Chediak-Higashi syndrome is not due to a defect in microtubule-based lysosomal mobility

The lysosomal trafficking regulator "LYST": an 80-year traffic jam

Lysosomes and lysosome related organelles (LROs) are dynamic organelles at the intersection of various pathways involved in maintaining cellular hemostasis and regulating cellular functions. Vesicle trafficking of lysosomes and LROs are critical to maintain their functions. The lysosomal trafficking regulator (LYST) is an elusive protein important for the regulation of membrane dynamics and intracellular trafficking of lysosomes and LROs. Mutations to the LYST gene result in Chédiak-Higashi syndrome, an autosomal recessive immunodeficiency characterized by defective granule exocytosis, cytotoxicity, etc. Despite eight decades passing since its initial discovery, a comprehensive understanding of LYST's function in cellular biology remains unresolved. Accumulating evidence suggests that dysregulation of LYST function also manifests in other disease states. Here, we review the available literature to consolidate available scientific endeavors in relation to LYST and discuss its relevance for immunomodulatory therapies, regenerative medicine and cancer applications.

LYST deficiency impairs autophagic lysosome reformation in neurons and alters lysosome number and size

Chediak-Higashi syndrome (CHS) is a rare, autosomal recessive disorder caused by biallelic mutations in the lysosomal trafficking regulator (LYST) gene. Even though enlarged lysosomes and/or lysosome-related organelles (LROs) are the typical cellular hallmarks of CHS, they have not been investigated in human neuronal models. Moreover, how and why the loss of LYST function causes a lysosome phenotype in cells has not been elucidated. We report that the LYST-deficient human neuronal model exhibits lysosome depletion accompanied by hyperelongated tubules extruding from enlarged autolysosomes. These results have also been recapitulated in neurons differentiated from CHS patients' induced pluripotent stem cells (iPSCs), validating our model system. We propose that LYST ensures the correct fission/scission of the autolysosome tubules during autophagic lysosome reformation (ALR), a crucial process to restore the number of free lysosomes after autophagy. We further demonstrate that LYST is recruited to the lysosome membrane, likely to facilitate the fission of autolysosome tubules. Together, our results highlight the key role of LYST in maintaining lysosomal homeostasis following autophagy and suggest that ALR dysregulation is likely associated with the neurodegenerative CHS phenotype.

In Vitro Disease Modeling of Hermansky-Pudlak Syndrome Type 2 Using Human Induced Pluripotent Stem Cell-Derived Alveolar Organoids

It has been challenging to generate in vitro models of alveolar lung diseases, as the stable culture of alveolar type 2 (AT2) cells has been difficult. Methods of generating and expanding AT2 cells derived from induced pluripotent stem cells (iPSCs) have been established and are expected to be applicable to disease modeling. Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder characterized by dysfunction of lysosome-related organelles, such as lamellar bodies (LBs), in AT2 cells. From an HPS type 2 (HPS2) patient, we established disease-specific iPSCs (HPS2-iPSCs) and their gene-corrected counterparts. By live cell imaging, the LB dynamics were visualized and altered distribution, enlargement, and impaired secretion of LBs were demonstrated in HPS2-iPSC-derived AT2 cells. These findings provide insight into the AT2 dysfunction in HPS patients and support the potential use of human iPSC-derived AT2 cells for future research on alveolar lung diseases.

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HPS2-iPSCs and cHPS2-iPSCs were generated from HPS2 patient fibroblasts

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Anti-NaPi2b antibody was useful for isolating AT2 cells from human lung and AOs

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The enlargement and abnormal distribution of LBs were observed in HPS2-AOs

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Impaired surfactant secretion was demonstrated in HPS2-AOs

