Calpain mediates eukaryotic initiation factor 4G degradation during global brain ischemia.
Global brain ischemia and reperfusion result in the degradation of the eukaryotic initiation factor (eIF) 4G, which plays a critical role in the attachment of the mRNA to the ribosome. Because eIF-4G is a substrate of calpain, these studies were undertaken to examine whether calpain I activation during global brain ischemia contributes to the degradation of eIF-4G in vivo. Immunoblots with antibodies against calpain I and eIF-4G were prepared from rat brain postmitochondrial supernatant incubated at 37 degrees C with and without the addition of calcium and the calpain inhibitors calpastatin or MDL-28,170. Addition of calcium alone resulted in calpain I activation (as measured by autolysis of the 80-kDa subunit) and degradation of eIF-4G; this effect was blocked by either 1 micromol/L calpastatin or 10 micromol/L MDL-28,170. In rabbits subjected to 20 minutes of cardiac arrest, immunoblots of brain postmitochondrial supernatants showed that the percentage of autolyzed calpain I increased from 1.9% +/- 1.1% to 15.8% +/- 5.0% and that this was accompanied by a 68% loss of eIF-4G. MDL-28,170 pretreatment (30 mg/kg) decreased ischemia-induced calpain I autolysis 40% and almost completely blocked eIF-4G degradation. We conclude that calpain I degrades eIF-4G during global brain ischemia.
Neumar
R W
RW
Department of Emergency Medicine, Wayne State University School of Medicine, Detroit, Michigan, USA.
DeGracia
D J
DJ
Konkoly
L L
LL
Khoury
J I
JI
White
B C
BC
Krause
G S
GS
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000494:pharmacology; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology; D039603:Eukaryotic Initiation Factor-4G; D005260:Female; D002546:Ischemic Attack, Transient / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D010448:Peptide Initiation Factors / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D015424:Reperfusion; D013347:Subcellular Fractions / Q000378:metabolism
D002135:Calcium-Binding Proteins; D015853:Cysteine Proteinase Inhibitors; D004151:Dipeptides; D039603:Eukaryotic Initiation Factor-4G; D010448:Peptide Initiation Factors; C033668:calpastatin; D002154:Calpain; D002118:Calcium; C058076:calpain inhibitor III