沉默Bmi-1基因表达稳定细胞株的建立及其生物学特性的研究

B细胞特异性莫洛尼鼠白血病病毒插入位点1(B-cell-specific moloney murine leukemia virus insertionsite 1,Bmi-1)基因是多梳基因家族成员,参与细胞增殖调控.研究发现Bmi-1基因可能参与肿瘤的形成,可能成为肿瘤潜在的治疗靶点.用RNA干扰(RNA interference,RNAi)沉默Bmi-1基因表达观察其对乳腺癌细胞株MCF-7侵袭和转移等生物学特性的影响,以探讨Bmi-1在乳腺癌发生发展中的作用.PT67细胞包装质粒后产生的逆转录病毒感染MCF-7细胞,嘌呤霉素筛选建立稳定细胞株,稳定抑制Bmi-1的细胞株命名为MCF-7/Bmi-1si.通过RT-PCR和Western blot分别从mRNA和蛋白水平检测Bmi-1的表达量;平板克隆形成实验检测细胞克隆形成能力;Transwell侵袭小室模型检测细胞体外侵袭和转移能力.MCF-7/Bmi-1si组与MCF-7和MCF-7/GFPsi组相比,Bmi-1 mRNA和蛋白表达量明显减少,克隆形成数及形成率也明显减少(P<0.05).侵袭和转移实验表明:与MCF-7和MCF-7/GFPsi组相比,MCF-7/Bmi-1si组细胞在Transwell侵袭小室中24 h穿膜细胞数明显减少(P<0.05).结果表明沉默Bmi-1基因表达稳定细胞株构建成功,Bmi-1基因表达的沉默能显著降低MCF-7细胞的体外增殖及侵袭转移能力.     

Silencing of Bmi-1 gene by RNA interference enhances sensitivity to doxorubicin in breast cancer cells

The oncogene Bmi-1 is highly up-regulated in breast carcinoma and is found to be efficient in preventing apoptosis of the cancer cells. Doxorubicin is an important chemotherapeutic agent against breast carcinoma. However, the effective therapeutic response to doxorubicin is often associated with severe toxicity. The present study is targetted at developing a strategy to increase doxorubicin sensitivity to lower doses without compromising its efficacy. A stable cell line with a persistent silencing of Bmi-1 was established. MTT assay was performed to evaluate 50% inhibitory concentration (IC50) values of doxorubicin. Apoptosis was detected by FCM and the expression of related genes [phosphor-Akt (pAkt), totle-Akt (tAkt), Bcl-2 and Bax] was studied by Western blot. In vivo, the sensitivity of the tumor tissues against doxorubicin was evaluated by transplanted MCF-7 nude mice model and the apoptosis of tissue cells was detected by TUNEL assay. The expression of pAkt and Bcl-2 was down-regulated, whereas Bax was up-regulated in Bmi-1 silencing cells. The results obtained indicated that silencing of Bmi-1 can render MCF-7 cells more sensitive to doxorubicin which induced a significantly higher percentage of apoptosis cells in vitro and in vivo. All together these results clearly demonstrate that Bmi-1 siliencing combined treatment of doxorubicin might be a new strategy for biological treatment on breast cancer.     

Cathepsin G-induced malignant progression of MCF-7 cells involves suppression of PAF signaling through induced expression of PAFAH1B2

