Direct binding of occupied urokinase receptor (uPAR) to LDL receptor-related protein is required for endocytosis of uPAR and regulation of cell surface urokinase activity.

Low-density lipoprotein receptor-related protein (LRP) mediates internalization of urokinase:plasminogen activator inhibitor complexes (uPA:PAI-1) and the urokinase receptor (uPAR). Here we investigated whether direct interaction between uPAR, a glycosyl-phosphatidylinositol-anchored protein, and LRP, a transmembrane receptor, is required for clearance of uPA:PAI-1, regeneration of unoccupied uPAR, activation of plasminogen, and the ability of HT1080 cells to invade extracellular matrix. We found that in the absence of uPA:PAI-1, uPAR is randomly distributed along the plasma membrane, whereas uPA:PAI-1 promotes formation of uPAR-LRP complexes and initiates redistribution of occupied uPAR to clathrin-coated pits.

Lectin binding sites on CD34+ human haematopoietic stem cells and lymphocytes from peripheral blood: an ultrastructural post-embedding study.

This study was performed to obtain a better insight into the glycosylation pattern of human CD34+ haematopoietic stem cells and lymphocytes from peripheral blood using an ultrastructural post-embedding technique. Lectins applied were derived from Canavalia ensiformis (Con A), Triticum vulgare (WGA), Lycopersicon esculentum (LEA), Limulus polyphemus (LPA), Ulex europaeus-I (UEA-I), Bauhinia purpurea (BPA), Glycine max (SBA), Helix pomatia (HPA), Arachis hypogaea (PNA) and Erythrina cristagalli (ECA). Our results showed almost identical staining patterns with both CD34+ cells and mature lymphocytes from peripheral blood.

Light and electron microscopic analysis of the central and peripheral nervous systems of acid sphingomyelinase-deficient mice resulting from gene targeting.

The acid sphingomyelinase (aSmase)-deficient mouse line recently generated by gene targeting (Otterbach and Stoffel, 1995) develops a lethal storage disease which is phenotypically comparable to the neurovisceral form of the human sphingomyelinosis, Niemann-Pick disease type A (NPA). This report describes the progressive accumulation of uncatabolized lipid substrates at the cellular and ultrastructural level in different regions of the nervous system of homozygous aSmase-/- mice, including cerebrum, cerebellum, spinal cord, optic nerve and peripheral nerves. We saw a cytoplasmic accumulation of pleomorphic lysosomal structures in cells of all regions under study, most extensively in macrophages, vascular endothelial cells, and also in neuronal perikarya.

Pathology of visceral organs and bone marrow in an acid sphingomyelinase deficient knock-out mouse line, mimicking human Niemann-Pick disease type A. A light and electron microscopic study.

A recently generated aSmase knock-out mouse line develops a lethal storage disease which mimics the neurovisceral form of Niemann-Pick disease in man. In extension to the previously described neuropathological changes, the purpose of this study was to provide a detailed morphological, particularly ultrastructural analysis of the visceral organs of these animals including spleen, liver, intestine, lung, and kidney along with a sequential histological investigation of the bone marrow. Our results showed a progressive lysosomal storage as indicated by an increasing amount of foam cells in the bone marrow with age, extending to all visceral organs.

Distribution of lectin binding sites in human bone marrow. Identification by use of an ultrastructural postembedding technique.

The purpose of this ultrastructural study was to detect various carbohydrate residues on mature elements of the major human haematopoietic cell lines (granulopoiesis, erythropoiesis and megakaryopoiesis), sinus endothelium and plasma cells under comparable experimental conditions. Marrow specimens were processed according to a modified postembedding technique with Unicryl as embedding resin. A broad panel of 10 digoxigenin (dig)-conjugated lectins was applied for staining and specificity was evaluated by incubation with their corresponding inhibitory sugars.