mdm2／p53通路相关的乳腺癌差异表达基因分析

目的比较乳腺癌和正常乳腺组织的基因表达差异，探讨与mdm2／p53通路相关的差异表达基因。方法提取11例乳腺癌和将5例正常乳腺组织等比例混合的组织总RNA进行芯片杂交，用SAM软件筛选差异表达基因，用GoMiner软件检索差异表达基因的功能，挑选参与细胞周期和凋亡的基因，通过Pathway分析方法检索与mdm2／p53通路相关的差异基因；用免疫组化方法验证差异基因cyclin A2及其相关基因CDK2在乳腺癌（38例）和正常乳腺组织（16例）中的表达。结果乳腺癌与正常乳腺组织的差异表达基因共548个，其中参与细胞周期的基因有35个，参与凋亡的基因有23个；与mdm2／p53通路相关的差异基因有4个，分别是cyclin A2，cyclin B1，PCNA，YWHAZ；经免疫组化验证的38例乳腺癌和16例正常乳腺组织的cyclin A2表达阳性率分别为42．1％（16／38，和6．25％（1／16）；CDK2表达阳性率分别为47．3％（18／38）和6．25％（1／16），两者均有统计学差异（P〈0．05）；在乳腺癌中cyclin A2与CDK2的表达呈正相关，特别值得一提的是如果以≥2^＋为阳性在乳腺癌cyclin A2为26．3％，CDK2为31．5％，而在正常组几乎看不到≥2^＋的表达。结论乳腺癌组织与正常乳腺组织相比存在着差异表达基因，与mdm2／p53通路相关的差异基因的异常高表达促进细胞增殖，与乳腺癌的发生密切相关，而cyclin A2和CDK2在乳腺癌共表达并明显高于正常组织其意义还不清楚。     

Inhibition of p53-murine double minute 2 interaction by nutlin-3A stabilizes p53 and induces cell cycle arrest and apoptosis in Hodgkin lymphoma.

PURPOSE: p53 is frequently expressed but rarely mutated in Hodgkin and Reed-Sternberg (HRS) cells of Hodgkin's lymphoma (HL). p53 protein levels are regulated by murine double minute 2 (MDM2) through a well-established autoregulatory feedback loop. In this study, we investigated the effects of nutlin-3A, a recently developed small molecule that antagonizes MDM2 and disrupts the p53-MDM2 interaction, on p53-dependent cell cycle arrest and apoptosis in cultured HRS cells. EXPERIMENTAL DESIGN: HL cell lines carrying wild-type (wt) or mutated p53 gene were treated with the potent MDM2 inhibitor nutlin-3A or a 150-fold less active enantiomer, nutlin-3B. RESULTS: We show that nutlin-3A, but not nutlin-3B, stabilizes p53 in cultured HRS cells carrying wt p53 gene resulting in p53-dependent cell cycle arrest and apoptosis. Cell cycle arrest was associated with up-regulation of the cyclin-dependent kinase inhibitor p21. Nutlin-3A-induced apoptotic cell death was accompanied by Bax and Puma up-regulation and caspase-3 cleavage and was abrogated, in part, by inhibition of caspase-9 and caspase-3 activity. By contrast, no effects on cell cycle or apoptosis were found in HL cell lines harboring mutated p53 gene. Furthermore, combined treatment with nutlin-3A and doxorubicin revealed enhanced cytotoxicity in HRS cells with wt p53 gene. Blocking of nuclear export by leptomycin B, or inhibition of proteasome by MG132, stabilized p53 at a level comparable with that of nutlin-3A treatment in HRS cells with wt p53. CONCLUSIONS: These data suggest that nutlin-3A stabilized p53 by preventing MDM2-mediated p53 degradation in HRS cells. wt p53 stabilization and activation by nutlin-3A may be a novel therapeutic approach for patients with HL.     

Cul4A physically associates with MDM2 and participates in the proteolysis of p53

The cullin 4A (Cul4A) gene is amplified and overexpressed in breast and hepatocellular carcinomas. Cul4A functions as an E3 ligase and participates in the proteolysis of several regulatory proteins through the ubiquitin-proteasome pathway. Here, we show that Cul4A associates with MDM2 and p53. Depletion of Cul4A leads to an accumulation of p53. Moreover, expression of Cul4A increases the decay-rate of p53 and delays the accumulation of p53 in response to DNA damage. Cul4A fails to increase the decay of p53 in mouse embryonic fibroblasts lacking MDM2. In addition, the Cul4A-mediated rapid decay of p53 is blocked by p19ARF. The results provide evidence for a role of Cul4A in the MDM2-mediated proteolysis of p53.     

