García J F, Piris M A, Lloret E, Orradre J L, Murillo P G, Martínez J C
Department of Pathology, Virgen de la Salud Hospital, Toledo, Spain.
Histopathology. 1997 Feb;30(2):120-5. doi: 10.1046/j.1365-2559.1997.d01-577.x.
The p53 tumour suppressor gene is a cell cycle regulator, able to induce cell cycle arrest to allow DNA repair or apoptosis. The molecular mechanisms underlying p53 action imply transactivation of p53 dependent genes such as WAF1 (for wild type p53 associated fragment 1) and the murine double minute (MDM2) gene. In some cases, inactivation of the p53 gene results from p53 gene mutations leading to p53 protein accumulation, but in others it may results from mechanisms other than mutation, such as interaction with viral or cellular proteins. The expression of p53 protein and p53 transactivated gene proteins p21/WAF1 and MDM2, combined with in situ detection of apoptosis, was studied in specimens of CMV-infected patients as an in vivo model of p53 alteration not due to point mutation. p53 positivity was found in CMV + cells in different tissues, in cells with typical inclusion bodies, and in in situ hybridization and immunohistochemistry CMV + cells without inclusions (hidden infection). Although this p53 reactivity was accompanied by the expression of MDM2 and p21/WAF1 proteins, the patterns of MDM2 and p21/WAF1 protein expression were mutually exclusive, and were associated with the presence or absence of inclusion bodies. Nuclei bearing inclusion bodies were usually MDM2+, p21/ WAF1-, while hidden infected cells were usually MDM2-, p21/WAF1+. Apoptosis was not detected in any tissue section from CMV-infected patients. Two alternative patterns were found in CMV-infected tissues: p53+, p21/WAF1+, MDM2-, or p53+, p21/WAF1-. MDM2+ protein expression. These may represent examples of p53 dependent alternative effects in the course of CMV infection. Early stages are represented by CMV + cells without inclusion bodies, which display p53 and p21/ WAF1 expression, suggesting that p53 could be acting as a growth suppressor protein. Late CMV infection is represented by cells harbouring inclusion bodies. These cells showed a p53+, p21/WAF1-, MDM2+ profile, consistent with MDM2 mediated p53 inactivation. The absence of p21/WAF1 expression and lack of apoptosis suggest that the p53 protein expressed by MDM2+ cells could be functionally inactivated in CMV-infected cells with inclusion bodies. Previous studies have suggested that p53 inactivation by MDM2 over-expression occurs in sarcomas and lymphomas. Our observations seem to indicate that this mechanism of MDM2 mediated p53 inactivation may play a role in the late phase of CMV infection.
p53肿瘤抑制基因是一种细胞周期调节因子，能够诱导细胞周期停滞，以允许DNA修复或凋亡。p53作用的分子机制意味着p53依赖性基因的反式激活，如WAF1（野生型p53相关片段1）和鼠双微体（MDM2）基因。在某些情况下，p53基因的失活是由p53基因突变导致p53蛋白积累引起的，但在其他情况下，可能是由突变以外的机制引起的，如与病毒或细胞蛋白的相互作用。作为p53改变（非点突变所致）的体内模型，我们研究了巨细胞病毒（CMV）感染患者标本中p53蛋白、p53反式激活基因蛋白p21/WAF1和MDM2的表达，并结合凋亡的原位检测。在不同组织的CMV+细胞、具有典型包涵体的细胞以及原位杂交和免疫组化检测中无包涵体的CMV+细胞（隐匿感染）中发现了p53阳性。尽管这种p53反应性伴随着MDM2和p21/WAF1蛋白的表达，但MDM2和p21/WAF1蛋白的表达模式相互排斥，且与包涵体的有无相关。带有包涵体的细胞核通常MDM2阳性、p21/WAF1阴性，而隐匿感染细胞通常MDM2阴性、p21/WAF1阳性。在CMV感染患者的任何组织切片中均未检测到凋亡。在CMV感染的组织中发现了两种不同的模式：p53阳性、p21/WAF1阳性、MDM2阴性，或p53阳性、p21/WAF1阴性、MDM2阳性蛋白表达。这些可能代表了CMV感染过程中p53依赖性替代效应的例子。早期阶段以无包涵体的CMV+细胞为代表，这些细胞显示p53和p21/WAF1表达，表明p53可能作为一种生长抑制蛋白发挥作用。CMV感染后期以含有包涵体的细胞为代表。这些细胞显示出p53阳性、p21/WAF1阴性、MDM2阳性的特征，与MDM2介导的p53失活一致。p21/WAF1表达缺失和凋亡缺失表明，MDM2阳性细胞表达的p53蛋白在有包涵体的CMV感染细胞中可能功能失活。先前的研究表明，MDM2过表达导致的p53失活发生在肉瘤和淋巴瘤中。我们的观察结果似乎表明，这种MDM2介导的p53失活机制可能在CMV感染的后期发挥作用。
