Hydroxyurea: differential lethal effects on cultured mammalian cells during the cell cycle

Hydroxyurea has a differential lethal effect on cultured Chinesehamster cells that are at different stages in their cell cycle. Cells synthesizing DNA at the time of exposure to the drug are lethally damaged. Cells in the phase of growth preceding DNA synthesis (G(1)) survive but are prevented from beginning DNA synthesis. Cells in the phase after DNA synthesis (G(2)) survive and appear to progress until just before the beginning of the next period of DNA synthesis. This differential lethal and inhibitory effect of hydroxyurea may be useful for synchronizing asynchronous cell populations and explaining effects of the drug in human therapy.     

Roscovitine同期化供核细胞对猴—猪异种核移植胚胎发育的影响

[目的]探讨Roscovitine同期化供核细胞对食蟹猴—猪异种体细胞核移植胚胎体外发育的影响,为提高灵长类的核移植效率奠定基础.[方法]活体采集4岁雄性食蟹猴的耳组织,经组织块培养获得纯化的食蟹猴耳成纤维细胞,细胞经固定、染色后用流式细胞仪分析细胞周期分布.以不同同期化方法处理的食蟹猴耳纤维细胞为供体细胞,以体外成熟、去核的猪卵母细胞为受体细胞,利用电融合法构建食蟹猴—猪异种核移植胚胎,观察异种核移植重构胚胎的体外发育情况.[结果]以15 μmol/L Roscovitine处理食蟹猴耳成纤维细胞24、48、72 h获得的G0/G1期细胞比率分别为76.51％、89.69％和90.49％,其中处理48和72h的G0/G1期细胞比率显著高于对照组（P＜0.05）.血清饥饿、接触抑制72 h同期化获得的G0/G1期细胞比率分别为91.12％和90.46％.Roscovitine同期化处理食蟹猴耳成纤维细胞48 h可有效提高食蟹猴—猪异种核移植重构胚胎的囊胚形成率（15.05％）,显著高于血清饥饿同期化处理和接触抑制同期化处理的效果（P＜0.05）.[结论]Roscovitine可有效同期化食蟹猴耳成纤维细胞在G0/G1期,最终提高食蟹猴—猪异种核移植重构胚胎的囊胚形成率.     

The RAD9 gene controls the cell cycle response to DNA damage in Saccharomyces cerevisiae

Cell division is arrested in many organisms in response to DNA damage. Examinations of the genetic basis for this response in the yeast Saccharomyces cerevisiae indicate that the RAD9 gene product is essential for arrest of cell division induced by DNA damage. Wild-type haploid cells irradiated with x-rays either arrest or delay cell division in the G2 phase of the cell cycle. Irradiated G1 and M phase haploid cells arrest irreversibly in G2 and die, whereas irradiated G2 phase haploid cells delay in G2 for a time proportional to the extent of damage before resuming cell division. In contrast, irradiated rad9 cells in any phase of the cycle do not delay cell division in G2, but continue to divide for several generations and die. However, efficient DNA repair can occur in irradiated rad9 cells if irradiated cells are blocked for several hours in G2 by treatment with a microtubule poison. The RAD9-dependent response detects potentially lethal DNA damage and causes arrest of cells in G2 until such damage is repaired.     

DNA replication-independent silencing in S. cerevisiae

In Saccharomyces cerevisiae, the silent mating loci are repressed by their assembly into heterochromatin. The formation of this heterochromatin requires a cell cycle event that occurs between early S phase and G(2)/M phase, which has been widely assumed to be DNA replication. To determine whether DNA replication through a silent mating-type locus, HMRa, is required for silencing to be established, we monitored heterochromatin formation at HMRa on a chromosome and on a nonreplicating extrachromosomal cassette as cells passed through S phase. Cells that passed through S phase established silencing at both the chromosomal HMRa locus and the extrachromosomal HMRa locus with equal efficiency. Thus, in contrast to the prevailing view, the establishment of silencing occurred in the absence of passage of the DNA replication fork through or near the HMR locus, but retained a cell cycle dependence.     

An origin unwinding activity regulates initiation of DNA replication during mammalian cell cycle

An in vitro assay was developed to study the positive factors that regulate the onset of DNA replication during the mammalian cell cycle. Extracts prepared from cells at defined positions in the cell cycle were used to examine the replication of SV40 DNA in a cell free system. Extracts prepared from S phase cells were ten times more efficient at initiating replication at the SV40 origin than were extracts from G1 cells, whereas elongation rates were similar in G1 and S reactions. At a discrete point in the cell cycle, just before the cell's entry into S, an activity appeared that was required, in conjunction with SV40 T antigen, for site specific initiation at the SV40 origin. This factor had a role in unwinding DNA at the replication origin.     

