cyclin D1反义寡核苷酸对胃癌细胞生长和G1期调控的影响

目的：研究cyclin D1反义寡核苷酸(ASODN)对胃癌细胞SGC7901和HS746T的生长、细胞周期和G1期调控的影响。方法：采用脂质体Lipofect AMINE2000包裹硫代修饰的cyclin D1 ASODN转染细胞，观察量效曲线和生长曲线，应用RT-PCR检测cyclin D1 mRNA的表达，流式细胞仪检测细胞周期，并用免疫组织化学技术检测胃癌细胞中cyclin D1、p21、p27、pRb蛋白的表达。结果：cyclln D1 ASODN对胃癌细胞产生剂量依赖性的抑制效应，0．2μmol/L cyclin D1 ASODN转染24h能显著抑制胃癌细胞生长，cyclin D1 mRNA表达分别是对照组的26．3％(SGC7901)和17．3％(HS746T)，G0／G1期比例明显增加，并使2种细胞中cyclin D1、pRb表达降低，p21表达升高，在HS746T中p27表达下降，但在SGC7901中p27表达无改变。结论：cyclin D1反义寡核苷酸能有效抑制胃癌细胞的生长，降低cyclin D1 mRNA表达水平，并能影响细胞周期及其调控的表达。     

苯并芘对HELF细胞周期及相关基因表达的影响

背景与目的： 探讨苯并芘(benzo[a]pyrene, BaP)影响人胚肺成纤维细胞(HELF)周期的途径和作用机制。 材料与方法： 用5 μmol/L的BaP处理HELF细胞后,采用细胞计数,流式细胞仪检测BaP对细胞生长和周期的影响,用PCR和Western-blotting检测BaP对细胞周期相关基因mRNA和蛋白的影响。 结果： BaP处理HELF细胞后,显著促进细胞的生长,在处理后第8 d时细胞数目约增加50％(P<0.01),细胞体积增大,促进细胞由G1期向S期和G2/M期的转换。 mRNA和蛋白检测结果显示：BaP处理细胞后可以促进p53、cyclin D1、CDK2、CDK4和p21 mRNA及蛋白的表达(P<0.05或P<0.01),抑制cyclin E mRNA及蛋白的表达(P均<0.01),而对cyclin A和p27 mRNA及蛋白表达没有明显影响(P均>0.05)。 结论： BaP对HELF细胞周期的调控逃脱了p53-p21的关卡作用,而通过诱导cyclin D1、CDK2和CDK4的表达来加快细胞周期的进程,该途径为cyclin A和p27非依赖型。     

Cyclin E、CDK2和p21WAF1在食管上皮癌变过程中的表达及意义

目的探讨食管上皮癌变过程中细胞周期调控因子cyclin E、CDK2和p21WAF1的表达状况及其意义.方法应用免疫组化SP法和原位杂交方法分别检测48例食管癌组织、31例非典型增生组织和17例正常食管粘膜中cyclin E、CDK2和p21WAF1蛋白及mRNA表达.应用半定量RT-PCR和Western blot检测22例新鲜食管癌及相应癌旁组织的mRNA和蛋白表达.结果从食管正常粘膜、非典型增生组织到癌组织,cyclin E和CDK2蛋白和mRNA阳性表达率逐渐上升,差异具有统计学意义(P＜0.01或P＜0.05).食管癌组织中cyclin E、CDK2和p21WAF1蛋白及mRNA高表达,与癌旁组织或切缘正常食管粘膜有显著性差异(P＜0.01).cyclin E、CDK2和p21WAF1基因表达显著正相关(P＜0.01或P＜0.05).结论食管上皮癌变过程中,细胞周期相关基因cyclin E和CDK2表达逐渐增强.cyclin E基因表达异常是食管癌变过程中的早期事件.p21WAF1基因在食管癌中高表达,可能与细胞周期调控的反馈机制有关.     

