Retinoic acid enhances adhesiveness, laminin and integrin β1 synthesis, and retinoic acid receptor expression in F9 teratocarcinoma cells

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Abstract
The teratocarcinoma‐derived F9 cells respond to retinoic acid (RA) and RA plus dibutyrylcyclic adenosine monophosphate (dcAMP) by differentiating into endoderm cells, which elaborate a laminin and type IV collagen‐rich matrix. We found that the induction of differentiation is accompanied by a small but consistent increase in cell adhesiveness to a variety of substrates, including laminin. Therefore we investigated biochemical mechanisms involved in this phenomenon. Endoglycosidase treatment showed that laminin contains complex and hybrid oligosaccharide structures. RA enhanced general biosynthesis of laminin without a specific increase in galactose incorporation: this sugar was mainly in polylactosamine structures in the A chain of laminin and as terminal galactose α 1,3 galactose in the B chain. Laminin receptor analysis showed that RA decreased laminin binding protein‐37 (LBP‐37) but increased the amount of β1 integrin, suggesting the involvement of β1 integrin in the attachment process. Northern blot analysis showed increased expression of retinoid receptors within hours of RA exposure. These studies demonstrate that RA increases cell to substrate interactions by increasing the biosynthesis of laminin and β1 integrin. These effects are most likely subsequent to the RA‐induced biosynthesis of the retinoid receptors.