An element of the transforming growth factor-beta 1 5'-untranslated region represses translation and specifically binds a cytosolic factor.
In many cell types, there is a discrepancy between transforming growth factor-beta 1 (TGF-beta 1) mRNA and TGF-beta 1 protein, suggesting that expression of TGF-beta 1 is regulated posttranscriptionally. We have previously shown that a 137-nucleotide (nt) region of the TGF-beta 1 5'-untranslated region (UTR) potently inhibits the expression of a heterologous reporter gene, suggesting a role for this region in the posttranscriptional inhibition of TGF-beta 1 expression. To study the mechanism of inhibition, a chimeric plasmid containing this region of the TGF-beta 1 5'-UTR and the reading frame of the human GH gene was stably transfected into C2C12 myoblastic cells. Our results show that the TGF-beta 1 5'-UTR inhibits GH expression by inhibiting GH mRNA translation. In vitro gel retardation and cross-linking assays using a radiolabelled RNA probe transcribed from this region of the TGF-beta 1 5'-UTR demonstrate the specific binding of a cytosolic factor. Deletion of a potential stem-loop-forming region abolishes binding of this factor and partially restores GH production. These results suggest that posttranscriptional inhibition of TGF-beta 1 expression is at the level of mRNA translation and that a cytosolic factor may regulate TGF-beta 1 mRNA translation.
Romeo
D S
DS
National Cancer Institute, Laboratory of Chemoprevention, Bethesda, Maryland 20892.
Park
K
K
Roberts
A B
AB
Sporn
M B
MB
Kim
S J
SJ
D000818:Animals; D015152:Blotting, Northern; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism*; D003609:Dactinomycin / Q000494:pharmacology; D015870:Gene Expression; D013006:Growth Hormone / Q000235:genetics; D006801:Humans; D051379:Mice; D009132:Muscles / Q000378:metabolism; D009693:Nucleic Acid Hybridization; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000187:drug effects*; D015347:RNA Probes; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D012260:Ribonucleases / Q000378:metabolism; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000235:genetics*; D014466:Ultraviolet Rays
D015347:RNA Probes; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D003609:Dactinomycin; D013006:Growth Hormone; D012260:Ribonucleases