Small molecule-based analysis of regulatory mechanisms of the human telomerase reverse transcriptase (hTERT) gene in normal cells

Abstract

Activation of telomerase is crucial for cells to gain immortality. Most normal human somatic cells have a limited proliferative life span and the expression of the rate-limiting telomerase catalytic subunit, known as human telomerase reverse transcriptase (hTERT), has been believed to be tightly repressed. Its suppression acts as an important gatekeeper against tumorigenesis. Despite numerous efforts to elucidate the regulatory mechanisms of hTERT, many things remain elusive. To explore hTERT regulatory mechanisms more efficiently, we exploited a small molecule-based chemical genetic approach. Our strategy was to identify small molecules that could derepress hTERT in normal human cells in a forward chemical genetic screen and to reveal the regulatory mechanisms of hTERT by analyzing the mode of action of these molecules. In this study, six small molecules (J25, J41, Q13, Q28, Q39, and T35 ) activating the hTERT gene expression in human normal cells were identified from the screening of chemical libraries. TRAP assay showed the increased level of endogenous telomerase activity induced by the identified small molecules. Among 6 small molecules, Q28, Q39, T35, and J25 showed HDAC inhibitory effects whereasQ13 and J41 had no effect of HDAC inhibition. Consistently, Q13 and J41 have no cytotoxicity effects on human normal cells. These two chemicals might have a different action mechanism on the hTERT promoter activation comparing HDAC inhibitors. Thus, identifying the target proteins of these identified small molecules suggests the starting point for the study of the novel telomerase regulation pathway in human normal cell. In addition, they might have a potential to recover the cells from senescence because they induce the hTERT promoter transcriptional activity.