The p53 mRNA-Mdm2 interaction controls Mdm2 nuclear trafficking and is required for p53 activation following DNA damage

The ATM kinase and p53 are key tumor suppressor factors that control the genotoxic stress response pathway. The ATM substrate Mdm2 controls p53 activity by either targeting p53 for degradation or promoting its synthesis by binding the p53 mRNA. The physiological role and regulation of Mdm2's dual function toward p53 is not known. Here we show that ATM-dependent phosphorylation of Mdm2 at Ser395 is required for the p53 mRNA-Mdm2 interaction. This event also promotes SUMO-conjugation of Mdm2 and its nucleoli accumulation. Interfering with the p53 mRNA-Mdm2 interaction prevents p53 stabilization and activation following DNA damage. These results demonstrate how ATM activity switches Mdm2 from a negative to a positive regulator of p53 via the p53 mRNA.     

Cytogenetic observations on a carcinoma of the cervix uteri with double minute chromatin bodies

In contrast to previous carcinomas at this site studied by chromosome banding techniques, no abnormalities or relative excess of the No. 1 chromosomes were found in a stage I carcinoma of the cervix. A feature of the tumour metaphases, however, was the presence of double minute chromatin bodies, including some rather larger bodies in a few of the metaphases. It is suggested that the absence of changes involving the No. 1 chromosomes might be related to the early stage and good prognosis of the tumour.     

p53 phosphorylation and association with murine double minute 2, c-Jun NH2-terminal kinase, p14ARF, and p300/CBP during the cell cycle and after exposure to ultraviolet irradiation

p53 phosphorylation and association with proteins is implicated in its stability and activity. We have compared the association of DNA-bound and overall pools of p53 with murine double minute 2 (Mdm2), c-Jun NH2-terminal kinase (JNK), p300/CBP, and p14ARF during cell cycle progression. Whereas DNA-bound p53 associates with JNK at G0-G1 and with Mdm2 and p300 during S and G2-M phases, the general pool of p53 was found in complex with JNK and Mdm2 almost throughout the cell cycle. Phosphorylation of p53 at serines 9, 15, and 20 is at the highest levels at G1 and at serines 37 and 392 during G2-M phase. Whereas a high dose of UV irradiation was required for phosphorylation of serines 15 and 392 between 8 and 24 h after treatment, a low dose caused immediate phosphorylation on serines 9, 20, and 372. These dynamic changes in the phosphorylation of p53 are expected to play a pivotal role in p53 association, stability, and function.     

Phosphorylation of p53 on Thr55 by ERK2 is necessary for doxorubicin-induced p53 activation and cell death

We recently reported that exposure of human cervical carcinoma cells to doxorubicin results in extracellular signal-regulated kinase (ERK)2 activation, which in turn phosphorylates p53 on a previously uncharacterized site, Thr55. This study sought to clarify the biological significance of doxorubicin-induced Thr55 phosphorylation. In breast carcinoma MCF7 cells, doxorubicin (300 nM) activated ERK2 and induced phosphorylation of p53 on Thr55 residues. Pretreatment of MCF7 cells with an ERK2 chemical inhibitor, PD98059 or U0126, blocked doxorubicin-induced p53 activation and suppressed phosphorylation of p53Thr55. MCF55a cells were established by transfection of full-length p53 carrying Thr55 mutation (Thr to Ala) into MCF7 cells. Doxorubicin (500 nM) could not induce p53 activation in MCF55a cells, which showed significantly increased drug resistance toward doxorubicin. While the expression of the apoptotic protein, Bax, showed no difference between MCF7 and MCF55a cells, Bcl-2, an antiapoptotic protein, was constitutively expressed in MCF55a cells. The increase of Bcl-2 protein and/or Bcl-2/Bax ratio might at least partly contribute to the drug resistance of MCF55a cells. In summary, our results suggest that phosphorylation of p53Thr55 by ERK2 is important for doxorubicin-induced p53 activation and cell death.     

Doxorubicin-induced mitochondrial dysfunction is secondary to nuclear p53 activation in H9c2 cardiomyoblasts

Purpose  Doxorubicin (DOX) is a widely prescribed chemotherapeutic. The hypothesis for the present study is that DOX-induced myocyte apoptosis involves mitochondrial dysfunction that is a consequence of nuclear DOX effects. Methods  H9c2 myoblasts were incubated with 0, 0.5 and 1 μM DOX and nuclear and mitochondrial alterations were determined. Results  Doxorubicin accumulation in the nucleus was detected after 3 h treatment, followed by an increase in p53 and a decrease in mitochondrial membrane potential. Apoptotic markers, such as caspase activation and chromatin condensation were detected after 24 h of DOX treatment. Bax and p53 translocation to mitochondria as well as the formation of Bax clusters in the cytosol were observed. Importantly, pifithrin-alpha, a p53 inhibitor, protected against DOX-induced mitochondrial depolarization, caspase activation and cell death. Conclusion  Mitochondrial dysfunction in H9c2 myoblasts treated with DOX is a consequence of nuclear p53 activation rather than a direct effect of the drug on mitochondria.