Differential cis-regulation of human versus mouse TERT gene expression in vivo: Identification of a human-specific repressive element

doi:10.1073/pnas.0508964102

Differential cis-regulation of human versus mouse TERT gene expression in vivo: Identification of a human-specific repressive element

^*Laboratory of Biosystems and Cancer and ^§Experimental Immunology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892; and ^∥Science Applications International Corporation (SAIC), Frederick Cancer Research Center, National Cancer Institute, National Institutes of Health, Frederick, MD 21702

Communicated by Elizabeth H. Blackburn, University of California, San Francisco, CA, October 22, 2005 (received for review June 17, 2005)

Abstract

In vivo expression of human telomerase is significantly different from that of mouse telomerase. To assess the basis for this difference, a bacterial artificial chromosome clone containing the entire hTERT (human telomerase reverse transcriptase) gene was introduced in mice. In these transgenic mice, expression of the hTERT transgene was similar to that of endogenous hTERT in humans, rather than endogenous mTERT (mouse telomerase reverse transcriptase). In tissues and cells showing a striking difference in expression levels between hTERT in humans and mTERT in mice (i.e., liver, kidney, lung, uterus, and fibroblasts), expression of the hTERT transgene in transgenic mice was repressed, mimicking hTERT in humans. The transcriptional activity of the hTERT promoter was much lower than that of the mTERT promoter in mouse embryonic fibroblasts or human fibroblasts. Mutational analysis of the hTERT and mTERT promoters revealed that a nonconserved GC-box within the hTERT promoter was responsible for the human-specific repression. These results reveal that a difference in cis-regulation of transcription, rather than transacting transcription factors, is critical to species differences in tissue-specific TERT expression. Our data also suggest that the GC-box-mediated, human-specific mechanism for TERT repression is impaired in human cancers. This study represents a detailed characterization of the functional difference in a gene promoter of mice versus humans and provides not only important insight into species-specific regulation of telomerase and telomeres but also an experimental basis for generating mice humanized for telomerase enzyme and its pattern of expression.

Footnotes

↵ ‡ To whom correspondence may be addressed. E-mail: hodesr{at}31.nia.nih.gov or horikawi{at}mail.nih.gov.
↵ † I.H. and Y.J.C. contributed equally to this work.
↵ ¶ Present address: Nanogen, Inc., San Diego, CA 92121.
↵ ** Present address: Department of Biology, Dong-A University, Busan 604-714, Korea.
↵ †† J.C.B. and R.J.H. contributed equally to this work.
↵ ‡‡ Present address: Novartis Institutes for BioMedical Research, Cambridge, MA 02139.
Author contributions: I.H., Y.J.C., L.F., S.-H.L., V.L., R.J.H., and J.C.B. designed research; I.H., Y.J.C., T.P., L.F., S.-H.L., and E.M. performed research; I.H., Y.J.C., L.F., S.-H.L., E.M., and V.L. contributed new reagents/analytic tools; I.H., Y.J.C., T.P., E.M., V.L., R.J.H., and J.C.B. analyzed data; and I.H., Y.J.C., R.J.H., and J.C.B. wrote the paper.
Conflict of interest statement: No conflicts declared.
Abbreviations: BAC, bacterial artificial chromosome; MEF, mouse embryonic fibroblasts; NHF, normal human fibroblasts; TERT, telomerase reverse transcriptase; hTERT, human TERT; mTERT, mouse TERT.