SCF^FBXO17 E3 ligase modulates inflammation by regulating proteasomal degradation of glycogen synthase kinase-3β in lung epithelia.

Glycogen synthase kinase-3β (GSK3β) has diverse biological roles including effects on cellular differentiation, migration, and inflammation. GSK3β phosphorylates proteins to generate phosphodegrons necessary for recognition by Skp1/Cullin-1/F-box (SCF) E3 ubiquitin ligases leading to subsequent proteasomal degradation of these substrates. However, little is known regarding how GSK3β protein stability itself is regulated and how its stability may influence inflammation. Here we show that GSK3β is degraded by the ubiquitin-proteasome pathway in murine lung epithelial cells through lysine 183 as an acceptor site for K48 polyubiquitination. We have identified FBXO17 as an F-box protein subunit that recognizes and mediates GSK3β polyubiquitination. Both endogenous and ectopically expressed FBXO17 associate with GSK3β, and its overexpression leads to decreased protein levels of GSK3β. Silencing FBXO17 gene expression increased the half-life of GSK3β in cells. Furthermore, overexpression of FBXO17 inhibits agonist-induced release of keratinocyte-derived cytokine (KC) and interleukin-6 (IL-6) production by cells. Thus, the SCF^FBXO17 E3 ubiquitin ligase complex negatively regulates inflammation by targeting GSK3β in lung epithelia.

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