Cell adhesion to follicular dendritic cells (HK cells) protects B-lymphoma cell lines from drug-induced apoptosis and induces down-regulation of Bim and up-regulation of miR-181a. Jeko-1 (A,D), Mino (B,E), or SUDHL-4 (C,F) lymphoma cells (105/mL) in suspension (Sus) adhered to the pre-established monolayer of HK cells (HK-Ad) or with a confluent HK monolayer but separated by transwell inserts were treated with and without mitoxantrone (2μM) or vehicle control (VC) for 12 hours, and the lymphoma cells were collected and analyzed for apoptosis with annexin V (A-C) and Bim protein (all Bim isoforms, EL, L, and S) by Western blot (D-F). Direct cell-cell contact but not soluble factor(s) decreased mitoxantrone-induced apoptosis and Bim expression in Jeko-1, Mino, and SUDHL-4 lymphoma cells. The relative change in Bim protein was measured by quantitative densotometry and is indicated below each lane in panels D through F. (G) Jeko-1, Mino, or SUDHL-4 lymphoma cells (105/mL) were placed in suspension (Sus) or adhered to HK cells (HK-Ad) for 24 hours, and miR-181a expression was analyzed by TaqMan microRNA qRT-PCR assays. Results represent 4 independent experiments with mean ± SD.
