Adenovirus E1B 55-Kilodalton Oncoprotein Inhibits p53 Acetylation by PCAF

The adenovirus E1B 55-kDa protein binds to cellular tumor suppressor p53 and inactivates its transcriptional transactivation function. p53 transactivation activity is dependent upon its ability to bind to specific DNA sequences near the promoters of its target genes. It was shown recently that p53 is acetylated by transcriptional coactivators p300, CREB bidning protein (CBP), and PCAF and that acetylation of p53 by these proteins enhances p53 sequence-specific DNA binding. Here we show that the E1B 55-kDa protein specifically inhibits p53 acetylation by PCAF in vivo and in vitro, while acetylation of histones and PCAF autoacetylation is not affected. Furthermore, the DNA-binding activity of p53 is diminished in cells expressing the E1B 55-kDa protein. PCAF binds to the E1B 55-kDa protein and to a region near the C terminus of p53 encompassing Lys-320, the specific PCAF acetylation site. We further show that the E1B 55-kDa protein interferes with the physical interaction between PCAF and p53, suggesting that the E1B 55-kDa protein inhibits PCAF acetylase function on p53 by preventing enzyme-substrate interaction. These results underscore the importance of p53 acetylation for its function and suggest that inhibition of p53 acetylation by viral oncoproteins prevent its activation, thereby contributing to viral transformation.

腺病毒E1B 55-kDa蛋白可结合细胞肿瘤抑制因子p53，并使其转录反式激活功能失活。p53的反式激活活性依赖于其结合靶基因启动子附近特定DNA序列的能力。近期研究证实，p53可被转录共激活因子p300、CREB结合蛋白（CBP）以及PCAF乙酰化，且上述因子对p53的乙酰化修饰可增强p53的序列特异性DNA结合能力。本研究发现，E1B 55-kDa蛋白可在体内及体外特异性抑制PCAF介导的p53乙酰化修饰，而组蛋白乙酰化及PCAF的自身乙酰化不受其影响。此外，在表达E1B 55-kDa蛋白的细胞中，p53的DNA结合活性会被显著削弱。PCAF可同时结合E1B 55-kDa蛋白，以及p53羧基末端附近包含赖氨酸320（Lys-320，PCAF特异性乙酰化位点）的区域。我们进一步证实，E1B 55-kDa蛋白可干扰PCAF与p53之间的物理相互作用，这表明该蛋白通过阻断酶-底物相互作用，抑制了PCAF对p53的乙酰化酶活性。上述研究结果凸显了p53乙酰化修饰对其功能的重要性，并提示病毒癌蛋白可通过抑制p53的乙酰化修饰阻断其激活，进而促进病毒介导的细胞转化。