Specificity of enhanced tyrosine phosphorylation in stromal cells. Stromal cells were incubated for 5 minutes at 37°C and collected, electrophoresed, and immunoblotted as detailed in the Materials and Methods. (A) Stromal cells incubated in medium alone (−) or after contact with KM-3 (K), BLIN-3 (B3), or BLIN-4 (B4) cells. (B) Stromal cells incubated in medium alone (−) or in contact with HL-60 cells (HL) or RAMOS-4c (R). (C) Untreated stromal cells (stro) or cytochalasin D-treated stromal cells (CD-stro) incubated in medium alone (−) or with RAMOS-wt (R). (D) Stromal cells incubated in medium alone (−), with polystyrene microspheres (pm), or with RAMOS-wt (R). Blots were probed with antiphosphotyrosine (upper panels), stripped, and reprobed with anti–β-tubulin (lower panels). Asterisks indicate the major stromal cell proteins demonstrating increases in tyrosine phosphorylation after RAMOS contact. (A), (B), (C), and (D) are representative of 3, 6, 3, and 1 individual experiments, respectively.