The H/ACA RNP assembly factor SHQ1 functions as an RNA mimic

SHQ1 is an essential assembly factor for H/ACA ribonucleoproteins (RNPs) required for ribosome biogenesis, pre-mRNA splicing, and telomere maintenance. SHQ1 binds dyskerin/NAP57, the catalytic subunit of human H/ACA RNPs, and this interaction is modulated by mutations causing X-linked dyskeratosis congenita. We report the crystal structure of the C-terminal domain of yeast SHQ1, Shq1p, and its complex with yeast dyskerin/NAP57, Cbf5p, lacking its catalytic domain. The C-terminal domain of Shq1p interacts with the RNA-binding domain of Cbf5p and, through structural mimicry, uses the RNA-protein-binding sites to achieve a specific protein-protein interface. We propose that Shq1p operates as a Cbf5p chaperone during RNP assembly by acting as an RNA placeholder, thereby preventing Cbf5p from nonspecific RNA binding before association with an H/ACA RNA and the other core RNP proteins.     

碱性成纤维细胞生长因子和环磷酸腺苷对神经前体细胞内源性端粒酶反转录酶基因转录水平的调控

目的 探讨人类神经前体细胞中内源性人端粒酶反转录酶(hTERT)基因的转录活性及增殖与分化相关调控机制.方法 采用系列hTERT基因启动子的荧光素酶报告载体和β-半乳苷酶表达载体,瞬时共转染HeLa细胞和hNPCs-G3细胞,检测不同长度启动子的活性.分析碱性成纤维细胞生长因子(bFGF)促进增殖过程中hTERT基因启动子活性,分析cAMP诱导分化过程中hTERT基因启动子活性.结果 hNPCs-G3神经前体细胞内源性hTERT基因的转录活性较低,主要依赖近端启动子区.bFGF上调hNPCs-G3神经前体细胞内源性hTERT基因的表达,其调控主要作用在-2 098～-1 099bp区域和-3 216bp～-2 098bp区域内;cAMP 抑制hNPCs-G3神经前体细胞hTERT基因的转录,其调控主要作用在近端启动子区.结论 神经前体细胞内源性hTERT基因的转录活性较低,bFGF可上调神经前体细胞内源性hTERT基因的表达,cAMP则可抑制hTERT基因的转录.     

IL-4基因转染诱导肝母细胞瘤分化及抑制端粒酶活性

目的 研究人白细胞介素４（ｈｕｍａｎ ｉｎｔｅｒｌｅｕｋｉｎ－４,ｈＩＬ－４）基因转染对肝母细胞瘤细胞的诱导分化和对端粒酶活性的影响。方法 以逆转录病毒载体（ＰＬ－ＩＬ－４－ＳＮ）将ｈＩＬ－４基因导入人肝母细胞瘤细胞系Ｈｅｐ Ｇ２细胞。台盼蓝拒梁,放射免疫测定,流式细胞仪细胞周期分析,原位杂交,ＰＣＲ－ＥＬＩＳＡ等方法检测基因转染后细胞形态,甲胎蛋白合成,原癌基因的表达及端粒酶活性变化。     

Genetic variants in telomerase-related genes are associated with an older age at diagnosis in glioma patients: evidence for distinct pathways of gliomagenesis

Background

Genome-wide association studies have implicated single nucleotide polymorphisms (SNPs) in 7 genes as glioma risk factors, including 2 (TERT, RTEL1) involved in telomerase structure/function. We examined associations of these 7 established glioma risk loci with age at diagnosis among patients with glioma.

Methods

SNP genotype data were available for 2286 Caucasian glioma patients from the University of California, San Francisco (n = 1434) and the Mayo Clinic (n = 852). Regression analyses were performed to test for associations between “number of risk alleles” and “age at diagnosis,” adjusted for sex and study site and stratified by tumor grade/histology where appropriate.

