Amino acid limitation negatively regulates insulin-like growth factor-II mRNA levels and E-domain peptide secretion at a post-transcriptional step in BRL-3A rat liver cells.
Deprivation of cultured BRL-3A rat liver cells for a single essential amino acid (leucine, methionine, tryptophan, or phenylalanine) under conditions in which the cells remain highly viable causes a decreased secretion of insulin-like growth factor-II (IGF-II) E-domain peptide into the culture medium. This decrease is observed within 8 h after shifting the cells into amino acid-deficient medium. The magnitude of this decrease is greatest in tryptophan-deprived cultures, in which there is a 66% decrease in IGF-II E-domain peptide secretion over a 24-h incubation as compared with E-domain peptide secretion in control cultures incubated in complete medium. Northern blot analysis has indicated that the decrease in IGF-II E-domain peptide secretion observed in amino acid-deprived cells is correlated with a decreased abundance of the major 3.6-kilobase (kb) species of IGF-II mRNA, as well as several minor species. In contrast, the level of a 1-kb species of IGF-II mRNA is not decreased in amino acid-limited cells. In addition, one other specific mRNA, that encoded by the alpha-tubulin gene, also is not significantly decreased in the leucine, phenylalanine, or tryptophan-limited cells. These results indicate that amino acid limitation specifically decreases the level of certain IGF-II mRNA species. The 3.6- and 1-kb IGF-II mRNA species differ only in the length of the 3'-untranslated region, suggesting the existence of a specific regulatory sequence in the long 3'-untranslated region of the 3.6-kb mRNA species that regulates levels of this mRNA species under conditions of amino acid limitation. IGF-II gene transcription is not decreased in the amino acid-limited cells. This indicates that the decrease in IGF-II mRNA and E-domain peptide secretion observed in the amino acid-deprived cells is caused primarily by a post-transcriptional regulatory mechanism.
Straus
D S
DS
Division of Biomedical Sciences, University of California, Riverside 92521.
Takemoto
C D
CD
D000601:Amino Acids, Essential / Q000494:pharmacology*; D000818:Animals; D002460:Cell Line; D007335:Insulin-Like Growth Factor II / Q000096:biosynthesis / Q000235:genetics*; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics*; D051381:Rats; D013002:Somatomedins / Q000235:genetics*
D000601:Amino Acids, Essential; D012333:RNA, Messenger; D013002:Somatomedins; D007335:Insulin-Like Growth Factor II