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

Background: The constitutive reverter of eIF2α phosphorylation (CReP/PPP1r15B) targets the catalytic subunit of protein phosphatase 1 (PP1c) to p-eIF2α to promote translation initiation. Results: CReP associates with membranes and regulates membrane traffic in a PP1c-independent manner. Conclusion: CReP is co-opted by the traffic machinery. Significance: The data reveal a novel link between the molecular machineries regulating translation and traffic. The constitutive reverter of eIF2α phosphorylation (CReP)/PPP1r15B targets the catalytic subunit of protein phosphatase 1 (PP1c) to phosphorylated eIF2α (p-eIF2α) 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 α-toxin by epithelial cells. This function was independent of PP1c and translation, although p-eIF2α was involved. The latter accumulated at sites of toxin attack and appeared conjointly with α-toxin in early endosomes. CReP localized to membranes, interacted with phosphomimetic eIF2α, 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 α-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-eIF2α and CReP, regulators of translation initiation.