Suppression of centrosome amplification after DNA damage depends on p27 accumulation

The centrosome plays a fundamental role in cell division, cell polarity, and cell cycle progression. Centrosome duplication is mainly controlled by cyclin-dependent kinase 2 (CDK2)/cyclin E and cyclin A complexes, which are inhibited by the CDK inhibitors p21Cip1 and p27Kip1. It is thought that abnormal activation of CDK2 induces centrosome amplification that is frequently observed in a wide range of aggressive tumors. We previously reported that overexpression of the oncogene MYCN leads to centrosome amplification after DNA damage in neuroblastoma cells. We here show that centrosome amplification after gamma-irradiation was caused by suppression of p27 expression in MYCN-overexpressing cells. We further show that p27-/- and p27+/- mouse embryonic fibroblasts and p27-silenced human cells exhibited a significant increase in centrosome amplification after DNA damage. Moreover, abnormal mitotic cells with amplified centrosomes were frequently observed in p27-silenced cells. In response to DNA damage, the level of p27 gradually increased in normal cells independently of the ataxia telangiectasia mutated/p53 pathway, whereas Skp2, an F-box protein component of an SCF ubiquitin ligase complex that targets p27, was reduced. Additionally, p27 levels in MYCN-overexpressing cells were restored by treatment with Skp2 small interfering RNA, indicating that down-regulation of p27 by MYCN was due to high expression of Skp2. These results suggest that the accumulation of p27 after DNA damage is required for suppression of centrosome amplification, thereby preventing chromosomal instability.     

Inhibitors of mammalian target of rapamycin downregulate MYCN protein expression and inhibit neuroblastoma growth in vitro and in vivo

Mammalian target of rapamycin (mTOR) has been shown to play an important function in cell proliferation, metabolism and tumorigenesis, and proteins that regulate signaling through mTOR are frequently altered in human cancers. In this study we investigated the phosphorylation status of key proteins in the PI3K/AKT/mTOR pathway and the effects of the mTOR inhibitors rapamycin and CCI-779 on neuroblastoma tumorigenesis. Significant expression of activated AKT and mTOR were detected in all primary neuroblastoma tissue samples investigated, but not in non-malignant adrenal medullas. mTOR inhibitors showed antiproliferative effects on neuroblastoma cells in vitro. Neuroblastoma cell lines expressing high levels of MYCN were significantly more sensitive to mTOR inhibitors compared to cell lines expressing low MYCN levels. Established neuroblastoma tumors treated with mTOR inhibitors in vivo showed increased apoptosis, decreased proliferation and inhibition of angiogenesis. Importantly, mTOR inhibitors induced downregulation of vascular endothelial growth factor A (VEGF-A) secretion, cyclin D1 and MYCN protein expression in vitro and in vivo. Our data suggest that mTOR inhibitors have therapeutic efficacy on aggressive MYCN amplified neuroblastomas.     

Altered complex formation between p21waf, p27kip and their partner G1 cyclins determines the stimulatory or inhibitory transforming growth factor-beta1 growth response of human fibroblasts

TGF-beta1 stimulates proliferation of WI38 human embryo fibroblasts but inhibits that of their SV40-transformed counterparts, VA13 cells. Protein expression levels of cyclins A, D1, E and that of cdk2 and cdk4 were not affected by TGF-beta1 in either of these cells. However, TGF-beta1-treatment increases cdk2 kinase activity in WI38 cells and reduces it in VA13 cells. The same treatment reduces the amount of p21waf present in complexes with cyclins D1 and E in growth-stimulated WI38 cells, but the reverse applies in growth-inhibited VA13 cells. Mitogenic stimulation of WI38 fibroblasts correlated with decreased expression of p27kip protein and reduced amounts of it in complex with cyclin E. In contrast, proliferative inhibition of VA13 fibroblasts by TGF-beta1 caused a reduction of p27kip in complexes with cyclin D1, but increased it in complexes with cyclin E, without affecting the overall level of p27kip protein expression. Thus, in this human fibroblast model, TGF-beta1-mediated stimulation or inhibition of proliferation depends on modulation in the amounts of p21waf and p27kip in complexes with cyclins D1 and E.     