肾细胞癌中cyclin D1、cyclin E和p21cip1的mRNA表达

目的探讨细胞周期素D1、E(cyclin D1、cyclin E)、p21cip1在pTNM Ⅰ期普通型肾细胞癌(CRCC)发生发展中的作用.方法用半定量RT-PCR方法,检测23例pTNM Ⅰ期CRCC组织和7例正常肾组织中cyclin D1、cyclin E及p21cip1的mRNA含量;用免疫组化方法检测CRCC中p53及ki-67的表达;并将以上指标与临床病理特征进行统计分析.结果 CRCC组织中cyclin D1、cyclin E、p21cip1mRNA含量分别为0.484±0.416、0.472±0.340、0.356±0.215,均高于正常对照组(0.078±0.051,P＜0.01;0.063±0.063,P＜0.01;0.178±0.114,P＜0.05);Cyclin D1含量低者肿瘤直径小于3 cm(P＜0.01);Cyclin E含量低者肿瘤常有坏死(P＜0.05),细胞核分级较高(P＜0.01);p21cip1低表达者细胞核分级较高(P＜0.05);p21cip1与cyclin E呈正相关(γ=0.602,P＜0.01).结论 pTNM Ⅰ期CRCC组织中cyclin D1、cyclin E、p21cip1mRNA含量升高,可能影响肿瘤的生物学行为及预后.     

NF-κB、cyclin D1和p27在非小细胞肺癌中的表达及意义

目的:探讨核转录因子-κB(NF-κB)、细胞周期素D1(cyclin D1)和p27在非小细胞肺癌中的表达及临床意义.方法:应用免疫组化S-P法检测58例非小细胞肺癌(NSCLC)和15例正常肺组织中NF-κBp65、cyclin D1、p27的表达.结果:NSCLC组织中NF-κBp65和cyclin D1的表达明显高于正常肺组织中的表达(P＜0.01),p27表达则明显低于正常肺组织(P＜0.01).NF-κBp65表达与NSCLC瘤体大小、淋巴结转移、临床分期密切相关(P＜0.05);cyclin D1表达与瘤体大小、肿瘤分化、淋巴结转移、临床分期密切相关(P＜0.05);p27表达与瘤体大小、肿瘤分化密切相关(P＜0.05).NF-κBp65与cyclin D1在NSCLC组织中的表达呈正相关(P＜0.05),cyclin D1与027的表达呈负相关(P＜0.05),NF-κBp65与p27的表达无相关性(P＞O.05).结论:NF-κB、cyclin D1、p27与非小细胞肺癌的发生、发展有关,检测三种蛋白的表达可以间接判断NSCLC的生物学行为.     

丙戊酸钠对Burkitt淋巴瘤Raji细胞增殖的影响及机制

目的 研究丙戊酸钠对Burkitt淋巴瘤Raji细胞增殖的影响及其机制.方法 细胞计数法检测不同浓度丙戊酸钠处理Raji细胞后细胞的增殖活性,制作生长抑制曲线.流式细胞仪检测细胞周期和凋亡率.Westernblot检测细胞周期蛋白cyclin D1和p21、凋亡抑制基因survivin的变化.结果 丙戊酸钠能明显抑制Raji细胞的增殖,其作用表现为剂量依赖性和时间依赖性(P＜0.01).流式细胞仪检测发现以3 mmol/L的丙戊酸钠处理Raji细胞后细胞阻滞于G0/G1期,其凋亡率呈时间依赖性上升(P＜0.01).Western blot检测发现3 mmol/L丙戊酸钠处理后Raji细胞cyclin D1表达明显下调而p21表达明显上调(均P＜0.05).survivin表达显著下降(P＜0.01).结论 丙戊酸钠对人Burkitt淋巴瘤Raji细胞具有明显的增殖抑制作用,其作用机制与细胞周期和诱导凋亡有关.     

