A Subunit of Eukaryotic Translation Initiation Factor 2α-Phosphatase (CreP/PPP1R15B) Regulates Membrane Traffic

The constitutive reverter of eIF2 alpha phosphorylation (CReP)/PPP1r15B targets the catalytic subunit of protein phosphatase 1 (PP1c) to phosphorylated eIF2 alpha (p-eIF2 alpha) to promote its dephosphorylation and translation initiation. Here, we report a novel role and mode of action of CReP. We found that CReP regulates uptake of the pore-forming Staphylococcus aureus alpha-toxin by epithelial cells. This function was independent of PP1c and translation, although p-eIF2 alpha was involved. The latter accumulated at sites of toxin attack and appeared conjointly with alpha-toxin in early endosomes. CReP localized to membranes, interacted with phosphomimetic eIF2 alpha, and, upon overexpression, induced and decorated a population of intracellular vesicles, characterized by accumulation of N-(lissamine rhodamine B sulfonyl) phosphatidylethanolamine (N-Rh-PE), a lipid marker of exosomes and intralumenal vesicles of multivesicular bodies. By truncation analysis, we delineated the CReP vesicle induction/association region, which comprises an amphipathic alpha-helix and is distinct from the PP1c interaction domain. CReP was also required for exocytosis from erythroleukemia cells and thus appears to play a broader role in membrane traffic. In summary, the mammalian traffic machinery co-opts p-eIF2 alpha and CReP, regulators of translation initiation.