Cell cycle control of DNA replication by a homologue from human cells of the p34cdc2 protein kinase

The regulation of DNA replication during the eukaryotic cell cycle was studied in a system where cell free replication of simian virus 40 (SV40) DNA was used as a model for chromosome replication. A factor, RF-S, was partially purified from human S phase cells based on its ability to activate DNA replication in extracts from G1 cells. RF-S contained a human homologue of the Schizosaccharomyces pombe p34cdc2 kinase, and this kinase was necessary for RF-S activity. The limiting step in activation of the p34 kinase at the G1 to S transition may be its association with a cyclin since addition of cyclin A to a G1 extract was sufficient to start DNA replication. These observations suggest that the role of p34cdc2 in controlling the start of DNA synthesis has been conserved in evolution.     

血清饥饿法同步化牛卵巢颗粒细胞周期的研究

研究了体细胞制备过程中细胞培养时间、血清饥饿浓度和饥饿对间对体细胞周期同步化的影响.体细胞为牛卵巢颗粒细胞,细胞用碘化丙啶(PI)染色法,用流式细胞仪检测细胞周期.细胞传代培养至第2、10和25代,在0.5％和0.05％的血清饥饿浓度下诱导处理2、3、4和5d.试验结果表明,第2、10和25代的细胞在G0/G1期的比例没有差异(P＞0.05).培养液中添加0.5％ FCS和0.05％ FCS较对照组(10％FCS)提高了细胞G0/G1期的比例(P＜0.05),0.5％FCS和0.05％ FCS试验组获得了相近的细胞G0/G1期比例(P＞0.05).血清饥饿至第5天的细胞较第2天的细胞有高的G0/G1期的比例(P＜0.05).结果显示,体外培养至不同代的牛卵巢颗粒细胞对G0/G1期的比例没有影响,血清饥饿和延长血清饥饿的时间能够有效诱导体细胞进入G0/G1期.     

Cell cycle-dependent regulation of phosphorylation of the human retinoblastoma gene product

The human retinoblastoma gene (RB1) encodes a protein (Rb) of 105 kilodaltons that can be phosphorylated. Analysis of Rb metabolism has shown that the protein has a half-life of more than 10 hours and is synthesized at all phases of the cell cycle. Newly synthesized Rb is not extensively phosphorylated (it is "underphosphorylated") in cells in the G0 and G1 phases but is phosphorylated at multiple sites at the G1/S boundary and in S phase. HL-60 cells that were induced to terminally differentiate by various chemicals lost their ability to phosphorylate newly synthesized Rb at multiple sites when cell growth was arrested. These findings suggest that underphosphorylated Rb may restrict cell proliferation.     

Inhibition of eukaryotic DNA replication by geminin binding to Cdt1

In all eukaryotic organisms, inappropriate firing of replication origins during the G2 phase of the cell cycle is suppressed by cyclin-dependent kinases. Multicellular eukaryotes contain a second putative inhibitor of re-replication called geminin. Geminin is believed to block binding of the mini-chromosome maintenance (MCM) complex to origins of replication, but the mechanism of this inhibition is unclear. Here we show that geminin interacts tightly with Cdt1, a recently identified replication initiation factor necessary for MCM loading. The inhibition of DNA replication by geminin that is observed in cell-free DNA replication extracts is reversed by the addition of excess Cdt1. In the normal cell cycle, Cdt1 is present only in G1 and S, whereas geminin is present in S and G2 phases of the cell cycle. Together, these results suggest that geminin inhibits inappropriate origin firing by targeting Cdt1.     

Restriction of DNA replication to the reductive phase of the metabolic cycle protects genome integrity

When prototrophic yeast cells are cultured under nutrient-limited conditions that mimic growth in the wild, rather than in the high-glucose solutions used in most laboratory studies, they exhibit a robustly periodic metabolic cycle. Over a cycle of 4 to 5 hours, yeast cells rhythmically alternate between glycolysis and respiration. The cell division cycle is tightly constrained to the reductive phase of this yeast metabolic cycle, with DNA replication taking place only during the glycolytic phase. We show that cell cycle mutants impeded in metabolic cycle-directed restriction of cell division exhibit substantial increases in spontaneous mutation rate. In addition, disruption of the gene encoding a DNA checkpoint kinase that couples the cell division cycle to the circadian cycle abolishes synchrony of the metabolic and cell cycles. Thus, circadian, metabolic, and cell division cycles may be coordinated similarly as an evolutionarily conserved means of preserving genome integrity.     