shRNA靶向沉默Eag 1钾通道对骨肉瘤细胞增殖、细胞周期及cyclin D1／E表达的影响

目的 探讨短发夹RNA（shRNA）靶向沉默Ether-go-go 1（Eag1）钾通道对骨肉瘤MG-63细胞增殖、细胞周期及cyclin D1／E表达的影响。 方法 使用成功构建的Ad5-Eag1-shRNA表达载体转染MG-63细胞（抑制组）,同时设转染无义序列（Ad5-Control-shRNA）的空转染组及不进行任何处理的对照组。采用逆转录聚合酶链式反应和Western blotting检测Ad5-Eag1-shRNA转染骨肉瘤MG-63细胞后的Eag1 mRNA和蛋白水平,分别采用CCK-8法和克隆形成实验检测各组的细胞增殖情况,流式细胞仪和Western blotting分别检测各组的细胞周期变化和细胞周期蛋白（cyclin D1和cyclin E）的蛋白水平。建立裸鼠骨肉瘤异种移植模型并测量各组裸鼠肿瘤体积的变化情况。结果 抑制组的Eag1 mRNA和蛋白水平均低于空转染组和对照组,差异有统计学意义（P＜0.05）;与其余两组相比,抑制组的细胞增殖、克隆形成数、S期细胞比例及细胞周期蛋白水平均降低,而G0／G1期细胞比例升高,以上差异均有统计学意义（P＜0.05）。抑制组裸鼠的瘤体积小于空转染组和对照组（P＜0.05）。结论 通过shRNA抑制Eag1基因表达可抑制MG-63细胞的增殖并诱导G0／G1期阻滞,可能与调控cyclin D1／E通路有关,有望成为骨肉瘤治疗和诊断的新靶点。     

Trastuzumab联合丁酸钠对人乳腺癌细胞株SKBR3细胞增殖和p27~（Kip1）表达的影响

目的：观察组蛋白去乙酰化酶抑制剂（HDACIs）丁酸钠（NaB）及曲妥珠单抗Trastuzumab对人乳腺癌细胞株SKBR3细胞增殖、细胞周期及细胞凋亡的影响,探讨NaB及Trastuzumab调控乳腺癌细胞增殖的分子机制。方法：乳腺癌SKBR3细胞经NaB、Trastuzumab单独或联合作用后,MTT法检测细胞增殖情况,流式细胞仪分析细胞周期分布及细胞凋亡,Western Blot方法检测p27Kip1的表达。结果：NaB单独用药显著抑制SKBR3细胞增殖,促进细胞G0/G1期阻滞,增加细胞凋亡和p27Kip1蛋白的表达,P〈0.05;20μg/mL Trastuzumab单独用药,对细胞有增殖抑制和细胞周期阻滞作用（P〈0.05）,但对细胞凋亡及p27Kip1蛋白表达无明显影响,P〉0.05。Trastuzumab可协助NaB增加对SKBR3的抗肿瘤作用及p27Kip1蛋白表达,P〈0.05。结论：Trastuzumab联合NaB抑制乳腺癌细胞的增殖,促进细胞周期阻滞及细胞凋亡的发生,以上过程可能是通过增加p27Kip1的蛋白表达来实现。     

