Abstrakt
Eukaryotic translation initiation factor 4E (eIF4E) plays a pivotal role in the control of cap-dependent translation initiation, occurs in processing bodies (PBs) and is required for formation of stress granules (SGs). In this study, we focused on the subcellular localization of a representative compendium of eIF4E protein isoforms, particularly on the less studied members of the human eIF4E protein family, eIF4E2 and eIF4E3.
We showed that unlike eIF4E1, its less studied isoform eIF4E3_A, localized to SGs but not PBs upon both heat shock and arsenite stress. Furthermore, we found that eIF4E3_A interacts with human translation initiation factors eIF4G1, eIF4G3 and PABP1 in vivo and sediments into the same fractions as canonical eIF4E1 during polysome analysis in sucrose gradients.
Contrary to this finding, the truncated human eIF4E3 isoform, eIF4E3_B, showed no localization to SGs and no binding to eIF4G. We also highlighted that eIF4E2 may exhibit distinct functions under different stresses as it readily localizes to PBs during arsenite and heat stresses, whereas to SGs, it is redirected only upon the heat shock.
We extended our study to a number of protein variants of each of the three eIF4E isoforms. Our results surprisingly uncovered differences in the ability of eIF4E1_1 and eIF4E1_3 to form SGs in response to cellular stresses.
Our comparison of all three human eIF4E isoforms and their protein variants enrich the intriguing spectrum of roles attributed to the eukaryotic initiation translation factors of the 4E family. The localization of eIF4E3_A to SGs, but not to PBs, together with its binding to eIF4G and PABP1 suggests a role of eIF4E3_A in translation initiation in human cells.
The localization of eIF4E2 to SGs under the condition of heat shock but not during arsenite stress indicates its distinct function in cellular response to these stresses and points to the variable protein content of SGs as a consequence of different stress insults.