Protection of Extraribosomal RPL13a by GAPDH and Dysregulation by S-Nitrosylation

SummaryMultiple eukaryotic ribosomal proteins (RPs) are co-opted for extraribosomal “moonlighting” activities, but paradoxically, RPs exhibit rapid turnover when not ribosome-bound. In one illustrative case of a functional extraribosomal RP, interferon (IFN)-γ induces ribosome release of L13a and assembly into the IFN-gamma-activated inhibitor of translation (GAIT) complex for translational control of a subset of inflammation-related proteins. Here we show GAPDH functions as a chaperone, shielding newly released L13a from proteasomal degradation. However, GAPDH protective activity is lost following cell treatment with oxidatively modified low density lipoprotein and IFN-γ. These agonists stimulate S-nitrosylation at Cys247 of GAPDH, which fails to interact with L13a, causing proteasomal degradation of essentially the entire cell complement of L13a and defective translational control. Evolution of extraribosomal RP activities might require coevolution of protective chaperones, and pathological disruption of either protein, or their interaction, presents an alternative mechanism of diseases due to RP defects, and targets for therapeutic intervention.

Graphical AbstractFigure optionsDownload high-quality image (262 K)Download as PowerPoint slideHighlights
► GAPDH acts as a shield, protecting free ribosomal protein L13a from degradation
► Condition-dependent degradation of an extraribosomal ribosomal protein
► S-Nitrosylation of GAPDH at Cys247 suppresses its protective activity
► Degradation of unprotected L13a inactivates GAIT system and induces VEGF-A expression