Flk-1 ~ + Mesenchymal Stem Cells On Tumor Cell Proliferation Inhibitory Effect Of Molecular Mechanisms

As a special group of cells in the organism,stem cell has some specific functions and characteristics such as self-renewal,long-term proliferation and pluripotency to give rise to other progenitors of different lineages.Based on these features,stem cells are widely utilized in gene therapy,cell therapy and tissue engineering.With the development of stem cell biology,a sub-group of stem cells named "adult stem cells" was identified and isolated from fetal and adult tissues and was applied in clinical. Amongst them,mesenchymal stem cells(MSCs) possess some advantages such as low-immuogenity and immuo-modulatory capacity in addition to pluripotency compared with other adult stem cells,which contributes MSCs with broad prospects.Recent years,abundant research evidence has been reported on immuo-modulatory capacity of MSCs.However,new problems in clinical application have arisen with the suspect that immuo-modulatory capacity of MSCs will lead to original tumor cell proliferation in patients.Based on current research progress in this field,there is a contradiction on that MSCs inhibit or promote tumor cell proliferation.To clarify the suspect and further explore the possible mechanisms,we used AFMSC(adipose-derived Flk-1~+ mesenchymal stem cells) identified and isolated by our lab before to co-culture with different types of tumor cells and analysed subsequent changes on tumor cell prolifeation by ~3H-TdR assays.The results showed the significant and wide inhibitory effect of AFMSC on cell growth of different tumor cell lines including K562 cells.In addition,we applied transwell membrane to avoid the cell adherence between AFMSC and cocultured K562 and found the inhibitory effect of AFMSC still exist,which indicated that AFMSC could probably supress K562 cell proliferation by secreting some specific cytokines or molecules.To identify the possible cytokines which may be invovled in this process,we used neutralizing antibodies of DKK-1 and TGF-βto treat AFMSC when cocultured with K562 cells and found that it was DKK-1 not TGF-βthat participated the process.Since the well-differentiated matrix cells don't have the inhibitory effect on tumor cell growth,we predicted that some innate features of stem cells contribute to this effect of AFMSC.In fact,some reports gave the evidence that NANOG,a stem cell-specific transcriptional factor,could modulate many molecules of developmental signal pathways,one potential target of which is DKK-1.We performed chromatin immuno-precipitation(CHIP) to verify NANOG binding on DKK-1 promoter in AFMSC and provided the evidence that NANOG is indispensable for DKK-1 expression by the method of RNA interference on NANOG gene.Using Cellmax artificial capillary modules that eliminate the immunosuppressive properties of AFMSC,we further showed that AFMSC were able to inhibit proliferation of K562 cells in vivo.The above results together suggested that AFMSC can inhibit K562 cell proliferation by secreting DKK-1 and this inhibition effect is dependent on NANOG.And our results suggested that soluble anti-proliferative factors secreted by AFMSC,like DKK-1,could be used as therapeutic agents against cancer.According to this research,extreme caution should be taken when MSCs are exploited to treat human malignancies.