Triiodothyronine-induced accumulations of malic enzyme, fatty acid synthase, acetyl-coenzyme A carboxylase, and their mRNAs are blocked by protein kinase inhibitors. Transcription is the affected step.
Addition of triiodothyronine (T3) to chick-embryo hepatocytes in culture causes increased accumulations of malic enzyme, fatty acid synthase, acetyl-CoA carboxylase and their mRNAs. H-8 and other protein kinase inhibitors inhibited the T3-induced accumulations of these lipogenic enzymes and their mRNAs but had no effect on the activities of 6-phosphogluconate dehydrogenase and isocitrate dehydrogenase, enzymes not induced by T3 in chick-embryo hepatocytes. H-8 also had no effect on the activities of malic enzyme, fatty acid synthase, and acetyl-CoA carboxylase in hepatocytes not treated with T3. Synthesis of soluble protein, levels of mRNAs for beta-actin and glyceraldehyde-3-phosphate dehydrogenase, and induction of metallothionein mRNA by Zn2+ were unaffected by H-8 at concentrations that inhibited the T3-induced accumulation of lipogenic enzymes and their mRNAs. H-8 inhibited T3-induced transcription of the genes for both malic enzyme and fatty acid synthase but had little effect on transcription of the beta-actin or glyceraldehyde-3-phosphate dehydrogenase genes or on total RNA synthesis in isolated nuclei. H-8 also had no effect on binding of T3 to its nuclear receptor. In isolated nuclei, H-8 inhibited phosphorylation of total protein by 15-20%. Phosphorylation of only one major protein was consistently and substantially inhibited, indicating that the effect of H-8 was selective. These results suggest that on-going protein phosphorylation is required specifically for stimulation of transcription of the lipogenic genes by T3.
Swierczynski
J
J
Department of Biochemistry, University of Iowa, Iowa City 52242.
Mitchell
D A
DA
Reinhold
D S
DS
Salati
L M
LM
Stapleton
S R
SR
Klautky
S A
SA
Struve
A E
AE
Goodridge
A G
AG
D000103:Acetyl-CoA Carboxylase / Q000235:genetics / Q000378:metabolism*; D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo; D064429:Fatty Acid Synthases / Q000235:genetics / Q000378:metabolism*; D007546:Isoquinolines / Q000494:pharmacology; D008099:Liver / Q000201:enzymology; D008291:Malate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D008668:Metallothionein / Q000235:genetics; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger / Q000378:metabolism; D019311:Staurosporine; D014158:Transcription, Genetic / Q000187:drug effects*; D014284:Triiodothyronine / Q000037:antagonists & inhibitors* / Q000494:pharmacology
D000470:Alkaloids; D007546:Isoquinolines; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D014284:Triiodothyronine; C053177:N-(2-(methylamino)ethyl)-5-isoquinolinesulfonamide; D008668:Metallothionein; D008291:Malate Dehydrogenase; D064429:Fatty Acid Synthases; D000103:Acetyl-CoA Carboxylase; D019311:Staurosporine