Up-regulation of the integrin alpha 1/beta 1 in human neuroblastoma cells differentiated by retinoic acid: correlation with increased neurite outgrowth response to laminin.

Retinoic acid (RA) is known to induce differentiation of neuroblastoma cells in vitro. Here we show that treatment of two human neuroblastoma cell lines, SY5Y and IMR32, with RA resulted in a fivefold increase of the integrin alpha 1/beta 1 expression. The effect was selective because expression of the alpha 3/beta 1 integrin, also present in these cells, was not increased. The up-regulation of the alpha 1/beta 1 differentiated SY5Y cells correlated with increased neurite response to laminin. In fact, RA-treated SY5Y cells elongated neurites on laminin-coated substratum more efficiently compared with untreated cells or cells treated with nerve growth factor, insulin, or phorbol 12-myristate 13-acetate. These three agents induced partial morphological differentiation but did not increase alpha 1 integrin expression. Neurite extension in RA-treated cells was more efficient on laminin than on fibronectin or collagen type I and was inhibited with beta 1 integrin antibodies on all three substrates. Affinity chromatography experiments showed that alpha 1/beta 1 is the major laminin receptor in both untreated and RA-treated SY5Y cells. These data show that RA, a naturally occurring morphogen implicated in embryonic development, can selectively regulate the expression of integrin complexes in neuronal cells and suggest an important role of the alpha 1/beta 1 laminin receptor in the morphological differentiation of nerve cells.