p^27Kip1和细胞周期蛋白D1在胃癌中的表达及其预后意义

目的：研究p^27Kip1、细胞周期蛋白D1（cyclinD1)在胃癌组织中的表达水平以及与生物学行为的关系和对预后评价的意义。方法：以免疫组化方法检测92例胃癌组织中p^27Kip1、 cyclinD1蛋白的表达水平。结果：本组92例胃癌中,p^27Kip1蛋白阳性39例,占42．4％;cyclinD1蛋白表达阳性44例,占47．8％;胃癌组织中,p^27Kip1蛋白水平与胃壁浸润深度、TNM分期、病理组织学分级、区域淋巴结转移均相关（P＜0．05）;cyclinD1蛋白表达与病理组织学分级负相关（P＜0．05）;p^27Kipl与cyclinD1蛋白阳性表达显著相关（P＜0．05）;单变量生存分析结果,p^27Kip1高表达组三年、五年生存率分别为77．1％、57．8％,明显高于低表达组的33．7％、26．3％（P＝0．007）,多变量分析显示,p^27Kip1是一个独立的预后指标（P＝0．0003）。结论：p^27Kip1可作为反映肿瘤恶性表型的指标,对胃癌预后具有一定的价值;cyclin1 D1是胃癌发生、发展过程中早期的分子事件;p^27Kip1在胃癌进展中起着比cyclin D1更重要的作用。     

细胞周期素D1反义寡核苷酸对胃癌细胞株BGC—823的作用

目的：通过基因反义封闭技术体外抑制细胞周期素D1(cyclin D1)的表达，并对胃癌细胞增殖的影响。方法：以胃腺癌BGC-823细胞株为研究对象，采用硫代修饰的cyclin D1反义寡脱氧核苷酸(ASODN)处理BGC-823细胞后，观察cyclin D1 ASODN对BGC-823细胞基因表达及体外增殖活性的影响。结果：MTT法测细胞增殖活性见不同浓度ASODN均能抑制BGC-823细胞增殖，抑制作用在48小时最强。RT-PCR检测结果cyclin D1 mRNA减少。免疫组化S-P法结果cyclin D1蛋白表达明显降低。结论：使用人工合成的cyclin D1 ASODN可以特异性的抑制胃腺癌BGC-823细胞株cyclin D1的表达，从而调控细胞周期，抑制细胞增殖。     

Mutant B-RAF signaling and cyclin D1 regulate Cks1/S-phase kinase-associated protein 2-mediated degradation of p27Kip1 in human melanoma cells

Levels of cyclins and cyclin-dependent kinase (Cdk) inhibitors are tightly controlled during normal cell proliferation and are frequently dysregulated in cancerous cells. In melanoma, cyclin D1 is highly expressed and downregulation of the Cdk inhibitor, p27(Kip1), is associated with a poor prognosis. Mutant B-RAF is frequently expressed in melanoma and overrides growth factor and matrix adhesion control of cyclin D1 and p27(Kip1) levels in human melanocytes. Here, we demonstrate that p27(Kip1) expression is regulated by multiple mechanisms in melanoma cells. B-RAF regulates p27(Kip1) mRNA abundance independently of cyclin D1. Additionally, B-RAF and cyclin D1 control the levels of S-phase kinase-associated protein 2 (Skp2) that directs ubiquitin-mediated proteolysis of p27(Kip1). The cofactor for Skp2, Cdc kinase subunit 1 (Cks1) controls levels of Skp2 in melanoma cells and acts jointly with Skp2 to regulate p27(Kip1) levels. Importantly, expression of Cks1 is regulated by B-RAF and cyclin D1 at the mRNA level. Reduced Cks1 or Skp2 expression and enhanced p27(Kip1) levels inhibit melanoma cell growth. In summary, p27(Kip1) expression in melanoma is regulated by B-RAF at the mRNA level, and via B-RAF and cyclin D1 control of Cks1/Skp2-mediated proteolysis.     

大蒜素对人胃癌细胞BGC823 cyclin D1和p27Kip1表达的影响

背景与目的：在研究大蒜素抑制人胃癌细胞BGC823恶性增殖,将其阻滞于G1期并诱导BGC823细胞凋亡的分子机制及其靶基因过程中,我们发现cvclin D1和p27^Kip1。蛋白在G1期阻滞中起重要作用。本实验从mRNA和蛋白水平探讨大蒜素对人胃癌细胞BGC823 cvclin D1和p27^Kip1表达水平的影响。方法：用25μg／ml大蒜素处理BGC823细胞,并分别提取对照组和大蒜素处理组的总RNA和总蛋白,然后采用RT-PCR和Western blot法检测大蒜素处理前后cvclin D1和p27^Kip1 mRNA和蛋白的变化。结果：经25μg／ml大蒜素处理BGC823细胞24h,cyclin D1蛋白表达下调,p27^Kip1蛋白表达上调,处理48h,上述变化更明显。而mRNA水平未见明显改变。结论：大蒜素可影响cyclin D1和p27^Kip1蛋白的表达,而不影响mRNA的转录。     