Results

Four SNPs were significantly associated with age at diagnosis. Carrying a greater number of risk alleles at rs55705857 (CCDC26) and at rs498872 (PHLDB1) was associated with younger age at diagnosis (P = 1.4 × 10⁻²² and P = 9.5 × 10⁻⁷, respectively). These SNPs are stronger risk factors for oligodendroglial tumors, which tend to occur in younger patients, and their association with age at diagnosis varied across tumor subtypes. In contrast, carrying more risk alleles at rs2736100 (TERT) and at rs6010620 (RTEL1) was associated with older age at diagnosis (P = 6.2 × 10⁻⁴ and P = 2.5 × 10⁻⁴, respectively). These SNPs are risk factors for all glioma grades/histologies, and their association with age at diagnosis was consistent across tumor subgroups.

Conclusions

Carrying a greater number of risk alleles might be expected to decrease age at diagnosis. However, glioma susceptibility conferred by variation in telomerase-related genes did not follow this pattern. This supports the hypothesis that telomerase-related mechanisms of telomere maintenance are more associated with gliomas that develop later in life than those utilizing telomerase-independent mechanisms (ie, alternative lengthening of telomeres).     

Putative tumour suppressor gene necdin is hypermethylated and mutated in human cancer

Background:

Necdin (NDN) expression is downregulated in telomerase-immortalised normal human urothelial cells. Telomerase-immortalised normal human urothelial cells have no detected genetic alterations. Accordingly, many of the genes whose expression is altered following immortalisation are those for which epigenetic silencing is reported.

Methods:

NDN expression was examined in normal tissues and tumour cell lines by quantitative real-time PCR and immunoblotting. Immunohistochemistry was performed on urothelial carcinoma (UC). Urothelial carcinoma and UC cell lines were subject to HumanMethylation27 BeadChip Array-based methylation analyses. Mutation screening was performed. The functional significance of NDN expression was investigated using retroviral-mediated downregulation or overexpression.

Results:

NDN protein was widely expressed in normal tissues. Loss of expression was observed in 38 out of 44 (86%) of UC cell lines and 19 out of 25 (76%) of non-UC cell lines. Loss of NDN protein was found in the majority of primary UC. Oncomine analysis demonstrated downregulation of expression in multiple tumour types. In UC, tumour-specific hypermethylation of NDN and key CpG sites where hypermethylation correlated with reduced expression were identified. Six novel mutations, including some of predicted functional significance, were identified in colorectal and ovarian cancer cell lines. Functional studies showed that NDN could suppress colony formation at low cell density and affect anchorage-independent growth and anoikis in vitro.

Conclusion:

NDN is a novel tumour suppressor candidate that is downregulated and hypermethylated or mutated in cancer.     

Role of HSPs and telomerase in radiotherapy

The inability of radiotherapy to control tumour growth is still a daunting clinical problem leading to failure of the overall treatment regimens. The fundamental question is; could tumour cells be specifically sensitized to ionizing radiation (IR) by heat or factors exclusively expressed in tumour cells? One such factor, expressed in most tumours and silent in somatic cells, is telomerase. Biochemical and genetic studies have established an association between telomere maintenance and extended life span of human cells mediated through the expression of the catalytic sub-unit of telomerase (hTERT). Because of this, telomerase is an attractive target for inhibition in anti-cancer therapy. Telomeres are maintained by telomerase and hTERT interacts with heat shock protein (HSP) chaperones. This review will focus on the possible role of HSPs and telomerase in sensitizing tumour cells and, thus, enhancing the potential of targeted radiotherapy.     

人端粒酶逆转录酶、B细胞淋巴瘤-2基因在宫颈鳞癌中的表达及其临床意义

目的探讨人端粒酶逆转录酶（hTERT）、B细胞淋巴瘤-2基因（Bcl-2）在宫颈鳞癌中的表达及其临床意义。方法应用免疫组织化学SABC法检测87例宫颈鳞癌和20例正常宫颈组织中hTERT、Bcl-2的表达。结果在正常宫颈组织和宫颈鳞癌中,hTERT表达的阳性率分别为20．0％和77．0％,其差异有高度统计学意义（P〈0．01）;Bcl-2的表达阳性率分别为35．0％和80．5％,差异也有高度统计学意义（P〈0．01）;且在宫颈鳞癌中hTERT的阳性表达与Bcl-2的阳性表达显著相关（P〈0．05）。结论hTERT和Bcl-2在宫颈鳞癌中表达显著升高,二者的表达密切相关,提示二者共同参与,并协同促进宫颈鳞癌的发生。