Mon1a protein acts in trafficking through the secretory apparatus

Mon1a was originally identified as a modifier gene of vesicular traffic, as a mutant Mon1a allele resulted in increased localization of cell surface proteins, whereas reduced levels of Mon1a showed decreased secretory activity. Here we show that Mon1a affects different steps in the secretory pathway including endoplasmic reticulum-to-Golgi traffic. siRNA-dependent reduction of Mon1a levels resulted in a delay in the reformation of the Golgi apparatus after Brefeldin A treatment. Endoglycosidase H treatment of ts045VSVG-GFP confirmed that knockdown of Mon1a delayed endoplasmic reticulum-to-Golgi trafficking. Reductions in Mon1a also resulted in delayed trafficking from Golgi to the plasma membrane. Immunoprecipitation and mass spectrometry analysis showed that Mon1a associates with dynein intermediate chain. Reductions in Mon1a or dynein altered steady state Golgi morphology. Reductions in Mon1a delayed formation of ERGIC-53-positive vesicles, whereas reductions in dynein did not affect vesicle formation. These data provide strong evidence for a role for Mon1a in anterograde trafficking through the secretory apparatus.

The enlarged lysosomes in beige j cells result from decreased lysosome fission and not increased lysosome fusion

Chediak-Higashi syndrome is an autosomal recessive disorder that affects vesicle morphology. The Chs1/Lyst protein is a member of the BEige And CHediak family of proteins. The absence of Chs1/Lyst gives rise to enlarged lysosomes. Lysosome size is regulated by a balance between vesicle fusion and fission and can be reversibly altered by acidifying the cytoplasm using Acetate Ringer's or by incubating with the drug vacuolin-1. We took advantage of these procedures to determine rates of lysosome fusion and fission in the presence or absence of Chs1/Lyst. Here, we show by microscopy, flow cytometry and in vitro fusion that the absence of the Chs1/Lyst protein does not increase the rate of lysosome fusion. Rather, our data indicate that loss of this protein decreases the rate of lysosome fission. We further show that overexpression of the Chs1/Lyst protein gives rise to a faster rate of lysosome fission. These results indicate that Chs1/Lyst regulates lysosome size by affecting fission.

Defective surfactant secretion in a mouse model of Hermansky-Pudlak syndrome

Hermansky-Pudlak syndrome (HPS) in humans represents a family of disorders of lysosome-related organelle biogenesis associated with severe, progressive pulmonary disease. Human case reports and a mouse model of HPS, the pale ear/pearl mouse (ep/pe), exhibit giant lamellar bodies (GLB) in type II alveolar epithelial cells. We examined surfactant proteins and phospholipid from ep/pe mice to elucidate the process of GLB formation. The 2.8-fold enrichment of tissue phospholipids in ep/pe mice resulted from accumulation from birth through adulthood. Tissue surfactant protein (SP)-B and -C were increased in adult ep/pe mice compared with wild-type mice (WT), whereas SP-A and -D were not different. Large aggregate surfactant (LA) from adult ep/pe mice had decreased phospholipid, SP-B, and SP-C, with no differences in SP-A and -D compared with WT. Although LA from ep/pe animals exhibited an increased total protein-to-total phospholipid ratio compared with WT, surface tension was not compromised. Phospholipid secretion from isolated type II cells showed that basal and stimulated secretion from ep/pe cells were approximately 50% of WT cells. Together, our data indicate that GLB formation is not associated with abnormal trafficking or recycling of surfactant material. Instead, impaired secretion is an important component of GLB formation in ep/pe mice.

Mammalian class E Vps proteins, SBP1 and mVps2/CHMP2A, interact with and regulate the function of an AAA-ATPase SKD1/Vps4B

