Insulin regulates enzyme activity, malonyl-CoA sensitivity and mRNA abundance of hepatic carnitine palmitoyltransferase-I.
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.
Park
E A
EA
Department of Pharmacology, College of Medicine, University of Tennessee, Memphis-The Health Science Center 38163, USA.
Mynatt
R L
RL
Cook
G A
GA
Kashfi
K
K
D000818:Animals; D002334:Carnitine O-Palmitoyltransferase / Q000096:biosynthesis / Q000378:metabolism*; D002460:Cell Line; D003609:Dactinomycin / Q000494:pharmacology; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology*; D003922:Diabetes Mellitus, Type 1 / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000201:enzymology; D008297:Male; D008316:Malonyl Coenzyme A / Q000494:pharmacology*; D008930:Mitochondria, Liver / Q000201:enzymology*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013217:Starvation / Q000201:enzymology*
D004791:Enzyme Inhibitors; D007004:Hypoglycemic Agents; D007328:Insulin; D012333:RNA, Messenger; D003609:Dactinomycin; D008316:Malonyl Coenzyme A; D002334:Carnitine O-Palmitoyltransferase