Plasma Levels of SDF-1 and Expression of SDF-1 Receptor on Multiply Myeloma Cells of Human Multiply Myeloma.

Multiple myeloma(MM) is a monoclonal expansion of malignant cells with a plasmablast-plasma cell morphology that is almost exclusively localized to the bone marrow, except at the final stages of disease, when they proliferate in the extramedullary area. The mechanisms of the selective homing of MM cells to the bone marrow compartment are poorly understood. The chemokine stromal cell-derived factor-1 (SDF-1) and its receptor CXCR4 contribute to stem cell homing and play a role in trafficking of leukemic cells. In this study we have investigated expression and biological behavior of SDF-1/CXCR4 in MM-derived cell lines and primary MM cells. FACS and RT-PCR analysis was used to study the expression of CXCR4 and ICAM-1(CD54) on the surface of MM cells from 4 IL-6 dependant cell lines (XG1,XG2,XG6 and XG7) and 25 freshly isolated tumor samples from patients with diagnosed MM. Mononuclear cells were purified by positive selection of magnetical and FACS sorting. Chemotaxis assay through transwell bore polycaronate and ELISA assay were employed to monitor the SDF-1, IL-6, and sICAM-1 levels. We found that[circ1]Fresh MM cells and MM cell lines expressed various levels of functional CXCR4 ranging from 23.1% to 77.7%,which was correlated with the in vitro migration ability of MM cells[(23.2±1.08)%, P<0.01]; [circ2]SDF-1 levels in the bone marrow(BM) of MM patients were significantly higher than the those of healthy persons (3489.23±651.63)pg/ml, (2818.57±597.79)pg/ml, P<0.05; but plasma levels of SDF-1 in peripheral blood of MM patients were lower than those of healthy persons[(1973±133)pg/ml, (2334.857±574.92), P=0.062]; [circ3]Plasma levels of PCL(4097.14±680.71) were significantly higher than those of healthy persons, P<0.01. The results firstly demonstrated abnormal expression of SDF-1 and its receptor CXCR4 on Human MM cells, which is closely correlated with the migration of MM cells. Furthermore, we discovered that SDF-1 could up-regulate the expression of ICAM-1 on MM cells; the plasma level of soluble ICAM-1 was correlated with the expression of CXCR4 on MM cells. These findings suggested that SDF-1/CXCR4 axis play a key role on the trafficking of MM cells via mediating the effect of adhesion molecules. Moreover, we observed higher plasma levels of IL-6 in PB of 60% MM patients compared with those of healthy individuals. Finally, the levels of IL-6 were closely correlated with SDF-1 levels (γ=0.8, P<0.01), These data indicated that in the IL-6-dependent myeloma cell lines or fresh myeloma samples and myeloma cell growth triggered by SDF-1 maybe due to up-regulation of autocrine and paracrine IL-6 by myeloma cells and stromal cells in BM. The results suggested that the expression of CXCR4 have an essential role in the proliferation and migration of myeloma cells in patients with multiple myeloma.In conclusion, MM cells expressed various levels of functional CXCR4, which were correlated with the migration ability of MM cells in vitro; SDF-1/CXCR4 axis plays a key role in the trafficking of MM cells via mediating the effect of adhesion molecules; The plasma levels of IL-6 closely correlated with SDF-1 plasma levels, myeloma cell growth triggered by SDF-1 may be due to up-regulation of autocrine and paracrine IL-6 by myeloma cells and stromal cells in BM. All these suggested that the expression of CXCR4 play an essential role in the proliferation and migration of myeloma cells in patients with multiple myeloma.