Breast cancer is primarily classified into ductal and lobular types, as well as into noninvasive and invasive cancer. Invasive cancer involves lymphatic and hematogenous metastasis. In breast cancer patients with distant metastases, a neutrophil-derived serine protease; cathepsin G (Cat G), is highly expressed in breast cancer cells. Cat G induces cell migration and multicellular aggregation of MCF-7 human breast cancer cells; however, the mechanism is not clear. Recently, platelet-activating factor (PAF)-acetylhydrolase (PAF-AH), the enzyme responsible for PAF degradation, was reported to be overexpressed in some tumor types, including pancreatic and breast cancers. In this study, we investigated whether PAF-AH is involved in Cat G-induced aggregation and migration of MCF-7 cells. We first showed that Cat G increased PAF-AH activity and elevated PAFAH1B2 expression in MCF-7 cells. The elevated expression of PAFAH1B2 was also observed in human breast cancer tissue specimens by immunohistochemical analysis. Furthermore, knockdown of PAFAH1B2 in MCF-7 cells suppressed the cell migration and aggregation induced by low concentrations, but not high concentrations, of Cat G. Carbamoyl PAF (cPAF), a nonhydrolyzable PAF analog, completely suppressed Cat G-induced migration of MCF-7 cells. In addition, PAF receptor (PAFR) inhibition induced cell migration of MCF-7 cells even in the absence of Cat G, suggesting that Cat G suppresses the activation of PAFR through enhanced PAF degradation due to elevated expression of PAFAH1B2 and thereby induces malignant phenotypes in MCF-7 cells. Our findings may lead to a novel therapeutic modality for treating breast cancer by modulating the activity of Cat G/PAF signaling.     

Silencing MAP3K1 expression through RNA interference enhances paclitaxel-induced cell cycle arrest in human breast cancer cells

The objective of this study is to compare the expression level of MAP3K1 between normal mammary gland cells and breast cancer cells, and to analyze the effects of silencing MAP3K1 on breast cancer cells with paclitaxel treatment. Western blotting analysis was used to detect the expression level of MAP3K1 in MCF-7 and MCF-12F cells. The effect of gene silencing through different siRNAs was determined by realtime-PCR. MTT assay was used to test the cell proliferation. Cell cycle was detected by flow cytometry. MAP3K1 protein expression level in breast cancer cells was higher than that in normal mammary gland cells. MAP3K1 siRNA transfection significantly reduced the expression level of MAP3K1, and enhanced paclitaxel-induced cell proliferation inhibition and cell cycle arrest in breast cancer cells. Targeting MAP3K1 expression through small RNA interference can promote the therapeutic effects of paclitaxel in breast cancer.     

Possible role of Pax-6 in promoting breast cancer cell proliferation and tumorigenesis

Pax 6, a member of the paired box (Pax) family, has been implicated in oncogenesis. However, its therapeutic potential has been never examined in breast cancer. To explore the role of Pax6 in breast cancer development, a lentivirus based short hairpin RNA (shRNA) delivery system was used to knockdown Pax6 expression in estrogen receptor (ER)-positive (MCF-7) and ER-negative (MDA-MB-231) breast cancer cells. Effect of Pax6 silencing on breast cancer cell proliferation and tumorigenesis was analyzed. Pax6-RNAi-lentivirus infection remarkably downregulated the expression levels of Pax6 mRNA and protein in MCF-7 and MDA-MB-231 cells. Accordingly, the cell viability, DNA synthesis, and colony formation were strongly suppressed, and the tumorigenesis in xenograft nude mice was significantly inhibited. Moreover, tumor cells were arrested at G0/G1 phase after Pax6 was knocked down. Pax6 facilitates important regulatory roles in breast cancer cell proliferation and tumor progression, and could serve as a diagnostic marker for clinical investigation.     

Protein kinase D1 stimulates proliferation and enhances tumorigenesis of MCF-7 human breast cancer cells through a MEK/ERK-dependent signaling pathway

