The Regulation of Telomerase Activity and Cell Cycle Regulators in Human Hepatocarcinogenesis

• Main Authors: Cheng-Jueng Chen, 陳正榮
• Other Authors: Horng-Jyh Harn
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/07739258963609399296

博士 === 國防醫學院 === 醫學科學研究所 === 90 === Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, with its highest prevalence occurring in Asia and Africa. Despite some progress in its clinical management in recent years, HCC remains a disease having a poor prognosis. It is important to improve the early diagnosis and treatment strategy of HCC by better understanding the molecular events involved tumor development and progression. Telomerase, a ribonucleoprotein with two components required for core enzyme activity: telomerase RNA (hTR) and a telomerase reverse transcriptase protein (hTERT). It compensates for the continued shortening telomere length by adding hexameric (TTAGGG) repeat to the telomeric ends of the chromosomes. Telomerase activity (TA) is expressed in almost all malignant tumors, but is rarely detected in normal somatic cells. At first stage, we analyzed the TA by PCR-based telomerase repeat amplification protocol assay in the tissues of 25 HCC. The fraction of telomerase positive tumors was 84 % (21/25) and only five non-tumorous tissues had very weak TA. To explore the possible regulatory mechanisms of telomerase, we examined the TA, expression of human telomerase RNA (hTR), human telomerase reverse transcriptase (hTERT) mRNA isoforms and cell cycle modulators in HCC cell lines (J5) and a normal human immortalized hepatic epithelial cell line (Chang-liver). The cell lines were chemically synchronized in G1, G1/S, G2/M or M phases. The hTR and hTERT mRNA levels were analyzed by reverse transcriptase polymerase chain reaction. Western blotting was used to assay the cell cycle modulators. The TA of J5 and Chang-liver cell lines tested was highest in M phase.The expression level of hTERT mRNA associated with the highest TA detected in the M phase of HCC cell lines. Chang-liver expressed markedly less TA and hTERT mRNA than J5. The elevated TA and expression of hTERT mRNA in M phase of HCC cell lines did not significantly correlate with that of the cell cycle modulators except p21. There is significant different expression level of TA between tumor part and non-tumor part of HCC that suggests the analysis of TA in specimens might contribute to assessment of the severity of HCC. The highest TA in the M phase suggested that there were other unidentified factors which controlled the progressive cell cycle of tumor and might be correlated with the telomerase activity. Moreover, the result implicates that regulation of TA is related to hTERT mRNA isoform expression.