trans-Golgi retention of a plasma membrane protein: mutations in the cytoplasmic domain of the asialoglycoprotein receptor subunit H1 result in trans-Golgi retention

To determine whether Hl(A4-33A) is localized in the trans-Gol#, endosomes, or lysosomes, the immunofluorescenee staining pattern of Hl(A4-33A) was compared to that of defined markers. As markers for endosomes and lysosomes we used fluorescein-conjugated dextran internalized for 5-15 rain at 37°C, and the lysosomal membrane protein LAMP-I, respectively. As illustrated in Fig. 5 (A-C), the staining patterns of these markers differed considerably from the labeling of Hl(A4-33A). Trans-Golg~ was visualized using antibodies directed against human galactosyltransferase transiently expressed in MDCK cells, yielding a staining pattern similar to that of Hl(A4-33A) (E). Furthermore, endogenous ~/-adaptin (a TGN marker; D) and the cation-independent mannose-6-phosphate (M6P) receptor (present in the TGN, endosomes, and the plasma membrane; F) were predominantly immunolocalized to a similar j uxtanuclear region as H1(A4-33A).