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Neurodegeneration-associated mutant TREM2 proteins abortively cycle between the ER and ER-Golgi intermediate compartment.

ABSTRACT: Triggering receptor expressed on myeloid cells 2 (TREM2) is a transmembrane protein expressed on microglia within the brain. Several rare mutations in TREM2 cause an early-onset form of neurodegeneration when inherited homozygously. Here we investigate how these mutations affect the intracellular transport of TREM2. We find that most pathogenic TREM2 mutant proteins fail to undergo normal maturation in the Golgi complex and show markedly reduced cell-surface expression. Prior research has suggested that two such mutants are retained in the endoplasmic reticulum (ER), but we find, using a cell-free coat protein complex II (COPII) vesicle budding reaction, that mutant TREM2 is exported efficiently from the ER. In addition, mutant TREM2 becomes sensitive to cleavage by endoglycosidase D under conditions that inhibit recycling to the ER, indicating that it normally reaches a post-ER compartment. Maturation-defective TREM2 mutants are also efficiently bound by a lectin that recognizes O-glycans added in the ER-Golgi intermediate compartment (ERGIC) and cis-Golgi cisterna. Finally, mutant TREM2 accumulates in the ERGIC in cells depleted of COPI. These results indicate that efficient ER export is not sufficient to enable normal cell-surface expression of TREM2. Moreover, our findings suggest that the ERGIC may play an underappreciated role as a quality-control center for mutant and/or malformed membrane proteins.

SUBMITTER: Sirkis DW

PROVIDER: S-EPMC5620379 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

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Neurodegeneration-associated mutant TREM2 proteins abortively cycle between the ER and ER-Golgi intermediate compartment.

Sirkis Daniel W DW Aparicio Renan E RE Schekman Randy R

Molecular biology of the cell 20170802 20

Triggering receptor expressed on myeloid cells 2 (TREM2) is a transmembrane protein expressed on microglia within the brain. Several rare mutations in <i>TREM2</i> cause an early-onset form of neurodegeneration when inherited homozygously. Here we investigate how these mutations affect the intracellular transport of TREM2. We find that most pathogenic TREM2 mutant proteins fail to undergo normal maturation in the Golgi complex and show markedly reduced cell-surface expression. Prior research has ...[more]

PMID: 28768830

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Project description:Yeast Sec22p participates in both anterograde and retrograde vesicular transport between the endoplasmic reticulum (ER) and the Golgi apparatus by functioning as a v-SNARE (soluble N-ethylmaleimide-sensitive factor [NSF] attachment protein receptor) of transport vesicles. Three mammalian proteins homologous to Sec22p have been identified and are referred to as Sec22a, Sec22b/ERS-24, and Sec22c, respectively. The existence of three homologous proteins in mammalian cells calls for detailed cell biological and functional examinations of each individual protein. The epitope-tagged forms of all three proteins have been shown to be primarily associated with the ER, although functional examination has not been carefully performed for any one of them. In this study, using antibodies specific for Sec22b/ERS-24, it is revealed that endogenous Sec22b/ERS-24 is associated with vesicular structures in both the perinuclear Golgi and peripheral regions. Colabeling experiments for Sec22b/ERS-24 with Golgi mannosidase II, the KDEL receptor, and the envelope glycoprotein G (VSVG) of vesicular stomatitis virus (VSV) en route from the ER to the Golgi under normal, brefeldin A, or nocodazole-treated cells suggest that Sec22b/ERS-24 is enriched in the pre-Golgi intermediate compartment (IC). In a well-established semi-intact cell system that reconstitutes transport from the ER to the Golgi, transport of VSVG is inhibited by antibodies against Sec22b/ERS-24. EGTA is known to inhibit ER-Golgi transport at a stage after vesicle/transport intermediate docking but before the actual fusion event. Antibodies against Sec22b/ERS-24 inhibit ER-Golgi transport only when they are added before the EGTA-sensitive stage. Transport of VSVG accumulated in pre-Golgi IC by incubation at 15 degreesC is also inhibited by Sec22b/ERS-24 antibodies. Morphologically, VSVG is transported from the ER to the Golgi apparatus via vesicular intermediates that scatter in the peripheral as well as the Golgi regions. In the presence of antibodies against Sec22b/ERS-24, VSVG is seen to accumulate in these intermediates, suggesting that Sec22b/ERS-24 functions at the level of the IC in ER-Golgi transport.

Dataset Information

Neurodegeneration-associated mutant TREM2 proteins abortively cycle between the ER and ER-Golgi intermediate compartment.

Publications

Neurodegeneration-associated mutant TREM2 proteins abortively cycle between the ER and ER-Golgi intermediate compartment.

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