外泌体microRNA在猪成熟和闭锁卵泡中的表达差异及功能分析

【目的】通过分析成熟卵泡液外泌体（mature follicular fiuid Exosomes, mffEXs）和闭锁卵泡液外泌体（atretic follicular fiuid Exosomes, affEXs）miRNA的表达差异,探索卵泡液外泌体（EXs）miRNA在卵泡发育和闭锁过程中的调控作用。【方法】本研究通过抽提4—6 mm猪成熟发育和闭锁卵泡的卵泡液分离外泌体,进行粒径分析及Western Blot检测对EXs进行鉴定,接下来对特征性EXs携带的miRNA测序和功能富集分析,筛选关键信号通路和差异基因。最后,将mffEXs和affEXs作为添加剂进行颗粒细胞培养,利用Q-PCR检测技术分析关键基因的表达,验证两类卵泡液内EXs miRNA在卵泡发育中的调控功能。【结果】成功分离了mffEXs和affEXs,对比mffEXs测序结果,affEXs中有90个miRNA上调表达,220个miRNA下调表达,表明了卵泡液中的miRNA表达水平与调控卵泡发育有关;KEGG富集分析结果显示两类卵泡的差异信号通路主要集中在Ras、cAMP、P53和MAPK等信号通路,涉及调控卵母细胞发育、减数分裂以及颗粒细胞细胞周期等生物学功能。在闭锁卵泡中,上调表达的ssc-let-7a和ssc-miR-133a-3p分别潜在靶向调控细胞周期蛋白依赖性激酶（CDK1）和胰岛素生长因子（IGF1）,抑制了G1和G2/M期的运转和类固醇激素代谢,促使颗粒细胞周期运转受阻和颗粒细胞凋亡,引起卵泡闭锁的发生;下调的ssc-miR-21-5p潜在靶向肿瘤抑癌基因（P53）,抑制细胞周期运转,促使颗粒细胞凋亡。在体外培养的颗粒细胞中分别添加mffEXs和affEXs,Q-PCR结果显示CDK1在mffEXs中显著上调表达,而P53显著下调表达,表明了测序分析结果的可靠性。这些结果均显示了affEXs中miRNA表达水平的变化促使颗粒细胞凋亡和细胞周期阻滞,引起卵泡闭锁。【结论】猪affEXs携带miRNA增加了对CDK1、IGF1和P53的表达调控,抑制颗粒细胞细胞周期运转和类固醇激素代谢等信号通路,引起颗粒细胞凋亡,导致卵泡闭锁。     

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.     

Function and molecular mechanism of acetylation in autophagy regulation

Protein acetylation emerged as a key regulatory mechanism for many cellular processes. We used genetic analysis of Saccharomyces cerevisiae to identify Esa1 as a histone acetyltransferase required for autophagy. We further identified the autophagy signaling component Atg3 as a substrate for Esa1. Specifically, acetylation of K19 and K48 of Atg3 regulated autophagy by controlling Atg3 and Atg8 interaction and lipidation of Atg8. Starvation induced transient K19-K48 acetylation through spatial and temporal regulation of the localization of acetylase Esa1 and the deacetylase Rpd3 on pre-autophagosomal structures (PASs) and their interaction with Atg3. Attenuation of K19-K48 acetylation was associated with attenuation of autophagy. Increased K19-K48 acetylation after deletion of the deacetylase Rpd3 caused increased autophagy. Thus, protein acetylation contributes to control of autophagy.     

Mediation of poly(ADP-ribose) polymerase-1-dependent cell death by apoptosis-inducing factor

Poly(ADP-ribose) polymerase-1 (PARP-1) protects the genome by functioning in the DNA damage surveillance network. PARP-1 is also a mediator of cell death after ischemia-reperfusion injury, glutamate excitotoxicity, and various inflammatory processes. We show that PARP-1 activation is required for translocation of apoptosis-inducing factor (AIF) from the mitochondria to the nucleus and that AIF is necessary for PARP-1-dependent cell death. N-methyl-N'-nitro-N-nitrosoguanidine, H2O2, and N-methyl-d-aspartate induce AIF translocation and cell death, which is prevented by PARP inhibitors or genetic knockout of PARP-1, but is caspase independent. Microinjection of an antibody to AIF protects against PARP-1-dependent cytotoxicity. These data support a model in which PARP-1 activation signals AIF release from mitochondria, resulting in a caspase-independent pathway of programmed cell death.     

