衰老过程中原癌基因及抑癌基因的表达谱

细胞衰老时增殖能力逐渐减退,实质细胞不断减少,是脏器功能衰退的原因之一。原癌基因及抑癌基因与细胞增殖调控密切相关,因而它们与细胞衰老的关系早已引起人们的关注。本文就此进行了概括介绍。总的看来,衰老时多数原癌基因表达降低,抑癌基因表达增强,但亦因细胞的类型而有所差异。     

抑癌基因的负转录调控

抑癌基因在正常细胞中适度表达,抑制细胞永生及转化,其转录下调见于某些肿瘤,而在衰老细胞中常见表达上调或活性增强。抑癌基因INK4a／ARF、p53和p21^Cipl的表达及其负调控与肿瘤及细胞衰老的关系十分密切。     

抑癌基因DPC4

抑癌基因ＤＰＣ４李贵新张玲（山东省医学科学院基础医学研究所,济南２５００６２）关键词胰腺癌抑癌基因ＤＰＣ４人类肿瘤的发生通常是由原癌基因和抑癌基因的改变而获得生长优势的细胞群体引起的。研究较多的抑癌基因有Ｒｂ、ＷＴ１、ＮＦ１、ｐ５３、ｐ１６和ＤＣＣ等...     

抑癌基因研究进展

肿瘤的发生与原癌基因的激活及／或抑癌基因的缺失或灭活关系密切,尤其是抑癌基因的研究成为近几年来肿瘤发生方面的研究热点。本文从抑癌基因的定义,发现过程,已发现的抑癌基因及几种重要抑癌基因的功能等方面作以综述。     

细胞周期与细胞凋亡

从海洋生物胚胎细胞到哺乳动物的细胞周期,主要是在其细胞周期基因产物周期素及Ｐ３４的调控下启动,运行和脱出周期的;某些原癌基因或抑癌基因的产物如ｐ５３,ｐＲＢ也直接调控着细胞周期。     

p53通过PKA-Drp1途径诱导肿瘤细胞衰老

正细胞衰老是指细胞进入一种不可逆的增殖阻滞状态,被认为是一种有效的肿瘤抑制机制。很多研究表明,抑癌基因p53在诱导细胞衰老中起着关键作用,但其具体机制尚未完全清楚。最近,一项研究发现在肿瘤细胞中过表达p53可引起细胞衰老和线粒体形态及功能障碍,包括线粒体延伸、膜电位降低、呼吸速率降低和线粒体活性氧(ROS)水平升高;而线粒体选择性和非选择性抗氧化剂均能够通过降低ROS水平来改善由p53所引起的线粒体功能障碍和细胞衰老,但对线粒体延伸无影响。     

视网膜母细胞瘤基因1(RB1)研究进展

视网膜母细胞瘤基因1(Retinoblastoma1,RB1)是人类第一个分离克隆的抑癌基因。RB1基因是细胞周期的负调控因子,通过与转录因子结合调节细胞增殖和分化所需基因的表达,从而维持细胞生长发育的平衡。因此,该基因的功能与细胞周期、细胞衰老、细胞凋亡、细胞分化和生长抑制等有关。文章对RB1基因的结构、表达及其功能的研究进展进行了综述。     

小檗胺衍生物（EBB）体外抑制肺癌细胞增殖机制的初探

本文研究并发现了新型半天然钙调素(CaM)拮抗剂--O-4-乙氧基丁基小檗胺(O-4-ethoxy-butyl-berbamine,EBB),具有选择性抑制肺巨细胞癌(PG)的增殖和降低细胞内CaM水平的能力,对人胚肺细胞(HEL)的增殖和细胞内CaM的水平影响较小.同时观察到EBB引起肿瘤细胞内CaM水平降低的原因,是对CaM基因的转录产物(mRNA)和翻译产物(CaM)两方面作用的结果.此外,EBB还能部分降低PG细胞内原癌基因和突变的抑癌基因转录产物mRNA的水平.EBB抑制肿瘤细胞增殖的机制,除了对CaM基因的表达水平和CaM活性调控外,可能还直接或间接地影响了相关的原癌基因和突变的抑癌基因的表达.     

抑癌因子对Ehrlich腹水癌细胞结构、表面形态和聚集能力的影响

本文用透射与扫描电镜方法研究了抑癌因子对Ehrlich腹水癌细胞的作用。发现,在抑癌因子作用下,肿瘤细胞内部结构破坏,表面形态趋于简化。在抑癌因子作用早期(4—8小时),肿瘤细胞聚集能力增加,这种变化可能具有肿瘤专一性;在抑癌因子作用18小时时,肿瘤细胞聚集能力下降,这可能与此时细胞大部分死亡有关。     

原癌基因抑或原瘤基因

原癌基因抑或原瘤基因姚开泰（湖南医科大学病理生理学教研室）Ｐｒｏｔｏ－ｏｎｃｏｇｅｎ应译为原瘤基因,而不是原癌基因。其理由是：Ｏｎｃｏ是肿瘤,而不是专指癌,癌是恶性肿瘤之一种。例如,在以往的译名中,ｔｕｍｏｒ－ｓｕｐｐｒｅｓｓｉｖｅｆａｃｔｏｒ译为抑...     

