Lysine-rich domains of eukaryotic initiation factor 2-associated glycoprotein, p67 are involved in the suppression of phosphorylation of several cellular kinases

摘要

Eukaryotic initiation factor 2 (eIF2)-associated glycoprotein, p67 protects eIF2a from phosphorylation by kinases, and this requires its lysine-rich domains I & II. On the other hand, the acidic residue-rich domain present within the two lysine-rich domains, has stimulatory effect on eIF2a phosphorylation. In this study, we investigated the effects on eIF2a phosphorylation due to constitutive expression of two mutant forms of p67-D6/2 and K1K2 in rat tumor hepatoma (KRC-7) cells. KRC-7 cells expressing D6/2 mutant had a low level of eIF2a phosphorylation, and that in K1K2 mutant it was high. In addition, D6/2 mutant showed a higher protein synthesis rate that correlated with its higher levels of glycosylation. In contrast, K1K2 mutant had opposite effects as compared to D6/2 mutant. These two mutants also showed effects on overall kinase activities, and these effects were more prominent when serum-starved synchronized cells were grown in medium containing serum. During serum-starved condition, we found that the D6/2 mutant could suppress the activities of certain cellular kinases, and the K1K2 mutant could activate those. Some of these kinases possibly can phosphorylate eIF2a, p67, p67-deglycosylase, and several unknown substrates. Taken together,these results suggest that the acidic residue-rich domain of p67 can activate several cellular kinases and the lysine-rich domains can suppress the activity of these kinases in mammalian cells.