Degradation of misfolded proteins originated in the endoplasmic reticulum is dependent on COPI and II vesicular trafficking
2Arava Science Center, Dead sea & Arava Science Center, Israel
Proper protein folding is essential for normal cellular functions. In order to ensure correct folding and removal of misfolded secretory proteins, the ER has protein quality control mechanisms, which activate signalling pathways in an effort to promote chaperone-mediated folding, and to identify terminally misfolded molecules and target them to ER associated degradation (ERAD). We have observed in previous studies conducted in our lab that enzymes and chaperones involved in quality control and ERAD concentrate together with misfolded proteins in the ER derived Quality Control compartment (ERQC). We have studied the accumulation in the ERQC of the luminal chaperone calreticulin (CRT) together with a model ERAD substrate, asialoglycoprotein receptor H2a, upon inhibition of proteasomal degradation. Removal of the inhibitor allowed the proteins to recycle back to the peripheral ER, and mutations in the CRT lectin domain prevented its accumulation in the ERQC. Interference with the activities of COPI or COPII, using dominant negative mutants of ARF1 and Sar1 or drugs, strongly affected the trafficking and degradation of H2a, suggesting involvement of vesicular coats in the movement from the peripheral ER to the ERQC and back. COPI inhibition resulted in accumulation in the ERQC and an increase in retrotranslocation and ERAD, whereas COPII inhibition had the opposite effect. Our results indicate that the ERQC is a staging ground for retrotranslocation and ERAD, and that the transport of misfolded proteins to the ERQC and subsequent targeting to ERAD depends on COPII, whereas their retrieval to the peripheral ER is COPI-dependent.