Protein kinase D1, PKD1, is a novel serine/threonine kinase whose altered expression and dysregulation in many tumors as well as its activation by several mitogens suggest that this protein could regulate proliferation and tumorigenesis. Nevertheless, the precise signaling pathways used are still unclear and the potential direct role of PKD1 in tumor development and progression has not been yet investigated. In order to clarify the role of PKD1 in cell proliferation and tumorigenesis, we studied the effects of PKD1 overexpression in a human adenocarcinoma breast cancer cell line, MCF-7 cells. We demonstrated that overexpression of PKD1 specifically promotes MCF-7 cell proliferation through accelerating G0/G1 to S phase transition of the cell cycle. Moreover, inhibition of endogenous PKD1 significantly reduced cell proliferation. Taken together, these results clearly strengthen the regulatory role of PKD1 in cell growth. We also demonstrated that overexpression of PKD1 specifically diminished serum- and anchorage-dependence for proliferation and survival in vitro and allowed MCF-7 cells to form tumors in vivo. Thus, all these data highlight the central role of PKD1 in biological processes which are hallmarks of malignant transformation. Analysis of two major signaling pathways implicated in MCF-7 cell proliferation showed that PKD1 overexpression significantly increased ERK1/2 phosphorylation state without affecting Akt phosphorylation. Moreover, PKD1 overexpression-stimulated cell proliferation and anchorage-independent growth were totally impaired by inhibition of the MEK/ERK kinase cascade. However, neither of these effects was affected by blocking the PI 3-kinase/Akt signaling pathway. Thus, the MEK/ERK signaling appears to be a determining pathway mediating the biological effects of PKD1 in MCF-7 cells. Taken together, all these data demonstrate that PKD1 overexpression increases the aggressiveness of MCF-7 breast cancer cells through enhancing their oncogenic properties and would, therefore, define PKD1 as a potentially new promising anti-tumor therapeutic target.     

Short-hairpin RNA-mediated Heat shock protein 90 gene silencing inhibits human breast cancer cell growth in vitro and in vivo

Hsp90 interacts with proteins that mediate signaling pathways involved in the regulation of essential processes such as proliferation, cell cycle control, angiogenesis and apoptosis. Hsp90 inhibition is therefore an attractive strategy for blocking abnormal pathways that are crucial for cancer cell growth. In the present study, the role of Hsp90 in human breast cancer MCF-7 cells was examined by stably silencing Hsp90 gene expression with an Hsp90-silencing vector (Hsp90-shRNA). RT-PCR and Western blot analyses showed that Hsp90-shRNA specifically and markedly down-regulated Hsp90 mRNA and protein expression. NF-kB and Akt protein levels were down-regulated in Hsp90-shRNA transfected cells, indicating that Hsp90 knockout caused a reduction of survival factors and induced apoptosis. Treatment with Hsp90-shRNA significantly increased apoptotic cell death and caused cell cycle arrest in the G1/S phase in MCF-7 cells, as shown by flow cytometry. Silencing of Hsp90 also reduced cell viability, as determined by MTT assay. In vivo experiments showed that MCF-7 cells stably transfected with Hsp90-shRNA grew slowly in nude mice as compared with control groups. In summary, the Hsp90-shRNA specifically silenced the Hsp90 gene, and inhibited MCF-7 cell growth in vitro and in vivo. Possible molecular mechanisms underlying the effects of Hsp90-shRNA include the degradation of Hsp90 breast cancer-related client proteins, the inhibition of survival signals and the upregulation of apoptotic pathways. shRNA-mediated interference may have potential therapeutic utility in human breast cancer.     

Downregulation of Choline Kinase-Alpha Enhances Autophagy in Tamoxifen-Resistant Breast Cancer Cells

Choline kinase-α (Chk-α) and autophagy have gained much attention, as they relate to the drug-resistance of breast cancer. Here, we explored the potential connection between Chk-α and autophagy in the mechanisms driving to tamoxifen (TAM) resistance, in estrogen receptor positive (ER+) breast cancer cells (BCCs). Human BCC lines (MCF-7 and TAM-resistant MCF-7 (MCF-7/TAM) cells) were used. Chk-α expression and activity was suppressed by the transduction of shRNA (shChk-α) with lentivirus and treatment with CK37, a Chk-α inhibitor. MCF-7/TAM cells had higher Chk-α expression and phosphocholine levels than MCF-7 cells. A specific downregulation of Chk-α by the transduction of shChk-α exhibited a significant decrease in phosphocholine levels in MCF-7 and MCF-7/TAM cells. The autophagy-related protein, cleaved microtubule-associated protein light chain 3 (LC3) and autophagosome-like structures were significantly increased in shChk-α-transduced or CK37-treated MCF-7 and MCF-7/TAM cells. The downregulation of Chk-α attenuated the phosphorylation of AKT, ERK1/2, and mTOR in both MCF-7 and MCF-7/TAM cells. In MCF-7 cells, the downregulation of Chk-α resulted in an induction of autophagy, a decreased proliferation ability and an activation of caspase-3. In MCF-7/TAM cells, despite a significant decrease in proliferation ability and an increase in the percentage of cells in the G0/G1 phase of the cell cycle, the downregulation of Chk-α did not induced caspase-dependent cell death and further enhanced autophagy and G0/G1 phase arrest. An autophagy inhibitor, methyladenine (3-MA) induced death and attenuated the level of elevated LC3 in MCF-7/TAM cells. Elucidating the interplay between choline metabolism and autophagy will provide unique opportunities to identify new therapeutic targets and develop novel treatment strategies that preferentially target TAM-resistance.     

