Insulin regulates enzyme activity, malonyl-CoA sensitivity and mRNA abundance of hepatic carnitine palmitoyltransferase-I

• Published in: Biochemical journal Vol. 310 ( Pt 3); no. 3; pp. 853 - 858
• Main Authors: Park, E A, Mynatt, R L, Cook, G A, Kashfi, K
• Format: Journal Article
• Language: English
• Published: England 15-09-1995
• Subjects: Animals; Carnitine O-Palmitoyltransferase - biosynthesis; Carnitine O-Palmitoyltransferase - metabolism; Cell Line; Dactinomycin - pharmacology; Diabetes Mellitus, Experimental - enzymology; Diabetes Mellitus, Type 1 - enzymology; Enzyme Inhibitors - pharmacology; Hypoglycemic Agents - pharmacology; Insulin - pharmacology; Intracellular Membranes - enzymology; Male; Malonyl Coenzyme A - pharmacology; Mitochondria, Liver - enzymology; Rats; Rats, Sprague-Dawley; RNA, Messenger - metabolism; Starvation - enzymology
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj3100853

The regulation of hepatic mitochondrial carnitine palmitoyltransferase-I (CPT-I) was studied in rats during starvation and insulin-dependent diabetes and in rat H4IIE cells. The Vmax. for CPT-I in hepatic mitochondrial outer membranes isolated from starved and diabetic rats increased 2- and 3-fold respectively over fed control values with no change in Km values for substrates. Regulation of malonyl-CoA sensitivity of CPT-I in isolated mitochondrial outer membranes was indicated by an 8-fold increase in Ki during starvation and by a 50-fold increase in Ki in the diabetic state. Peroxisomal and microsomal CPT also had decreased sensitivity to inhibition by malonyl-CoA during starvation. CPT-I mRNA abundance was 7.5 times greater in livers of 48-h-starved rats and 14.6 times greater in livers of insulin-dependent diabetic rats compared with livers of fed rats. In H4IIE cells, insulin increased CPT-I sensitivity to inhibition by malonyl-CoA in 4 h, and sensitivity continued to increase up to 24 h after insulin addition. CPT-I mRNA levels in H4IIE cells were decreased by insulin after 4 h and continued to decrease so that at 24 h there was a 10-fold difference. The half-life of CPT-I mRNA was 4 h in the presence of actinomycin D or with actinomycin D plus insulin. These results suggest that insulin regulates CPT-I by inhibiting transcription of the CPT-I gene.