ECRG1, a novel candidate of tumor suppressor gene in the esophageal carcinoma, triggers a senescent program in NIH3T3 cells

Esophageal cancer-related gene 1 (ECRG1) is a novel tumor-suppressor gene candidate identified from the human esophagus. Previous studies showed that ECRG1 overexpression could inhibit cell growth and induce G1 cell cycle arrest and p15(INK4b) expression by interacting with Miz-1 (Myc-interacting zinc finger protein). Such evidence suggests the alterations in ECRG1 may play an important role in tumorigenesis. To further study the biological function of the ECRG1 gene, we transfected ECRG1 into NIH3T3 cells. Expression of ECRG1 in these cells caused senescence-like changes characterized in terms of altered cell morphology, cell cycle arrest at the G1/S phase, and significantly impaired cell proliferation (P < 0.01). Moreover, NIH3T3 cells transfected with ECRG1 stained positive for SA-beta-gal staining (pH 6.0), which is a specific marker of cellular senescence. We also studied changes in telomerase activity and the related senescence genes, such as p21 and p16. The results indicated that when ECRG1 induced a senescence-like state, telomerase activity was markedly decreased (P < 0.05), and expression of p21 was distinctly increased, whereas no changes were detected in p16 and telomerase-component RNA levels. These findings suggest that ECRG1 may be of importance in murine cell senescence, promoting senescence by regulating expression of p21.     

Cellular senescence induced by cathepsin X downregulation

Cellular senescence represents a powerful tumor suppressor mechanism to prevent proliferation and invasion of malignant cells. Since tumor cells as well as primary fibroblasts lacking the lysosomal cysteine-type carboxypeptidase cathepsin X exhibit a reduced invasive capacity, we hypothesized that the underlying reason may be the induction of cellular senescence. To investigate the cellular and molecular mechanisms leading to diminished migration/invasion of cathepsin X-deficient cells, we have analyzed murine embryonic fibroblasts (MEF) derived from cathepsin X-deficient mice and neonatal human dermal fibroblasts (NHDF) transfected with siRNAs targeting cathepsin X. Remarkably, both cell types exhibited a flattened and enlarged cell body, a characteristic phenotype of senescent cells. Additional evidence for accelerated senescence was obtained by detection of the common senescence marker β-galactosidase. Further examination revealed increased expression levels of senescence-associated genes such as p16, p21, p53, and caveolin in these cells along with a reduced proliferation rate. The accelerated cellular senescence induced by cathepsin X deficiency was rescued by simultaneous expression of exogenous cathepsin X. Finally, cell cycle analysis confirmed a marked reduction of the synthesis rate and prolongation of the S-phase, while susceptibility to apoptosis of cathepsin X-deficient cells remained unchanged. In conclusion, cathepsin X deficiency leads to accelerated cellular senescence and consequently to diminished cellular proliferation and migration/invasion implying a potential role of cathepsin X in bypassing cellular senescence.     

A small-molecule probe of the histone methyltransferase G9a induces cellular senescence in pancreatic adenocarcinoma

Post-translational modifications of histones alter chromatin structure and play key roles in gene expression and specification of cell states. Small molecules that target chromatin-modifying enzymes selectively are useful as probes and have promise as therapeutics, although very few are currently available. G9a (also named euchromatin histone methyltransferase 2 (EHMT2)) catalyzes methylation of lysine 9 on histone H3 (H3K9), a modification linked to aberrant silencing of tumor-suppressor genes, among others. Here, we report the discovery of a novel histone methyltransferase inhibitor, BRD4770. This compound reduced cellular levels of di- and trimethylated H3K9 without inducing apoptosis, induced senescence, and inhibited both anchorage-dependent and -independent proliferation in the pancreatic cancer cell line PANC-1. ATM-pathway activation, caused by either genetic or small-molecule inhibition of G9a, may mediate BRD4770-induced cell senescence. BRD4770 may be a useful tool to study G9a and its role in senescence and cancer cell biology.     