SKD1 belongs to the AAA-ATPase family and is one of the mammalian class E Vps (vacuolar protein sorting) proteins. Previously we have reported that the overexpression of an ATPase activity-deficient form of SKD1 (suppressor of potassium transport growth defect), SKD1(E235Q), leads the perturbation of membrane transport through endosomes and lysosomes, however, the molecular mechanism behind the action of SKD1 is poorly understood. We have identified two SKD1-binding proteins, SBP1 and mVps2, by yeast two-hybrid screening and we assign them as mammalian class E Vps proteins. The primary sequence of SBP1 indicates 22.5% identity with that of Vta1p from Saccharomyces cerevisiae, which was recently identified as a novel class E Vps protein binding to Vps4p. In fact, SBP1 binds directly to SKD1 through its C-terminal region (198-309). Endogenous SBP1 is exclusively localized to cytosol, however it is redirected to an aberrant endosomal structure, the E235Q compartment, in the cells expressing SKD1(E235Q). The ATPase activity of SKD1 regulates both the membrane association of, and assembly of, a large hetero-oligomer protein complex, containing SBP1, which is potentially involved in membrane transport through endosomes and lysosomes. The N-terminal half (1-157) of human SBP1 is identical to lyst-interacting protein 5 and intriguingly, SKD1 ATPase activity significantly influences the membrane association of lyst protein. The SKD1-SBP1 complex, together with lyst protein, may function in endosomal membrane transport. A primary sequence of mVps2, a mouse homologue of human CHMP2A/BC-2, indicates 44.4% identity with Vps2p/Did4p/Chm2p from Saccharomyces cerevisiae. mVps2 also interacts with SKD1 and is localized to the E235Q compartment. Intriguingly, the N-terminal coiled-coil region of mVps2 is required for the formation of the E235Q compartment but not for binding to SKD1. We propose that both SBP1 and mVps2 regulate SKD1 function in mammalian cells.

Use of expression constructs to dissect the functional domains of the CHS/beige protein: identification of multiple phenotypes

The Chediak-Higashi Syndrome (CHS) and the orthologous murine disorder beige are characterized at the cellular level by the presence of giant lysosomes. The CHS1/Beige protein is a 3787 amino acid protein of unknown function. To determine functional domains of the CHS1/Beige protein, we generated truncated constructs of the gene/protein. These truncated proteins were transiently expressed in Cos-7 or HeLa cells and their effect on membrane trafficking was examined. Beige is apparently a cytosolic protein, as are most transiently expressed truncated Beige constructs. Expression of the Beige construct FM (amino acids 1-2037) in wild-type cells led to enlarged lysosomes. Similarly, expression of a 5.5-kb region (amino acids 2035-3787) of the carboxyl terminal of Beige (22B) also resulted in enlarged lysosomes. Expression of FM solely affected lysosome size, whereas expression of 22B led to alterations in lysosome size, changes in the Golgi and eventually cell death. The two constructs could be used to further dissect phenotypes resulting from loss of the Beige protein. CHS or beigej fibroblasts show an absence of nuclear staining using a monoclonal antibody directed against phosphatidylinositol 4,5 bisphosphate [PtdIns(4,5) P2]. Transformation of beige j fibroblasts with a YAC containing the full-length Beige gene resulted in the normalization of lysosome size and nuclear PtdIns(4,5)P2 staining. Expression of the carboxyl dominant negative construct 22B led to loss of nuclear PtdIns(4,5)P2 staining. Expression of the FM dominant negative clone did not alter nuclear PtdIns(4,5) P2 localization. These results suggest that the Beige protein interacts with at least two different partners and that the Beige protein affects cellular events, such as nuclear PtdIns(4,5)P2 localization, in addition to lysosome size.

Chediak-Higashi Syndrome: a rare disorder of lysosomes and lysosome related organelles

Chediak-Higashi Syndrome (CHS) is a rare autosomal recessive disorder characterized by severe immunologic defects including recurrent bacterial infections, impaired chemotaxis and abnormal natural killer (NK) cell function. Patients with this syndrome exhibit other symptoms such as an associated lymphoproliferative syndrome, bleeding tendencies, partial albinism and peripheral neuropathies. The classic diagnostic feature of CHS is the presence of huge lysosomes and cytoplasmic granules within cells. Similar defects are found in other mammals, the most well studied being the beige mouse and Aleutian mink. A positional cloning approach resulted in the identification of the Beige gene on chromosome 13 in mice and the CHS1/LYST gene on chromosome 1 in humans. The protein encoded by this gene is 3801 amino acids and is highly conserved throughout evolution. The identification of CHS1/Beige has defined a family of genes containing a common BEACH motif. The function of these proteins in vesicular trafficking remains unknown.

