Partial resialylation of human asialotransferrin type 3 in the rat.

Abstract

After the injection of a small dose (1 jtg/100 g of body weight) of _151-labeled human asialotransferrin type 3 in rats, the radioactivity became rapidly associated with the liver. However, during the ensuing 12 hr a significant fraction of the dose returned to the circulation as protein-bound S5I. The protein released by the liver was indistinguishable by gel filtration from the original preparation and was precipitable by an antiserum to human transferrin. Nevertheless, it no longer bound to the immobilized Gal/GalN-specific lectin from rabbit liver. However, binding could be restored to a large extent by treatment with neuraminidase, indicating that the loss of binding was due to resialylation. Changes in the electrophoretic mobility of asialotransferrin released by the liver showed that resialylation was partial-i.e., it involved the attachment oftwo or three sialyl residues. From analysis by deconvolution of the plasma curve of partially resialylated asialotransferrin it was calculated that the liver "repaired" this way approximately one asialotransferrin molecule out of four. Plasma clearance of partially resialylated asialotransferrin was similar to that of nondesialylated transferrin.A minor portion (15-17%) of human transferrin phenotype C consists of molecules which, after desialylation, bind avidly (1) to the Gal/GalN-specific lectin (2) of the rat liver. We designated this fraction human asialotransferrin type 3 (HAsTf-3; ref.3). Suspended rat hepatocytes internalize HAsTf-3 via the above lectin (4). However, only a small fraction of the intracellular HAsTf-3 undergoes catabolism, whereas the rest is released showing no signs of proteolytic digestion. Cell-associated radioactivity decreases considerably more slowly in the suspension than is the time required for "2I-labeled HAsTf-3 ('"IHAsTf-3) to emerge from the hepatocytes, implying that the ligand is being repeatedly endo-and exocytosed. We termed this movement of HAsTf-3 the diacytic pathway (4) in contradistinction to the well-known lysosomal pathway for other asialoglycoproteins (5). During diacytosis, HAsTf-3 is entrapped in a subcellular particle that is ofa lesser equilibrium density than the vesicle that transports internalized asialoorosomucoid (6).The unusual handling of HAsTf-3 by the hepatocyte raises the question of how the liver ofthe intact rat ultimately disposes of this asialoglycoprotein. Because our earlier experiments in vivo were too short to provide an answer (3), we have now conducted studies lasting up to 12 hr. These showed that rat liver processed small doses of HAsTf-3 slowly in (at least) two ways-namely, catabolism and partial resialylation. Here we report our findings relating to resialylation. MATERIALS AND METHODSMaterials. Na125I, Na1311, 59FeC13, and N-acetyl-D-[6-3H(N)]mannosamine (19 Ci/mmol; 1 Ci = 3.7 X 1010 becquerels) were obtained from New England Nuclear. Neuraminidase from Vibrio cholerae was from GIBCO and neuraminidase from Diplococcus pneumoniae was a gift from M. Lowe and G. Ashwell (National ...

The trans Golgi Network: Sorting at the Exit Site of the Golgi Complex

“…Both transferrin and the transferrin receptor, if desialylated in vitro, seem to be resialylated during membrane recycling (71). This resialylation presumably occurs in the TGN.…”

Endocytic routes to the Golgi apparatus

“…Several studies with different cell types showed the trans Golgi network and Golgi stacks to be visited by plasma membrane constituents and internalised materials (e.g. Antoine et al 1974;Brändli and Simons 1989;Duncan and Kornfeld 1988;Farquhar 1982;Gonatas et al 1975Gonatas et al , 1983Gonatas et al , 1998Kelly 1990, 1992;Hedman et al 1987;Hopkins 1983;Huang and Snider 1983;Jin et al 1989;Kreisel et al 1988;Mukherjee et al 1997;Reaves et al 1993;Recoeczi et al 1982;Roth 1974Roth , 1975van Deurs 1994, 1996;Rogers 1985, 1986;Stoorvogel et al 1988;Trojanowski and Schmidt 1984;van Deurs et al 1988;van Weert et al 1997). Uptake of recycling and internalised molecules into the stacked Golgi cisternae, though rare, has been shown to be possible and considered in connection with reprocessing of membrane glycoproteins and with retrograde routes of toxins (e.g.…”

Localization of galactosyl- and sialyltransferase by immunofluorescence: evidence for different sites.

“…Second: the likely presence of sialyltransferase in the transtubular network may be of importance in the functional definition of this compartment. Regoeczi et al (27) has found partial resialylation of asialotransferrin after endocytosis, a finding which has found recent support by an analysis of the intracellular pathway taken by transferrin after endocytosis. Yamashiro et al (28) reported that transferrin is transported to a para-Golgi compartment whose shape and cytoplasmic location could be compatible with sialyl-and perhaps galactosyltransferase containing subcompartments.…”