雌激素对奶牛乳腺上皮细胞增殖及细胞周期变化规律的影响

目的 研究雌激素对乳腺上皮细胞增殖及细胞生长周期变化规律的影响。方法 选取扩增生长状态良好的乳腺上皮细胞,添加0、50、100、200 μmol/L雌激素孵育乳腺上皮细胞后,分别在0、12、24、48、72 h后检测各组细胞增殖及细胞周期。结果 培养12 h时,50 μmoL/L雌激素组的OD值显著高于对照组及100 μmoL/L雌激素组(P＜0.05),且极显著高于200 μmoL/L雌激素添加组(P＜0.01);培养至12 h时,对照组及添加50 μmoL/L雌激素组其G1期极显著高于其他两组(P＜0.01),对照组S期极显著高于其他各组(P＜0.01),添加100 μmoL/L雌激素组其G2期极显著高于其他各组(P＜0.01)。结论 添加雌激素可以促进乳腺上皮细胞的增殖,且50 μmoL/L、12 h时雌激素促进乳腺上皮细胞的增殖效果最好。添加雌激素不影响乳腺上皮细胞在各时期时细胞生长的基本规律,各雌激素添加组在12 h时的细胞周期由G1、S期向G2期转化较快。     

Zeylenone对急性淋巴细胞白血病细胞增殖及凋亡的影响

目的探讨Zeylenone体外抗急性淋巴细胞白血病(Acute Lymphoblastic Leukemia,ALL)效应及作用的可能机制。方法应用MTT法比较Zeylenone对肿瘤细胞、正常细胞增殖的影响;AO/EB染色观察其对ALL细胞(Reh、RS4;11)凋亡形态学的改变;流式细胞仪检测药物对细胞凋亡及细胞周期的影响。结果 Zeylenone对多种细胞呈现增殖抑制作用,且对ALL细胞株呈现更高的敏感性,而对外周血单个核细胞(Peripheral blood mononuclear cell,PBMC)抑制作用较小,抑制Reh、RS4;11细胞增殖呈时间依赖性和剂量依赖性;Zeylenone能够诱导ALL细胞凋亡,阻滞细胞周期于G0/G1期。结论 Zeylenone体外具有抗ALL细胞增殖的作用,其作用与诱导细胞凋亡、阻滞细胞周期相关。     

辛伐他汀对人高转移卵巢癌细胞HO-8910PM增殖的抑制作用

目的研究辛伐他汀(SIM)对人高转移卵巢癌细胞HO-8910PM体外增殖的抑制作用。方法MTT法检测SIM对HO-8910PM细胞增殖的抑制作用;流式细胞术分析SIM对细胞周期的影响;Hoechst 33258荧光染色观察细胞凋亡的形态学改变。结果SIM抑制HO-8910PM细胞的增殖,细胞被阻滞在G0/G1期;荧光染色法显示经SIM作用后细胞出现变形,染色质浓缩,产生凋亡小体。结论SIM在体外能有效地抑制癌细胞的增殖,其作用可能是通过诱导其凋亡产生的。     

Vc对黑色素癌细胞A375生长抑制作用的研究

[目的]探讨Vc对黑色素癌细胞A375的生长抑制作用。[方法]利用MTT法分析不同剂量组的Vc对A375增殖的影响,并通过荧光染色和荧光显微镜观察A375细胞的形态学变化,用流式细胞术检测Vc对各组A375的细胞周期变化。[结果]流式方法测定的结果显示,Vc对黑色素癌细胞A375的增殖具有抑制作用;Vc能以浓度依赖和时间依赖方式阻滞黑色素癌细胞A375细胞于G0/G1期,抑制其生长并诱导凋亡。[结论]Vc对黑色素癌细胞的生长有明显抑制作用。     

Rapid destruction of human Cdc25A in response to DNA damage

To protect genome integrity and ensure survival, eukaryotic cells exposed to genotoxic stress cease proliferating to provide time for DNA repair. Human cells responded to ultraviolet light or ionizing radiation by rapid, ubiquitin- and proteasome-dependent protein degradation of Cdc25A, a phosphatase that is required for progression from G1 to S phase of the cell cycle. This response involved activated Chk1 protein kinase but not the p53 pathway, and the persisting inhibitory tyrosine phosphorylation of Cdk2 blocked entry into S phase and DNA replication. Overexpression of Cdc25A bypassed this mechanism, leading to enhanced DNA damage and decreased cell survival. These results identify specific degradation of Cdc25A as part of the DNA damage checkpoint mechanism and suggest how Cdc25A overexpression in human cancers might contribute to tumorigenesis.     

