Cell adhesion to bone marrow stroma induces a reversible cell-cycle arrest and increases p27^Kip protein levels. Jeko-1 (A) or SUDH-10 (B) lymphoma cells (10⁵/mL) were incubated for 12 hours either in the absence of HS-5 bone marrow stromal cells (Sus), or on a confluent HS-5 monolayer (HS5-adhesion), or in the same well with a confluent HS-5 monolayer but separated by cell culture inserts (HS-5 + Transwell). (C) Jeko-1 cells were resuspended for 12 hours after adhering to HS-5 (Resuspension). After the indicated time, lymphoma cells were followed by pulsing with BrdU for 40 minutes and staining with anti-BrdU-FITC for detection of S-phase cells and PI for cell-cycle distribution. Data shown are the mean of 3 experiments. (D) Direct cell-cell contact but not soluble factor(s) increased p27^Kip1 expression analyzed by Western blot in Jeko-1 and SUDH-10 lymphoma cells. All data are representative of at least 4 experiments (means ± SD).