The NH₂‐Terminal Transmembrane and Lumenal Domains of LGP85 are Needed for the Formation of Enlarged Endosomes/Lysosomes

Abstract

LGP85 is a lysosomal membrane protein possessing a type III topology and is also known as a member of the CD36 superfamily of proteins, such as CD36 and the scavenger-receptor BI (SR-BI). We have recently demonstrated that overexpression of LGP85 in various mammalian cell lines causes the enlargement of endosomal/lysosomal compartments (ELCs). Using chimeras and deletion mutants, we show here that the lumenal region of LGP85 is necessary, but not sufficient, for the development of ELCs. Effective formation of enlarged ELC was largely dependent on the presence of a preceding NH(2)-terminal transmembrane segment. Analyses of deletion mutants within the lumenal domain further revealed a requirement of the NH(2)-terminal transmembrane proximal lumenal region, with high sequence similarity with SR-BI for the enlargement of ELC. These results suggest that an interaction of the NH(2)-terminal transmembrane proximal lumenal domain of LGP85 with the inner leaflet of endosomal/lysosomal membranes through the connection with the transmembrane domain is an essential determinant for the regulation of endosomal/lysosomal membrane traffic. Interestingly, although the NH(2)-terminal transmembrane domain itself was not sufficient for the enlargement of ELCs, it appeared to be required for direct targeting of LGP85 from the trans-Golgi network to late endosomes/lysosomes. Taken together, these results indicate the involvement of distinct domain of LGP85 in the targeting to, and biogenesis and maintenance of, ELC.

SCARB2/LIMP-2 Regulates IFN Production of Plasmacytoid Dendritic Cells by Mediating Endosomal Translocation of TLR9 and Nuclear Translocation of IRF7

“…7B, 7C). Such a finding is supported by the following evidence: First, after synthesized in ER, SCARB2 translocates into late endosome/lysosome and regulates the biogenesis and reorganization of endosomes and lysosomes (7, 9–12, 15). Similarly, TLR9 must traffic into these vesicles to undergo a proteolytic processing and become functional (28, 48).…”

“…As an abundant LMP, SCARB2 plays a critical role in the biogenesis and reorganization of endosomes and lysosomes. Over-expression of SCARB2 in mammalian cells results in direct disturbance of membrane trafficking and accumulation of cholesterol, which leads to enlargement of endosomal/lysosomal compartments (12, 15). SCARB2 has been reported to transport β-glucocerebrosidase (β-GC), a lysosomal hydrolase whose mutation might cause lysosomal storage disorder Gaucher disease (GD), from endoplasmic reticulum (ER) to lysosome (16).…”

LIMP-2 Links Late Phagosomal Trafficking with the Onset of the Innate Immune Response to Listeria monocytogenes

“…The specific intracellular action of LIMP-2/SCARB2 in LM phagocytosis and the lack of involvement in bacterial cell surface adherence or TLR2/TLR4 signaling correlate with the role assigned to LIMP-2 in endocytosis participating in late trafficking events (27)(28)(29)38) and also correlate with TLR2/ TLR4-independent killing of LM by activated MØ (39 -41). In fact, LIMP-2 Ϫ/Ϫ BM-DM showed a failure in listericidal abilities and acute phase cytokines production, whereas they displayed normal LPS responses and oxidative burst capacity.…”

“…In fact, LIMP-2 Ϫ/Ϫ BM-DM showed a failure in listericidal abilities and acute phase cytokines production, whereas they displayed normal LPS responses and oxidative burst capacity. This intracellular specificity of LIMP-2/SCARB2 for late endocytic vesicles appears dependent on the presence of a coiled-coil domain in the luminal region and a preceding Nterminal transmembrane segment (36,38). These LIMP-2/ SCARB2 domains are absent in other CD36 family members such as CLA-1/SCARB1 or CD36, which have been shown to participate in bacterial recognition and uptake (7)(8)(9).…”

HM1.24 Is Internalized from Lipid Rafts by Clathrin-mediated Endocytosis through Interaction with α-Adaptin

“…Point mutations of the HM1.24 tail were generated with the QuikChange site-directed mutagenesis kit (Stratagene) according to the manufacturer's manual. For the construct of HN1.24dNT, the NH 2 -terminal cleavable signal sequence of rat LGP107 corresponding to amino acid residues 1-23 and the extracellular domain of HM1.24 corresponding to amino acid residues 49 -180 were jointed by splicing with the overlap extension method as described previously (21). HM1.24dCT was obtained by deleting amino acids 163-180 of full-length HM1.24.…”