COUP-TFI (Chicken ovalbumin upstream promoter-transcription factor I) regulates cell migration and axogenesis in differentiating P19 embryonal carcinoma cells

The developmental expression patterns of the nuclear orphan receptors COUP- TFs (chicken ovalbumin upstream promoter-transcription factors) have been c orrelated to neurogenesis in several animal species. Nevertheless, the role of COUP-TFs in neurogenesis remains unknown. We have studied the functiona l involvement of COUP-TFI in retinoic acid (RA)-induced neuronal differenti ation of pig embryonal carcinoma cells through two complementary approaches : 1) deregulated expression of COUP-TFI, and 2) inactivation of endogenous COUP-TFs by means of a dominant-negative COUP-TFI mutant. Low levels of wil d-type (wt)COUP-TFI transgene expression did not inhibit neural cell fate a nd primarily enhanced neuron outgrowth from RA-treated P19 aggregates. In c ontrast, high COUP-TFI expression impeded the neuronal differentiation of p ig cells induced with RA, resulting in cell cultures lacking neurons. This morphological effect was correlated to an elevated level of E-cadherin mRNA . The dominant-negative COUP-TFI mutant induced cell packing after RA treat ment and inhibited neurite extension and neuron outgrowth from aggregates. A RGD peptide interference assay indicated that endogenous COUP-TFs could f avor migration of neurons through an integrin-dependent mechanism. Accordin gly, vitronectin mRNA levels were shown to be up-regulated by COUP-TFI by R T-PCR analysis, and COUP-TFI stimulated the mouse vitronectin promoter acti vity in transient transfection assays. Taken together, these data indicate that COUP-TFI is not simply a global repressor of retinoid functions, but s hows a high selectivity for regulating genes involved in cellular adhesion and migration processes that are particularly important for neuronal differ entiation.