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

This modification did not alter the intracellular distribution. Double labeling of MDCK cells cotransfected with Hl(A4-33A) myc and human galactosyltransferase cDNAs showed that the tubular structures characteristic for Hl(A4-33A) were almost indistinguishable from the structures labeled with anti-galactosyltransferase antibody (Fig. 6, A and B ). In the stable cell line M1A, the structures labeled with the HI-specific antibody also overlapped with the or- This localization is supported by the effect of agents known to perturb specific organelles. Treatment of MIA cells with okadaic acid or nocodazole, which are known to induce fragmentation of the Golgi apparatus (Lucocq et al., 1991; Ho et al., 1989b; Turner and Tartakoff, 1989 ), re-suited in redistribution of Hl(A4-33A) staining throughout the cytoplasm (not shown). The fungal metabolite brefeldin A was recently shown to cause the formation of tubules of the TGN in MDCK cells, while the medial-Golgi stacks were unaffected (Wagner et al., 1994) . Under similar conditions, we observed the appearance of thin tubules containing Hl(A4-33A) as well as galactosyltransferase extending from the juxtanuclear region into the cytoplasm (not shown). In contrast, the distribution of Hl(A4-33A) was not affected by chloroquine, which causes lysosomal proteins to be depleted from lysosomes (Lippincott-Schwartz and Fambrough, 1987) .