XBP1s overexpression in hBMSCs enhances their support of MM cell growth. (A) Overexpression of XBP1s enhanced the baseline and TNFα (10 ng/mL)–induced IL-6 secretion in healthy donor BMSCs, as determined by ELISA (n = 3; mean ± SD; *P < .05). (B) Overexpression of Flag-hXBP1s increased the baseline and TNFα (10 ng/mL for 24 hours)–induced VCAM-1 protein expression in healthy donor BMSCs. The schematic quantitative representation of Western blot results was performed by normalizing VCAM-1 protein levels to those of β-actin. The relative protein levels of VCAM-1 in the control BMSCs without TNFα is arbitrarily defined as 1 (right; n = 3; mean ± SD; *P < .05). (C) Overexpression of Flag-hXBP1s enhanced the baseline and TNFα-induced VCAM-1 protein expression in KM101 cells. The experiments were performed and analyzed as described in panel B. (D) Overexpression of hXBP1s in healthy donor BMSCs significantly enhanced the adhesion of MM1.S and ANBL6 cells to the hBMSCs (n = 3; mean ± SD; *P < .05). (E-F) Overexpression of Flag-hXBP1s enhanced the capacity of healthy donor BMSCs (E) and KM101 cells (F) to support MM cell growth. The cells with or without Flag-hXBP1s overexpression were cocultured with either 5TGM1 or the ANBL-6 MM cell line for 3 days. MM cells growth was determined by counting MM cells (n = 3; mean ± SD; *P < .05).