Repression of telomerase gene promoter requires human‐specific genomic context and is mediated by multiple HDAC1‐containing corepressor complexes

Abstract

The human telomerase reverse transcriptase () gene is repressed in most somatic cells, whereas the expression of the mouse gene is widely detected. To understand the mechanisms of this human-specific repression, we constructed bacterial artificial chromosome (BAC) reporters using human and mouse genomic DNAs encompassing the genes and neighboring loci. Upon chromosomal integration, the hTERT, but not the mTert, reporter was stringently repressed in telomerase-negative human cells in a histone deacetylase (HDAC)-dependent manner, replicating the expression of their respective endogenous genes. In chimeric BACs, the mTert promoter became strongly repressed in the human genomic context, but the hTERT promoter was highly active in the mouse genomic context. Furthermore, an unrelated herpes simplex virus-thymidine kinase (HSV-TK) promoter was strongly repressed in the human, but not in the mouse, genomic context. These results demonstrated that the repression of gene was dictated by distal elements and its chromatin environment. This repression depended on class I HDACs and involved multiple corepressor complexes, including HDAC1/2-containing Sin3B, nucleosome remodeling and histone deacetylase (NuRD), and corepressor of RE1 silencing transcription factor (CoREST) complexes. Together, our data indicate that the lack of telomerase expression in most human somatic cells results from its repressive genomic environment, providing new insight into the mechanism of long-recognized differential telomerase regulation in mammalian species.-Cheng, D., Zhao, Y., Wang, S., Zhang, F., Russo, M., McMahon, S. B., Zhu, J. Repression of telomerase gene promoter requires human-specific genomic context and is mediated by multiple HDAC1-containing corepressor complexes.

Regulation of human and mouse telomerase genes by genomic contexts and transcription factors during embryonic stem cell differentiation

“…To directly compare hTERT and mTERT gene regulation during development, we first integrated H(wt) and M(wt), which contained genomic sequences encompassing the consecutive CRR9 , TERT , and Xtrp2 loci of the 160-bp human and 135-bp mouse genomic regions, respectively 21 , into T2-5 cells. Circular BAC DNAs and pCBM were co-transfected into T2-5 cells.…”

“…In addition to H(wt) and M(wt), we also generated ESC clones containing H(mPro) and M(hPro). H(mPro) and M(hPro) were resulted from swapping of the hTERT and mTERT promoters (472- and 474-bp genomic sequences immediately upstream of the hTERT and mTERT initiation codons, respectively) between H(wt) and M(wt) 21 . Thus, all these single-copy BAC reporters were integrated at the same chromosomal site and analyzed in the same chromatin environment.…”

“…Recently, we reported that hTERT repression in immortal human fibroblasts involved multiple HDAC1-containing corepressor complexes (CRCs) 21 . To verify that HDACs were also involved in hTERT repression during ESC differentiation, differentiated mouse cells containing H(wt) were treated with chemical inhibitors, trichostatin A (TSA, an inhibitor of both classes I & II HDACs), MS-275 (a specific inhibitor of class I HDACs), and MC-1568 (an inhibitor of class II HDACs).…”

“…Previously, we used the RMBT technique to study hTERT regulation in immortal human fibroblasts 20 , 21 . In those experiments, the de novo chromatin around BAC reporters was assembled from transfected naked BAC DNAs without going through the same stepwise epigenetic modifications as those of endogenous loci 19 , 27 .…”

Father Loss and Child Telomere Length

“…Distribution of samples in the 96-well plates was randomized, and each plate contained repeats from previous runs to detect and limit potential batch effects. To mitigate batch effects, reference DNA from a cell line with a relatively short telomere (3C167b) 57 and a fibroblast cell line after stable integration of the hTERT gene (cell line NHFpreT) 58 were included in each plate (both cell lines were a gift from Dr Yuanjun Zhao of Pennsylvania State University). In our laboratory, 3C167b has a mean TL of 3.1 kb, whereas NHFpreT has a mean TL of 16.8 kb.…”