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ARCHIVES OF BIOCHEMJSTRY AND BIOPHYSICS
Vol. 337. No. 2, January 15, pp. 169—175, 1997
Article No. BB969784
Control of Hepatio Fatty Acid Oxidation by 5’—AMP-
Activated Protein Kinase Involves a Malonyl-CoA-
Dependent and a Malonyl-CoA-Independent Mechanism
Guillermo Velasco,* Math J. H. Geelen,t” arad Manuel Guzmán*
*Department of Biochemistry and Molecular Biology 1, Faculty of Biology, Complutense University, 28040-Madrid, Spain;
aná tLaboratory of Veterinary Biochemistry, Graduate School of Animal Health, Utreche Uniuersity, PO. Box 80.176,
3508 TD Utreeht, Tite Netherlands
Received July 30, 1996, and in revised fon,, October 25, 1996
Incubation of rat hepatocytes with 5-aminoimidazo¡e-4-carboxamide
ribonucleoside (AICAR), aix activaliar
of the 5’-AM?P-activated protein kinase (AMPK),
produced a twofoíd stimuíation of palmitate oxidation
arad of the activity of carnitine pahnitoyltransferase
1 (CPT-I), together with a profonrad decrease of the
activity of acetyí-CoA carboxyíase arad of lihe iratracellular
level of malorayí-CoA. AICAR-induced CPT-I stimulation
progressively blunted with time after ccli permeabilization,
pointing to reversal of conformational
eonstraints of the enzyme ira control celis due to the
permeabilizatiora-triggered dilution of intracelular
malonyl-CoA. The stimulation stabilized at a steady
20—25%. This 20—25% mercase ira CPT-I activity survived
upon complete removal of malonyl-CaA from the
permeabilized celís, indicating that it was not dependent
on the malonyí-CoA concentration oflibe eclI. This
malonyl-CoA-indcpendeixt activatiora of CPT-I was not
cvident wheix mitochondria wcre isolated for assay of
enzyme activity or when celís were disrupted by vigoraus
sonication. lix addition, libe microtubule stabilizcr
taxol prevented lihe malonyí-CoA-independent stimulation
of CPT-I induced by AICAR. Henee, stimuíation
of hepatic fatty acid oxidatiora by AMPK seems to rely
on lihe activation of CPT-I by two different mechanisms:
deinhibition of CPT-I induced by depíetion of
intracellular maíonyl-CoA leveís and maíonyl-CoA-iradcpendent
stimulation of CPT-I, which might involve
modulation of interaetioras between CPT-I arad cytoskelctal
Components. o 1997 Academie Press
To whom correspondence should be addressed. Fax: **3130
2535492. E-mail: m.geelen~biochemdgk.niunl.
0003-9861,97 $2500
Copyright 0 1997 by Academic Presa
MI rights of reproduction jo any form reserved.
The 5’-AMP-activated proteira kinase (AMPK? plays
a majar role ira tbe regulatiora of lipid metabolism ira
mammals. Thus, AMPK pbospborylates and inactivates
key regulatory enzymes of lipid metabolism such
as aeetyl-CoA carboxylase (fatty acid syratbesis), 3-hydroxy-S-methylglutaryl-CoA
reductase (sterol/isopreraoid
syratbesis), arad bormone-serasitive lipase (triacylglycerol/cholesteryl
ester breakdowra) [reviewed ira Ref.
(1)]. Although several protein kinases cara pbospborylate
purified acetyl-CoA earboxylase arad S-hydroxy-3metbylglutaryl-CoA
reductase in vitro, it is curreratly
accepted thaI ira iratact hepatocytes arad ira the liver in
vivo this phosphorylation. is mairaly performed by
AMPK [cf. Refs. (1—3)].
Several studies have beera performed ora the potential
involvemerat ofAMPK ira Ibe control offatty acid oxidatiora
ira the isehemié beart (4, 5) arad the workirag muscle
(6). However, the possible role of this kiraase ira tbe
control of hepatie fatty acid oxidation has raot beera
studied to date. Uralike tbe beart arad the skeletal muscíe,
the liver is capable of expressirag eitber bigh rates
of lipogeraesis or higb rates of fatty acid oxidatiora deperadirag
on Ihe hormonal arad rautritional status of the
animal, arad herace regulatiora of fatty acid axidatiora
seems to be more complex ira liver [reviewed ira Ref. (7)]
than ira heart [reviewed ira Ref. (8)] arad skeletal niuscle
[reviewed ira Ref. (9)]. Carnitine palmitoyltrarasferase
1 (CPT-I) is the key regulatory erazyme ira the trarasport
of long-chaira fatty acids irato the mitochoradrial matrix
(7, 10, 11). This enzyme is subject to allosterie inhibition
by malorayl-CoA, the produet of the reactiora caía-
2 Ahbreviations used: AMPK, 5’-AMP-activated protein kinnse:
CoA, coenzyme A: CPT-I, carnitine palmitoyltransferase 1; AICAR,
5-aminoimidazote-4-carboxamide ribonucleoside; ZMP, 5-aminoin,idazole-4-carboxamide
ribonucleoside monophosphate.
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