Phosphorylation of ULK1 (hATG1) by AMP-activated protein kinase connects energy sensing to mitophagy

Adenosine monophosphate-activated protein kinase (AMPK) is a conserved sensor of intracellular energy activated in response to low nutrient availability and environmental stress. In a screen for conserved substrates of AMPK, we identified ULK1 and ULK2, mammalian orthologs of the yeast protein kinase Atg1, which is required for autophagy. Genetic analysis of AMPK or ULK1 in mammalian liver and Caenorhabditis elegans revealed a requirement for these kinases in autophagy. In mammals, loss of AMPK or ULK1 resulted in aberrant accumulation of the autophagy adaptor p62 and defective mitophagy. Reconstitution of ULK1-deficient cells with a mutant ULK1 that cannot be phosphorylated by AMPK revealed that such phosphorylation is required for mitochondrial homeostasis and cell survival during starvation. These findings uncover a conserved biochemical mechanism coupling nutrient status with autophagy and cell survival.     

马尾松树皮提取物体外抑制人大肠癌细胞生长机理初探

为探讨马尾松树皮提取物(PMBE)体外抑制大肠癌LoVo细胞生长的作用特点和机理,通过MTT、显微镜术、凝胶电泳和流式细胞术,研究PMBE抑制LoVo细胞生长的特点,运用免疫组化和RT-PCR探究相关分子机理。结果表明:PMBE时间-剂量依赖地抑制LoVo细胞的体外生长;PMBE处理后,流式细胞检测发现LoVo细胞周期阻滞于G1或S期,同时可检测到亚二倍体峰的出现;荧光镜检和透射电镜观察可看到LoVo细胞的核皱缩、边集甚或碎裂,以及有凋亡小体形成,其基因组经过凝胶电泳呈现典型的梯形Ladder;RT-PCR和免疫组化结果显示PMBE处理可上调LoVo细胞中p53和p21基因的转录效率,并下调Bcl-2的蛋白表达量。说明PMBE通过上调p53和p21的表达量阻滞细胞周期、下调Bcl-2的表达量诱导细胞凋亡的双重机制,抑制LoVo细胞的体外生长,可供进一步探索相关信号传导通路参考。     

Suppression of human colorectal carcinoma cell growth by wild-type p53

Mutations of the p53 gene occur commonly in colorectal carcinomas and the wild-type p53 allele is often concomitantly deleted. These findings suggest that the wild-type gene may act as a suppressor of colorectal carcinoma cell growth. To test this hypothesis, wild-type or mutant human p53 genes were transfected into human colorectal carcinoma cell lines. Cells transfected with the wild-type gene formed colonies five- to tenfold less efficiently than those transfected with a mutant p53 gene. In those colonies that did form after wild-type gene transfection, the p53 sequences were found to be deleted or rearranged, or both, and no exogenous p53 messenger RNA expression was observed. In contrast, transfection with the wild-type gene had no apparent effect on the growth of epithelial cells derived from a benign colorectal tumor that had only wild-type p53 alleles. Immunocytochemical techniques demonstrated that carcinoma cells expressing the wild-type gene did not progress through the cell cycle, as evidenced by their failure to incorporate thymidine into DNA. These studies show that the wild-type gene can specifically suppress the growth of human colorectal carcinoma cells in vitro and that an in vivo-derived mutation resulting in a single conservative amino acid substitution in the p53 gene product abrogates this suppressive ability.     

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.     

Caenorhabditis elegans p53: role in apoptosis, meiosis, and stress resistance

We have identified a homolog of the mammalian p53 tumor suppressor protein in the nematode Caenorhabditis elegans that is expressed ubiquitously in embryos. The gene encoding this protein, cep-1, promotes DNA damage-induced apoptosis and is required for normal meiotic chromosome segregation in the germ line. Moreover, although somatic apoptosis is unaffected, cep-1 mutants show hypersensitivity to hypoxia-induced lethality and decreased longevity in response to starvation-induced stress. Overexpression of CEP-1 promotes widespread caspase-independent cell death, demonstrating the critical importance of regulating p53 function at appropriate levels. These findings show that C. elegans p53 mediates multiple stress responses in the soma, and mediates apoptosis and meiotic chromosome segregation in the germ line.     

Association of human papillomavirus types 16 and 18 E6 proteins with p53

Human papillomavirus type 16 (HPV-16) is a DNA tumor virus that is associated with human anogenital cancers and encodes two transforming proteins, E6 and E7. The E7 protein has been shown to bind to the retinoblastoma tumor suppressor gene product, pRB. This study shows that the E6 protein of HPV-16 is capable of binding to the cellular p53 protein. The ability of the E6 proteins from different human papillomaviruses to form complexes with p53 was assayed and found to correlate with the in vivo clinical behavior and the in vitro transforming activity of these different papillomaviruses. The wild-type p53 protein has tumor suppressor properties and has also been found in association with large T antigen and the E1B 55-kilodalton protein in cells transformed by SV40 and by adenovirus type 5, respectively, providing further evidence that the human papillomaviruses, the adenoviruses, and SV40 may effect similar cellular pathways in transformation.     

