A GC-rich domain with bifunctional effects on mRNA and protein levels: implications for control of transforming growth factor beta 1 expression.
Chimeric plasmids containing selected reporter coding domains and portions of the transforming growth factor beta 1 (TGF-beta 1) 3' untranslated region (UTR) were prepared and used to identify potential mechanisms involved in regulating the biosynthesis of TGF-beta 1. Transient transfections with core and chimeric constructs containing the chloramphenicol acetyltransferase (CAT) reporter showed that steady-state CAT mRNA levels were decreased two- to threefold in response to the TGF-beta 1 3' UTR. Interestingly, CAT activity was somewhat increased in the same transfectants. Thus, production of CAT protein per unit of mRNA was stimulated by the TGF-beta 1 3' UTR (approximately fourfold in three cell lines of distinct lineage). The translation-stimulatory effect of the TGF-beta 1 3' UTR suggested by these studies in vivo was confirmed in vitro by cell-free translation of core and chimeric transcripts containing the growth hormone coding domain. These studies showed that production of growth hormone was stimulated threefold by the TGF-beta 1 3' UTR. A deletion analysis in vivo indicated that the GC-rich domain in the TGF-beta 1 3' UTR was responsible for both the decrease in mRNA levels and stimulation of CAT activity-mRNA. We conclude that this GC-rich domain can have a bifunctional effect on overall protein expression. Moreover, the notable absence of this GC-rich domain in TGF-beta 2, TGF-beta 3, TGF-beta 4, and TGF-beta 5 indicates that expression of distinct TGF-beta family members can be differentially controlled in cells.
Department of Biochemistry and Molecular Biophysics, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
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D000818:Animals; D001483:Base Sequence; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D002999:Clone Cells; D003596:Cytosine; D006147:Guanine; D006801:Humans; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D010957:Plasmids; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D015183:Restriction Mapping; D012156:Reticulocytes / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000096:biosynthesis* / Q000235:genetics*; D014407:Tumor Cells, Cultured
D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D016212:Transforming Growth Factor beta; D006147:Guanine; D003596:Cytosine; D015500:Chloramphenicol O-Acetyltransferase