JUNB and osteoporosis: WWP1 inhibits the differentiation of mesenchymal stem cells (MSCs) into osteoblasts through ubiquitination and proteasomal degradation of JUNB and the lysosomal degradation of CXCR4 following induction by tumor necrosis factor (TNF), thereby promoting inflammation-mediated osteoporosis (Fig. 3E, [77, 78]).