Dissecting the influence of cellular senescence on cell mechanics and extracellular matrix formation in vitro

Tissue formation and healing both require cell proliferation and migration, but also extracellular matrix production and tensioning. In addition to restricting proliferation of damaged cells, increasing evidence suggests that cellular senescence also has distinct modulatory effects during wound healing and fibrosis. Yet, a direct role of senescent cells during tissue formation beyond paracrine signaling remains unknown. We here report how individual modules of the senescence program differentially influence cell mechanics and ECM expression with relevance for tissue formation. We compared DNA damage-mediated and DNA damage-independent senescence which was achieved through over-expression of either p16^Ink4a or p21^Cip1 cyclin-dependent kinase inhibitors in primary human skin fibroblasts. Cellular senescence modulated focal adhesion size and composition. All senescent cells exhibited increased single cell forces which led to an increase in tissue stiffness and contraction in an in vitro 3D tissue formation model selectively for p16 and p21-overexpressing cells. The mechanical component was complemented by an altered expression profile of ECM-related genes including collagens, lysyl oxidases, and MMPs. We found that particularly the lack of collagen and lysyl oxidase expression in the case of DNA damage-mediated senescence foiled their intrinsic mechanical potential. These observations highlight the active mechanical role of cellular senescence during tissue formation as well as the need to synthesize a functional ECM network capable of transferring and storing cellular forces.     

Carnitine palmitoyltransferase 1C reverses cellular senescence of MRC‐5 fibroblasts via regulating lipid accumulation and mitochondrial function

Cellular senescence, a state of growth arrest, is involved in various age‐related diseases. We previously found that carnitine palmitoyltransferase 1C (CPT1C) is a key regulator of cancer cell proliferation and senescence, but it is unclear whether CPT1C plays a similar role in normal cells. Therefore, this study aimed to investigate the role of CPT1C in cellular proliferation and senescence of human embryonic lung MRC‐5 fibroblasts and the involved mechanisms. The results showed that CPT1C could reverse the cellular senescence of MRC‐5 fibroblasts, as evidenced by reduced senescence‐associated β‐galactosidase activity, downregulated messenger RNA (mRNA) expression of senescence‐associated secretory phenotype factors, and enhanced bromodeoxyuridine incorporation. Lipidomics analysis further revealed that CPT1C gain‐of‐function reduced lipid accumulation and reversed abnormal metabolic reprogramming of lipids in late MRC‐5 cells. Oil Red O staining and Nile red fluorescence also indicated significant reduction of lipid accumulation after CPT1C gain‐of‐function. Consequently, CPT1C gain‐of‐function significantly reversed mitochondrial dysfunction, as evaluated by increased adenosine triphosphate synthesis and mitochondrial transmembrane potential, decreased radical oxygen species, upregulated respiratory capacity and mRNA expression of genes related to mitochondrial function. In summary, CPT1C plays a vital role in MRC‐5 cellular proliferation and can reverse MRC‐5 cellular senescence through the regulation of lipid metabolism and mitochondrial function, which supports the role of CPT1C as a novel target for intervention into cellular proliferation and senescence and suggests CPT1C as a new strategy for antiaging.     

Cloning and characterization of cellular senescence-associated genes in human fibroblasts by suppression subtractive hybridization

Cellular senescence marks the end of the proliferative life span of normal cells in tissue culture and occurs after cells have undergone a certain number of population doublings (PDLs). It is accompanied by alterations in the pattern of gene expression. A specific human embryonic lung diploid fibroblast cell line, 2BS, has been studied as a model of senescence in our laboratory. Here, we report a set of cellular senescence-associated genes identified from suppression subtractive cDNA libraries from senescent and young 2BS cells. They include three novel genes and six previously identified genes of unknown function. The genes whose functions are known belong to various functional pathways that have been reported to change with the onset of senescence. These include three pre-mRNA splicing factors with reduced expression in senescent cells, indicating that the regulation of mRNA splicing is altered during cell senescence. In addition, the expression of the gene TOM1 (target of Myb 1), which has not previously been associated with cellular senescence, is shown to increase in senescent cells, and we demonstrate that the expression of antisense TOM1 gene in 2BS cells can delay the progress of senescence.     

Early BrdU-responsive genes constitute a novel class of senescence-associated genes in human cells

We identified genes that immediately respond to 5-bromodeoxyuridine (BrdU) in SUSM-1, an immortal fibroblastic line, with DNA microarray and Northern blot analysis. At least 29 genes were found to alter gene expression greater than twice more or less than controls within 36 h after addition of BrdU. They took several different expression patterns upon addition of BrdU, and the majority showed a significant alteration within 12 h. When compared among SUSM-1, HeLa, and TIG-7 normal human fibroblasts, 19 genes behaved similarly upon addition of BrdU. In addition, 14 genes, 9 of which are novel as regards senescence, behaved similarly in senescent TIG-7 cells. The genes do not seem to have a role in proliferation or cell cycle progression. These results suggest that the early BrdU-responsive genes represent early signs of cellular senescence and can be its new biomarkers.