Regulation of eukaryotic translation initiation factor expression during T-cell activation

Abstract

Primary T-cells are metabolically quiescent, with little DNA, RNA or protein synthesis. Upon mitogenic stimulation the rate of protein synthesis increases 10-fold. We have studied the role of eIF-2 and eIF-4α (eIF-4E) expression in the mechanism of translational activation. During this period, the levels of eIF-2α and eIF-4α mRNA increase some 50-fold. Similar to the increase in ribosomes and mRNA, the number of eIF-2α, eIF-2β, and eIF-4α molecules per cell also increase 2–3-fold. This suggests that in addition to an increase in the pool size of translational components, an additional mechanism exists which results in an increased efficiency of factor utilization. We have looked at initiation factor phosphorylation. We find that eIF-2α does not undergo significant changes in its phosphorylation state nor is there a change in the efficiency of eIF-2 utilization. However, there is a rapid increase in the phosphorylation state of eIF-4α which correlates with the rapid increase in translational activity. It thus appears there are 2 distinct components responsible for the translational activation of quiescent T-cells during mitogenic stimulation. The first is the phosphorylation of eIF-4α, with a concomitant increase in the efficiency of eIF-4α utilization. The second is an increase in the pool sizes of eIF-2 and eIF-4α.