Expression of constructs of the neuronal isoform of myosin-Va interferes with the distribution of melanosomes and other vesicles in melanoma cells

Myosin-Va has been implicated in melanosome translocation, but the exact molecular mechanisms underlying this function are not known. In the dilute, S91 melanoma cells, melanosomes move to the cell periphery but do not accumulate in the tips of dendrites as occurs in wild-type B16 melanocytes; rather, they return and accumulate primarily at the pericentrosomal region in a microtubule-dependent manner. Expression of the full-length neuronal isoform of myosin-Va in S91 cells causes melanosomes to disperse, occupying a cellular area approximately twice that observed in non-transfected cells, suggesting a partial rescue of the dilute phenotype. Overexpression of the full tail domain in S91 cells is not sufficient to induce melanosome dispersion, rather it causes melanosomal clumping. Overexpression of the head and head-neck domains of myosin-Va in B16 cells does not alter the melanosome distribution. However, overexpression of the full tail domain in these cells induces melanosome aggregation and the appearance of tail-associated, aggregated particles or vesicular structures that exhibit variable degrees of staining for melanosomal and Golgi beta-COP markers, as well as colocalization with the endogenous myosin-Va. Altogether, the present data suggest that myosin-Va plays a role in regulating the direction of microtubule-dependent melanosome translocation, in addition to promoting the capture of melanosomes at the cell periphery as suggested by previous studies. These studies also reinforce the notion that myosin-V has a broader function in melanocytes by acting on vesicular targeting or intracellular protein trafficking.

Clinical, molecular, and cell biological aspects of Chediak-Higashi syndrome

Chediak-Higashi syndrome (CHS) is a rare autosomal recessive disorder characterized by variable degrees of oculocutaneous albinism, easy bruisability, and bleeding as a result of deficient platelet dense bodies, and recurrent infections, with neutropenia, impaired chemotaxis and bactericidal activity, and abnormal NK cell function. Neurologic involvement is variable, but often includes peripheral neuropathy. Most patients also undergo an "accelerated phase," which is a nonmalignant lymphohistiocytic infiltration of multiple organs resembling lymphoma. Death often occurs in the first decade from infection, bleeding, or development of the accelerated phase. The hallmark of CHS is the presence of huge cytoplasmic granules in circulating granulocytes and many other cell types. These granules are peroxidase-positive and contain lysosomal enzymes, suggesting that they are giant lysosomes or, in the case of melanocytes, giant melanosomes. The underlying defect in CHS remains elusive, but the disorder can be considered a model for defects in vesicle formation, fusion, or trafficking. Because the beige mouse demonstrates many characteristics similar to those of human CHS patients, including dilution of coat color, recurrent infections, and the presence of giant granules, it is considered the animal homologue of CHS. The beige gene, Lyst, was mapped and sequenced in 1996, prompting identification of the human LYST gene on chromosome 1q42. Lyst and LYST show 86.5% sequence homology. LYST encodes a 429 kDa protein with a function that remains unknown, but the source of extensive speculation among students of cell biology.

Opposing motor activities of dynein and kinesin determine retention and transport of MHC class II-containing compartments

MHC class II molecules exert their function at the cell surface by presenting to T cells antigenic fragments that are generated in the endosomal pathway. The class II molecules are targetted to early lysosomal structures, termed MIIC, where they interact with antigenic fragments and are subsequently transported to the cell surface. We previously visualised vesicular transport of MHC class II-containing early lysosomes from the microtubule organising centre (MTOC) region towards the cell surface in living cells. Here we show that the MIIC move bidirectionally in a ‘stop-and-go’ fashion. Overexpression of a motor head-deleted kinesin inhibited MIIC motility, showing that kinesin is the motor that drives its plus end transport towards the cell periphery. Cytoplasmic dynein mediates the return of vesicles to the MTOC area and effectively retains the vesicles at this location, as assessed by inactivation of dynein by overexpression of dynamitin. Our data suggest a retention mechanism that determines the perinuclear accumulation of MIIC, which is the result of dynein activity being superior over kinesin activity. The bidirectional nature of MIIC movement is the result of both kinesin and dynein acting reciprocally on the MIIC during its transport. The motors may be the ultimate targets of regulatory kinases since the protein kinase inhibitor staurosporine induces a massive release of lysosomal vesicles from the MTOC region that is morphologically similar to that observed after inactivation of the dynein motor.

