Osteoblasts release several growth factors and, among them, TGF-β1 (Transforming Growth Factor – β1) is an important contributor to extracellular signal-related kinase (ERK), p38, and c-Jun N-terminal kinase (JNK) activation [72], which lead to the activation of activator protein 1(AP-1) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) on the IL-8 promoter, and which initiate IL-8 release, thus promoting breast cancer cell migration and osteoclastogenesis [21,54,69,72]. Here, JUN is linked to breast cancer.