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-g (IFN-g) 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-g and tumor necrosis factor-a (IFN-g+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 butmarked increase inthe expression of a1, a2, a3, and b1 chains after IFN-g+TNF treatment of LAN-5 cells, and only a1 and b1 chains upon RA induction. Treatment with IFN-g+TNF induced GI-LI-N cells to show only a late and remarkable increase of a1/b1 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 betweenup-regulation of integrins and neuronal morphogenesis.