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The role of eukaryotic initiation factor 2
during the metabolic depression associated with estivation
1 Biochemistry and Molecular Biology, School of Biomedical and Chemical
Sciences, University of Western Australia, 35 Stirling Highway, Crawley, WA
6009, Australia
2 Department of Cellular and Molecular Physiology, Penn State College of
Medicine, 500 University Drive, Hershey, PA 17033, USA
* Author for correspondence at present address: Cellular Regulation, MRC Dunn Human Nutrition Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 2XY, UK (e-mail: jlp{at}mrc-dunn.cam.ac.uk)
Accepted 31 March 2003
We have investigated the role of eukaryotic initiation factor 2
(eIF2) in two estivating organisms previously shown to downregulate
protein synthesis during metabolic depression, the land snail Helix
aspersa Müller and the desert frog Neobatrachus sutor Main
1957. We have developed a method using a single antibody (which binds
specifically to the phosphorylated, conserved phosphorylation region) by which
the total levels of eIF2 and the ratio of phosphorylated eIF2
[eIF2(P)] to total (phosphorylated and unphosphorylated) eIF2
can be determined. In H. aspersa, we have shown that the level of
eIF2 mRNA expression is unchanged between the awake and estivating
states. The amount of total eIF2 is the same in the estivating and
awake states, and eIF2(P) is undetectable and must represent ≤10% of
total eIF2 in both states. Conversely, in N. sutor during
estivation, the level of total eIF2 increases approximately 1.6-fold
and the ratio of eIF2(P)/eIF2 increases from 0.22±0.11 to
0.52±0.08, implicating eIF2 phosphorylation in the
downregulation of protein synthesis during estivation in this animal. The
differences in the amounts of eIF2 and the level of its phosphorylation
between these two species also suggest possible differences either in the
mechanism by which protein synthesis is downregulated during estivation or in
the sensitivity of the initiation of translation to eIF2(P) levels.
Key words: eIF2, eukaryotic initiation factor, estivation, protein synthesis, metabolic depression, Helix aspersa, Neobatrachus sutor, phosphorylation
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