Dysregulated expression of the major telomerase components in leukaemic stem cells.

Telomere loss is rapid during the progression of chronic myeloid leukaemia (CML) and correlates with prognosis. We therefore sought to measure expression of the major telomerase components (hTR and hTERT) in CD34+ cells from CML patients and normal controls, to determine if their altered expression may contribute to telomere attrition in vivo. High-purity (median 94.1%) BCR-ABL+ CD34+ cells from CML (n=16) and non-CML (n=14) patients were used. CML samples had a small increase in telomerase activity (TA) compared to normal samples (approximately 1.5-fold, P=0.004), which was inversely correlated with the percentage of G0 cells (P=0.02) suggesting TA may not be elevated on a cell-to-cell basis in CML. Consistent with this, hTERT mRNA expression was not significantly elevated; however, altered mRNA splicing appeared to play a significant role in determining overall full length, functional hTERT levels. Interestingly, Q-RT-PCR for hTR demonstrated a mean five-fold reduction in levels in the chronic phase (CP) CML samples (P=0.002), raising the possibility that telomere homeostasis is disrupted in CML. In summary, the molecular events regulating telomerase gene expression and telomere maintenance during the CP of CML may influence the disease progression observed in these patients.     

食管鳞癌组织端粒酶亚基的表达及端粒酶活性的关系

目的　探讨食管鳞癌组织中端粒酶活性、端粒酶逆转录酶 (h TERT)及端粒酶相关蛋白 - 1(TP- 1)的表达及其关系。方法　应用 TRAP-银染法对 45例食管鳞癌组织端粒酶活性的检测 ,同时应用原位杂交对癌组织切片进行 h TERT、TP- 1的 m RNA表达的检测。结果　癌组织端粒酶活性阳性率为 82 .2 %。癌组织中不同分化程度的端粒酶活性差异无显著性 (P>0 .0 5 )。有淋巴结转移者癌组织端粒酶活性明显高于无淋巴结转移者 ,差异有显著性(P<0 .0 5 )。癌组织中 h TERTm RNA表达的阳性率为 6 4.4%,TP- 1的阳性率为 6 2 .2 %。 h TERT的 m RNA表达与端粒酶活性密切相关 ,而 TP- 1的 m RNA表达与端粒酶活性无相关。结论　食管鳞癌组织中端粒酶活性及h TERT、TP- 1的 m RNA表达均较高。端粒酶活性与淋巴结转移有关。 h TERT与端粒酶活性有密切关系。     

Epigenetic regulation of telomerase in retinoid-induced differentiation of human leukemia cells

Changes in the promoter methylation of hTERT, the gene that encodes telomerase, a ribonucleoprotein responsible for replacing telomeric repeats, have been demonstrated in differentiating cells where hTERT is inhibited, suggesting epigenetic regulation of hTERT. All-trans retinoic acid (ATRA) induces differentiation in human leukemia cells and has had significant clinical success treating promyelocytic leukemia in what is termed 'differentiation therapy'. It is thought that the inhibition of telomerase is a target of retinoids and is closely tied to the differentiated phenotype. This study demonstrates the epigenetic changes associated with ATRA-induced inhibition of telomerase activity, including the hypoacetylation and hypermethylation of the hTERT promoter. Further, we have found changes in the differential expression of the three DNA methyltransferases during ATRA-induced differentiation of HL60 human leukemia cells. These results suggest that alteration of DNA methylation may play a role in the activation of telomerase in cancer cells and that epigenetic mechanisms may represent a target for differentiation therapy mechanisms. We propose that epigenetic changes in the hTERT promoter represent a stable locking mechanism in the retionoid-induced suppression of telomerase activity.     

高三尖杉酯碱对Jurkat细胞端粒酶活性的影响及机制研究

目的 探讨高三尖杉酯碱（HHT）对人T淋巴细胞白血病细胞株Jurkat细胞端粒酶活性的影响及其机制.方法 采用改良的Krupp荧光素标记的端粒重复扩增（TRAP）方法检测HHT对Jurkat细胞端粒酶活性的影响.半定量RT-PCR方法检测HHT作用后Jurkat细胞端粒酶逆转录酶（hTERT）及c-myc原癌基因mRNA的表达水平.结果 HHT对Jurkat细胞端粒酶活性及hTERTmRNA、c-myc基因mRNA表达有明显抑制作用.结论 HHT可通过下调hTERT基因转录抑制淋巴细胞的端粒酶活性.c-myc可能参与调控淋巴细胞hTERT基因转录.