siRNA-cyclin D1对乳腺癌MCF-7细胞增殖的抑制作用

研究小干扰RNA(small interfering RNA,siRNA)对乳腺癌MCF-7细胞株cyclin D1表达的抑制及对细胞增殖的影响。化学合成针对cyclin D1基因的siRNA,转染MCF-7细胞株;分别应用荧光定量PCR和免疫印迹测定cyclin D1 mRNA和蛋白的表达,CCK-8测定细胞的增殖活性,流式细胞仪检测细胞周期,软琼脂培养检测细胞克隆形成能力。在实验中,10、50、100 nmol/L siRNA-cyclin D1分别使MCF-7细胞cyclin D1 mRNA表达降低了57．85%、63．22%和68．02%,蛋白表达降低了51．13%、62．09%、77．68%。转染siRNA-cyclin D1后,细胞增殖受到抑制,细胞周期阻滞于G1期,软琼脂克隆形成率降低。结果提示siRNA可以有效抑制MCF-7细胞株中cyclin D1的表达,使细胞周期阻滞于G1期,从而抑制细胞增殖。     

TLK1B mediated phosphorylation of Rad9 regulates its nuclear/cytoplasmic localization and cell cycle checkpoint

Breast cancer is the most frequent malignancy in women and drug resistance is the major obstacle for its successful chemotherapy. In the present study, we analyzed the involvement of an oncofetal gene, sal-like 4 (SALL4), in the tumor proliferation and drug resistance of human breast cancer. Our study showed that SALL4 was up-regulated in the drug resistant breast cancer cell line, MCF-7/ADR, compared to the other five cell lines. We established the lentiviral system expressing short hairpin RNA to knockdown SALL4 in MCF-7/ADR cells. Down-regulation of SALL4 inhibited the proliferation of MCF-7/ADR cells and induced the G1 phase arrest in cell cycle, accompanied by an obvious reduction of the expression of cyclinD1 and CDK4. Besides, down-regulating SALL4 can re-sensitize MCF-7/ADR to doxorubicin hydrochloride (ADMh) and had potent synergy with ADMh in MCF-7/ADR cells. Depletion of SALL4 led to a decrease in IC50 for ADMh and an inhibitory effect on the ability to form colonies in MCF-7/ADR cells. With SALL4 knockdown, ADMh accumulation rate of MCF-7/ADR cells was increased, while the expression of BCRP and c-myc was significantly decreased. Furthermore, silencing SALL4 also suppressed the growth of the xenograft tumors and reversed their resistance to ADMh in vivo. SALL4 knockdown inhibits the growth of the drug resistant breast cancer due to cell cycle arrest and reverses tumor chemo-resistance through down-regulating the membrane transporter, BCPR. Thus, SALL4 has potential as a novel target for the treatment of breast cancer.     

