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Role of Smad3 in the regulation of rat telomerase reverse transcriptase by TGFβ
Author(s) -
Hu Biao,
Tack David C.,
Liu Tianju,
Wu Zhe,
Ullenbruch Matthew R.,
Phan Sem H.
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a78
Subject(s) - telomerase reverse transcriptase , microbiology and biotechnology , transfection , telomerase , transcription (linguistics) , luciferase , smad , promoter , chemistry , gene expression , biology , transforming growth factor , gene , biochemistry , linguistics , philosophy
Telomerase is induced in certain pathological conditions such as cancer and tissue injury and repair. This induction in fibroblasts from injured lung is repressed by TGFβ via yet unknown mechanisms. In this study, the role of Smad3 in the inhibition of telomerase reverse transcriptase ( TERT ) gene transcription by TGFβ was investigated. The rat TERT ( rTERT ) gene promoter was cloned by PCR amplification and fused with a luciferase reporter gene. This construct was used to analyze regulation of promoter acticity in fibroblasts isolated from bleomycin‐injured lung with induced telomerase activity. The results showed that TGFβ inhibited rTERT transcription while stimulating Smad3 expression. Interestingly, TGFβ also inhibited the expression of c‐myc. Co‐transfection with a Smad3 expressing plasmid further repressed rTERT transcription and c‐myc expression, while co‐transfection with the corresponding anti‐sense Smad3 construct had the opposite effect. Mutation of an E‐box in the rTERT promoter suppressed its activity, which could be further reduced by TGFβ treatment. In contrast mutation at a Smad binding element enhanced promoter activity whose inhibition by TGFβ treatment was impaired. Thus TGFβ inhibition of rTERT gene expression was directly mediated by Smad3 via the Smad binding element, while c‐myc appears to primarily regulate its constitutive or induced expression.