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Biomedical subjects

M S Bretscher

Publications and source records attributed to M S Bretscher.

At least 19 recordsLinked to original sources
PubMed1992

Cells can use their transferrin receptors for locomotion.

Cells of the B lymphoblastoid cell line JY attach to substrata made of antibodies to the transferrin receptor. Many of these attached cells migrate considerable distances. JY cells also attach to an anti-integrin substratum (anti LFA-1), but on this surface they do not migrate. These results suggest that a circulating receptor--the transferrin receptor--can be used for locomotory purposes, whereas LFA-1, which is not endocytosed in these cells, cannot be used for locomotion. This indicates that the endocytotic cycle can drive cell locomotion.

B-Lymphocytes↗
PubMed1992

Circulating integrins: alpha 5 beta 1, alpha 6 beta 4 and Mac-1, but not alpha 3 beta 1, alpha 4 beta 1 or LFA-1.

The alpha 5 beta 1, alpha 6 beta 4 and Mac-1 integrins all participate in the endocytotic cycle. By contrast, alpha 3 beta 1, alpha 4 beta 1 and LFA-1 do so much more slowly, or not at all, in the cell lines examined. This indicates that the alpha-chains appear to determine whether an integrin cycles or not, and that alpha 5 beta 1, alpha 6 beta 4 and Mac-1 can be brought to the leading edge of a moving cell by endocytosis and recycling.

Animals↗
PubMed1989

Endocytosis and recycling of the fibronectin receptor in CHO cells.

An anti-fibronectin receptor monoclonal antibody preferentially labels the leading edges of freshly plated CHO fibroblasts, suggesting that this receptor circulates through the endocytic cycle. Using a new labelling reagent, I show that this receptor is indeed endocytosed at 37 degrees C and then returned to the cell surface. These findings imply that fibronectin receptors are recirculated to the leading edge of a motile cell by the endocytic cycle, and establish that the processes of endocytosis/exocytosis and cell locomotion are intimately linked.

Animals↗
PubMed1989

Distinct endocytotic pathways in epidermal growth factor-stimulated human carcinoma A431 cells.

Addition of EGF to human epidermoid carcinoma A431 cells increases the rate of fluid-phase pinocytosis 6-10-fold as measured by horseradish peroxidase uptake (Haigler, H.T., J. A. McKanna, and S. Cohen. 1979. J. Cell Biol. 83:82-90). We show here that in the absence of extracellular Na+ or in the presence of amiloride the stimulation of pinocytosis by EGF is substantially reduced. Amiloride had no effect on the endocytosis of EGF itself or of transferrin, demonstrating that the receptor-mediated endocytotic pathway operated normally under conditions that blocked stimulated pinocytosis. Amiloride blocked EGF-stimulated pinocytosis in both HCO3(-)-containing and HCO3(-)-free media. The EGF-stimulated pinocytotic activity can frequently be localized to areas of the cell where membrane spreading and ruffling are taking place. These results demonstrate that (a) EGF induces a distinct amiloride-sensitive endocytotic pathway on A431 cells; (b) occupied EGF receptors do not utilize this pathway for their own entry; (c) endocytosis of occupied EGF receptors is not in itself sufficient to stimulate pinocytosis.

Amiloride↗
PubMed1988

A new method for detecting endocytosed proteins.

A new reagent, DPSgt, is described which has been designed to label cell surface proteins at 0 degree C. The reagent is easily made; it is water soluble and contains a reactive impermeant ester at one end, a tyrosine which can be radioiodinated at the other, and a disulphide in-between. The label can be removed from cells by cleaving the disulphide linkage in it with glutathione at 0 degree C. When cells are warmed to 37 degrees C between labelling and reduction, labelled proteins which are endocytosed acquire resistance to reduction. This provides a simple way of measuring the endocytosis of surface proteins. The intracellular pools of transferrin and LDL receptors in K562 cells and fibroblasts have been estimated. The results indicate that intracellular receptors are in non-reducing compartments, and that uptake of average cell surface (by non-coated pit processes) in K562 cells is small.

Cell Line↗
PubMed1985

Heparan sulphate proteoglycans and their polypeptide chains from BHK cells.

A simple procedure for partially purifying membrane-associated 35S-labelled proteoglycans from BHK cells is described. The labelled molecules are mainly heparan sulphate glycoproteins, and their average half-lives are approximately 3 h in culture. A new method, which depends on the degradation of heparan sulphate by nitrous acid at low pH, has been devised to determine the size of the polypeptide moiety of this class of molecule. The BHK cell heparan sulphate proteoglycans contain three main polypeptides having mol. wts. of approximately 65, 85 and 120 kd.

Animals↗
PubMed1985

The morphology of endosomes in giant HeLa cells.

The endosomal compartment of giant HeLa cells was labelled with a transferrin-horse radish peroxidase (HRP) conjugate. Serial thin sections from the leading lamella of a cell are presented; they show that the endosomal compartment contains a tubular system connected to vesicular structures. In addition, small (approximately 50 nm) coated vesicles are seen in the leading lamella.

Cell Membrane↗
PubMed1983

Distribution of ferritin receptors and coated pits on giant HeLa cells.

HeLa cells bind horse spleen ferritin when the two are incubated at 0 degrees C. Since the majority of this bound ferritin is located in coated pits, we conclude that the ferritin binds to a specific receptor which takes part in an endocytic cycle. When substrate-attached and well-spread giant HeLa cells are briefly labelled at 0 degrees C with ferritin, ferritin particles are found to be concentrated towards the cell periphery, where they exist largely outside coated pits. This peripheral concentration is a property of circulating (and not just newly synthesized) receptors because it is not affected by prior incubation of giant cells in cycloheximide. However, coated pits are themselves roughly uniformly distributed over the surface of these cells. These results provide evidence that the membrane internalised by coated pits on these cells is returned to the cell surface at the leading edge of the cell. Because of this separation of the sites of endocytosis and exocytosis, a flow of membrane must occur across the cell surface. This flow is composed of lipid plus receptors. The implications of this for capping and for cell spreading are discussed.

Biological Transport, Active↗
PubMed1979

Capping of exogenous Forssman glycolipid on cells.

When motile cells are incubated with Forssman glycolipid, the antigen is incorporated into the cells' plasma membranes. If cross-linked by antibody, the patched glycolipids cap. This process is sensitive to those drugs that are known to inhibit capping of protein antigens. The results support a flow mechanism for capping.

Animals↗