siRNA对乳腺癌细胞Cyclin E表达和生长抑制作用

研究siRNA对乳腺癌MCF-7细胞株cyclin E表达的抑制及对细胞生长的影响。化学合成针对cyclin E基因的小干扰RNA（siRNA）,转染MCF-7细胞株;分别应用荧光定量PCR和免疫印迹测定cyclin E mRNA和蛋白质的表达,CCK-8测定细胞的增殖活性,流式细胞仪检测细胞周期,软琼脂培养检测细胞克隆形成能力。10、50、100nmol／L siRNA-cyclin E分别使MCF-7细胞cyclin E基因表达降低了24．7％、62．5％和71．0％,蛋白质表达降低了40．8％、66．5％和71．3％。转染siRNA-cyclin E后,G1期细胞增多,S期减少,增殖受到抑制,软琼脂克隆形成率降低。结果提示,在MCF-7细胞株中,导入针对cyclin E的siRNA,可有效抑制cyclin E的表达,进而使细胞增殖减缓,逆转其恶性表型。     

PPAR??激动剂罗格列酮对人乳腺癌细胞生长 抑制及诱导凋亡作用研究

目的:观察氧化酶体激活物增殖受体(PPARγ)激动剂罗格列酮(ROZ)在体外激活PPARγ后对MCF-7细胞的生长抑制及诱导凋亡作用。方法:MTT法检测ROZ对MCF-7细胞的生长抑制作用;集落形成实验观察ROZ对MCF-7细胞集落形成的影响;不同浓度ROZ作用72h,Hoechst33342染色观察MCF-7细胞的形态变化,流式细胞光度分析术(FCM)检测凋亡细胞百分率以及ROZ对细胞周期的影响;Western blot方法检测ROZ对MCF-7细胞Bcl-2、Caspase-3表达的影响。结果:ROZ可呈剂量依赖性抑制MCF-7细胞的生长及集落形成。ROZ浓度为6×10-5M和3×10-4M时则G1期细胞数明显增加,S期相应减少。Hoechst33342染色经ROZ处理的肿瘤细胞染色质呈颗粒状,且有凋亡小体出现。FCM检测结果显示,ROZ作用72h凋亡细胞数达22.05%。Western blot提示ROZ可抑制Bcl-2表达,促进Caspase3表达。结论:ROZ在体外可抑制MCF-7细胞的增殖并诱导其凋亡,这可能与其抑制Bcl-2表达、促进caspase3表达有关。提示ROZ有望成为乳腺癌治疗药或肿瘤治疗的辅助用药,PPARγ有潜力成为肿瘤治疗的新靶点。     

RNA干涉介导的Plk1沉默对乳腺癌细胞恶性生物表型的影响

目的：研究乳腺癌细胞中丝／苏氨酸蛋白激酶Plk1基因表达下调后对其恶性生物表型的影响。方法：利用pSitencer4．1-CMVneo质粒,分别构建针对Plk1基因的RNA干涉载体（pSilencer4．1-shPlk1）,利用脂质体Lipofectamine2000转染MCF-7细胞,G418筛选稳定的转染细胞系。半定量RT—PCR和Western blot分别检测Plk1基因mRNA和蛋白表达,MTT和克隆形成试验检测细胞增殖活性的变化,流式细胞仪分析细胞周期和凋亡的变化,最后分析MCF-7细胞对紫杉类药物（紫杉醇和多西他赛）化疗敏感性的变化。结果：成功筛选了稳定转染细胞系（MCF-7／shPlk1和MCF-7／shcontro1）。同MCF-7／shPlk1细胞相比,MCF-7／shPtkl细胞中Plk1基因mRNA和蛋白表达水平分别下调65．8％和74．4％（P〈0．05）。同MCF-7／shcontrol,MCF-7tshPlk1细胞增殖速度显著抑制,到第5天时抑制率达到44．9±3．2％（P〈0．05）。同时,MCF-7／shPlk1细胞的克隆形成能力显著降低（P〈0．01）流式细胞仪技术分析细胞周期结果表明：MCF-7／shPlk1细胞的G2／M期细胞比例显著增加了21．1±4．1％,而S期细胞比例则显著降低了（18．5±3．1％;P〈0．05）。流式细胞仪技术分析细胞凋亡结果表明：MCF-7／shPlk1细胞的凋亡率约显著增加了13．1±213％（P〈0．05）,同时还发现：MCF-7／shPlk1细胞中激活的caspase-3蛋白显著增加,Bcl-2蛋白显著降低,而Bax蛋白则显著增加。结论：RNA干涉载体能特异性下调乳腺癌细胞中Plk1基因的表达,从而抑制乳腺癌细胞的增殖和体外克隆形成能力,同时诱导乳腺癌细胞的G2／M期阻滞和细胞凋亡率显著增加。因此,靶向Plk1基因的生物治疗有望成为未来临床乳腺癌的一个重要的辅助治疗策略.     