Involvement of p27Kip1 in G1 arrest by high dose 5 alpha-dihydrotestosterone in LNCaP human prostate cancer cells

The cell cycle is governed by cyclin dependent kinases (cdks), which are activated by binding of cyclins, inhibited by cdk inhibitors and regulated by phosphorylation and dephosphorylation. Exposure to high dose dihydrotestosterone (DHT) inhibits population growth of the human prostate carcinoma cell line, LNCaP. To determine the mechanism of growth arrest by high dose DHT, we assayed the changes in cell cycle profile and the cell cycle regulators that mediate these effects. Treatment of asynchronously growing LNCaP cells with 100 nM DHT caused a G1 arrest. The proportion of cells in S phase fell from 22 to 2%, while the G1 fraction rose from 74 to 92% by 24 h. Loss of phosphorylation of the retinoblastoma protein was noted and cdk4 and cyclin E/ cdk2 activities fell. Inhibition of these G1 cyclin dependent kinases was not due to loss of either cyclin or cdk proteins nor to increases in the cdk inhibitors p16INK4A and p21CiP1. p21Cip1 protein levels remained constant, and cyclin E-associated p21CiP1 fell, suggesting that p21CiP1 is not relevant to this form of cyclin E/cdk2 inhibition. Of note, total p27KiP1 levels and cyclin E-associated p27Kip1 increased as cells arrested and the amount of the CAK activated cdk2 bound to cyclin E decreased. p27KiP1 immunodepletion experiments demonstrated that the DHT-mediated increase in p27Kip1 was sufficient to fully saturate and inhibit target cyclin E/ cdk2. The inhibition of cyclin E/cdk2 by p27Kip1 contributes to G1 arrest of LNCaP following high dose DHT. p27KiP1 may be a key effector of androgen dependent growth modulation in prostate cancer cells.     

BCR signals target p27(Kip1) and cyclin D2 via the PI3-K signalling pathway to mediate cell cycle arrest and apoptosis of WEHI 231 B cells.

Cross-linking of the B cell antigen receptor (BCR) on immature WEHI 231 B cells results in G1 cell cycle arrest and apoptosis. Here we investigated the molecular mechanisms that are necessary and sufficient for these changes to occur. We show that BCR stimulation of WEHI 231 cells results in down-regulation of cyclin D2 and up-regulation of p27(Kip1), which are associated with pocket protein hypophosphorylation and E2F inactivation. Ectopic expression of p27(Kip1) by TAT-fusion protein or retroviral transduction is sufficient to cause G1 cell cycle arrest, followed by apoptosis. In contrast, over-expression of cyclin D2 overcomes the cell cycle arrest and apoptosis induced by anti-IgM, indicating that down-regulation of cyclin D2 is necessary for the cell cycle arrest and apoptosis activated by BCR stimulation. Thus, cyclin D2 and p27(Kip1) have opposing roles in these pathways and our data also suggest that cyclin D2 functions upstream of p27(Kip1) and the pRB pathway and therefore plays an essential part in integrating the signals from BCR with the cell cycle machinery. We next investigated which signal transduction pathways triggered by the BCR regulate cell proliferation and apoptosis via cyclin D2 and p27(Kip1). Inhibition of PI3-K signalling by LY294002 down-regulated cyclin D2 and up-regulated p27(Kip1) expression at both protein and RNA levels, mimicking the effects of BCR-stimulation. Furthermore, ectopic expression of a constitutively active form of AKT blocked the cell cycle arrest and apoptosis triggered by anti-IgM and also abrogated down-regulation of cyclin D2 and up-regulation of p27(Kip1) expression induced by BCR-engagement. These results indicate that BCR activation targets p27(Kip1) and cyclin D2 to mediate cell cycle arrest and apoptosis and that down-regulation of PI3-K/AKT activity post BCR stimulation is necessary for these to occur.     

