Lysosomes are membrane-bound cytoplasmic organelles involved in intracellular protein degradation. They contain an assortment of soluble acid-dependent hydrolases and a set of highly glycosylated integral membrane proteins. Most of the properties of lysosomes are shared with a group of cell type-specific compartments referred to as 'lysosome-related organelles', which include melanosomes, lytic granules, MHC class II compartments, platelet-dense granules, basophil granules, azurophil granules, and Drosophila pigment granules. In addition to lysosomal proteins, these organelles contain cell type-specific components that are responsible for their specialized functions. Abnormalities in both lysosomes and lysosome-related organelles have been observed in human genetic diseases such as the Chediak-Higashi and Hermansky-Pudlak syndromes, further demonstrating the close relationship between these organelles. Identification of genes mutated in these human diseases, as well as in mouse and Drosophila: pigmentation mutants, is beginning to shed light on the molecular machinery involved in the biogenesis of lysosomes and lysosome-related organelles. (+info)
Defective mononuclear leukocyte chemotaxis in the Chediak-Higashi syndrome of humans, mink, and cattle.
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Chemotaxis of mononuclear leukocytes from humans, mink, and cattle was evaluated in vitro using a morphologic Boyden chamber technique and a new 51-Cr-labeled mononuclear radioassay with a double micropore filter system. Significantly decreased mononuclear leukocyte chemotactic response were noted when human, mink, or cattle Chediak-Higashi cells were tested using autologous serum or endotoxin-activated autolotous serum. A similar Chediak-Higashi mononuclear leukocyte defect was noted in humans when kallikrein or dialyzable transfer factor were used as the chemotactic stimulus. Studies using smaller pore filters in the chemotactic chamber exaggerated the chemotactic defect. Serum from Chediak-Higashi subjects had normal chemotactic activity. Additional studies on the spontaneous (random) locomotion of Chediak-Higashi mononuclear leukocytes revealed normal results when a capillary tube assay system was used, but abnormal results were obtained when a Boyden chamber micropore filter assay was used, demonstrating fundamental differences in these two assays of random locomotion. It is clear from these studies that defective mononuclear leukocyte chemotaxis is another feature of the imparied host defenses in the Chediak-Higashi syndrome that may contribute to the marked susceptibility to pyogenic infections so characteristic of this dease. (+info)
Alterations in erythrocyte membrane lipid and fatty acid composition in Chediak-Higashi syndrome.
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Chediak-Higashi syndrome (CHS) is an autosomal recessive disease characterized by the presence of abnormally large cytoplasmic organelles in all body granule producing cells. The molecular mechanism for this disease is still unknown. Functional disorders in membrane-related processes have been reported. Erythrocyte membranes from four CHS patients and 15 relatives including obligatory heterozygous were studied to examine potential alterations in the lipid and fatty acid profile of erythrocyte membranes associated with this syndrome. Plasma concentrations of cholesterol, triglycerides, phospholipids, and apolipoproteins AI and B100, and the lipid components of very low-, intermediate-, low- and high-density lipoproteins were also determined. CHS erythrocyte membranes were found to be enriched with lipids in relation to protein and to show: (1) an increase in cholesterol and choline-containing phospholipids (sphingomyelin and phosphatidylcholine) that predominate in the outer monolayer, which is higher than the increase in phosphatidylserine and phosphatidylethanolamine, that are chiefly limited to the inner monolayer in normal red blood cells; (2) a relative palmitic acid and saturated fatty acid increase and arachidonic acid and unsaturated fatty acid decrease, this resulting in a lower unsaturation index than controls. Changes in CHS erythrocyte membrane lipids seem to be unrelated to serum lipid disorders as plasma lipid and apolipoprotein concentrations were apparently in the normal range, with the exception of a modest hypertriglyceridemia in patients and relatives and a decreased concentration of HDL cholesterol in patients. These findings indicate that CHS erythrocyte membranes contain an abnormal lipid matrix with which membrane proteins are defectively associated. The anomalous CHS membrane composition can be explained on the postulated effects of the CHS1/Lyst gene. (+info)
Neurobeachin: A protein kinase A-anchoring, beige/Chediak-higashi protein homolog implicated in neuronal membrane traffic.
