Department of Microbiology and Immunology, Seoul National University Medical Research Center, Seoul 110-799, Korea.
Microbiol Immunol. 2012 May;56(5):324-31. doi: 10.1111/j.1348-0421.2012.00446.x.
Human cytomegalovirus (HCMV) stimulates cellular synthesis of DNA and proteins and induces transition of the cell cycle from G(1) to S and G(2) /M phase, in spite of increased amounts of p53 in the infected cells. The immediate early protein IE2-86 kDa (IE86) tethers a transcriptional repression domain to p53; however, its repression of p53 function is not enough to abrogate the G(1) checkpoint function of p53. Other HCMV proteins that suppress the activity of p53 were investigated in this study. Of the HCMV proteins that bind to p53 when assessed by immunoprecipitation and immunoblot analysis, HCMV UL44 was chosen as a candidate protein. It was found that reporter gene containing p53 consensus sequence was activated by transfection with wild type p53, but when plasmids of p53 with IE86 or UL44 were co-transfected, p53 transcriptional activity was decreased to 3-7% of the p53 control in a dose-dependent manner. When the deletion mutant of UL44 was co-transected with p53, the carboxyl one-third portion of UL44 had little effect on inhibition of p53 transcriptional activity. The amount of mRNA p21 was measured in H1299 by real time PCR after transfection of the combination of p53 and UL44 vectors and it was found that p21 transcription by p53 was inhibited dose-dependently by UL44. Increased G0/G1 and decreased S phases in p53 wild type-transfected H1299 cells were recovered to the level of p53 mutant type-transfected ones by the additional transfection of UL44 in a dose-dependent manner. In conclusion, the transcriptional activity of p53 is suppressed by UL44 as well as by IE86.
人巨细胞病毒（HCMV）刺激细胞合成 DNA 和蛋白质，并诱导细胞周期从 G1 期进入 S 和 G2/M 期，尽管感染细胞中的 p53 含量增加。早期即刻蛋白 IE2-86kDa（IE86）将转录抑制结构域与 p53 连接；然而，其对 p53 功能的抑制作用不足以消除 p53 的 G1 检验点功能。在这项研究中还研究了其他抑制 p53 活性的 HCMV 蛋白。在通过免疫沉淀和免疫印迹分析评估与 p53 结合的 HCMV 蛋白时，选择 HCMV UL44 作为候选蛋白。发现含有 p53 共有序列的报告基因通过转染野生型 p53 被激活，但当共转染 p53 与 IE86 或 UL44 的质粒时，p53 转录活性以剂量依赖性方式降低至 p53 对照的 3-7%。当共转染 UL44 的缺失突变体时，UL44 的羧基三分之一部分对抑制 p53 转录活性几乎没有影响。通过实时 PCR 测量 H1299 中转染 p53 和 UL44 载体组合后 p21 的 mRNA 量，发现 UL44 以剂量依赖性方式抑制 p53 转录。通过 UL44 的额外转染，p53 野生型转染的 H1299 细胞中 G0/G1 期增加和 S 期减少恢复到 p53 突变型转染的水平。总之，UL44 与 IE86 一样抑制 p53 的转录活性。
