Hsp90 Physically Interacts with hTERT Promoter and Enhances hTERT Expression

Objectives: Unlike normal cells, most cancer cells contain very high level of telomerase, which is consisted of human telomerase reverse transcriptase (hTERT) and human telomerase mRNA component (hTERC). It is well known that the telomerase activity mostly depends on the expression status of hTERT. The present study is designed to investigate the mechanisms hTERT expression in immortalized and cancer cells. Methods: We used DNA-protein binding assay to examine differential protein binding patterns on the hTERT promoter in immortalized cells with high telomerase activity and cells without telomerase. Chromatin immunoprecipiation (ChIP) assay and electromagnetic shift assay (EMSA) were used to confirm binding capacity. Results: We found that heat shock protein 90 (hsp90) physically interacts with hTERT promoter in vitro. The hsp90 interaction with the promoter was detected more strongly in the telomerase-positive HOK-Bmi-1/E6 cells compared with that in senescing NHOK which exhibits no telomerase activity. ChIP assay confirmed the in vivo interaction between hsp90 and hTERT promoter in SCC4 cells, a telomerase-positive oral cancer cell line, but not in senescing NHOK. Exposure of SCC-4 cells to geldanamycin (GA), a competitive inhibitor of hsp90, notably decreased the hTERT promoter activity, hTERT mRNA expression, and telomerase activity. Also, it abolished the in vivo physical interaction of the hTERT promoter with hsp90. Conclusions: These results indicate that physical interaction between hsp90 and the hTERT promoter is necessary for the expression of hTERT and telomerase activity in cancer cells. This study was supported by NIDCR/NIH (DE14147, DE15316, and DE017121).