Expression of p27Kip1 and cyclin D1 proteins is inversely correlated and is associated with poor clinical outcome in human gastric cancer.

BACKGROUND AND OBJECTIVES: p27Kip1 is an inhibitor of cyclin-dependent kinases and is speculated to be a potential prognostic indicator in numerous human cancers. We investigated expression of p27Kip1 along with cyclin D1 in gastric cancer to estimate the clinical utility of p27Kip1. METHODS: Immunohistochemical assay for p27Kip1 and cyclin D1 proteins was performed in 64 patients with primary gastric cancer. Correlation between p27Kip1 expression and clinical-biological parameters including patient survival was analyzed. RESULTS: p27Kip1 expression was suppressed in 40 (62.5%) of 64 gastric cancer patients and cyclin D1 was overexpressed in 22 (34.4%) out of 64. Expression of p27Kip1 was significantly reduced in poorly differentiated cancers (82.1%, 23/28; P = 0.015) and was also reduced in the tumors with high S-phase fraction (86.7%, 26/30) compared with tumors showing low S-phase fraction (41.2%, 14/34; P = 0.0002). Expression of p27Kip1 and cyclin D1 was inversely correlated (P = 0.021). In univariate analysis, extent of the disease (P < 0.001), expression of cyclin D1 (P = 0.0001), and reduced expression of p27Kip1 (P = 0. 0006), were statistically significant to predict patient's outcome, but depth of invasion (P = 0.008) and pathologic stage (P = 0.009) emerged as significant prognostic indicators in multivariate analysis. CONCLUSION: Expression of p27Kip1 is closely linked with cell proliferation and differentiation of human gastric cancer. p27Kip1 seems to have potential as a prognostic marker in the management of gastric cancer patients.     

Insufficient effect of p27(KIP1) to inhibit cyclin D1 in human esophageal cancer in vitro

The cell cycle is controlled by protein complexes composed of cyclins and cyclin-dependent kinases. p27KIP1 (p27) is one of the Kip/Cip family cyclin-dependent kinase inhibitory proteins which negatively regulate cell cycle progression, and have been proposed as candidate tumor suppressor genes. To examine the role of p27 in the development of human esophageal squamous cell carcinoma (ESCC), we performed Western blot and immunoprecipitation analyses of the levels of expression of p27 protein in a series of ESCC cell lines. This protein was expressed at various levels in these cell lines during exponential growth. p27 level was significantly associated with that of cyclin D1, but not of cyclin E. Further cell cycle synchronization studies demonstrated that p27 was free or bound with affinity to cyclin E-CDK2 more than to cyclin D1-CDK4 or cyclin D1-CDK6. It is known that overexpression of cyclin D1 rather than cyclin E is involved in the pathogenesis of ESCC. Our findings indicated that high expression of p27 throughout the G1 to S phase may inhibit more likely cyclin E, than cyclin D1, which promotes tumor growth of esophageal squamous cell carcinoma.     