Deficient peptide loading and MHC class II endosomal sorting in a human genetic immunodeficiency disease: the Chediak-Higashi syndrome

The Chediak-Higashi syndrome (CHS) is a human recessive autosomal disease caused by mutations in a single gene encoding a protein of unknown function, called lysosomal-trafficking regulator. All cells in CHS patients bear enlarged lysosomes. In addition, T- and natural killer cell cytotoxicity is defective in these patients, causing severe immunodeficiencies. We have analyzed major histocompatibility complex class II functions and intracellular transport in Epstein Barr Virus-transformed B cells from CHS patients. Peptide loading onto major histocompatibility complex class II molecules and antigen presentation are strongly delayed these cells. A detailed electron microscopy analysis of endocytic compartments revealed that only lysosomal multilaminar compartments are enlarged (reaching 1-2 micron), whereas late multivesicular endosomes have normal size and morphology. In contrast to giant multilaminar compartments that bear most of the usual lysosomal markers in these cells (HLA-DR, HLA-DM, Lamp-1, CD63, etc.), multivesicular late endosomes displayed reduced levels of all these molecules, suggesting a defect in transport from the trans-Golgi network and/or early endosomes into late multivesicular endosomes. Further insight into a possible mechanism of this transport defect came from immunolocalizing the lysosomal trafficking regulator protein, as antibodies directed to a peptide from its COOH terminal domain decorated punctated structures partially aligned along microtubules. These results suggest that the product of the Lyst gene is required for sorting endosomal resident proteins into late multivesicular endosomes by a mechanism involving microtubules.

L is for lytic granules: lysosomes that kill

CTL are important cells in the immune system which are able to recognise and directly destroy virally infected, tumorigenic or foreign cells. The proteins which mediate this destruction are packaged into specialised secretory granules, termed lytic granules, which are secreted in response to target cell recognition. Curiously these specialised secretory granules also contain all the lysosomal hydrolases, and in CTL the lytic granules serve two separate functions: as a lysosome within the cell, and as a secretory granule when a target cell is recognised. These "secretory lysosomes", which serve important roles in both protein degradation within the cells as well as regulated secretion of proteins from the cells, are also found in other cell types, all of which are derived from the hemopoietic lineage. This observation raises the possibility that cells of the hemopoietic lineage possess specialised sorting and secretory mechanisms which allow the lysosomes to be used as secretory organelles. Studies on Chediak Higashi syndrome support this idea, since in this naturally occurring genetic mutation, cells with secretory lysosomes are unable to secrete their granules while other conventional secretory cells are able to do so. Further studies on the mechanisms which regulate secretion of lytic proteins from CTL should identify the proteins involved in this unusual secretory pathway. Some aspects of the differences between conventional and "secretory" lysosomes remain unresolved. How the biogenesis of the secretory lysosome differs from that of a conventional secretory granule is unclear. While conventional secretory cells sort proteins destined for the granule by a selective condensation in the TGN, the secretory lysosomes seem to use a combination of lysosomal and other sorting signals. Our preliminary studies suggest that haemopoietic cells possess specialised sorting mechanisms which allow the correct sorting of the secreted products to the lysosome, and that these signals are different from those found in conventional secretory (e.g. neurosecretory) cells. This finding and the observation that fibroblast lysosomes can undergo calcium-mediated exocytosis suggests that the unusual secretory system found in haemopoietic cells may be a result of specialised sorting mechanisms in these cells. In this case the Chediak lesion may turn out to be a sorting defect.

