Triptolide Down-Regulates Telomerase Reverse Transcriptase mRNA Expression and Telomerase Activity in Leukemia Cell Lines
Jin, J.; Lou, Y.
Blood 100(11): Abstract No. 4386
Recently, the derepressed expression of the catalytic subunit of telomerase, human telomerase reverse transcriptase (hTERT), the enzyme that elongates telomeres, has been implicated as an important step in the immortalization process.As transformed cells seem to be dependent on a constitutive telomerase activity, the availability of inhibitors would potentially be of great value in antineoplastic therapy.Triptolide, a traditional Chinese medicine, has been reported to be effective in the treatment of auto-immune diseases, and it can also induce antineoplastic activity on several human tumor cell lines. This study investigates the cytotoxic function and the functional mechanism of Triptolide on Jurkat, K562, and Raji cells. Cell growth inhibition was examined by MTT cell viability assay.To assess telomerase activity, a PCR-based telomeric repeat amplification protocol assay (TRAP) was used. Reverse transcription-PCR (RT-PCR) was performed to examine the mRNA levels hTERT, bcl-2 (B cell leukemia/lymphoma 2 gene), bax and c-myc in leukemia cells before and after Triptolide treatment. Apoptosis was determined by agarose electrophoresis. Triptolide inhibited 50% of cell growth (IC50 ) on Jurkat cells at 10ng/ml, on K562 cells at 50ng/ml,on Raji at 15ng/ml. After Jurkat cells were cultured in Triptolide 10ng/ml for 48 hours, the telomerase activity was repressed to about 10% of control cells, and the expression of hTERT was undetected. Moreover, the downregulation of c-Myc preceded the change of hTERT.Characteristic apoptotic features internucleosomal DNA fragmentation were observed in Triptolide treated Jurkat cells while expression of bcl-2 was progressively down-regulated. In K-562 cells, Triptolide 40ng/ml for 48 hours repressed the telomerase activity to about 30% of control cells, and hTERT expression could not be detected after 24hours.we also demonstrated that Triptolide at 15ng/ml for 24hours significantly down-regulated the expression of hTERT and strongly inhibited telomerase activity in Raji cells. However, there were no relationship between hTERT and c-Myc in K562 and Raji cells. In addition,the proliferation of all three cells was inhibited by Triptolide at dose of IC50. These findings suggest that Triptolide down-regulated telomerase activity via suppression of hTERT mRNA expression in leukemia cell lines.