γ-secretase facilitates retromer-mediated retrograde transport.

Abstract

Retromer mediates retrograde transport of protein cargos from endosomes to the trans-Golgi network (TGN). γ-secretase is a protease that cleaves the transmembrane domain of its target proteins. Although retromer can form a stable complex with γ-secretase, the functional consequences of this interaction are not known. Here, we report that retromer-mediated retrograde protein trafficking in cultured human epithelial cells is impaired by the γ-secretase inhibitor XXI or by knockout of the catalytic subunit of γ-secretase. These treatments inhibited endosome to TGN trafficking of retromer-dependent retrograde cellular cargos, divalent metal transporter 1 isoform II, cation-independent mannose-6-phosphate receptor, and shiga toxin, whereas trafficking of retromer-independent cargos cholera toxin and a mutant CIMPR unable to bind retromer was not affected. Moreover, we found that g-secretase associates with retromer cargos even in the absence of retromer. XXI treatment and PS1 knockout did not inhibit the ability of retromer or g-secretase to associate with cargo and did not affect the expression of retromer subunits or Rab7-GTP, which regulates retromer-cargo interaction. These results imply that the γ-secretase-retromer interaction facilitates retromer-mediated retrograde trafficking of cellular transmembrane proteins.