| Summary: | 碩士 === 長庚大學 === 基礎醫學研究所 === 88 === Telomerase is a specialized ribonucleoprotein that directs the synthesis of telomeric repeats (TTAGGG in human) at chromosome ends. Normal human somatic cells express low or undetectable telomerase activity and are mortal. In contrast, moderate or high telomerase activity is present in the majority of immortal and cancer cells, indicating that expression of telomerase plays an important role in cellular immortalization and carcinogenesis. Exactly how the telomerase activity is regulated in human cell is not known.
In this study, the role of protein kinase C (PKC) in the regulation of telomerase activity was studied in human nasopharyngeal cancer cells (NPC-076). Treatment of NPC-076 cells with bisindolylmaleimide I (BIM), an inhibitor for PKC, resulted in an inhibition of telomerase activity. However, the expression of hTERT, which is the reverse transcriptase subunit and key determinant of enzyme activity, was not inhibited. Treatment of NPC-076 cells with phobol-12-myristate-13-acetate (PMA), an agent that downregulates PKC upon prolonged treatment, led to the degradation of PKCα, β1, and δ, but not PKCζ. Surprisely, there is no loss of telomerase activity in TPA-treated cells.Treatment of NPC-076 cells with anti-sense oligonucleotide against each individual PKC isoform revealed that telomerase activity was inhibited only by anti-sense PKCζ, but not by anti-sense PKCα, or PKCβ1. Finally, the putative role of each PKC isoform in the activation of telomerase activity by protein phosphorylation was investigated in vitro with the cell extracts obtained from BIM-treated cell. Exogenous addition of PKCα or β1 to the cell extracts failed to restore telomerase activity, but addition of PKCζ, did lead to a restoration of telomerase activity. Taken together, these results indicate that PKCζ, is the PKC isoform that participates in the regulation of telomerase activity in NPC-076 cells and it acts at the level of protein phosphorylation.
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