Lack of telomerase activity in human mesenchymal stem cells.

Telomerase activity and telomere maintenance have been associated with immortality in tumor and embryonic stem cells. Whereas most normal somatic cells are telomerase negative, low levels of this enzyme have been found in adult stem cells from the skin, gut and the hematopoietic system. Here, we show that telomerase activity is not detectable in human mesenchymal stem cells (hMSCs), which have the phenotype SH2+, SH3+, SH4+, CD29+, CD44+, CD14-, CD34- and CD45-, and have the capacity to differentiate into adipocytes, chondrocytes and osteoblasts. These data suggest that hMSCs have a different telomere biology compared to other adult stem cells. Alternatively, true mesenchymal stem cells might be a very rare subpopulation that have a detection level that is below the sensitivity of the TRAP assay.     

Dysregulated expression of stem cell factor Bmi1 in precancerous lesions of the gastrointestinal tract.

PURPOSE: It is important to identify the definitive molecular switches involved in the malignant transformation of premalignant tissues. Cellular senescence is a specific characteristic of precancerous tissues, but not of cancers, which might reflect tumorigenesis-protecting mechanisms in premalignant lesions. Polycomb protein Bmi1, which is a potent negative regulator of the p16INK4 gene, suppresses senescence in primary cells and is overexpressed in various cancers. We hypothesized that Bmi1 expression would also be dysregulated in precancerous lesions in human digestive precancerous tissues. EXPERIMENTAL DESIGN: Bmi1 expression was investigated in cancerous and precancerous tissues of the digestive tract. The expression of p16, beta-catenin, and Gli1 and the in vivo methylation status of the p16 gene were also analyzed in serial sections of colonic precancerous lesions. RESULTS: Bmi1 was clearly overexpressed across a broad spectrum of gastrointestinal cancers, and the expression of Bmi1 increased in a manner that reflected the pathologic malignant features of precancerous colonic tissues (low-grade dysplasia, 12.9 +/- 2.0%; high-grade dysplasia, 82.9 +/- 1.6%; cancer, 87.5 +/- 2.4%). p16 was also strongly expressed in high-grade dysplasia, but not in cancers. p16 promoter methylation was detected only in some Bmi1-positive neoplastic cells. CONCLUSIONS: Bmi1 overexpression was correlated with the malignant grades of human digestive precancerous tissues, which suggests that advanced Bmi1 dysregulation might predict malignant progression. The abnormal Bmi1 expression might link to malignant transformation via the disturbance of orderly histone modification.     

Telomeres and telomerase in cancer stem cells

Alterations in telomere dynamics both suppress and facilitate malignant transformation by regulating genomic stability and cell lifespan. Checkpoints induced by telomere dysfunction play a major role in tumour suppression, whereas telomere shortening contributes to the initiation of cancer by inducing chromosomal instability. Since stem cells are exposed to various tumourigenic agents and stresses throughout their lifetime, the ageing stem cell is a major target of malignant transformation. This review summarises our knowledge of telomere length and telomerase activity in stem cells during ageing and carcinogenesis.     

Cytostatic concentrations of anticancer agents do not affect telomerase activity of leukaemic cells in vitro

Telomerase, the enzyme that maintains the ends of linear eukaryotic chromosomes, is more active in the majority of malignant tumours than in normal somatic cells. Telomerase plays a key role in the maintenance of chromosomal stability in tumours, but it still remains unknown whether anticancer agents can inhibit telomerase activity. In this study, we evaluated the effect of various anticancer agents (etoposide, cisplatin, irinotecan, mitomycin C and daunorubicin) on the telomerase activity of three human haematopoietic cancer cell lines (Daudi, K562 and U937). A decrease of telomerase activity was not observed in cells treated with ic₅₀ doses of the drugs, except for irinotecan-treated Daudi cells and daunorubicin- and irinotecan-treated U937 cells. Propidium iodide staining disclosed that the cells with decreased telomerase activity were severely damaged. U937 cells exposed to 5 μM (ic₉₀) etoposide showed three different stages of cell viability during treatment. Apoptotic cells with an intact plasma membrane still maintained high telomerase activity, while cells with plasma membrane damage lost telomerase activity. The mRNA of the telomerase catalytic subunit (hTERT) showed a decrease in expression along with the decline of telomerase activity. These results indicate that the concentrations of drugs resulting in cytostatic effects on cells do not affect telomerase activity.     