Inhibition of endothelial regeneration by type-beta transforming growth factor from platelets

Damage to the vessel wall is a signal for endothelial migration and replication and for platelet release at the site of injury. Addition of transforming growth factor-beta (TGF-beta) purified from platelets to growing aortic endothelial cells inhibited [3H]thymidine incorporation in a concentration-dependent manner. A transient inhibition of DNA synthesis was also observed in response to wounding; cell migration and replication are inhibited during the first 24 hours after wounding. By 48 hours after wounding both TGF-beta-treated and -untreated cultures showed similar responses. Flow microfluorimetric analysis of cell cycle distribution indicated that after 24 hours of exposure to TGF-beta the cells were blocked from entering S phase, and the fraction of cells in G1 was increased. The inhibition of the initiation of regeneration by TGF-beta could allow time for recruitment of smooth muscle cells into the site of injury by other platelet components.     

IL-24对瘢痕疙瘩成纤维细胞增殖、细胞周期和缺氧诱导因子-1α表达的影响

目的观察IL-24对瘢痕疙瘩成纤维细胞（KF）的抑制效应及缺氧诱导因子-1α（HIF-1α）表达的影响。方法建立KF组、携带绿色荧光蛋白表达质粒的KF组（pEGFP-KF组）、携带转染IL-24基因表达质粒的KF组（IL-24-pEGFP-KF组）,用噻唑蓝法及流式细胞术检测KF增殖、细胞周期变化。建立KF、pEGFP-KF、IL-24-pEGFP-KF细胞株裸鼠移植瘤模型,免疫组织化学检测KF中HIF-1α表达。结果 IL-24-pEGFP-KF组较pEGFP-KF组、KF组到达平台期延迟,IL-24明显抑制了细胞增殖（P〈0.05）。IL-24-pEGFP-KF组的G0/G1期比例明显高于pEGFP-KF组、KF组,而S、G2/M期比例明显降低（P〈0.05）。IL-24-pEGFP-KF组的HIF-1α表达明显低于pEGFP-KF组和KF组。结论 IL-24可抑制KF增殖和HIF-1α表达,阻止细胞周期于G0/G1期。     

蛋白激酶B短发夹环RNA表达载体的构建及其对血管平滑肌细胞增殖活性的影响

目的构建靶向蛋白激酶B基因的短发夹环RNA表达载体,观察其对血管平滑肌细胞增殖活性的影响。方法设计多个针对大鼠蛋白激酶B基因的短发夹环RNA序列,化学合成方法合成并经pGEM-T载体克隆后双酶切,将cDNA序列插入逆转录病毒载体pLXIN,包装后获得蛋白激酶B的逆转录表达载体,感染血管平滑肌细胞,Northern blot和Western blot法检测蛋白激酶B及其下游底物的表达变化,流式细胞仪检测细胞周期变化,MTT法检测血管平滑肌细胞增殖活性的改变。结果成功构建蛋白激酶B基因的逆转录病毒载体并包装,感染血管平滑肌细胞,证实其能显著抑制蛋白激酶B的mRNA和蛋白产物表达,下游的p70s6k表达相应减少;被感染血管平滑肌细胞的分裂、增殖过程受阻,更多细胞停滞在G0/G1期。结论成功构建蛋白激酶B基因逆转录病毒RNA干扰表达载体,感染血管平滑肌细胞能够明显抑制其分裂、分化和增殖。     

Insulin as a potent, specific growth factor in a rat hepatoma cell line

A line or rat hepatoma cells in culture which, in response to serum starvation, become arrested in the early G1 phase of growth, can be stimulated by insulin alone to enter the cell cycle and traverse S phase. A half-maximum response is observed at 30 to 70 picomolar concentrations and the maximum response is essentially identical to that found with optimum serum concentrations.     

红细胞裂解法及不同培养条件对兔骨髓间充质干细胞体外增殖的影响

研究采用红细胞裂解液法从兔骨髓中分离BMSCs,相差显微镜观察其形态,四甲基偶氮唑盐法(MTT法)筛选基础培养液和血清浓度,绘制生长曲线,用流式细胞仪检测细胞周期,免疫细胞化学鉴定表面抗原。分离的细胞在形态学观察与生长动力学上均符合BMSCs特征;在实验范围内DMEM/F12+20%FBS是体外培养兔BMSCs的最佳体系;细胞周期结果显示,BMSCs平均82%处于G0/G1期,18%处于S+G2期;免疫细胞化学结果显示所分离的BMSCsCD90、CD44阳性表达,CD34阴性表达。本研究结果表明,通过红细胞裂解液法分离的兔BMSCs,其具有体外增殖和多向分化的潜能,可以作为组织工程的种子细胞。