Schavinsky-Khrapunsky Yana, Huleihel Mahmoud, Aboud Mordechai, Torgeman Amram
Department of Microbiology and Immunology, Cancer Research Center, Ben Gurion University of the Negev, Beer Sheva 84105, Israel.
Oncogene. 2003 Aug 14;22(34):5315-24. doi: 10.1038/sj.onc.1206782.
Previous reports have shown that, in certain cell types, p21(WAF-1), which plays a central role in cell proliferation, can be activated by HTLV-I Tax protein and by TPA. Tax and TPA are also known to stimulate HTLV-I gene expression. Since cell proliferation has a major impact on HTLV-I replication, it was of interest to investigate their effect on p21(WAF-1) in human T cells, which are the main target of HTLV-I in human infection. This study demonstrates that p21(WAF-1) is activated in such cells by both factors, each acting through a different mechanism that does not influence the other. The effect of TPA is shown to require PKC activity. Notably, however, examination of different PKC isoforms revealed that PKC-alpha and PKC-epsilon stimulated p21(WAF-1) expression, whereas PKC-eta was rather inhibitory and PKC-beta1 and beta2 were ineffective. All these isoforms were found to be activated by TPA in the employed T cells, but this apparent paradox was resolved by the observation that when coexpressed together in these cells, the stimulatory PKCs override the inhibitory isoform. Further experiments demonstrated that the PKC-induced p21(WAF-1) activation was mediated by binding of Sp1-p53 complex to the second most upstream of the six Sp1 recognition sites present in its promoter and that this effect did not require the cooperation of an p53-binding site.
先前的报告表明，在某些细胞类型中，在细胞增殖中起核心作用的p21（WAF-1）可被HTLV-I Tax蛋白和佛波酯（TPA）激活。已知Tax和TPA也能刺激HTLV-I基因表达。由于细胞增殖对HTLV-I复制有重大影响，因此研究它们对人类T细胞中p21（WAF-1）的作用很有意义，人类T细胞是人类感染中HTLV-I的主要靶细胞。本研究表明p21（WAF-1）在这类细胞中被这两种因子激活，每种因子通过不同的机制起作用，且互不影响。结果显示TPA的作用需要蛋白激酶C（PKC）的活性。然而，值得注意的是，对不同PKC亚型的检测发现，PKC-α和PKC-ε刺激p21（WAF-1）表达，而PKC-η具有抑制作用，PKC-β1和β2则无作用。在所使用的T细胞中，所有这些亚型都被TPA激活，但通过观察发现，当这些亚型在这些细胞中共表达时，具有刺激作用的PKC会抑制具有抑制作用的亚型，从而解决了这一明显的矛盾。进一步的实验表明，PKC诱导的p21（WAF-1）激活是通过Sp1-p53复合物与p21（WAF-1）启动子中六个Sp1识别位点中第二上游的位点结合介导的，且这种作用不需要p53结合位点的协同作用。
