The JAK2/STAT3- mediated SDF-1/CXCR4 axis promotes mesenchymal stem cell migration in response to the tumor microenvironment. Free

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Stromal cell-derived factor-1 (SDF-1) and its cognate receptor CXCR4 play an important role in hematopoiesis, development, the pathogenesis of HIV infection, and carcinogenesis. The SDF-1/CXCR4- expressing mesenchymal stem cells (MSCs) are a potential therapeutic tool in tissue regeneration, gene therapy and cell therapy, due to their multipotentiality and specific localization to tumors both in vitro and in vivo. However, little is known about the molecular mechanisms involved in MSC migration towards tumor microenvironments. The present study investigates the role of the SDF-1/CXCR4 axis and its downstream signaling during MSCs migration towards tumor cells. Gene expression profiling analysis reveals that SDF-1 is significantly up-regulated in MSCs exposed to tumor conditioned medium, as compared to the cells treated with control medium, suggesting that SDF-1/CXCR4 signaling may play an important role in mediating MSC migration. When stimulated with SDF-1, increased migration was observed in MSCs in a dose-dependent manner. This migration is blocked by knocking down SDF-1 using small interfering RNA specifically targeting SDF-1. Western blotting analyses reveal increased phosphorylation of signal transducer and transcription activator 3 (STAT3) and extracellular signal- related kinase (ERK1/2) in MSCs when stimulated with SDF-1, while no changes in phosphorylation status were observed in other STAT proteins. To further confirm the role of STAT3 and ERK1/2, in vitro migration assays were performed using specific inhibitors for JAK2 and MEK and significant blocking of migration was observed in the presence of ERK1/2 inhibitor PD98059, whereas JAK2 inhibitor completely abolishes the migration induced by tumor conditioned medium. Impaired MSC migration correlates with decreased expression of phosphorylated STAT3 and ERK1/2, suggesting that SDF-1 stimulation activates JAK2/STAT3 as well as MEK/ERK1/2 signaling, which in turn promotes the migration of MSCs towards tumor cells. Taken together, our results provide an insight into the molecular pathways responsible for the MSC migration towards tumor microenvironments and may provide the molecular basis for modifying MSCs for therapeutic purposes.