The E3 ubiquitin ligase membrane-associated ring-CH–type finger 2 (MARCH2) is known to be involved in intracellular vesicular trafficking, but its role in the early secretory pathway between the endoplasmic reticulum (ER) and Golgi compartments is largely unknown. Human ER–Golgi intermediate compartment protein 2 (ERGIC2) and ERGIC3 are orthologs of Erv41 and Erv46 in yeast, proteins that form a heteromeric complex, cycle between the ER and Golgi, and function as cargo receptors in both anterograde and retrograde protein trafficking. Here, we report that MARCH2 directs ubiquitination and subsequent degradation of ERGIC3 and that MARCH2 depletion increases endogenous ERGIC3 levels. We provide evidence that the lysine residues at positions 6 and 8 of ERGIC3 are the major sites of MARCH2-mediated ubiquitination. Of note, MARCH2 did not significantly decrease the levels of an ERGIC3 variant with lysine-to-arginine substitutions at residues 6 and 8. We also show that ERGIC3 binds to itself or to ERGIC2, whereas ERGIC2 is unable to interact with itself. Our results indicate that 1-antitrypsin and haptoglobin are likely to be cargo proteins of ERGIC3. We further observed that 1-antitrypsin and haptoglobin specifically bind to ERGIC3 and that ERGIC3 depletion decreases their secretion. Moreover, MARCH2 reduced secretion of 1-antitrypsin and haptoglobin, and coexpression of the ubiquitination-resistant ERGIC3 variant largely restored their secretion, suggesting that MARCH2-mediated ERGIC3 ubiquitination is the major cause of the decrease in trafficking of ERGIC3-binding secretory proteins. Our findings provide detailed insights into the regulation of the early secretory pathway by MARCH2 and into ERGIC3 function.
Bibliographical noteFunding Information:
This work was supported by the National Research Foundation of Korea (NRF) Grants NRF-2019R1A2C1010777 and NRF-2018R1A2B6003455 funded by the Korea government (Ministry of Science and ICT (MSIT)) and the Brain Korea 21 (BK21) PLUS Program (to J.-B. Y.). The authors declare that they have no conflicts of interest with the contents of this article.
© 2019 Yoo et al.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology