Fibronectin-mediated binding of these exosomes to integrin on fibroblast cells and to HSPG on myeloma cells, respectively, activate p38 and pERK signaling; expression of downstream target genes, DKK1 and MMP-9, in myeloma cells; and activation of invasion-associated signaling pathways involving focal adhesion kinase (FAK) and Src family kinases (SFKs) in fibroblasts [103,120]. Here, DKK1 is linked to plasma cell myeloma.