was only transient in the case of araC. In both HuT-78 and serum-activated LPS-stimulated Jurkat (SA-LPS/Jkt) cells that expressed NF-kappaB, TNF or ceramide treatments did not affect the NF-kappaB expression whereas araC downregulated it. AraC, but not TNF or ceramide was able to induce apoptosis in these cells as detected by assays for lipid peroxidation, reactive oxygen intermediates generation, caspase activation, cytotoxicity, Bcl-2 degradation, and DNA fragmentation. AraC also potentiated apoptosis mediated by cis-platin, etoposide, or taxol in these cells. AraC was able to induce protein phosphatases (PP) 2A and 2B-A, and phosphorylation of p65 subunit of NF-kappaB in the HuT-78 and SA-LPS/Jkt cells was downregulated by araC treatment. Furthermore, calyculin A, a specific phospho-serine/phospho-threonine phosphatase inhibitor, protected HuT-78 and SA-LPS/Jkt cells from araC-mediated NF-kappaB downregulation and apoptosis. These observations collectively suggest that araC induces apoptosis in NF-kappaB-expressing cells by dephosphorylating the p65 subunit of NF-kappaB.
核转录因子κB（NF-κB）已被证明既能阻断细胞凋亡又能促进细胞增殖，因此被认为是抗癌药物开发的重要靶点。嘧啶类似物阿糖胞苷（araC）是治疗急性白血病最有效的药物之一，我们在本研究中证明其化疗活性可能是通过抑制NF-κB介导的。我们发现，在Jurkat细胞中，尽管肿瘤坏死因子（TNF）、araC或神经酰胺可诱导NF-κB，但araC诱导的NF-κB只是短暂的。在表达NF-κB的HuT-78细胞和血清激活的LPS刺激的Jurkat（SA-LPS/Jkt）细胞中，TNF或神经酰胺处理不影响NF-κB的表达，而araC可使其下调。通过脂质过氧化、活性氧中间体生成、半胱天冬酶激活、细胞毒性、Bcl-2降解和DNA片段化检测发现，araC而非TNF或神经酰胺能够诱导这些细胞凋亡。araC还能增强顺铂、依托泊苷或紫杉醇介导的这些细胞的凋亡。araC能够诱导蛋白磷酸酶（PP）2A和2B-A，araC处理可下调HuT-78细胞和SA-LPS/Jkt细胞中NF-κB的p65亚基的磷酸化。此外，特异性磷酸丝氨酸/磷酸苏氨酸磷酸酶抑制剂Calyculin A可保护HuT-78细胞和SA-LPS/Jkt细胞免受araC介导的NF-κB下调和凋亡。这些观察结果共同表明，araC通过使NF-κB的p65亚基去磷酸化来诱导表达NF-κB的细胞凋亡。
