Regulation of global protein translation and protein degradation in aerobic dormancy.

We hypothesized that protein turnover would be substantially suppressed during estivation in the land snail, Otala lactea, as part of a wholesale move to conserve ATP in the hypometabolic state, and that decreased rates of protein synthesis and degradation would be mediated by altering the phosphorylation state of key proteins. Rates of protein translation, measured in vitro, decreased by approximately 80% in extracts of foot muscle and hepatopancreas after 2 days of estivation, and this reduction was associated with strong increases in the phosphorylation of ribosomal factors, eIF2 alpha and eEF2, as well as decreased phosphorylation of 4E-BP1. Reductions in levels of markers of ribosomal biogenesis and a tissue-specific reduction in the phosphorylation state of eIF4E and eIF4GI were also evident after 14 days of estivation. Activity of the 20S proteasome decreased by 60-80% after 2 days of estivation and this decrease was mediated by protein kinase G in vitro, whereas protein phosphatase 2A activated the proteasome. Levels of protein carbonyls did not change in snail tissues during estivation whereas the expression heat shock proteins increased, suggesting that protein resistance to damage is enhanced in estivation. In conclusion, protein synthesis and degradation rates were coordinately suppressed during estivation in O. lactea and this is associated with the phosphorylation of ribosomal initiation and elongation factors and the 20S proteasome.