The Beige/Chediak-Higashi syndrome gene encodes a widely expressed cytosolic protein

The human autosomal recessive disorder Chediak-Higashi syndrome and its murine homologue beige are associated with the formation of giant lysosomes that cluster near the perinuclear region of cells. We prepared a polyclonal antiserum against a glutathione S-transferase-Beige fusion protein and demonstrated by Western analysis that the beige gene encodes a protein of 400 kDa that is expressed in cultured murine fibroblasts as well as most mouse tissues. The protein was not detected in either cultured fibroblasts or mouse tissues from two different beige mutants. Cultured fibroblasts transformed with multiple copies of yeast artificial chromosomes that contain the full-length beige gene showed much higher levels of Beige protein than either wild type fibroblasts or mouse tissues. Subcellular fractionation experiments demonstrated that the Beige protein was cytosolic and, under the conditions of isolation, had no measurable membrane association. Cultured mouse fibroblasts in which the Beige protein was overexpressed had smaller than normal lysosomes that were more peripherally distributed than in control cells. These findings, coupled with earlier published results, suggest that the Beige protein regulates lysosomal fission.

Homotypic lysosome fusion in macrophages: analysis using an in vitro assay

Lysosomes are dynamic structures capable of fusing with endosomes as well as other lysosomes. We examined the biochemical requirements for homotypic lysosome fusion in vitro using lysosomes obtained from rabbit alveolar macrophages or the cultured macrophage-like cell line, J774E. The in vitro assay measures the formation of a biotinylated HRP-avidin conjugate, in which biotinylated HRP and avidin were accumulated in lysosomes by receptor-mediated endocytosis. We determined that lysosome fusion in vitro was time- and temperature-dependent and required ATP and an N-ethylmaleimide (NEM)-sensitive factor from cytosol. The NEM-sensitive factor was NSF as purified recombinant NSF could completely replace cytosol in the fusion assay whereas a dominant-negative mutant NSF inhibited fusion. Fusion in vitro was extensive; up to 30% of purified macrophage lysosomes were capable of self-fusion. Addition of GTPgammas to the in vitro assay inhibited fusion in a concentration-dependent manner. Purified GDP-dissociation inhibitor inhibited homotypic lysosome fusion suggesting the involvement of rabs. Fusion was also inhibited by the heterotrimeric G protein activator mastoparan, but not by its inactive analogue Mas-17. Pertussis toxin, a Galphai activator, inhibited in vitro lysosome fusion whereas cholera toxin, a Galphas activator did not inhibit the fusion reaction. Addition of agents that either promoted or disrupted microtubule function had little effect on either the extent or rate of lysosome fusion. The high value of homotypic fusion was supported by in vivo experiments examining lysosome fusion in heterokaryons formed between cells containing fluorescently labeled lysosomes. In both macrophages and J774E cells, almost complete mixing of the lysosome labels was observed within 1-3 h of UV sendai-mediated cell fusion. These studies provide a model system for identifying the components required for lysosome fusion.

The biogenesis of lysosomes: is it a kiss and run, continuous fusion and fission process?

Molecules are transferred to lysosomes, the major, acid pH, digestive compartment in eukaryotic cells, by a complex series of pathways that converge at a late endosome/prelysosomal compartment. Here, we discuss the relationship between this compartment and the lysosome. We propose that lysosomes are maintained within cells by a repeated series of kiss and run, transient fusion and fission processes with the late endosome/prelysosome compartment. Directionality to these processes may be conferred by pH gradients and retrieval mechanisms. The future challenge in testing this and any other proposed hypothesis for lysosomal biogenesis will be the establishment of molecular mechanisms.

