C/EBPα基因与肿瘤

C/EBPα基因是抑癌基因,有抑制增殖、促进分化和调节DNA损伤反应等作用。各种机制如对抗性的蛋白质-蛋白质相互作用、基因突变和翻译后修饰等导致C/EBPα转录抑制或活性丧失,可能诱发肿瘤。本文结合国内外研究现状,介绍C/EBPα基因的结构、功能及与肿瘤的诊断、治疗和预后的关系。     

Sequences near both termini of the C/EBPβ mRNA 3＇ untranslated region are important for its tumor suppression activity

The 3＇ untranslated region （3＇ UTR） of eukaryotic mRNA is an important regulation element that affects not only mRNA translation, but also cell growth. We had found that the 3＇ UTR of CCAAT-enhancerbinding protein β （C/EBPβ） mRNA had tumor suppression activity. Herein, we reported that deletion of two short sequences at both termini of the C/EBPβ 3t UTR reduced the tumor suppression activity of this 3＇ UTR, as demonstrated by reduced cell growth, colony formation ability, and tumorigenicity in nude mice. It is noteworthy that the only deletion of a single such sequence was enough for the reduction of tumor sup- pression effect, and the reducing effect of deletion of the sequence near 3r terminus was stronger. Therefore, specific short sequences in the C/EBPβ 3＇ UTR are crucial for the tumor suppression activity of C/EBPβ.     

C/EBPα在非小细胞肺癌中的表达及其与微血管密度的关系

目的:探讨C/EBPα在非小细胞肺癌(non-small cell lung cancer,NSCLC)组织中的表达及其与肿瘤微血管密度(microvessel density,MVD)的关系.方法:应用免疫组织化学EnVision法检测40例手术切除的NSCLC组织及其配对的40例距肿瘤＞5 cm以上癌旁正常肺组织中C/EBPα蛋白的表达,并分析C/EBPα在NSCLC中的表达与其临床病理特征的关系.采用CD34标记肺癌组织中的肿瘤微血管,分析C/EBPα的表达与肿瘤MVD的关系.结果:NSCLC组织中C/EBPα的阳性表达率明显低于癌旁正常肺组织(P＜0.05).C/EBPα与NSCLC患者的年龄、性别、TNM分期及有无淋巴结转移均无关(P＞0.05),与NSCLC组织的分化程度及病理类型有关(P＜0.05).在NSCLC组织中,C/EBPα蛋白表达阳性组MVD明显低于C/EBPα蛋白表达阴性组(P＜0.05).结论:C/EBPα在NSCLC中的低表达可能通过调节MVD介导NSCLC的发生和发展.     

C/EBPα蛋白在新疆维吾尔族妇女子宫颈鳞癌组织中的表达及临床意义

目的:研究C/EBPα蛋白在新疆维吾尔族妇女子宫颈鳞癌组织中的表达及临床意义。方法:采用免疫组化S-P法对36例子宫颈鳞癌组织、26例慢性子宫颈炎组织中C/EBPα蛋白的表达进行检测。结果:新疆维吾尔族妇女慢性子宫颈炎与子宫颈鳞癌组织中C/EBPα蛋白的表达具有显著性差异(P<0.05);并且C/EBPα蛋白的表达与肿瘤的病理分级有关(P<0.05)。结论:C/EBPα蛋白与新疆维吾尔族的子宫颈鳞癌有着密切的关系,该基因可能是一种潜在的抑制子宫颈鳞癌发生的基因。     

