Lundgren K, Montes de Oca Luna R, McNeill Y B, Emerick E P, Spencer B, Barfield C R, Lozano G, Rosenberg M P, Finlay C A
Cell Cycle Project, Glaxo Wellcome Research and Development, Research Triangle Park, North Carolina 27709, USA.
Genes Dev. 1997 Mar 15;11(6):714-25. doi: 10.1101/gad.11.6.714.
MDM2 is a cellular protein that binds to and inactivates the p53 tumor suppressor protein. Although mdm2 has been shown to function as an oncogene in vitro, all studies to date have assessed MDM2 activities in the presence of p53, implicating p53 inactivation in MDM2-directed transformation. To determine the role of MDM2 in the cell cycle and in tumorigenesis and whether or not this role is dependent on p53, an MDM2 minigene was expressed during gestation and lactation in the mammary gland of both wild-type p53 (p53+/+) and p53 knockout (p53-/-) mice using the bovine beta-lactoglobulin promoter. In six different transgenic mouse lines, deregulated expression of MDM2 inhibited normal development and morphogenesis of the mammary gland, and caused cellular hypertrophy and nuclear abnormalities. These abnormalities included both multinucleated cells and enlarged cells with giant nuclei. Although there were fewer epithelial cells present in the transgenic mammary gland, no apoptosis was observed. Instead, BrdU incorporation and PCNA staining showed that 12%-27% of the transgenic mammary epithelial cells were in S phase at a time when normal cells were terminally differentiated. Analysis of DNA content showed that 30%-45% of the cells were polyploid, with DNA contents up to 16N, indicating that overexpression of MDM2 caused mammary epithelial cells to undergo multiple rounds of S phase without cell division. This phenotype was similar in the p53+/+ and p53-/- background, demonstrating a role for MDM2 in the regulation of DNA synthesis that is independent of the ability of MDM2 to inhibit p53 activity. Additionally, multiple lines of BLGMDM2 transgenic mice developed mammary tumors, confirming that overproduction of MDM2 contributes to tumorigenesis in epithelial cells in vivo.
MDM2是一种细胞蛋白，它与p53肿瘤抑制蛋白结合并使其失活。尽管MDM2在体外已被证明具有癌基因功能，但迄今为止所有研究都是在有p53存在的情况下评估MDM2的活性，这表明p53失活与MDM2介导的转化有关。为了确定MDM2在细胞周期和肿瘤发生中的作用，以及该作用是否依赖于p53，我们使用牛β-乳球蛋白启动子在野生型p53（p53+/+）和p53基因敲除（p53-/-）小鼠的乳腺妊娠期和哺乳期表达了一个MDM2小基因。在六个不同的转基因小鼠品系中，MDM2的失调表达抑制了乳腺的正常发育和形态发生，并导致细胞肥大和核异常。这些异常包括多核细胞和具有巨大细胞核的增大细胞。尽管转基因乳腺中的上皮细胞较少，但未观察到细胞凋亡。相反，BrdU掺入和PCNA染色显示，在正常细胞终末分化时，12%-27%的转基因乳腺上皮细胞处于S期。DNA含量分析表明，30%-45%的细胞是多倍体，DNA含量高达16N，这表明MDM2的过表达导致乳腺上皮细胞在不进行细胞分裂的情况下经历多轮S期。这种表型在p53+/+和p53-/-背景中相似，表明MDM2在DNA合成调节中发挥作用，且该作用独立于MDM2抑制p53活性的能力。此外，多个BLG-MDM2转基因小鼠品系发生了乳腺肿瘤，证实了MDM2的过量产生在体内上皮细胞肿瘤发生中起作用。
