Bone marrow stromal cells induced activation of nuclear factor κB signaling protects non-Hodgkin’s B lymphoma cells from apoptosis

The microenvironment encompassing a variety of non-malignant cells in close proximity with malignant tumor cells has been well known to significantly affect the behavior of tumor cells. In this study, we therefore studied the mechanism of bone marrow stromal cells in protection of lymphoma cells from spontaneous apoptosis. We demonstrated that adhesion of the freshly isolated lymphoma B cells to bone marrow stromal cells or freshly isolated lymphoma stromal cells inhibited B cell spontaneous apoptosis in culture. This inhibition of apoptosis correlated with decreased cleavage of caspase-3/8 and increased activation of canonical and non-canonical NF-κB signaling pathway. In addition to BAFF signaling which has been reported as a functional determinant for B lymphoma cell survival in the bone marrow environment, we demonstrated RANKL from BMSCs works synergistically with BAFF to activate NF-κB signaling pathway and thus protects lymphoma B cells from spontaneous apoptosis.