Induction of apoptosis in human neuroblastoma cells by abrogation of integrin-mediated cell adhesion

The survival, proliferation and differentiation of neuroblastoma (NB) cells are largely dependent on adhesion to extracellular matrix (ECM) proteins. Integrin occupancy seems to play a primary role. To elucidate the role of integrin heterodimers during neuronal cell death, we have analysed the changes in integrin expression in 2 human NE cell lines which represent different stages of neuronal maturation. Retinoic acid (RA) had different effects on the 2 NE cell lines: on LAN-5 cells it acted as a differentiation-promoting agent, while it had an anti-proliferative effect on GI-LI-N cells, driving them to apoptosis. Indeed, this occurrence was evidenced by the visualization of a 'DNA ladder' on gel electrophoresis, by propidium iodide staining, and by DNA flow cytofluorimetric analysis. RA treatment rapidly and drastically decreased integrin expression and cell adhesion on CI-LI-N cells. These findings were also obtained by treating both NE cell lines with the apoptotic agent fenretinide. Furthermore, treatment of NE cells with anti-sense oligonucleotides to β₁ integrin chain specifically induced chromatin condensation and nucleosomal DNA laddering. Moreover, blocking cell-matrix interactions by means of perturbing antibody against β₁ subunit resulted in the induction of typical features of apoptotic cells. In conclusion, these findings indicate that abrogation of cell adhesion through down-modulation of integrin receptors plays a crucial role in the induction of neuroblastoma programmed cell death.