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We describe the identification and initial characterization of neurobeachin, a neuron-specific multidomain protein of 327 kDa with a high-affinity binding site (K(d), 10 nm) for the type II regulatory subunit of protein kinase A (PKA RII). Neurobeachin is peripherally associated with pleomorphic tubulovesicular endomembranes near the trans sides of Golgi stacks and throughout the cell body and cell processes. It is also found in a subpopulation of synapses, where it is concentrated at the postsynaptic plasma membrane. In live cells, perinuclear neurobeachin is dispersed by brefeldin A (BFA) within 1 min, and in permeabilized cells a recruitment of neurobeachin from cytosol to Golgi-near membranes is stimulated by GTPgammaS and prevented by brefeldin A. Spots of neurobeachin recruitment are close to but distinct from recruitment sites of COP-I, AP-1, and AP-3 coat proteins involved in vesicle budding. These observations indicate that neurobeachin binding to membranes close to the trans-Golgi requires an ADP-ribosylation factor-like GTPase, possibly in association with a novel type of protein coat. A neurobeachin isoform that does not bind RII, beige-like protein (BGL), is expressed in many tissues. Neurobeachin, BGL, and approximately 10 other mammalian gene products share a characteristic C-terminal BEACH-WD40 sequence module, which is also present in gene products of invertebrates, plants, protozoans, and yeasts, thus defining a new protein family. The prototype member of this family of BEACH domain proteins, lysosomal trafficking regulator (LYST), is deficient in genetic defects of protein sorting in lysosome biogenesis (the beige mouse and Chediak-Higashi syndrome). Neurobeachin's subcellular localization, its coat protein-like membrane recruitment, and its sequence similarity to LYST suggest an involvement in neuronal post-Golgi membrane traffic, one of its functions being to recruit protein kinase A to the membranes with which it associates. (+info)
Chediak-Higashi syndrome--a case report.
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Chediak Higashi anomaly is a very rare disorder in which patients suffer frequent and severe pyogenic infections that are secondary to abnormal functions of polymorphonuclear leukocytes, associated with albinism and bleeding tendency. Blume RS and Wolff SM (1972) reported that only 59 cases were diagnosed after the first description of Chediak-Higashi Syndrome in 1943 by Cesar AB (cited by Wintrobe MM Clinical Haematology). As per recent literature available (Internet) last case was reported on 16th July, 1997. (+info)
Lysosomes and melanin granules of the retinal pigment epithelium in a mouse model of the Chediak-Higashi syndrome.
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The origin of giant granules in the retinal pigment epithelium of the beige mouse was investigated with electron microscopy and ultrastructural histochemistry. These granules were found to contain melanin and acid phosphatase. Apparently they arise from fusions of primary lysosomes with melanin granules which are already enlarged from multiple fusions among melanosomes. Therefore, the giant granules are not primary lysosomes, nor are they simply enlarged melanin granules as suspected from light microscopic studies. A deficiency of primary lysosomes in the pigment epithelium results, suggesting a defect in intracellular digestion similar to that found in the leukocytes of Chediak-Higashi patients and several animal models. Affected humans probably have defective digestion in their retinal pigment epithelium also; which could impair the renewal process for rod outer segments. Thus, Chediak-Higashi patients may show an increased susceptibility to light damage due not only to hypopigmentation, but to defective intracellular digestion, as well. (+info)
Identification of a novel lipopolysaccharide-inducible gene with key features of both A kinase anchor proteins and chs1/beige proteins.
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Mutations in chs1/beige result in a deficiency in intracellular transport of vesicles that leads to a generalized immunodeficiency in mice and humans. The function of NK cells, CTL, and granulocytes is impaired by these mutations, indicating that polarized trafficking of vesicles is controlled by CHS1/beige proteins. However, a molecular explanation for this defect has not been identified. Here we describe a novel gene with orthologues in mice, humans, and flies that contains key features of both chs1/beige and A kinase anchor genes. We designate this novel gene lba for LPS-responsive, beige-like anchor gene. Expression of lba is induced after LPS stimulation of B cells and macrophages. In addition, lba is expressed in many other tissues in the body and has three distinct mRNA isoforms that are differentially expressed in various tissues. Strikingly, LBA-green-fluorescent protein (GFP) fusion proteins are localized to vesicles after LPS stimulation. Confocal microscopy indicates this protein is colocalized with the trans-Golgi complex and some lysosomes. Further analysis by immunoelectron microscopy demonstrates that LBA-GFP fusion protein can localize to endoplasmic reticulum, plasma membrane, and endocytosis vesicles in addition to the trans-Golgi complex and lysosomes. We hypothesize that LBA/CHS1/BG proteins function in polarized vesicle trafficking by guiding intracellular vesicles to activated receptor complexes and thus facilitate polarized secretion and/or membrane deposition of immune effector molecules. (+info)
Normal and abnormal secretion by haemopoietic cells.
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The secretory lysosomes found in haemopoietic cells provide a very efficient mechanism for delivering the effector proteins of many immune cells in response to antigen recognition. Although secretion shows some similarities to the secretion of specialized granules in other secretory cell types, some aspects of secretory lysosome release appear to be unique to melanocytes and cells of the haemopoietic lineage. Mast cells and platelets have provided excellent models for studying secretion, but recent advances in characterizing the immunological synapse allow a very fine dissection of the secretory process in T lymphocytes. These studies show that secretory lysosomes are secreted from the centre of the talin ring at the synapse. Proper secretion requires a series of Rab and cytoskeletal elements which play critical roles in the specialized secretion of lysosomes in haemopoietic cells. (+info)