Transcriptional and posttranscriptional regulation of malic enzyme synthesis by insulin and triiodothyronine.
To investigate the transcriptional and posttranscriptional regulation of malate dehydrogenase (EC 1.1.1.40) induction by insulin, the transcriptional rate, mRNA concentration and enzyme induction of malic enzyme were compared in livers of normal and diabetic rats fed a high-carbohydrate diet. When rats were fed the diet for 4 days, the enzyme induction and mRNA concentration in livers of diabetic rats were only about 10% and 39%, respectively, of the values of normal rats, and the transcriptional rate was about 64%. Insulin treatment restored the transcriptional rate and mRNA concentration in 8 h and the enzyme induction in 4 days. Thus, it is suggested that insulin is involved in malic enzyme transcription of the gene and also possibly in the translation of the cytoplasm. On the other hand, by giving triiodothyronine treatment, the transcriptional rate and mRNA concentration were increased about twice and the enzyme induction, about 10-times in the diabetic animals. Triiodothyronine appears to stimulate malic enzyme transcription and possibly post-transcriptional steps even at a very low insulin level.
Katsurada
A
A
Tezukayama Gakuin College, Sakai, Japan.
Iritani
N
N
Fukuda
H
H
Noguchi
T
T
Tanaka
T
T
D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D004040:Dietary Carbohydrates / Q000502:physiology; D004790:Enzyme Induction / Q000187:drug effects; D005786:Gene Expression Regulation; D007328:Insulin / Q000494:pharmacology*; D008099:Liver / Q000503:physiopathology; D008291:Malate Dehydrogenase / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D014158:Transcription, Genetic / Q000187:drug effects*; D014284:Triiodothyronine / Q000494:pharmacology*
D004040:Dietary Carbohydrates; D007328:Insulin; D012333:RNA, Messenger; D014284:Triiodothyronine; D008291:Malate Dehydrogenase