Regulation of Derlin-1-mediated degradation of NADPH oxidase partner p22phoX by thiol modification

The transmembrane protein p22(phoX) heterodimerizes with NADPH oxidase (Nox) 1-4 and is essential for the reactive oxygen species-producing capacity of oxidases. Missense mutations in the p22(phoX) gene prevent the formation of phagocytic Nox2-based oxidase, which contributes to host defense. This results in chronic granulomatous disease (CGD), a severe primary immunodeficiency syndrome. In this study, we characterized missense mutations in p22(phoX) (L51Q, L52P, E53V, and P55R) in the A22? type (wherein the p22(phoX) protein is undetectable) of CGD. We demonstrated that these substitutions enhanced the degradation of the p22(phoX) protein in the endoplasmic reticulum (ER) and the binding of p22(phoX) to Derlin-1, a key component of ER-associated degradation (ERAD). Therefore, the L-51-L-52-E-53-P-55 sequence is responsible for protein stability in the ER. We observed that the oxidation of the thiol group of Cys-50, which is adjacent to the L-51-L-52-E-53-P-55 sequence, suppressed p22(phoX) degradation. However, the suppression effect was markedly attenuated by the serine sub-stitution of Cys-50. Blocking the free thiol of Cys-50 by alkylation or C50S substitution promoted the association of p22(phoX) with Derlin-1. Derlin-1 depletion partially suppressed the degradation of p22(phoX) mutant proteins. Furthermore, heterodimerization with p22(phoX) (C50S) induced rapid degradation of not only Nox2 but also nonphagocytic Nox4 protein, which is responsible for redox signaling. Thus, the redox-sensitive Cys-50 appears to determine whether p22(phoX) becomes a target for degradation by the ERAD system through its interaction with Derlin-1.

Automated summary

This study characterized missense mutations in p22(phoX) (L51Q, L52P, E53V, and P55R) that enhance the degradation of the protein in the endoplasmic reticulum (ER) and its binding to Derlin-1, a component of ER-associated degradation (ERAD). These mutations contribute to chronic granulomatous disease (CGD). The oxidation of Cys-50 appears to regulate the degradation of p22(phoX) and its interaction with Derlin-1.