Mutations of the gene encoding sequestosome1 (SQSTM1/p62), clustering in or near the UBA domain, have been described in Paget's disease of bone (PDB); among these the P392L substitution is the most prevalent. Protein p62 mediates several cell functions, including the control of NF-κB signaling, and autophagy. This scaffolding protein interacts with atypical PKCζ in the RANKL-induced signaling complex. We have previously shown that osteoclasts (OCs) overexpressing the p62P392L variant were in a constitutively activated state, presenting activated kinase p-PKCζ/λ and activated NF-κB prior to RANKL stimulation. In the present study, we investigated the relationships between PKCζ and NF-κB activation in human OCs transfected with p62 variants. We showed that PKCζ and p-PKCζ/λ co-localize with p62, and that PKCζ is involved in the RANKL-induced NF-κB activation and in the RANKL-independent activation of NF-κB observed in p62P392L-transfected cells. We also observed a basal and RANKL-induced increase in IκBα levels in the presence of the p62P392L mutation that contrasted with the NF-κB activation. In this study we propose that PKCζ plays a role in the activation of NF-κB by acting as a p65 (RelA) kinase at Ser536, independently of IκBα; this alternative pathway could be used preferentially in the presence of the p62P392L mutation, which may hinder the ubiquitin–proteasome pathway. Overall, our results highlight the importance of p62-associated PKCζ in the overactive state of pagetic OCs and in the activation of NF-κB, particularly in the presence of the p62P392L mutation.
Highlights
► PKCζ is involved in the RANKL-induced NF-κB activation in human osteoclasts (OCs). ► PKCζ is involved in the basal activation of NF-κB observed in p62P392L-OCs. ► Increased IκBα levels in p62P392L-OCs contrasted with simultaneous NF-κB activation. ► PKCζ contributes to p65 (RelA) phosphorylation at Ser536 in RANKL-induced NF-κB activation. ► PKCζ-induced phosphorylation of Ser536p65 in p62P392L containing OCs contributes to IκBα-independent NF-κB activation.