A Novel Transgenic Mouse Model Reveals Humanlike Regulation of an 8-kbp Human TERT Gene Promoter Fragment in Normal and Tumor Tissues

Abstract

Telomerase activity is repressed in most human somatic tissues during differentiation processes but strongly upregulated in most human tumors. Regulation of human telomerase activity primarily occurs at the level of transcriptional initiation of the TERT gene, which encodes the catalytic subunit of telomerase. We have generated a novel transgenic mouse model to study the regulation of the human TERT gene promoter in an in vivo system. For this purpose, we have cloned an 8.0-kbp human TERT promoter fragment in front of the bacterial lacZ reporter gene (hTERTp-lacZ), which encodes the B-galactosidase enzyme. Expression of the reporter gene was monitored by reverse transcription-PCR analysis, 5-bromo-4-chloro-3-indolyl-B-D-galactopyranoside staining of whole mount preparations, and histologic sections. We find that the activity of the human TERT promoter in most normal mouse tissues recapitulates the expression of the hTERT gene in normal human tissues and is under tighter control when compared with the endogenous mouse TERT gene expression. In testis, where highest lacZ expression was observed, the expression of the reporter gene was restricted to the spermatogonial stem cells and the spermatocytes. Intriguingly, we find increased levels of lacZ expression in mammary tumors of hTERTp-lacZ Â p53 +/À bitransgenic mouse mammary tumor model. Thus, this transgenic mouse model provides a suitable in vivo system to analyze the expression of the human TERT gene under physiologic conditions and during tumorigenesis. (Cancer Res 2005; 65(4): 1187-96)

The Promoter of Human Telomerase Reverse Transcriptase Is Activated During Liver Regeneration and Hepatocyte Proliferation

“…34 Experimental systems to investigate the activation of hTERT in regenerating hepatocytes have been missing. In contrast to humans, a constitutive expression of telomerase activity has been documented in mouse liver 15 and this species-dependent regulation of TERT gene has been attributed to its promoter organization. 16,17 Here, a humanized mouse model was employed allowing to monitor hTERT promoter activity in vivo during liver regeneration.…”

“…14 Indeed, there is a marked difference in TERT mRNA levels in human and mouse livers. 15 Together, these results indicate that there is an important, species-specific difference in the regulation of TERT during liver regeneration. There is experimental evidence that the differential regulation is based on different promoter organization.…”

“…The endogenous enzymatic activity of telomerase in mouse liver and HepaRG cell extracts was determined by Telomeric Repeat Amplification Protocol (TRAP) with the TRAPeze kit (Serologicals Corporation) as described earlier. 15 Immunohistochemistry. Tissues were routinely fixed in 4% buffered formalin and paraffinembedded.…”

“…15 Specifically, hTERT promoter activity was seen in stem cell compartments of the testis and in tumor cells, but not in normal somatic tissues. To investigate hTERT promoter activity in liver cells in vivo we determined hTERT promoter activity during regeneration induced by two-thirds partial hepatectomy (PH).…”

“…In this study, using the human TERT promoter (hTERTp)-lacZ transgenic mouse model 15,19 we provide the first experimental evidence that human TERT promoter is activated in hepatocytes during liver regeneration in response to acute liver injury as induced by partial hepatectomy as well as in proliferating human hepatocytes in culture using the HepaRG cell line, a new model system for human hepatocytes. 20 These studies support the new concept that activation of telomerase in adult hepatocytes contributes to the maintenance of liver regenerative capacity in humans.…”