Gene Silencing of FANCF Potentiates the Sensitivity to Mitoxantrone through Activation of JNK and p38 Signal Pathways in Breast Cancer Cells

Fanconi anemia complementation group-F (FANCF) is a key factor to maintain the function of FA/BRCA, a DNA-damage response pathway. However, the functional role of FANCF in breast cancer has not been elucidated. In this study, we examined the effects and mechanisms of FANCF-RNAi on the sensitivity of breast cancer cells to mitoxantrone (MX). FANCF silencing by FANCF-shRNA blocked functions of FA/BRCA pathway through inhibition of FANCD2 mono-ubiquitination in breast cancer cell lines MCF-7 and T-47D. In addition, FANCF shRNA inhibited cell proliferation, induced apoptosis, and chromosome fragmentation in both breast cancer cells. We also found that FANCF silencing potentiated the sensitivity to MX in breast cancer cells, accompanying with an increase in intracellular MX accumulation and a decrease in BCRP expression. Furthermore, we found that the blockade of FA/BRCA pathway by FANCF-RNAi activated p38 and JNK MAPK signal pathways in response to MX treatment. BCRP expression was restored by p38 inhibitor SB203580, but not by JNK inhibitor SP600125. FANCF silencing increased JNK and p38 mediated activation of p53 in MX-treated breast cancer cells, activated the mitochondrial apoptosis pathway. Our findings indicate that FANCF shRNA potentiates the sensitivity of breast cancer cells to MX, suggesting that FANCF may be a potential target for therapeutic strategies for the treatment of breast tumors.     

Recombinant adenovirus-mediated p14(ARF) overexpression sensitizes human breast cancer cells to cisplatin

p14(ARF), the alternative product from the human INK4a/ARF locus, is one of the major targets for alterations in the development of human cancers. Overexpression of p14(ARF) results in cell cycle arrest and apoptosis. To examine the potential therapeutic role of re-expressing p14(ARF) gene product in human breast cancer, a recombinant adenovirus expressing the human p14(ARF) cDNA (Adp14(ARF)) was constructed and used to infect breast cancer cells. Five days after infection, Adp14(ARF) had considerable cytotoxicity on p53-wild-type MCF-7 cells. A time-course study showed that Adp14(ARF) infection of MCF-7 cells at 100pfu/cell increased the number of cells in G0/G1 phase and decreased that in S and G2/M phases. The presence of apoptotic cells was confirmed using the TUNEL assay. Adp14(ARF)-mediated expression of p14(ARF) also resulted in a considerable increase in the amounts of p53 and its target proteins, p21(WAF1) and MDM2. Furthermore, the combination treatment of MCF-7 cells with Adp14(ARF) and cisplatin resulted in a significantly greater cell death. Together, we conclude that p14(ARF) plays an important role in the induction of cell cycle arrest and apoptosis in breast cancer cells and recombinant adenovirus-mediated p14(ARF) expression greatly increases the sensitivity of these cells to cisplatin. These results demonstrate that the proper combination of Adp14(ARF) with conventional chemotherapeutic drug(s) could have potential benefits in treating breast cancer that carries wild-type p53 gene.     

