In contrast, Na+/K+-ATPase maintains its basolateral localization in Muc4/SMC-transfected cells, indicating that the translocation of ErbB2 is not the result of depolarization of the cells.     ///    Expression of apical Muc4/SMC in these cells by transient transfection results in the localization of the ErbB2 at the apical surface.     ///    "Because Muc4/SMC is found at the apical surfaces of polarized epithelial cells and ErbB2 is often basolateral, the question arises as to whether these components become associated in polarized cells. "    ///    "A potential physiological role for the apical localization of ErbB2 is indicated by the fact that ErbB2 phosphorylated at tyrosine 1248 is found predominantly in Muc4/SMC-transfected cells, but not in untransfected cells, and is co-localized with the apical Muc4/SMC. "    ///    "The ability of Muc4/SMC to alter the localization of ErbB2, particularly a phosphorylated form of it, in epithelial cells, suggests that it has an important role in regulating ErbB2 signaling.. "    ///    Two-color confocal microscopy indicated that ErbB2 is colocalized with Muc4/SMC in the transfected cells but not in untransfected cells in the same culture. 