KLHL12 can form large COPII structures in the absence of CUL3 neddylation

CUL3-RING ubiquitin ligases (CRL3s) are involved in various cellular processes through different Bric-a-brac, Tramtrack, and Broad-complex (BTB)-domain proteins. KLHL12, a BTB-domain protein, is suggested to play an essential role in the export of large cargo molecules such as procollagen from the endoplasmic reticulum (ER). CRL3KLHL12 monoubiqui-tylates SEC31, leading to an increase in COPII vesicle dimension. Enlarged COPII vesicles can accommodate procollagen molecules. Thus, CRL3KLHL12 is essential for the assembly of large COPII structures and collagen secretion. CRL3s are activated by CUL3 neddylation. Here, we evaluated the importance of CUL3 neddylation in COPII assembly and collagen secretion. Unexpectedly, the assembly of large COPII-KLHL12 structures persisted and cellular collagen levels decreased on treatment with MLN4924, a potent inhibitor of NEDD8-activating en-zyme. When we introduced mutations into KLHL12 at the CUL3 interface, these KLHL12 vari-ants did not interact with neddylated CUL3, but one of them (Mut A) still supported large COPII-KLHL12 structures. Overexpression of wild-type KLHL12, but not Mut A, lowered cel-lular collagen levels most likely via lysosomal degradation. Our results suggest that CUL3 neddylation is not necessary for the formation of large COPII-KLHL12 structures, but active CRL3KLHL12 contributes to the maintenance of collagen levels in the cell.

Automated summary

CUL3-RING ubiquitin ligases (CRL3s) play a crucial role in various cellular processes through different BTB-domain proteins. KLHL12, a BTB-domain protein, is involved in the export of large cargo molecules, such as procollagen, from the endoplasmic reticulum (ER). CRL3KLHL12 monoubiquitylates SEC31, leading to increased size of COPII vesicles and facilitating procollagen secretion.