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首页> 外文期刊>Molecular and Cellular Biology >Dephosphorylation of simian virus 40 large-T antigen and p53 protein by protein phosphatase 2A: inhibition by small-t antigen.
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Dephosphorylation of simian virus 40 large-T antigen and p53 protein by protein phosphatase 2A: inhibition by small-t antigen.

机译：猿猴病毒40大T抗原和p53蛋白被蛋白磷酸酶2A脱磷酸：被小t抗原抑制。

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Simian virus 40 (SV40) large-T antigen and the cellular protein p53 were phosphorylated in vivo by growing cells in the presence of 32Pi. The large-T/p53 complex was isolated by immunoprecipitation and used as a substrate for protein phosphatase 2A (PP2A) consisting of the catalytic subunit (C) and the two regulatory subunits, A and B. Three different purified forms of PP2A, including free C, the AC form, and the ABC form, could readily dephosphorylate both proteins. With both large-T and p53, the C subunit was most active, followed by the AC form, which was more active than the ABC form. The activity of all three forms of PP2A toward these proteins was strongly stimulated by manganese ions and to a lesser extent by magnesium ions. The presence of complexed p53 did not affect the dephosphorylation of large-T antigen by PP2A. The dephosphorylation of individual phosphorylation sites of large-T and p53 were determined by two-dimensional peptide mapping. Individual sites within large-T and p53 were dephosphorylated at different rates by all three forms of PP2A. The phosphates at Ser-120 and Ser-123 of large-T, which affect binding to the origin of SV40 DNA, were removed most rapidly. Three of the six major phosphopeptides of p53 were readily dephosphorylated, while the remaining three were relatively resistant to PP2A. Dephosphorylation of most of the sites in large-T and p53 by the AC form was inhibited by SV40 small-t antigen. The inhibition was most apparent for those sites which were preferentially dephosphorylated. Inhibition was specific for the AC form; no effect was observed on the dephosphorylation of either protein by the free C subunit or the ABC form. The inhibitory effect of small-t on dephosphorylation by PP2A could explain its role in transformation.
机译：猿猴病毒40（SV40）大T抗原和细胞蛋白p53在32Pi存在下通过使细胞生长而体内磷酸化。大T / p53复合物通过免疫沉淀分离，并用作蛋白质磷酸酶2A（PP2A）的底物，由催化亚基（C）和两个调节亚基A和B组成.PP2A的三种不同纯化形式，包括游离C，AC形式和ABC形式可以很容易地使两种蛋白质脱磷酸化。无论是大T还是p53，C亚基都是最活跃的，其次是AC形式，比ABC形式更活跃。锰离子强烈刺激所有三种形式的PP2A对这些蛋白质的活性，而镁离子强烈刺激这种活性。复合p53的存在不影响PP2A对大T抗原的去磷酸化作用。通过二维肽图分析确定了大T和p53的单个磷酸化位点的去磷酸化。所有三种形式的PP2A均以不同的速率使大T和p53内的单个位点脱磷酸。大T的Ser-120和Ser-123处的磷酸盐会影响与SV40 DNA起源的结合，因此去除速度最快。 p53的六个主要磷酸肽中的三个很容易被去磷酸化，而其余三个则对PP2A具有相对抗性。 SV40 small-t抗原抑制了AC形式的大T和p53中大多数位点的去磷酸化。对于那些优先去磷酸化的位点，抑制作用最为明显。抑制作用是针对AC形式的;没有观察到游离C亚基或ABC形式对蛋白质的去磷酸化作用。 small-t对PP2A的去磷酸化的抑制作用可以解释其在转化中的作用。

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