Neurothelin: Amino Acid Sequence, Cell Surface Dynamics and Actin Colocalization

Neurothelin is a cell surface protein of chicken endothelial cells at the blood-brain barrier and also of pigment epithelial cells forming the blood-eye barrier. Peptide sequencing of affinity-purified neurothelin revealed that it is likely to be identical with the protein called HT7. It belongs to the immunoglobulin superfamily having two extracellular C2-type domains, a membrane spanning region and a cytoplasmic tail. During development neurothelin cell surface localization changed on pigment epithelial cells. In early embryogenesis neurothelin was found preferentially at lateral sites of neighboring epithelial cells, but after hatching, predominantly on basal cell surfaces and on apical microvilli of epithelial cells that contact retinal photoreceptors. Disruption of cell-cell contacts induced a rapid change of neurothelin distribution on the cell surface in vitro as could be shown by confocal laser microscopy. Disintegration of microfilaments by cytochalasin D hampered this specific cell surface rearrangement of neurothelin, whereas depolymerization of microtubules by demecolcine had no effect. In double-labeling experiments neurothelin and F-actin were colocalized. The data suggest that the polarized cell surface distribution of neurothelin is influenced intracellularly by F-actin and extracellularly by cell-cell interactions.