Differential effects of p63 mutants on transactivation of p53 and/or p63 responsive genes

p63, known to play a role in development, has more recently also been implicated in cancer progression. Mutations in p63 have been shown to be responsible for several human developmental diseases. Differential splicing of the p63 gene gives rise to p63 isoforms, which can act either as tumor suppressors or as oncogene. In this report, we studied the effects of naturally occurring TAp637 mutants on the regulation of p53/p63 and p63 specific target genes. We observed significant differences among p63 mutants to regulate the p53/p63 and p63 specific target genes. Additionally, we observed a differential effect of p63 mutants on wildtype-p63-mediated induction ofp53/p63 and p63 specific target genes. We also demonstrated that these mutants differentially regulate the binding of wildtype p63 to the promoter of target genes. Furthermore, the effects of these mutants on cell death and survival were consistent with their ability to regulate the downstream targets when compared to wildtype TAp63T. In summary, our data demonstrate that p63 mutants exhibit differential effects on p63 and p53/p63 specific target genes and on the induction of apoptosis, and provide further insight into the function of p63.     

mad—overexpression down regulates the malignant growth and p53 mediated apoptosis in human hepatocellular carcinoma BEL—7404 cells

Mad protein has been shown as an antagonist of cMyc protein in some cell lines.The effect of Mad protein to the malignant phenotype of human hepatoma BEL-7404 cell line was investigated experimentally.An eukarryotic vector pCDNA Ⅲ containing full ORF fragment of mad cDNA was transfected into targeted cells.Under G418 selection,stable Mad-overexpressed cells were cloned.Studies on the effect of Mad over-expression in cell proliferation and cell cycle revealed that cell morphology of the Mad-overexpressed BEL-7404-M1 cells was significantly different from the parent and control vector transfected cells.DNA synthesis,cell proliferation and anchorage-independent growth in soft-agar of the madtransfected cells were partially inhibited in comparison to control cells.Flos cytometry analysis indicated that mad over-expression might block more transfectant cells at G0/G1 phase,resulting in the retardation of cell proliferation.RT-PCR detected a marked inhibition of the expression of cdc25A,an important regulator gene of G0/G1 to S phase in cell cycle.It was also found that Mad protein overexpression could greatly suppress p53-mediated apoptosis in BEL-74040M1 cells in the absence of serume.Thus,Mad proteins may function as a negative regulator antagonizing c-Myc activity in the control of cell growth and apoptosis in human hepatocellular carcinoma BEL-7404 cells.     

Moderate hypothermia prevents neural cell apoptosis following spinal cord ischemia in rabbits

Paraplegia is a disastrous complication after operations of descending and thoracoabdominal aortic aneurysm. Regional hypothermia protects against spinal cord ischemia although the protective mechanism is not well know. The objective of this study is to examine whether hypothermia protects the spinal cord by preventing apoptosis of nerve cell and also investigate a possible mechanism involved in hypothermia neuroprotection. Cell apoptosis with necrosis was evident in the spinal cord 24 h after 30 min of ischemia. Moderate hypothermia decreased the incidence of apoptotic nerve cells. Both cell apoptosis and necrosis were attenuated by hypothermia, p53 expression increased and bcl-2 expression declined after ischemia, while hypothermia mitigated these changes. This study suggests that apoptosis contributes to cell death after spinal cord ischemia, and that moderate hypothermia can prevent nerve cell apoptosis by a mechanism associated with bcl-2 and p53 genes.     

Regulation of apoptotic and growth inhibitory activities of C/EBPalpha in different cell lines

C/EBPalpha is expressed in many tissues and inhibits cell growth. In this paper, we have examined mechanisms which regulate activities of C/EBPalpha in cell lines derived from different tissues. We found that C/EBPalpha possesses strong pro-apoptotic activity in NIH3T3 cells, while this activity is not detected in 3T3-L1, Hep3B2 and HEK293 cells. Micro-array data show that C/EBPalpha activates many genes of apoptosis signaling in NIH3T3 cells. One of these genes, ARL6IP5, is a direct target of C/EBPalpha and is a key mediator of the apoptosis. Using C/EBPalpha mutants which do not cause cell death; we have found that C/EBPalpha does not arrest proliferation of NIH3T3 cells. The lack of growth arrest in NIH3T3 cells correlates with the inhibition of p16INK4 and with low levels of cyclin D3. The limited growth inhibitory activity of C/EBPalpha is also observed in Hep3B2 cells which express low levels of cyclin D3. Elevation of cyclin D3 restores growth inhibitory activity of C/EBPalpha in NIH3T3 and in Hep3B2 cells. These data show that apoptotic and growth inhibitory activities of C/EBPalpha are differentially regulated in different cells and that cooperation of cyclin D3 and C/EBPalpha is required for the inhibition of proliferation.     

