Dual mechanisms regulating AMPK kinase action in the ischemic heart.
AMP-activated protein kinase (AMPK) is emerging as an important signaling protein during myocardial ischemia. AMPK is a heterotrimeric complex containing an alpha catalytic subunit and beta and gamma regulatory subunits. Phosphorylation of Thr172 in the activation loop of the alpha subunit by upstream AMPK kinase(s) (AMPKK) is a critical determinant of AMPK activity. However, the mechanisms regulating AMPK phosphorylation in the ischemic heart remain uncertain and were therefore investigated. In the isolated working rat heart, low-flow ischemia rapidly activated AMPKK activity when measured using recombinant AMPK (rAMPK) as substrate. The addition of AMP (10 to 200 micromol/L) augmented the ability of heterotrimeric alpha1beta1gamma1 or alpha2beta1gamma1 rAMPK to be phosphorylated by heart AMPKK in vitro, whereas physiologic concentrations of ATP inhibited rAMPK phosphorylation. However, neither AMP nor ATP directly influenced AMPKK activity: they had no effect on AMPKK-mediated phosphorylation of rAMPK substrates lacking normal AMP-binding gamma subunits (isolated truncated alpha1(1-312) or alpha1beta1gamma1 rAMPK containing an R70Q mutation in the gamma1 AMP-binding site). Regional ischemia in vivo also increased AMPKK activity and AMPK phosphorylation in the rat heart. AMPK phosphorylation could also be induced in vivo without activating AMPKK: AICAR infusion increased AMPK phosphorylation without activating AMPKK; however, the AMP-mimetic AICAR metabolite ZMP enhanced the ability of heterotrimeric rAMPK to be phosphorylated by AMPKK. Thus, heart AMPKK activity is increased by ischemia and its ability to phosphorylate AMPK is highly modulated by the interaction of AMP and ATP with the heterotrimeric AMPK complex, indicating that dual mechanisms regulate AMPKK action in the ischemic heart.
Baron
Suzanne J
SJ
Section of Cardiovascular Medicine, Yale University School of Medicine, New Haven, Conn, USA.
Li
Ji
J
Russell
Raymond R
RR
Neumann
Dietbert
D
Miller
Edward J
EJ
Tuerk
Roland
R
Wallimann
Theo
T
Hurley
Rebecca L
RL
Witters
Lee A
LA
Young
Lawrence H
LH
D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases; D000249:Adenosine Monophosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D007262:Infusions, Intravenous; D008297:Male; D009097:Multienzyme Complexes / Q000378:metabolism; D017202:Myocardial Ischemia / Q000201:enzymology*; D009206:Myocardium / Q000201:enzymology; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000378:metabolism; D012265:Ribonucleotides / Q000378:metabolism / Q000494:pharmacology
D009097:Multienzyme Complexes; D011994:Recombinant Proteins; D012265:Ribonucleotides; D000620:Aminoimidazole Carboxamide; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases; C031143:AICA ribonucleotide