端粒和端粒酶与肿瘤干细胞的研究现状

目的:总结国内外对端粒、端粒酶与肿瘤起源、肿瘤干细胞的病理研究现状。方法:应用检索MED-LINE及CHKD期刊全文数据库检索系统,以"端粒、端粒酶和肿瘤干细胞"为关键词,检索1997-2008年有关文献。纳入标准:端粒、端粒酶与肿瘤干细胞的论著性文章。根据标准,纳入分析24篇参考文献。结果:端粒酶激活和端粒稳定对肿瘤干细胞演进是必需的,端粒酶激活是肿瘤干细胞自我更新和不定向分化的必要条件,端粒的动力学代表肿瘤干细胞恶性来源和有丝分裂历史,分析肿瘤干细胞端粒长度,端粒酶活性和细胞遗传学特性有助于揭示肿瘤干细胞起源和肿瘤形成历史,从而深化对肿瘤病理的认识,为恶性肿瘤治疗提供依据。结论:端粒和端粒酶在肿瘤干细胞中表达,是消灭肿瘤理想的靶标,有待进一步研究总结。     

Dysregulated expression of claudins in cancer

Claudins are adhesion molecules located at the tight junctions between epithelial cells. A series of studies have now reported aberrant expression of claudin proteins in the context of neoplastic transformation, suggesting its role in tumorigenesis. However, the precise mechanisms are still not well understood. Studies on expression alterations of claudins have revealed a range of outcomes that reflect the complexity of claudins in terms of spatial localization, tumor type and stage of disease. The diverse and dynamic expression patterns of claudins in cancer are tightly controlled by a wide range of regulatory mechanisms, which are commonly modulated by oncogenic signaling pathways. The present review summarizes the recent knowledge describing the dysregulation of claudin expression in cancer and discusses the intrinsic and extrinsic determinants of the context-specific expression patterns of claudins.     

Dysregulated expression of adamalysin-thrombospondin genes in human breast carcinoma.

The adamalysin-thrombospondin (ADAMTS) proteinases are a relatively newly described branch of the metzincin family that contain metalloproteinase, disintegrin, and thrombospondin motifs. They have been implicated in various cellular events, including cleavage of proteoglycans, extracellular matrix degradation, inhibition of angiogenesis, gonadal development, and organogenesis. However, in many cases, their normal physiological roles and their potential for dysregulation in malignancy remain to be established. The expression profile of ADAMTS1-20 in human breast carcinoma was undertaken by real-time PCR using RNA isolated from malignant tumors, nonneoplastic mammary tissue, and breast cancer cell lines to identify altered regulation that may have potential pathogenetic and prognostic significance. Our studies show that seven of the ADAMTS genes (ADAMTS1, 3, 5, 8, 9, 10, and 18) are consistently down-regulated in breast carcinomas with respect to nonneoplastic mammary tissue, irrespective of the heterogeneity of the samples and the tumor type or grade (Mann-Whitney U test, P < 0.0001 for each gene). Conversely, ADAMTS4, 6, 14, and 20 are consistently up-regulated in breast carcinomas (P = 0.005, P < 0.0001, P = 0.003, and P = 0.001, respectively). ADAMTS2, 7, 12, 13, 15, 16, 17, and 19 show no significant difference between the sample types. ADAMTS1, 2, 7, 8, 10, and 12 are expressed predominantly in stromal fibroblasts. ADAMTS3, 4, 5, 6, 9, and 13-20 inclusive are expressed predominantly in myoepithelial cells; all appear to be relatively poorly expressed in luminal epithelial cells. ADAMTS15 has emerged as being an independent predictor of survival, with RNA expression levels significantly lower (P = 0.007) in grade 3 breast carcinoma compared with grade 1 and 2 breast carcinoma.     

