Regulation by glucagon of serine: pyruvate/alanine: glyoxylate aminotransferase gene expression in cultured rat hepatocytes.
The effects of glucagon on serine: pyruvate/alanine: glyoxylate aminotransferase (SPT/AGT) gene expression were studied in primary cultured rat hepatocytes. When hepatocytes had been precultured for 16-18 h under serum- and hormone-free conditions, the addition of glucagon caused (after a lag period of about 2 h) a remarkable increase in the cellular level of SPT/AGT mRNA by 4 h in a time- and dose-dependent manner. The induced mRNA was that for mitochondrial SPT/AGT, as judged by ribonuclease protection analysis. A nuclear run-on assay revealed that activation of transcription is responsible for the increase in mitochondrial SPT/AGT mRNA and that the maximal rate of transcription occurs 1.5 h after glucagon addition. The effect of glucagon was mimicked by 8-bromo-cAMP and suppressed by N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide, an inhibitor of cAMP-dependent protein kinase (protein kinase A), while both 12-O-tetradecanoylphorbol-13-acetate and A23187 were without effect in elevating the SPT/AGT mRNA level, suggesting that the cAMP/protein kinase A system is involved in the regulation of SPT/AGT gene expression. In hepatocytes precultured for 16-18 h under serum- and hormone-free conditions, the glucagon-induced transcription was severely inhibited by cycloheximide. When the preculture was for 2 h, on the other hand, the activation of transcription by glucagon was more rapid, and the inhibition by cycloheximide was less than that observed with cells precultured for 16-18 h, suggesting that a short-lived protein factor is involved in the hormonal regulation. The glucagon-induced expression of the SPT/AGT gene was also turned off by dexamethasone.
Uchida
C
C
Department of Biochemistry, Hamamatsu University School of Medicine, Shizuoka, Japan.
Funai
T
T
Oda
T
T
Ohbayashi
K
K
Ichiyama
A
A
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000410:Alanine Transaminase / Q000235:genetics*; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects; D005934:Glucagon / Q000494:pharmacology*; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology*; D008297:Male; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D000637:Transaminases / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects
D012333:RNA, Messenger; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000001:Calcimycin; D003907:Dexamethasone; D005934:Glucagon; D003513:Cycloheximide; D000637:Transaminases; D000410:Alanine Transaminase; C019635:Alanine-glyoxylate transaminase; C022638:serine-pyruvate aminotransferase; D013755:Tetradecanoylphorbol Acetate