Cell-matrix and cell-cell interactions modulate apoptosis of bronchial epithelial cells

Apoptosis is an important process maintaining cell number and tissue structure. To determine whether cell-extracellular matrix (ECM) and cell-cell interactions modulate apoptosis in bronchial epithelium, we cultured human bronchial epithelial cells in different conditions and evaluated the cells for apoptosis. We found that plating cells in conditions that prevent cell-ECM adhesion induced apoptosis. Plating cells on type I collagen, fibronectin, and biosynthesized matrix prevented apoptosis, due at least in part to integrin-mediated adhesion. When cells were cultured at high density but under conditions preventing cell-substratum adhesion, aggregation occurred. Apoptosis was inversely correlated with aggregation. Cell-cell adhesion in these conditions was mediated at least partly by integrins containing alpha v. Cell aggregation was not associated with activation of a signaling pathway that is usually activated by cell-ECM adhesion, phosphorylation of focal adhesion kinase, but was associated with Bcl-2 protein expression, consistent with the concept that Bcl-2 protects against apoptosis. We conclude that both cell-ECM and cell-cell interactions, likely mediated in part by integrins, modulate apoptosis in bronchial epithelium.