The novel agent ophiobolin O induces apoptosis and cell cycle arrest of MCF-7 cells through activation of MAPK signaling pathways

Ophiobolin O is a natural compound that has been isolated from Aspergillus ustus 094102. This is the first study to demonstrate the anti-proliferative effect of ophiobolin O in human breast cancer MCF-7 cells. The results of present study show that ophiobolin O induced cycle G(0)/G(1) phase arrest in MCF-7 cells using a cell cycle analysis. In addition, we demonstrated that ophiobolin O reduced the viability of human breast cancer MCF-7 cells in a time- and dose-dependent manner and efficiently induced apoptosis in MCF-7 cells using the Annexin V/PI binding assay. Ophiobolin O also caused the activation of JNK (c-Jun NH(2)-terminal kinase), p38 MAPK (mitogen activated protein kinase) and ERK (extracellular signal-regulated kinase) as well as the degradation of Bcl-2 phosphorylation (Ser70). Bax protein expression was not changed in ophiobolin O-treated cells. Taken together, ophiobolin O may be considered as a novel therapeutic agent in breast cancer.     

Dosing time dependent in vitro pharmacodynamics of Everolimus despite a defective circadian clock

Everolimus (EV), a rapamycin analogue mTOR inhibitor, is used in the clinic to treat Estrogen positive (ER⁺) breast cancer in order to avoid the resistance to hormonotherapy. Here, we investigated whether EV efficacy varied according to administration timing by using the ER⁺ breast cancer cell line MCF-7 as model system. Our results showed that instead of apoptosis, EV induced a G0/G1 phase blockage of MCF-7 cells. Following serum shock, MCF-7 cells displayed a statistically significant 24h rhythm of mammalian target of Rapamycin (mTOR) activity, but perturbed circadian clock genes oscillations. Interestingly, the different delivery schedule of EV presented different efficacy in G0/G1 phase blockage in serum shocked MCF-7 cells. Moreover, serum shock induced also a circadian-like oscillation in expression or activity of several important G1 phase progression proteins, such as Cyclin D1 and phosphorylated Retinoblastoma protein (RB). Inhibition mTOR activity by EV reduced Cyclin D1 and Cyclin D3 protein level as well as RB phosphorylation level. Taken together, the results indicated that serum shock synchronization induced a circadian oscillation in mTOR activity in MCF-7 cells, which rhythmically regulated the synthesis or phosphorylation of key G1 progression proteins, such as Cyclin D1 and phosphorylated RB, ultimately resulting in different G0/G1 blockage efficiency according to different EV administration timing.     

Abrogation of p53 by its antisense in MCF-7 breast carcinoma cells increases cyclin D1 via activation of Akt and promotion of cell proliferation

The p53 protein has been a subject of intense research interest since its discovery as about 50% of human cancers carry p53 mutations. Mutations in the p53 gene are the most frequent genetic lesions in breast cancers suggesting a critical role of p53 in breast cancer development, growth and chemosensitivity. This report describes the derivation and characterization of MCF-7As53, an isogenic cell line derived from MCF-7 breast carcinoma cells in which p53 was abrogated by antisense p53 cDNA. Similar to MCF-7 and simultaneously selected hygromycin resistant MCF-7H cells, MCF-7As53 cells have consistent basal epithelial phenotype, morphology, and estrogen receptor expression levels at normal growth conditions. Present work documents investigation of molecular variations, growth kinetics, and cell cycle related studies in relation to absence of wild-type p53 protein and its transactivation potential as well. Even though wild-type tumor suppressor p53 is an activator of cell growth arrest and apoptosis-mediator genes such as p21, Bax, and GADD45 in MCF-7As53 cells, no alterations in expression levels of these genes were detected. The doubling time of these cells decreased due to depletion of G0/G1 cell phase because of constitutive activation of Akt and increase in cyclin D1 protein levels. This proliferative property was abrogated by wortmannin, an inhibitor of PI3-K/Akt signaling pathway. Therefore this p53 null cell line indicates that p53 is an indispensable component of cellular signaling system which is regulated by caveolin-1 expression, involving Akt activation and increase in cyclin D1, thereby promoting proliferation of breast cancer cells.