p44/42MAPK and p90RSK modulate thermal stressed physiology response in Apostichopus japonicus.

Reversible protein phosphorylation (RPP) plays a key role in signal transduction, enzyme activity and metabolic maintenance in response to extreme changes in the environment. In this study, we identified 55 phosphorylated proteins in Apostichopus japonicus coelomocytes by iTRAQ analysis, and sixteen proteins displayed differently expressed profiles between thermal stressed and control groups. Mitogen-activated protein kinase (MAPK) signaling cascade was further characterized by Western blot. Spatial expression analysis revealed that phospho-p44/42MAPK levels were mainly detected in coelomocytes and muscle, and no signal in intestine and respiratory trees, although the protein were constitutively expressed in all examined tissues. Time-course expression analysis shown that the amount of phospho-p44/42MAPK decreased by 57-60% in coelomocytes and 29-40% in muscle in acute exposure stage of 20°C and 25°C, respectively. In higher temperature remaining stage, phospho-p44/42MAPK was both induced with 1.7-fold increase at 20°C and 5.2-fold at 25°C at the first 12h in coelomocytes, which was consistent with the change of p44/42MAPK. Similarly, 2.5-fold and 2.7-fold increases were detected in muscle at corresponding exposure temperature. In contrast, the p44/42MAPK in muscle showed depressed expression profiles. As time progressed, phospho-p44/42MAPK levels were all decreased significantly both in coelomocytes and in muscles. A reduction in phosphorylation levels was detected at 84h in 20°C exposed coelomocytes with 0.42-fold decrease, and at 36h in 25°C challenged muscle by 0.80-fold decrease. Correlated expression profiles between phospho-p90RSK and phospho-p44/42MAPK suggest that p44/42MAPK may be involved in temperature-induced metabolic suppression through targeting p90RSK in A. japonicus.