53BP1, a mediator of the DNA damage checkpoint

53BP1 binds to the tumor suppressor protein p53 and has a potential role in DNA damage responses. We used small interfering RNA (siRNA) directed against 53BP1 in mammalian cells to demonstrate that 53BP1 is a key transducer of the DNA damage checkpoint signal. 53BP1 was required for p53 accumulation, G2-M checkpoint arrest, and the intra-S-phase checkpoint in response to ionizing radiation. 53BP1 played a partially redundant role in phosphorylation of the downstream checkpoint effector proteins Brca1 and Chk2 but was required for the formation of Brca1 foci in a hierarchical branched pathway for the recruitment of repair and signaling proteins to sites of DNA damage.     

p53基因研究进展

转录调节因子p53作为一种抑癌基因,可诱导细胞生长阻滞,细胞凋亡,细胞分化以及DNA修复。但p53突变体可能会使野生型p53基因的抑癌功能失活,甚至发挥癌基因的功能。随着分子生物学技术的发展,人们对p53基因调控网络有很多新的认识。笔者就p53的调节通路以及在肿瘤治疗方面的新进展进行综述。     

An oncogene-induced DNA damage model for cancer development

Of all types of DNA damage, DNA double-strand breaks (DSBs) pose the greatest challenge to cells. One might have, therefore, anticipated that a sizable number of DNA DSBs would be incompatible with cell proliferation. Yet recent experimental findings suggest that, in both precancerous lesions and cancers, activated oncogenes induce stalling and collapse of DNA replication forks, which in turn leads to formation of DNA DSBs. This continuous formation of DNA DSBs may contribute to the genomic instability that characterizes the vast majority of human cancers. In addition, in precancerous lesions, these DNA DSBs activate p53, which, by inducing apoptosis or senescence, raises a barrier to tumor progression. Breach of this barrier by various mechanisms, most notably by p53 mutations, that impair the DNA damage response pathway allows cancers to develop. Thus, oncogene-induced DNA damage may explain two key features of cancer: genomic instability and the high frequency of p53 mutations.     

p53- and ATM-dependent apoptosis induced by telomeres lacking TRF2

Although broken chromosomes can induce apoptosis, natural chromosome ends (telomeres) do not trigger this response. It is shown that this suppression of apoptosis involves the telomeric-repeat binding factor 2 (TRF2). Inhibition of TRF2 resulted in apoptosis in a subset of mammalian cell types. The response was mediated by p53 and the ATM (ataxia telangiectasia mutated) kinase, consistent with activation of a DNA damage checkpoint. Apoptosis was not due to rupture of dicentric chromosomes formed by end-to-end fusion, indicating that telomeres lacking TRF2 directly signal apoptosis, possibly because they resemble damaged DNA. Thus, in some cells, telomere shortening may signal cell death rather than senescence.     

ATM engages autodegradation of the E3 ubiquitin ligase COP1 after DNA damage

The ataxia telangiectasia mutated (ATM) protein kinase is a critical component of a DNA-damage response network configured to maintain genomic integrity. The abundance of an essential downstream effecter of this pathway, the tumor suppressor protein p53, is tightly regulated by controlled degradation through COP1 and other E3 ubiquitin ligases, such as MDM2 and Pirh2; however, the signal transduction pathway that regulates the COP1-p53 axis following DNA damage remains enigmatic. We observed that in response to DNA damage, ATM phosphorylated COP1 on Ser(387) and stimulated a rapid autodegradation mechanism. Ionizing radiation triggered an ATM-dependent movement of COP1 from the nucleus to the cytoplasm, and ATM-dependent phosphorylation of COP1 on Ser(387) was both necessary and sufficient to disrupt the COP1-p53 complex and subsequently to abrogate the ubiquitination and degradation of p53. Furthermore, phosphorylation of COP1 on Ser(387) was required to permit p53 to become stabilized and to exert its tumor suppressor properties in response to DNA damage.     

Regulation of an ATG7-beclin 1 program of autophagic cell death by caspase-8

Caspases play a central role in apoptosis, a well-studied pathway of programmed cell death. Other programs of death potentially involving necrosis and autophagy may exist, but their relation to apoptosis and mechanisms of regulation remains unclear. We define a new molecular pathway in which activation of the receptor-interacting protein (a serine-threonine kinase) and Jun amino-terminal kinase induced cell death with the morphology of autophagy. Autophagic death required the genes ATG7 and beclin 1 and was induced by caspase-8 inhibition. Clinical therapies involving caspase inhibitors may arrest apoptosis but also have the unanticipated effect of promoting autophagic cell death.