The late chlamydial inclusion membrane is not derived from the endocytic pathway and is relatively deficient in host proteins

Chlamydiae are obligate intracellular parasites which multiply within infected cells in a membrane-bound structure termed an inclusion. Newly internalized bacteria are surrounded by host plasma membrane; however, the source of membrane for the expansion of the inclusion is unknown. To determine if the membrane for the mature inclusion was derived by fusion with cellular organelles, we stained infected cells with fluorescent or electron-dense markers specific for organelles and examined inclusions for those markers. We observed no evidence for the presence of endoplasmic reticulum, Golgi, late endosomal, or lysosomal proteins in the inclusion. These data suggest that the expansion of the inclusion membrane, beginning 24 h postinoculation, does not occur by the addition of host proteins resulting from either de novo host synthesis or by fusion with preexisting membranes. To determine the source of the expanding inclusion membrane, antibodies were produced against isolated membranes from Chlamydia-infected mouse cells. The antibodies were demonstrated to be solely against Chlamydia-specified proteins by both immunoprecipitation of [35S]methionine-labeled extracts and Western blotting (immunoblotting). Techniques were used to semipermeabilize Chlamydia-infected cells without disrupting the permeability of the inclusion, allowing antibodies access to the outer surface of the inclusion membrane. Immunofluorescent staining demonstrated a ring-like fluorescence around inclusions in semipermeabilized cells, whereas Triton X-100-permeabilized cells showed staining throughout the inclusion. These studies demonstrate that the inclusion membrane is made up, in part, of Chlamydia-specified proteins and not of existing host membrane proteins.

Granulocytes from chronic myeloid leukemia (CML) patients show differential response to different chemoattractants

Binding of chemoattractant to polymorphonuclear leukocytes (PMNL) triggers a series of events like polymerization of actin and tubulin, orientation of cells, chemotaxis, increase in fluid pinocytosis and phagocytosis, and stimulation of microbicidal pathways which includes lysosomal degranulation and generation of reactive oxygen species. Earlier studies from our laboratory have shown that stimulation of chemotaxis, fluid pinocytosis, and actin polymerization of CML PMNL in response to a synthetic chemotactic peptide formyl-methionyl-leucyl-phenylalanine (fMLP) is significantly lower than that in normal PMNL. It is not known whether this lower response of CML PMNL to fMLP is a global phenomenon involving different chemoattractant receptors or is restricted to the fMLP pathway. We have evaluated chemoattractant induced degranulation process in normal and CML PMNL to fMLP, platelet activating factor (PAF), leukotriene B4 (LTB4), and an analogue of fMLP viz formyl-methionine-1 aminocyclooctane 1 carboxylic acid-phenylalanine-O-methionine (FACC8) using release of lysozyme as a parameter. We find that after stimulation with fMLP and FACC8, the mean percent release of lysozyme was significantly lower in CML PMNL as compared to that in normal cells (P < 0.001). There was no significant difference between the two after stimulation with PAF and LTB4. The results indicate that the fMLP pathway is suppressed in CML granulocytes whereas PAF and LTB4 pathways appear unaltered in these cells. We therefore also studied the kinetics of peptide-receptor interaction with a labelled hexapeptide fNLPNTL which binds to the fMLP receptor. Our results show that the number of fMLP receptors/cell is significantly lower in CML PMNL (P < 0.05) than in normal PMNL, while their affinity constants and dissociation constants were comparable.

Identification of the murine beige gene by YAC complementation and positional cloning

The beige mutation is a murine autosomal recessive disorder, resulting in hypopigmentation, bleeding and immune cell dysfunction. The gene defective in beige is thought to be a homologue of the gene for the human disorder Chediak-Higashi syndrome. We have identified the murine beige gene by in vitro complementation and positional cloning, and confirmed its identification by defining mutations in two independent mutant alleles. The sequence of the beige gene message shows strong nucleotide homology to multiple human ESTs, one or more of which may be associated with the Chediak-Higashi syndrome gene. The amino acid sequence of the Beige protein revealed a novel protein with significant amino acid homology to orphan proteins identified in Saccharomyces cerevisiae, Caenorhabditis elegans and humans.