p27^Kip1基因及蛋白在骨肉瘤中的表达及其意义

目的 探讨p27^KIP1基因在骨肉瘤MG-63、U2细胞株及骨肉瘤组织中的表达情况及其与骨肉瘤生物学行为的关系。方法 培养人骨肉瘤细胞MG-63、U2和人成骨细胞OB；以半定量RT-PCR技术检测3种细胞中p27^KIP1基因的mRNA表达情况。以免疫细胞化学染色技术检测MG-63、U2及OB中p27^KIP1蛋白的表达情况。以免疫组织化学方法检测骨肉瘤、骨软骨瘤、正常骨3种组织中p27^KIP1蛋白的表达情况，并探讨其与临床病理学特征之间的关系。结果 p27^KIP1基因mRNA的表达在人骨肉瘤细胞MG-63、U2和人成骨细胞OB中没有差别。p27^KIP1蛋白的表达在OB中高于MG-63和U2，MG-63和U2间p27^KIP1蛋白的表达没有差别。骨肉瘤组织的p27^KIP1蛋白表达低于骨软骨瘤组织和正常骨组织，p27^KIP1蛋白表达与Enneking外科分期及是否发生转移相关。结论 骨肉瘤细胞、组织p27^KIP1蛋白表达明显降低；p27^KIP1蛋白的表达可作为骨肉瘤预后判断的一个有价值的指标。     

p27~(Kip1)和细胞周期蛋白D1在胃癌中的表达及其预后意义

目的 :研究p2 7Kip1、细胞周期蛋白D1(cyclinD1)在胃癌组织中的表达水平以及与生物学行为的关系和对预后评价的意义。方法 :以免疫组化方法检测 92例胃癌组织中p2 7Kip1、cyclinD1蛋白的表达水平。结果 :本组 92例胃癌中 ,p2 7Kip1蛋白阳性 39例 ,占 42 .4% ;cyclinD1蛋白表达阳性 44例 ,占 47.8% ;胃癌组织中 ,p2 7Kip1蛋白水平与胃壁浸润深度、TNM分期、病理组织学分级、区域淋巴结转移均相关 (P <0 .0 5 ) ;cyclinD1蛋白表达与病理组织学分级负相关 (P <0 .0 5 ) ;p2 7Kip1与cyclinD1蛋白阳性表达显著相关 (P <0 .0 5 ) ;单变量生存分析结果 ,p2 7Kip1高表达组三年、五年生存率分别为 77.1%、5 7.8% ,明显高于低表达组的 33.7%、2 6 .3 % (P =0 .0 0 7) ,多变量分析显示p2 7Kip1是一个独立的预后指标 (P =0 .0 0 0 3)。结论 :p2 7Kip1可作为反映肿瘤恶性表型的指标 ,对胃癌预后具有一定的价值 ;cyclinD1是胃癌发生、发展过程中早期的分子事件 ;p2 7Kip1在胃癌进展中起着比cyclinD1更重要的作用。     

Oncostatin M induces growth arrest by inhibition of Skp2, Cks1, and cyclin A expression and induced p21 expression

Oncostatin M has been characterized as a potent growth inhibitor for various tumor cells. Oncostatin M-treated glioblastoma cells cease proliferation and instigate astrocytal differentiation. The oncostatin M-induced cell cycle arrest in G(1) phase is characterized by increased level of the cyclin-dependent kinase (CDK) inhibitory proteins p21(Cip1/Waf1/Sdi1) and p27(Kip1). Induction of p21 protein corresponds to increased mRNA level, whereas p27 accumulates due to increased stability of the protein. Interestingly, stabilization of p27(Kip1) occurs even in S phase, showing that p27 stabilization is a direct consequence of oncostatin M signaling and not a result of the cell cycle arrest. Degradation of p27 in late G(1) and S phase is initiated by the ubiquitin ligase complex SCF-Skp2/Cks1. Oncostatin M inhibits expression of two components of this E3 ligase complex (Skp2 and Cks1). Although combined overexpression of Skp2 and Cks1 rescues p27 degradation in S phase, it can not override p27 accumulation in G(1) phase and cell cycle arrest by oncostatin M. In addition to increasing Cdk inhibitor level, oncostatin M also impairs cyclin A expression. Cyclin A mRNA and protein level decline shortly after oncostatin M addition. The accumulation of two CDK inhibitor proteins and the repression of cyclin A expression may explain the broad and potent antiproliferative effect of the cytokine.