Changes in the PI3K/Akt/TOR signalling pathway after methionine treatment in the primary muscle cells of cobia ( rachycentron canadum )

Methionine (Met) plays important roles in protein synthesis and in diverse cellular processes in eukaryotes. In the present study, primary muscle cells of cobia fish Rachycentron canadum were isolated and treated with Met at different concentrations (0.5, 1, 2, 5 or 10 mM) for 24 h in culture media. The results show that the 5 mM Met group had the highest cell viability and total protein content. The phosphorylation levels of phosphoinositide 3-kinase (PI3K) p85 on Tyr458 and of protein kinase B (Akt) on Ser371 were significantly affected by the Met concentration during incubation. Cells incubated with 5 or 10 mM Met showed higher mRNA levels of the target rapamycin (TOR) and higher phosphorylation levels of TOR on Ser2448. Cells incubated with 5 mM Met had the highest phosphorylation levels of ribosomal p70-S6 kinase (S6K1) on Ser371 and of 4E-binding protein 1 (4E-BP1) on Thr37/46. Cells incubated with PI3K and TOR inhibitors showed that LY294002 and rapamycin significantly inhibited the phosphorylation of Akt on Ser371 and of TOR on Ser2448 respectively. These results indicate that Met concentration affects cell viability and is associated with changes in the PI3K/Akt/TOR pathway.