Mutant p62 Stimulation of Osteoclast Differentiation in Paget’s Disease of Bone

Paget’s disease of the bone (PDB) is an autosomal dominant trait with genetic heterogeneity, characterized by abnormal osteoclastogenesis. Sequestosome 1 (p62) is a scaffold protein that plays an important role in receptor activator of nuclear factor B (RANK) signaling essential for osteoclast (OCL) differentiation. p62 mutation in the ubiquitin-associated (UBA) domain is widely associated with PDB; however, the mechanisms by which p62 stimulate OCL differentiation in PDB are not completely understood. Deubiquitinating enzyme cylindromatosis (CYLD) has been shown to negatively regulate RANK ligand-RANK signaling essential for OCL differentiation. Here, we report that CYLD binds with the p62 wild-type (p62), non-UBA mutant (p62) but not with the UBA mutant (p62) in OCL progenitor cells. Also, p62 induces expression of c-Fos (2.8-fold) and nuclear factor of activated T cells c1 (6.0-fold) transcription factors critical for OCL differentiation. Furthermore, p62 expression results in accumulation of polyubiquitinated TNF receptor-associated factor (TRAF)6 and elevated levels of phospho-I B during OCL differentiation. Retroviral transduction of p62/CYLD short hairpin RNA significantly increased TRAP positive multinucleated OCL formation/bone resorption activity in mouse bone marrow cultures. Thus, the p62 mutation abolished CYLD interaction and enhanced OCL development/bone resorption activity in PDB. (Endocrinology 152: 4180–4189, 2011)