Antiproliferative function of p27kip1 is frequently inhibited in highly malignant Burkitt's lymphoma cells

Lack of detectable expression of p27kip1 cyclin dependent kinase inhibitor has previously been correlated with high degree of malignancy in human breast, colorectal, gastric and small cell lung carcinomas. Here we demonstrate that an inverse correlation between p27kip1 expression and tumour malignancy also exists in most types of human B cell lymphomas examined. A clear exception was Burkitt's lymphoma (BL), a highly malignant tumour which often expresses high levels of p27kip1. Analysis of p27kip1 derived from Burkitt's lymphoma cell lines expressing high levels of p27kip1, BL40 and BL41, in a cyclin E/cdk2 kinase inhibition assay demonstrated that p27kip1 is not permanently inactivated since heat treatment can restore the inhibitory activity of p27kip1. However, p27kip1 expressed in these two cell lines is largely sequestered in inactive complexes and we have no evidence that c-myc or Epstein-Barr virus are responsible for the sequestration of p27kip1 in these two cell lines although c-myc and EBV are two oncogenic agents often associated with Burkitt's lymphomas. Interestingly, we observed that high level p27kip1 expression often correlated with cyclin D3 overexpression both in vivo and in BL cell lines. The majority of p27kip1 in BL40 cells was complexed with cyclin D3 indicating that overexpressed cyclin D3 may at least be part of the sequestering activity for the inhibitory function of p27kip1. Furthermore, cyclinD3/cdk4 complex could sequester p27kip1 in a cyclin E/cdk2 kinase assay in vitro. Finally, we show that cyclin D3 transfected into an inducible p27kip1 cell line could overcome the G1 arrest mediated by p27kip1. These results argue that in addition to down-regulation of p27kip1 expression, some tumour cells can sequester and tolerate the antiproliferative function of p27kip1. They also suggest a novel role for the overexpression of D-type cyclins as one pathway allowing tumour cells to overcome the antiproliferative function of p27kip1.     

细胞周期蛋白激酶抑制蛋白p27kip1在肿瘤预后中的研究现状

细胞增殖是可调控的，细胞周期正向和负向调节因素参与其中。目前已发现细胞周期蛋白／周期蛋白激酶抑制剂同细胞周期Ｇ１期的调控有关。这此抑制剂中，ｐ２７＾ｋｉｐ１的研究特别受重视，在Ｇ１期细胞周期蛋白／周期蛋白激酶复合物的调节中起主要作用。ｐ２７高表达可引起Ｇ１期阻滞，抑制多种癌细胞的生长。目前仅在少数种类的肿瘤中检测了ｐ２７的免疫活性。在结肠癌和乳腺癌中，ｐ２７低表达与肿瘤进展和低生存率相关。研究证明     

High Skp2 expression characterizes high-risk neuroblastomas independent of MYCN status.

