Head-down tilt increases rat cardiac muscle eIF-2 alpha phosphorylation.
We previously demonstrated that head-down tilt in rats decreases heart polypeptide initiation rate and proposed a mechanism whereby redistribution of the chaperone heat-shock cognate/heat-shock protein-70 (HSC/HSP-70) facilitates the phosphorylation of eukaryotic initiation factor-2 alpha (eIF-2 alpha). In this study, two-dimensional gel electrophoretic analysis of eIF-2 alpha showed no phosphorylation in control hearts. At 8 h of head-down tilt, there was a 45% increase in total eIF-2 alpha, and 79% was phosphorylated. At 18 h, eIF-2 alpha increased to 142% of control, of which 4% was phosphorylated. This is consistent with the previous study where, at 8 h, there was a 78% increase in polysomal HSC/HSP-70 and a shift in the polysome center-of-mass to lighter polysomes (indicating decreased initiation). After 18 h of suspension, polysomal HSC/HSP-70 levels were 24% relative to control, and the center-of-mass returned toward control. We conclude that the decrease in polypeptide initiation during head-down tilt is mediated by HSC/HSP-70 via phosphorylation of eIF-2 alpha.
Menon
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Department of Physiology and Biophysics, University of Tennessee Health Science Center, Memphis 38163, USA.
Thomason
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DB
D000818:Animals; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D005260:Female; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D018475:Head-Down Tilt; D009206:Myocardium / Q000378:metabolism*; D010766:Phosphorylation; D011132:Polyribosomes / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D015852:Eukaryotic Initiation Factor-2; D018840:HSP70 Heat-Shock Proteins