AC133 expression in human stem cells.

Expression of cell surface markers on human hematopoietic cells has provided a method for characterizing subsets of cells with distinct biological functions. This is largely due to the ability to separate highly purified subpopulations of cells for comparative analysis. Relationships between the cell surface phenotype of these subpopulations and their proliferative and differentiative capacity have been instrumental in defining the hierarchical organization of cells comprising the human hematopoietic system. The identification and isolation of human hematopoietic cells expressing AC133, combined with use of in vitro and in vivo assays, has provided novel insights into the hematopoietic progenitor and stem cell compartment in the human. More recent studies have offered evidence that AC133 expression is not limited to primitive blood cells, but also defines unique cell populations in non-hematopoietic tissues. These findings will be reviewed here in the context of human hematopoiesis and the potential role and utility of AC133 expression in the human.     

Influence of leukaemic cells on the colony formation of human bone marrow cells in vitro II. Suppressive effects of leukaemic cell extracts.

The influence of leukaemic cells on the colony formation of human bone marrow cells was studied in vitro as an extension of our previous work (Chiyoda et al., 1975). An extract of leukaemic bone marrow cells significantly suppressed colony forming ability of the normal bone marrow cells, whereas an extract of normal bone marrow cells did not suppress it except in two cases. The suppressive effect of normal bone marrow cells, however, was obviously less intense than that of leukaemic cells. This suppressive effect was dose dependent and was fairly stable to heat treatment. These results suggest that leukaemic bone marrow cells contain factor(s) which suppress normal colony formation.     

VLA molecule expression may be involved in the release of acute myeloid leukaemic cells from the bone marrow.

Acute myeloid leukaemia (AML) cells have a variable capacity to egress from bone marrow into peripheral blood. This may be due to a variable lack of adhesion molecules on leukaemic cells. The expression of VLA1, 3, 4, 5, 6, beta 1-chain, LFA1, beta 2-chain, ICAM1 and NCAM appeared to be higher in bone marrow as compared to peripheral blood leukaemic cells, although this only reached significance for beta 1-chain (p less than 0.01). The number of cases with more than 20% positive cells in bone marrow leukaemic cells was lower in immature FAB-subtypes (M1, M5a) as opposed to more mature subtypes (M2, M3, M4, M5b) for the adhesion molecules tested. This reached significance for VLA5 (p less than 0.05) and beta 1-chain (p less than 0.007), while there was trend for VLA4. It is discussed that VLA4 and 5 may play a role in the release of leukaemic cells from the bone marrow.     

Gene expression profiles of AML derived stem cells; similarity to hematopoietic stem cells.

Tumors contain a fraction of cancer stem cells that maintain the propagation of the disease. The CD34(+)CD38(-) cells, isolated from acute myeloid leukemia (AML), were shown to be enriched leukemic stem cells (LSC). We isolated the CD34(+)CD38(-) cell fraction from AML and compared their gene expression profiles to the CD34(+)CD38(+) cell fraction, using microarrays. We found 409 genes that were at least twofold over- or underexpressed between the two cell populations. These include underexpression of DNA repair, signal transduction and cell cycle genes, consistent with the relative quiescence of stem cells, and chromosomal aberrations and mutations of leukemic cells. Comparison of the LSC expression data to that of normal hematopoietic stem cells (HSC) revealed that 34% of the modulated genes are shared by both LSC and HSC, supporting the suggestion that the LSC originated within the HSC progenitors. We focused on the Notch pathway since Jagged-2, a Notch ligand was found to be overexpressed in the LSC samples. We show that DAPT, an inhibitor of gamma-secretase, a protease that is involved in Jagged and Notch signaling, inhibits LSC growth in colony formation assays. Identification of additional genes that regulate LSC self-renewal may provide new targets for therapy.