Takenaka I, Morin F, Seizinger B R, Kley N
Department of Molecular Genetics and Cell Biology, Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, New Jersey 08543-4000.
J Biol Chem. 1995 Mar 10;270(10):5405-11. doi: 10.1074/jbc.270.10.5405.
The p53 tumor suppressor protein is a transcription factor with sequence-specific DNA binding activity that is thought to be important for the growth-inhibitory function of p53. DNA binding appears to require activation of a cryptic form of p53 by allosteric mechanisms involving a negative regulatory domain at the carboxyl terminus of p53. The latent form of p53, reactive to the carboxyl-terminal antibody PAb421, is produced in a variety of eukaryotic cells, suggesting that activation of p53 is an important rate-limiting step in vivo. In this report we provide evidence that phosphorylation of serine 378 within the carboxyl-terminal negative regulatory domain of the human p53 protein by protein kinase C correlates with loss of PAb421 reactivity and a concomitant activation of sequence-specific DNA binding. These effects are reversed by subsequent dephosphorylation of the protein kinase C-reactive site by protein phosphatases 1 (PP1) and 2A (PP2A), which restore the reactivity of p53 to PAb421 and regenerate the latent form of p53 lacking significant DNA binding activity. Thus, p53 is subject to both positive and negative regulation by reversible enzymatic modifications affecting the latent or active state of the protein, suggesting a possible mechanism for the regulation of its tumor suppressor function.
p53肿瘤抑制蛋白是一种具有序列特异性DNA结合活性的转录因子，被认为对p53的生长抑制功能很重要。DNA结合似乎需要通过涉及p53羧基末端负调控域的变构机制激活p53的一种隐匿形式。对羧基末端抗体PAb421有反应的p53潜伏形式在多种真核细胞中产生，这表明p53的激活是体内一个重要的限速步骤。在本报告中，我们提供证据表明，蛋白激酶C对人p53蛋白羧基末端负调控域内丝氨酸378的磷酸化与PAb421反应性的丧失以及序列特异性DNA结合的伴随激活相关。蛋白磷酸酶1（PP1）和2A（PP2A）随后对蛋白激酶C反应位点的去磷酸化可逆转这些效应，恢复p53对PAb421的反应性，并使缺乏显著DNA结合活性的p53潜伏形式再生。因此，p53受到影响其潜伏或活性状态的可逆酶促修饰的正调控和负调控，这提示了一种调控其肿瘤抑制功能的可能机制。
