Increased phosphorylation of eukaryotic initiation factor 2α at the G2/M boundary in human osteosarcoma cells correlates with deglycosylation of p67 and a decreased rate of protein synthesis

The rate of protein synthesis in higher eukaryotes is largely regulated at the level of eIF2 alpha phosphorylation by its kinases. A cellular glycoprotein, p67, protects eIF2 alpha from phosphorylation. An enzyme, p67-deglycosylase, when active, removes the carbohydrate moieties from p67 and inactivates it. Subsequently, protein synthesis is inhibited, During mitosis the overall rate of protein synthesis sharply declines. To understand the molecular mechanism underlying this inhibition of protein synthesis, we have examined the phosphorylation of eIF2 alpha and the activity of p67. We find that the phosphorylation of eIF2 alpha increases at the G(2)/M border of cycling U2-OS cells, and p67 is deglycosylated at the same period of the cell cycle. In addition, the level and the activity of p67-deglycosylase also increase at the G(2)/M boundary of cycling U2-OS cells. These results thus provide an important in vivo correlation between the increased phosphorylation of eIF2 alpha and deglycosylation of p67 by p67-deglycosylase at the G(2)/M boundary of cycling U2-OS cells. This may explain in part the inhibition of protein synthesis in U2-OS cells approaching mitosis. (C) 1999 Academic Press.