Activation of the ribosomal DNA promoter in cells exposed to insulinlike growth factor I.
We constructed a stable cell line, 3T3A5, which carried a chimeric gene in which the simian virus 40 T-antigen-coding gene was under the control of the mouse ribosomal DNA promoter. These cells expressed T antigen when they were growing exponentially in 10% fetal calf serum, but they all became T negative when incubated for 5 days in low-concentration serum. The readdition of serum or platelet-poor plasma again induced the expression of T antigen, which was accompanied by an increase in steady-state levels of the corresponding RNA. Among the various growth factors tested for their ability to induce T-antigen expression in 3T3A5 cells, only insulinlike growth factor I (IGF-I) could induce T antigen at physiological concentrations. The effect of IGF-I or platelet-poor plasma was abolished by an antibody to IGF-I. Other growth factors, like insulin and epidermal growth factor, could induce the expression of T antigen in 3T3A5 cells, but only at concentrations far above the physiological range. Other growth factors were totally ineffective. These results indicate that exposure of cells to IGF-I can activate transcription from the ribosomal DNA promoter.
D000818:Animals; D000957:Antigens, Viral, Tumor / Q000235:genetics; D004261:DNA Replication / Q000187:drug effects; D004274:DNA, Recombinant; D004275:DNA, Ribosomal / Q000235:genetics*; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D006133:Growth Substances / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D051379:Mice; D010455:Peptides / Q000494:pharmacology; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D012335:RNA, Ribosomal / Q000235:genetics*; D013539:Simian virus 40 / Q000235:genetics; D013002:Somatomedins / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects; D014168:Transferrin / Q000494:pharmacology; D015291:Transforming Growth Factors
D000957:Antigens, Viral, Tumor; D004274:DNA, Recombinant; D004275:DNA, Ribosomal; D006133:Growth Substances; D007328:Insulin; D010455:Peptides; D010982:Platelet-Derived Growth Factor; D012335:RNA, Ribosomal; D013002:Somatomedins; D014168:Transferrin; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; D015291:Transforming Growth Factors