[Mechanism and Clinical Significance of NAMPT in Multiple Myeloma].

OBJECTIVE: To investigate the mechanism and clinical value of nicotinamide phosphoribosyltransferase (NAMPT) in multiple myeloma (MM).

METHODS: RT-qPCR and Western blot were used to detect the expression of NAMPT in MM cells and normal bone marrow mononuclear cells. The biological function of NAMPT was analyzed by cell proliferation and apoptosis assay, small interfering RNA silencing, overexpression assay and chromatin immunoprecipitation assay.

RESULTS: The mRNA and protein expression levels of NAMPT in MM cell lines (MM1R, MM1S, U266 and RPMI-8226) were significantly higher than those in normal bone marrow mononuclear cells ( P < 0.001), and were most obvious in U266 cells. Compared with Si-NC group, the proliferation of U266 cells in Si- NAMPT group was significantly inhibited at 24, 48 and 72 h after transfection ( P =0.006, P < 0.001, P =0.001), and the apoptosis rate of U266 cells was significantly increased at 48 h after transfection ( P < 0.001). Compared with Flag-NC group, U266 cell proliferation in Flag- NAMPT group was significantly increased ( P =0.003, P =0.002, P < 0.001), while the apoptosis rate decreased significantly at 48 h after transfection. The expression of NAMPT in U266 cells was regulated by XBP1 at transcriptional level. The proliferation rate of U266 cells with XBP1 or NAMPT stable knockout or MKC3946 pretreated with bortezomib was significantly decreased, the levels of BCL-2 mRNA and protein were also significantly decreased, while the levels of BAX mRNA and protein were significantly increased, moreover, the cleavage degree of caspase-3 significantly decreased, while caspase-3/7 activity increased dramatically ( P < 0.05).

CONCLUSIONS: The high expression of NAMPT in MM cell line can promote MM cell proliferation and inhibit apoptosis. NAMPT is regulated by IRE1α-XBP1 signaling pathway in U266 cells. Stable knockdown of NAMPT or blocking of IRE1α-XBP1 pathway can significantly increase the sensitivity of U266 cells to bortezomib.