Endoplasmic reticulum retention of the γ‐secretase complex component Pen2 by Rer1

Abstract

γ‐Secretase is involved in the production of amyloid β‐peptide, which is the principal component of amyloid plaques in the brains of patients with Alzheimer disease. γ‐Secretase is a complex composed of presenilin (PS), nicastrin, anterior pharynx‐defective phenotype 1 (Aph1) and PS enhancer 2 (Pen2). We previously proposed a mechanism of complex assembly by which unassembled subunits are retained in the endoplasmic reticulum (ER) and only the fully assembled complex is exported from the ER. We have now identified Retention in endoplasmic reticulum 1 (Rer1) as a protein that is involved in the retention/retrieval of unassembled Pen2 to the ER. Direct binding of unassembled Pen2 to Rer1 is mediated by the first transmembrane domain of Pen2, and a conserved asparagine in this domain is required. Downregulation of Rer1 leads to increased surface localization of Pen2, whereas overexpression of Rer1 stabilizes unassembled Pen2. To our knowledge, Rer1 is the first identified interaction partner of mammalian transmembrane‐based retention/retrieval signals.

Sorting receptor Rer1 controls surface expression of muscle acetylcholine receptors by ER retention of unassembled α-subunits

“…This finding was corroborated by immunohistochemical colocalization analysis in skeletal muscle (Fig. S1), and it is consistent with previous findings in other cell types (7,8). In C2C12 cells, Rer1 expression increased strongly during differentiation, concomitant with the up-regulation of AChRα ( Fig.…”

“…Like the KDEL receptor (KDELR), Rer1 is localized in early secretory compartments, mainly the cis-Golgi (7). Recently, mammalian Rer1 was shown to be involved in retaining/retrieving unassembled Pen2 (8) and Nicastrin (9), both membrane protein constituents of the γ-secretase, to the ER. Here, we provide in vitro and in vivo evidence that Rer1 blocks the surface exposure of unassembled AChRα subunits and that reduced expression of Rer1 affects the size of neuromuscular synapses.…”

Retention in Endoplasmic Reticulum 1 (RER1) Modulates Amyloid-β (Aβ) Production by Altering Trafficking of γ-Secretase and Amyloid Precursor Protein (APP)

“…6A, top panels). Considering the earlier reported roles for RER1 in regulating ␥-secretase assembly (41,42), it seems insufficient to explain our observation on the decreased levels of sAPP release, which is dependent on cleavage by ␣-or ␤-secretase. In addition, the Western blot analysis revealed that the steady-state levels of mature APP were significantly decreased and immature APP increased by RER1 overexpression (Fig.…”

“…Previous studies have suggested that RER1 competes with APH1 for NCT binding and negatively regulates the assembly of ␥-secretase (41); or that RER1 binds to PEN2 (42). However, we find that RER1 co-immunoprecipitates with the ␥-secretase complex, as opposed to selectively binding individual disassociated components of the complex.…”

“…Two groups have previously identified RER1 as a binding partner of different ␥-secretase subunits, NCT (41) and PEN2 (42). Both studies showed that RER1 could affect ␥-secretase assembly by regulating retention or retrieval of ␥-secretase subunits.…”