Maxwell S A
Department of Thoracic and Cardiovascular Surgery, University of Texas M. D. Anderson Cancer Center, Houston 77030.
Anticancer Res. 1994 Nov-Dec;14(6B):2541-7.
Overexpression of the mdm2 protooncogene protein, which can lead to the inactivation of normal p53, has been observed in some human cancers. The mdm2 gene is positively regulated by p53, providing for a feedback loop in the control of both p53 and mdm2 activity. The expression of the mdm2 and p53 proteins in different non-small cell lung carcinoma (NSCLC) cell types harboring wild-type or mutant p53, or lacking p53 altogether, were investigated to determine whether a correlation exists between the expression of these two proteins. The mdm2 protein was expressed at very low levels in all NSCLC lines examined, regardless of the p53 status. To determine whether mdm2 could be induced by p53 in NSCLC, NSCLC cells were transfected with a recombinant adenovirus expressing high levels of wild-type p53. The highest levels of exogenous wild-type p53 were observed in p53-null H358 and H1299 cells and in H226b cells expressing endogenous wild-type p53 were observed in p53-null H358 and H1299 cells and in H226b cells expressing endogenous wild-type p53. In these cells, wild-type p53 induced the expression of 90/92K M(r) mdm2 proteins, as well as several faster-migrating mdm2-related species exhibiting relative mobilities of 76/78K, 57/59K, 46K, 28K, and 12K. Northern analyses of H358 and H1299 cells transfected with wild-type p53 showed that these cells expressed three species of mdm2 mRNA of 5.5, 4.6-3.8, and 2.1 Kb in size. Subcellular fractionation revealed that the 90/92K M(r) mdm2 protein species was localized to both the crude plasma membrane/cytoplasmic and nuclear fractions, and that the smaller mdm2 proteins associated selectively with different nuclear substructures. The 76/78K, 57/59K, and 46K Mr(r) mdm2 proteins may be derived by differential splicing of the 5.5 Kb mRNA, and their differential compartmentalization within the nucleus suggests that each has a distinct function, potentially in the regulation of p53 and other gene products.
在一些人类癌症中已观察到mdm2原癌基因蛋白的过表达，其可导致正常p53失活。mdm2基因受p53正向调控，从而在p53和mdm2活性的控制中形成一个反馈环。研究了野生型或突变型p53或完全缺乏p53的不同非小细胞肺癌（NSCLC）细胞类型中mdm2和p53蛋白的表达，以确定这两种蛋白的表达之间是否存在相关性。在所检测的所有NSCLC细胞系中，无论p53状态如何，mdm2蛋白均以极低水平表达。为了确定在NSCLC中mdm2是否可被p53诱导，用表达高水平野生型p53的重组腺病毒转染NSCLC细胞。在p53缺失的H358和H1299细胞中观察到最高水平的外源性野生型p53，在表达内源性野生型p53的H226b细胞中也在p53缺失的H358和H1299细胞以及表达内源性野生型p53的H226b细胞中观察到。在这些细胞中，野生型p53诱导了90/92K M(r) mdm2蛋白以及几种迁移速度更快的mdm2相关蛋白的表达，这些蛋白的相对迁移率分别为76/78K、57/59K、46K、28K和12K。对转染野生型p53的H358和H1299细胞进行Northern分析表明，这些细胞表达三种大小分别为5.5、4.6 - 3.8和2.1 Kb的mdm2 mRNA。亚细胞分级分离显示，90/92K M(r) mdm2蛋白定位于粗质膜/细胞质和细胞核部分，而较小的mdm2蛋白选择性地与不同的核亚结构相关。76/78K、57/59K和46K Mr(r) mdm2蛋白可能是由5.5 Kb mRNA的差异剪接产生的，它们在细胞核内的差异区室化表明每种蛋白都有独特的功能，可能参与p53和其他基因产物的调控。
