Thy-1 expresses two signals for apical localization in epithelial cells.

Recent work has shown that anchoring via glycosyl phosphatidylinositol (GPI) results in apical targeting for a variety of endogenous and transfected plasma membrane proteins expressed in epithelial cells. To further determine the correlation between GPI anchoring and apical localization, we expressed GPI-anchored and secretory forms of Thy-1 in Madin-Darby canine kidney cells by transfection. Native GPI-anchored Thy-1, normally expressed in thymocytes and neurons, was localized to the apical surface. A truncated form of Thy-1, lacking 22 out of 31 hydrophobic amino acids at the COOH-terminus, was also constructed; this deletion blocked attachment of the GPI anchor and resulted in apical secretion of Thy-1. In combination with previous results, our observations indicate that Thy-1 contains apical targeting information in its protein sequence as well as in the GPI anchor.