Differential gene expression of human telomerase-associated protein hTERT and TEP1 in human hematopoietic cells

The maintenance of telomere length is crucial for the survival of cells. Recently, genes for proteins that consist of human telomerase have been cloned and the results have indicated a close relationship between telomerase activity and its gene expression. We studied the mRNA expression of the telomerase-associated genes, hTERT and TEP1, in hematopoietic cells in order to clarify the relation between them and telomerase activity using semiquantitative RT-PCR. In polymorphonuclear cells and monocytes isolated from peripheral blood, which had no detectable telomerase activity, no hTERT mRNA expression was seen. On the other hand, lymphocytes and CD34-positive cells both demonstrated hTERT mRNA expression. TEP1 mRNA was detected in all samples, showing no differential expression. We then assessed hTERT and TEP1 mRNA expression in CD34-positive cells cultured in vitro with growth factors. After 4 weeks of culture, all the cells showed myeloid differentiation and the telomerase activity was downregulated. hTERT mRNA was expressed in CD34-positive cells, but was downregulated in 4-week-cultured cells. TEP1 showed no apparent differential expression. We conclude that hTERT mRNA expression is downregulated in accordance with telomerase downregulation during the course of myeloid differentiation, which suggests that it plays a crucial role in the expression of enzyme activity, while TEP1 has a much smaller role to play, if any.     

HPV18 E6 E7基因诱发的人胎儿食管上皮永生化和恶性转化细胞端粒长度和端粒酶活性

目的：探讨端粒长度、端粒酶活性以及端粒酶亚单位组分（hTERT、hTR）的表达与食管上皮细胞永生化和恶性转化之间的关系。方法：对HPV18E6E7基因诱发的人胎儿食管上皮永生化细胞系SHEE和恶性转经细胞系SHEEC,通过Southern blot检测端粒长度（TRF）,TRAP法测定端粒酶活性,RT－PCR研究端粒酶催化亚单位（hTERT)端粒酶RNA成分（hTR）的表达。结果：SHEE细胞和SHEEC细胞的端料平均长度比正常食管上皮细胞的明显缩短,但稳定维持在一定长度范围内。SHEE细胞和SHEEC细胞均具有端料酶活性,并均有hTERT和hTR表达。结论：端粒酶表达活化使端粒维持在一定长度是永生化食管上皮细胞SHEE和恶性转化细胞SHEEC能够稳定分裂增殖的重要因素之一。     

Telomerase activity in B-cell non-Hodgkin lymphomas is regulated by hTERT transcription and correlated with telomere-binding protein expression but uncoupled from proliferation

Telomere maintenance is a prerequisite for immortalisation, and in most malignant cells is carried out by telomerase, an enzyme that synthesis new telomeric repeats on the chromosome ends. In normal or reactive tissues with a high regenerative capacity, telomerase is regulated according to the telomere loss that occurs during proliferation. To evaluate the interaction of proliferation and telomerase activity in malignant lymphomas, we quantified telomerase expression in different non-Hodgkin lymphomas in comparison to normal or reactive lymph nodes. Surprisingly, the activity levels were the same in most of the lymphomas analysed as compared to reactive lymph nodes. Significantly higher activity was detected only in Burkitt's lymphoma. Telomerase activity correlated well with hTERT and c-myc expression, but was independent of proliferation. To evaluate interactions of telomere-binding protein expression on telomerase expression in non-Hodgkin lymphoma, the mRNA levels of TRF1, TRF2, tankyrase and hPif1 were assessed by real-time RT-PCR. We demonstrate here that the magnitude of telomerase upregulation does not necessarily reflect the requirement of telomere compensation caused by proliferation. Telomerase regulation in non-Hodgkin lymphomas is therefore uncoupled from proliferative stimuli found in reactive lymphoid tissue. We suggest that the upregulation of specific telomere-binding proteins like TRF2 may contribute to telomere maintenance in malignant lymphoma.     

PAX8 regulates telomerase reverse transcriptase and telomerase RNA component in glioma

Paired box (PAX) developmental genes are frequently expressed in cancers and confer survival advantages on cancer cells. We have previously found that PAX genes are deregulated in glioma. We have now investigated the expression of PAX genes in glioma and their role in telomere maintenance. The mRNA level of PAX8 showed a positive correlation with telomerase activity in glioma biopsies (r(2) = 0.75, P < 0.001) and in established glioma cell lines (r(2) = 0.97, P = 0.0025). We found that PAX8 is able to coordinately transactivate the promoter for both the telomerase catalytic subunit (hTERT) and the telomerase RNA component (hTR) genes. By electrophoretic mobility shift assay, quantitative PCR, and a telomerase activity assay, we show that PAX8 binds directly to the hTERT and hTR promoters, up-regulating hTERT and hTR mRNA, as well as telomerase activity. Additionally, PAX8 small interfering RNA down-regulated hTERT and hTR. Collectively, these results show that PAX8 may have a role in telomerase regulation.