PURPOSE: Amplified MYCN oncogene defines a subgroup of neuroblastomas with poor outcome. However, a substantial number of MYCN single-copy neuroblastomas exhibits an aggressive phenotype similar to that of MYCN-amplified neuroblastomas even in the absence of high MYCN mRNA and/or protein levels. EXPERIMENTAL DESIGN: To identify shared molecular mechanisms that mediate the aggressive phenotype in MYCN-amplified and single-copy high-risk neuroblastomas, we defined genetic programs evoked by ectopically expressed MYCN in vitro and analyzed them in high-risk versus low-risk neuroblastoma tumors (n = 49) using cDNA microarrays. Candidate gene expression was validated in a separate cohort of 117 patients using quantitative PCR, and protein expression was analyzed in neuroblastoma tumors by immunoblotting and immunohistochemistry. RESULTS: We identified a genetic signature characterized by a subset of MYCN/MYC and E2F targets, including Skp2, encoding the F-box protein of the SCF(Skp2) E3-ligase, to be highly expressed in high-risk neuroblastomas independent of amplified MYCN. We validated the findings for Skp2 and analyzed its expression in relation to MYCN and E2F-1 expression in a separate cohort (n = 117) using quantitative PCR. High Skp2 expression proved to be a highly significant marker of dire prognosis independent of both MYCN status and disease stage, on the basis of multivariate analysis of event-free survival (hazard ratio, 3.54; 95% confidence interval, 1.56-8.00; P = 0.002). Skp2 protein expression was inversely correlated with expression of p27, the primary target of the SCF(Skp2) E3-ligase, in neuroblastoma tumors. CONCLUSION: Skp2 may have a key role in the progression of neuroblastomas and should make an attractive target for therapeutic approaches.     

口腔鳞状细胞癌细胞周期因子p27 cyclin D1及CDK4的表达与意义

目的：从细胞周期调控的角度来探讨口腔鳞状细胞癌（OSCC）的发生、发展及预后和p27、cyclin D1和CDK4的关系。方法：采用免疫组织化学方法，检测了50例口腔鳞状细胞癌及10例正常口腔粘膜中p27、cyclinD1和CDK4蛋白表达的水平，然后用Spearman 相关分析检查它们与临床病理学指标的关系以及它们三者之间的相关关系，用Kaplan-Meier方法绘制生存曲线并进行生存分析，Cox比例风险模型作预后分析。结果：1)p27在所有正常口腔粘膜上皮均呈现高表达，而在口腔鳞状细胞癌组织表达降低，p27的低表达与临床分期，淋巴结转移有显著性相关关系，cyclin D1和CDK4在正常粘膜上皮呈现低水平表达，在口腔钙状细胞癌组织中过表达。2)cyclinD1和CDK4在正常粘膜上皮呈现低水平表达，在口腔鳞状细胞癌组织中过表达.2)cyclin D1的表达与CDK4呈正相关（r=0.442,P=0.001）;p27与CDK4的表达呈负相关（r=-0.384,P=0.006）.3)Kaplan-Meier生存分析显示p27高表达组（ ）的各期的生存均高于低表达组（-）,cyclin D1染色（ ）组的生存率低于（-）组。4）Cox比例风险模型分析结果显示p27蛋白表达水平，cyclinD1蛋白表达水平，淋巴结转移和临床分期分别是口腔鳞状细胞癌的独立预后指标。结论：口腔鳞状细胞癌组织中，p27,cyclin D1和CDK4蛋白的异常表达说明它们均参与了口腔鳞状细胞癌的发生发展，且在这一过程中三者之间存在相互协同与制约关系。在临床应用中有可能将p27和cyclin D1蛋白的表达程度作为判断口腔鳞状癌患者预后的指标。     

Caspase-9 and Apaf-1 are expressed and functionally active in human neuroblastoma tumor cell lines with 1p36 LOH and amplified MYCN

Important roles have been suggested for caspase-8, caspase-9 and Apaf-1 in controlling tumor development and their sensitivity to chemotherapeutic agents. Methylation and deletion of Apaf-1 and CASP8 results in the loss of their expression in melanoma and neuroblastoma, respectively, while CASP9 localization to 1p36.1 suggests it is a good candidate tumor suppressor. The status of CASP9 and Apaf-1 expression in numerous neuroblastoma cell lines with/without amplified MYCN and chromosome 1p36 loss-of-heterozygosity (LOH) was therefore examined to test the hypothesis that one or both of these genes are tumor suppressors in neuroblastoma. Although CASP9 is included in the region encompassing 1p36 LOH in all neuroblastoma cell lines examined, the remaining CASP9 allele(s) express a functional caspase-9 enzyme. Apaf-1 is also expressed in all neuroblastoma tumor cell lines examined. Thus, the CASP9 or Apaf-1 genes do not appear to function as tumor suppressors in MYCN amplified neuroblastomas. However, approximately 20% of the neuroblastoma cell lines with methylated CASP8 alleles are also highly resistant to staurosporine (STS)- and radiation-induced cell death, presumably because cytochrome c is not released from mitochondria. This suggests that a second, smaller sub-group of MYCN amplified neuroblastoma tumors exists with defect(s) in apoptotic signaling components upstream of caspase-9 and Apaf-1. Since no consistent differences in Bcl-2, Bcl-x(L) or Bax expression were seen in the STS- and radiation-resistant neuroblastomas, it suggests that a unique mitochondrial signaling factor(s) is responsible for the defect in cytochrome c release in this sub-group of tumors.     

