Integrin up-regulation as marker of neuroblastoma cell differentiation: correlation with neurite extension

We have characterized the adhesion properties, integrin expression, and morphological changes due to extracellular matrix (ECM)-integrin interactions in a neuronal model. We showed that a modulation of some integrin heterodimers occurs during interferon-gamma (IFN-gamma) induced neuroblastoma (NB) cell differentiation. To better elucidate the possible implication and function of integrin receptors during neuronal maturation, we analyzed the changes in integrin expression in two human NB cell lines, LAN-5 and GI-LI-N, which represent different stages of neuronal differentiation. These models show opposite morphological maturation after interferon-gamma and tumor necrosis factor-alpha (IFN-gamma+TNF) treatment. While LAN-5 cells acquired the ability to extend long and branched neurites, GI-LI-N cells did not. Both cell lines showed enhanced expression of phenotypical and biochemical markers of neural maturation. Moreover, retinoic acid (RA) had different effects on the two NB cell lines: on LAN-5 cells it acts as a differentiation-promoting agent, while on GI-LI-N cells it has an antiproliferative effect, driving them to apoptosis. RT-PCR experiments and immunoprecipitation assays showed a late but marked increase in the expression of alpha1, alpha2, alpha3, and beta1 chains after IFN-gamma+TNF treatment of LAN-5 cells, and only alpha1 and beta1 chains upon RA induction. Treatment with IFN-gamma+TNF induced GI-LI-N cells to show only a late and remarkable increase of alpha1/beta1 heterodimer; on the contrary, RA treatment caused a decrease in all integrin chains. These changes are accompanied in differentiated cells by substantial increases in cell attachment to all purified ECM components tested and an increase of neurite-bearing cells and of average neurite length. In conclusion, these findings indicate a close correlation between up-regulation of integrins and neuronal morphogenesis.