Integrin β4 neoexpression is induced in fibroblasts through direct contact with invasive breast cancer cells. (A) Endogenous expression of integrin β1 and β4 in fibroblasts of IDC. Fibroblasts were prestained with CMFDA and cultured in RSM, MCF7 CM, or MDA-MB-231 CM for 72 hours before staining with PE-conjugated anti-integrin β1 or β4 antibodies. (B) Integrin β1 expression and (C) Integrin β4 expression in fibroblasts cocultured with MCF7 or MDA-MB-231 cells. Confluent fibroblasts on 100-mm dishes were stained with 5 μM CMFDA. MCF7 or MDA-MB-231 cells (5 × 105) were added to the stained fibroblasts and cocultured for 1 week. Mixed cells were collected and stained with PE-conjugated anti-integrin β1 or β4 antibodies. Integrin β1 or β4 expression in cocultured fibroblasts was confirmed by immunoblot analysis after sorting.