Knock-down of XBP1 in hBMSCs compromises their support of MM cell growth. (A) Western blot demonstrating the effects of XBP1 knockdown on the baseline and TNFα-induced VCAM-1 protein expression in BMSCs from 3 independent healthy donors and 4 independent MM patients. (B) A schematic quantitative representation of Western blot results shown in panel A. The VCAM-1 protein levels were normalized to those of β-actin. The baseline relative VCAM-1 protein levels of the healthy donor BMSCs in the absence of hXbp1 shRNA are arbitrarily defined as 1. Error bars represent means ± SD. (C) Effects of XBP1 knockdown on the baseline and TNFα-induced IL-6 secretion in the condition medium of both healthy donor and MM patient BMSCs as determined by ELISA (n = 3, mean ± SD, *P < .05). (D-E) Effects of XBP1 knockdown on the capacity of healthy donor and MM patient BMSCs to support the growth of human ANBL6 cells (D) or primary human MM cells (E; n = 3, mean ± SD, *P < .05).