C/EBPalpha regulates formation of S-phase-specific E2F-p107 complexes in livers of newborn mice

We previously showed that the rate of hepatocyte proliferation in livers from newborn C/EBPalpha knockout mice was increased. An examination of cell cycle-related proteins showed that the cyclin-dependent kinase (CDK) inhibitor p21 level was reduced in the knockout animals compared to that in wild-type littermates. Here we show additional cell cycle-associated proteins that are affected by C/EBPalpha. We have observed that C/EBPalpha controls the composition of E2F complexes through interaction with the retinoblastoma (Rb)-like protein, p107, during prenatal liver development. S-phase-specific E2F complexes containing E2F, DP, cdk2, cyclin A, and p107 are observed in the developing liver. In wild-type animals these complexes disappear by day 18 of gestation and are no longer present in the newborn animals. In the C/EBPalpha mutant, the S-phase-specific complexes do not diminish and persist to birth. The elevation of levels of the S-phase-specific E2F-p107 complexes in C/EBPalpha knockout mice correlates with the increased expression of several E2F-dependent genes such as those that encode cyclin A, proliferating cell nuclear antigen, and p107. The C/EBPalpha-mediated regulation of E2F binding is specific, since the deletion of another C/EBP family member, C/EBPbeta, does not change the pattern of E2F binding during prenatal liver development. The addition of bacterially expressed, purified His-C/EBPalpha to the E2F binding reaction resulted in the disruption of E2F complexes containing p107 in nuclear extracts from C/EBPalpha knockout mouse livers. Ectopic expression of C/EBPalpha in cultured cells also leads to a reduction of E2F complexes containing Rb family proteins. Coimmunoprecipitation analyses revealed an interaction of C/EBPalpha with p107 but none with cdk2, E2F1, or cyclin A. A region of C/EBPalpha that has sequence similarity to E2F is sufficient for the disruption of the E2F-p107 complexes. Despite its role as a DNA binding protein, C/EBPalpha brings about a change in E2F complex composition through a protein-protein interaction. The disruption of E2F-p107 complexes correlates with C/EBPalpha-mediated growth arrest of hepatocytes in newborn animals.     

C/EBPalpha regulation of the growth-arrest-associated gene gadd45.

CCAAT/enhancer-binding protein alpha (C/EBPalpha) is expressed in postmitotic, differentiated adipocytes and is required for adipose conversion of 3T3-L1 cells in culture. Temporal misexpression of C/EBPalpha in undifferentiated adipoblasts leads to mitotic growth arrest. We report here that growth arrest- and DNA damage-inducible gene 45 (gadd45) is preferentially expressed in differentiated 3T3-L1 adipocytes similar to phenotype-associated genes. Furthermore, C/EBPalpha transactivates a reporter plasmid containing 1.5 kb of the gadd45 promoter region. The proto-oncogene myc, which inhibits adipocyte differentiation, abrogates C/EBPalpha activation of gadd45. gadd45 is known to be a target of the tumor suppressor p53 in a G1 checkpoint activated by DNA damage. Immunoprecipitation of radiolabeled proteins with conformation-specific antibodies revealed that wild-type p53 is expressed throughout 3T3-L1 adipocyte development, including the postmitotic period characterized by the accumulation of gadd45 and C/EBPalpha. A stable 3T3-L1 subline was engineered to express a dominant negative p53, human p53(143ala). The p53(143ala) subline differentiated to adipocytes and showed appropriate developmental expression of gadd45. These findings suggest that postmitotic growth arrest is coupled to adipocyte differentiation via C/EBPalpha stimulation of growth arrest-associated and phenotype-associated genes.