Proton pump inhibitors reduce cell cycle abnormalities in Barrett's esophagus.

Neoplastic progression in Barrett's esophagus is a multi-step process in which the metaplastic columnar epithelium sequentially evolves through a metaplasia-dysplasia-carcinoma sequence. The expression and DNA copy number of key cell cycle regulatory genes in paired normal and Barrett's esophagus samples was evaluated. Protein levels were evaluated in 60 formalin-fixed, paraffin-embedded human tissues by immunohistochemistry. DNA copy number from 20 fresh tissue pairs was analysed by Southern blot analysis. All normal mucosal samples expressed the p27(kip1) protein, but did not display appreciable nuclear staining for p16(kip4), p21(cip1) or cyclins D1 and E. Barrett's metaplastic specimens displayed increased expression levels of p16(kip4) (74%), p21(cip1) (89%) and cyclins D1 (43%) and E (37%). p27 protein was absent in three cases. There was a significant correlation between the expression of p16(kip4) and cyclin E, and p21(cip1) and p27(kip4) with cyclin D1. DNA analysis did not reveal any amplification or deletion of these genes. Acid suppression, however, was associated with significantly lower expression levels of key cell cycle proteins. Increased expression of key cell cycle regulatory genes appears to occur early in the neoplastic progression associated with Barrett's esophagus. Treatment with proton pump inhibitors appears to alter this increased expression.     

Cyclin E和p27~(kip1)在膀胱移行细胞癌中的表达及其意义

目的　探讨CyclinE和p2 7kip1在膀胱移行细胞癌 (BTCC)中的表达 ,并评价其相关性和意义。方法　应用鼠抗人CyclinE和 p2 7kip1单克隆抗体对 65例BTCC和 12例正常粘膜进行免疫组化SP法染色。结果　CyclinE在BTCC中阳性表达率随着病理分级 (P <0 .0 5 )和临床分期 (P <0 .0 1)的升高而增高 ,有淋巴结转移组非常显著高于无淋巴结转移组 (P <0 .0 1) ;而p2 7kip1在BTCC中的阳性表达率随着临床分期和病理分级的增高而降低 (P <0 .0 5 ) ,有淋巴结转移组显著低于无淋巴结转移组 (P <0 .0 5 )。CyclinE和 p2 7kip1在BTCC中表达具有负相关性 (r =-0 .2 62 ,P <0 .0 5 )。结论　CyclinE对BTCC的分化、增殖、浸润和转移可能起促进作用 ;而p2 7kip1则对BTCC的分化、增殖、浸润和转移可能起抑制作用 :两者在细胞周期进展中的共同表达失调 ,可能是导致BTCC发生发展和向恶性表型转化的机制之一。     

p27Kip1与消化系肿瘤关系的研究进展

p27Kipl定位于染色体12p13,含2个外显p27-方面抑制CDK激活,另一方面尚可抑制激活后的cyclin-CDK的活性,p27不仅在细胞周期增殖调控中起关键作用。而且与细胞的分化发育及凋亡也有关系。p27蛋白缺失或低表达在消化系恶性肿瘤中是一个较为普遍的现象。且低表达预示不良结局。