Nuclear factor erythroid-derived 2 like 1 (NFE2L1) is reported to be embedded in the endoplasmic reticulum (ER) membrane and subsequently undergo N-glycosylation at several asparagine residues as well as other ER-resident factors including cAMP response element binding protein 3 (CREB3)/ATF6 family members. In this study, we investigated the regulation of NFE2L1 protein expression by treating wild-type HEK293 cells and HEK293 cells deficient in selected ER-associated degradation (ERAD) factors with various reagents. NFE2L1 protein expression in wild-type HEK293 cells was negligible, but MG132/bortezomib treatment induced Endo H-resistant two bands. Suppressor/enhancer of lin-12-like (SEL1L)/hydroxymethylglutaryl-CoA (HMG-CoA) reductase degradation 1 (Hrd1) loss increased NFE2L1 protein expression without any stimuli. In these deficient cells, the band shift of NFE2L1 by MG132 was mostly suppressed. Treatment with the valosin containing protein (VCP) inhibitor CB-5083 increased NFE2L1 expression, but deficiencies in other ERAD-associated factors (ER degradation-enhancing α -mannosidase-like protein 2 (EDEM2), thioredoxin domain-containing protein 11 (TXNDC11), gp78, ring finger protein 5 (RNF5), ring finger protein 185 (RNF185), and USP19) did not affect its expression. Comparing the stability of the two intrinsic NFE2L1, which increases with proteasome inhibition, the higher molecular weight form corresponding to full-length form, was more unstable. Therefore, we constructed NFE2L1 genes with mutations in the site where NFE2L1 is cleaved by DDI2 and in the four asparagine residues where N-glycosylation occurs, and found that the high molecular weight form, especially a hypoglycosylated mutant, tended to be more unstable. Taken together, this study using several ERAD disordered models shows that the regulation of NFE2L1 is different in some ways from the regulation of CREB3/ATF6 family, and these findings implicate the diversity of N-glycosylated protein regulation in the ER.
Yasui et al. (Fri,) studied this question.