McKendrick L, Meek D W
Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, UK.
Cell Mol Biol Res. 1994;40(5-6):555-61.
The tumor suppressor protein p53 is phosphorylated at a C-terminal residue (serine 386 in mouse p53) by the protein kinase CK2. Phosphorylation by CK2 activates the specific DNA binding function of p53 and stimulates its ability to suppress cellular growth. Previous reports have suggested that phosphorylation of p53 at the CK2 site is stimulated in cells expressing the large tumor antigen (T antigen) of simian virus 40 (SV40). To test this idea, we have expressed a C-terminal p53 "mini-protein" which comprises amino acids 154-387 of mouse p53 and therefore lacks the heavily phosphorylated N-terminus. In addition, the serine 309 phosphorylation site (targeted by cyclin-dependent kinases) has been mutated to encode alanine. We have expressed the p53 mini-protein in mammalian cells and shown by phosphopeptide mapping that it is phosphorylated at a single physiological phosphorylation site, serine 386. Using this mini-protein as a cellular target for CK2, we have shown that phosphorylation of p53 by CK2 is not affected by the presence of T antigen. The p53 mini-protein is likely to be a useful tool with which to probe the regulation of p53 phosphorylation by CK2 in response to other factors which influence cell growth.
肿瘤抑制蛋白p53在其C末端残基（小鼠p53中的丝氨酸386）处被蛋白激酶CK2磷酸化。CK2介导的磷酸化激活了p53的特异性DNA结合功能，并增强了其抑制细胞生长的能力。先前的报道表明，在表达猿猴病毒40（SV40）大肿瘤抗原（T抗原）的细胞中，p53在CK2位点的磷酸化受到刺激。为了验证这一观点，我们表达了一种C末端p53“小蛋白”，它包含小鼠p53的第154 - 387位氨基酸，因此缺少高度磷酸化的N末端。此外，丝氨酸309磷酸化位点（细胞周期蛋白依赖性激酶的作用靶点）已被突变为编码丙氨酸。我们在哺乳动物细胞中表达了p53小蛋白，并通过磷酸肽图谱分析表明它在单个生理磷酸化位点丝氨酸386处被磷酸化。以这种小蛋白作为CK2的细胞靶点，我们发现CK2对p53的磷酸化不受T抗原存在的影响。p53小蛋白可能是一种有用的工具，可用于探究CK2对p53磷酸化的调控，以响应其他影响细胞生长的因素。
