Cargo-selective endosomal sorting for retrieval to the Golgi requires retromer

TLDR

Endosome‑to‑Golgi retrieval of the mannose‑6‑phosphate receptor is essential for lysosome biogenesis, yet the pathway remains poorly understood; in yeast a conserved retromer complex of five proteins mediates this retrieval. mVPS26 was localized to multivesicular body endosomes by electron microscopy, and CD8 reporter constructs were used to assess how its loss affects trafficking of proteins cycling between endosome and Golgi. Retromer is essential for efficient retrieval of the cation‑independent MPR; VPS26‑deficient cells fail to retrieve CI‑MPR, leading to its degradation or mislocalization, and the data show retromer selectively mediates CI‑MPR retrieval but not furin.

Abstract

fEndosome-to-Golgi retrieval of the mannose 6-phosphate receptor (MPR) is required for lysosome biogenesis. Currently, this pathway is poorly understood. Analyses in yeast identified a complex of proteins called “retromer” that is essential for endosome-to-Golgi retrieval of the carboxypeptidase Y receptor Vps10p. Retromer comprises five distinct proteins: Vps35p, 29p, 26p, 17p, and 5p, which are conserved in mammals. Here, we show that retromer is required for the efficient retrieval of the cation-independent MPR (CI-MPR). Cells lacking mammalian VPS26 fail to retrieve the CI-MPR, resulting in either rapid degradation of or mislocalization to the plasma membrane. We have localized mVPS26 to multivesicular body endosomes by electron microscopy, and through the use of CD8 reporter protein constructs have examined the effect of loss of mVPS26 upon the trafficking of membrane proteins that cycle between the endosome and the Golgi. The data presented here support the hypothesis that retromer performs a selective function in endosome-to-Golgi transport, mediating retrieval of the CI-MPR, but not furin.