BLOC-1 Interacts with BLOC-2 and the AP-3 Complex to Facilitate Protein Trafficking on Endosomes

The adaptor protein (AP)-3 complex is a component of the cellular machinery that controls protein sorting from endosomes to lysosomes and specialized related organelles such as melanosomes. Mutations in an AP-3 subunit underlie a form of Hermansky-Pudlak syndrome (HPS), a disorder characterized by abnormalities in lysosome-related organelles. HPS in humans can also be caused by mutations in genes encoding subunits of three complexes of unclear function, named biogenesis of lysosome-related organelles complex (BLOC)-1, -2, and -3. Here, we report that BLOC-1 interacts physically and functionally with AP-3 to facilitate the trafficking of a known AP-3 cargo, CD63, and of tyrosinase-related protein 1 (Tyrp1), a melanosomal membrane protein previously thought to traffic only independently of AP-3. BLOC-1 also interacts with BLOC-2 to facilitate Tyrp1 trafficking by a mechanism apparently independent of AP-3 function. Both BLOC-1 and -2 localize mainly to early endosome-associated tubules as determined by immunoelectron microscopy. These findings support the idea that BLOC-1 and -2 represent hitherto unknown components of the endosomal protein trafficking machinery.

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BLOC-1 Is Required for Cargo-specific Sorting from Vacuolar Early Endosomes toward Lysosome-related Organelles

Molecular Biology of the Cell ◽

10.1091/mbc.e06-12-1066 ◽

2007 ◽

Vol 18 (3) ◽

pp. 768-780 ◽

Cited By ~ 139

Author(s):

Subba Rao Gangi Setty ◽

Danièle Tenza ◽

Steven T. Truschel ◽

Evelyn Chou ◽

Elena V. Sviderskaya ◽

...

Keyword(s):

Protein Complex ◽

Genetic Disorder ◽

Adaptor Protein ◽

Transport Pathways ◽

Cargo Transport ◽

Early Endosomes ◽

Hermansky Pudlak Syndrome ◽

Lysosome Related Organelles ◽

And Function ◽

Tyrosinase Related Protein

Hermansky-Pudlak syndrome (HPS) is a genetic disorder characterized by defects in the formation and function of lysosome-related organelles such as melanosomes. HPS in humans or mice is caused by mutations in any of 15 genes, five of which encode subunits of biogenesis of lysosome-related organelles complex (BLOC)-1, a protein complex with no known function. Here, we show that BLOC-1 functions in selective cargo exit from early endosomes toward melanosomes. BLOC-1–deficient melanocytes accumulate the melanosomal protein tyrosinase-related protein-1 (Tyrp1), but not other melanosomal proteins, in endosomal vacuoles and the cell surface due to failed biosynthetic transit from early endosomes to melanosomes and consequent increased endocytic flux. The defects are corrected by restoration of the missing BLOC-1 subunit. Melanocytes from HPS model mice lacking a different protein complex, BLOC-2, accumulate Tyrp1 in distinct downstream endosomal intermediates, suggesting that BLOC-1 and BLOC-2 act sequentially in the same pathway. By contrast, intracellular Tyrp1 is correctly targeted to melanosomes in melanocytes lacking another HPS-associated protein complex, adaptor protein (AP)-3. The results indicate that melanosome maturation requires at least two cargo transport pathways directly from early endosomes to melanosomes, one pathway mediated by AP-3 and one pathway mediated by BLOC-1 and BLOC-2, that are deficient in several forms of HPS.

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Reduced pigmentation (rp), a mouse model of Hermansky-Pudlak syndrome, encodes a novel component of the BLOC-1 complex

Blood ◽

10.1182/blood-2004-04-1538 ◽

2004 ◽

Vol 104 (10) ◽

pp. 3181-3189 ◽

Cited By ~ 35

Author(s):

Babette Gwynn ◽

Jose A. Martina ◽

Juan S. Bonifacino ◽

Elena V. Sviderskaya ◽

M. Lynn Lamoreux ◽

...

Keyword(s):

Amino Acid ◽

Protein Trafficking ◽

Protein Complexes ◽

Stop Codon ◽

Premature Stop Codon ◽

Amino Acid Identity ◽

Organelle Biogenesis ◽

Hermansky Pudlak Syndrome ◽

Human Orthologue ◽

Lysosome Related Organelles

Abstract Hermansky-Pudlak syndrome (HPS), a disorder of organelle biogenesis, affects lysosomes, melanosomes, and platelet dense bodies. Seven genes cause HPS in humans (HPS1-HPS7) and at least 15 nonallelic mutations cause HPS in mice. Where their function is known, the HPS proteins participate in protein trafficking and vesicle docking/fusion events during organelle biogenesis. HPS-associated genes participate in at least 4 distinct protein complexes: the adaptor complex AP-3; biogenesis of lysosome-related organelles complex 1 (BLOC-1), consisting of 4 HPS proteins (pallidin, muted, cappuccino, HPS7/sandy); BLOC-2, consisting of HPS6/ruby-eye, HPS5/ruby-eye-2, and HPS3/cocoa; and BLOC-3, consisting of HPS1/pale ear and HPS4/light ear. Here, we report the cloning of the mouse HPS mutation reduced pigmentation (rp). We show that the wild-type rp gene encodes a novel, widely expressed 195-amino acid protein that shares 87% amino acid identity with its human orthologue and localizes to punctate cytoplasmic structures. Further, we show that phosphorylated RP is part of the BLOC-1 complex. In mutant rp/rp mice, a premature stop codon truncates the protein after 79 amino acids. Defects in all the 5 known components of BLOC-1, including RP, cause severe HPS in mice, suggesting that the subunits are nonredundant and that BLOC-1 plays a key role in organelle biogenesis.

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The pink gene encodes the Drosophila orthologue of the human Hermansky–Pudlak syndrome 5 (HPS5) gene

Genome ◽

10.1139/g07-032 ◽

2007 ◽

Vol 50 (6) ◽

pp. 548-556 ◽

Cited By ~ 18

Author(s):

Monika Syrzycka ◽

Lori A. McEachern ◽

Jennifer Kinneard ◽

Kristel Prabhu ◽

Kathleen Fitzpatrick ◽

...

Keyword(s):

Protein Trafficking ◽

Protein Complexes ◽

Model Organism ◽

Autosomal Recessive Disorders ◽

Dense Granules ◽

Eye Colour ◽

Hermansky Pudlak Syndrome ◽

Lysosome Related Organelles ◽

Key Participants

Hermansky–Pudlak syndrome (HPS) consists of a set of human autosomal recessive disorders, with symptoms resulting from defects in genes required for protein trafficking in lysosome-related organelles such as melanosomes and platelet dense granules. A number of human HPS genes and rodent orthologues have been identified whose protein products are key components of 1 of 4 different protein complexes (AP-3 or BLOC-1, -2, and -3) that are key participants in the process. Drosophila melanogaster has been a key model organism in demonstrating the in vivo significance of many genes involved in protein trafficking pathways; for example, mutations in the “granule group” genes lead to changes in eye colour arising from improper protein trafficking to pigment granules in the developing eye. An examination of the chromosomal positioning of Drosophila HPS gene orthologues suggested that CG9770, the Drosophila HPS5 orthologue, might correspond to the pink locus. Here we confirm this gene assignment, making pink the first eye colour gene in flies to be identified as a BLOC complex gene.

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The schizophrenia susceptibility factor dysbindin and its associated complex sort cargoes from cell bodies to the synapse

Molecular Biology of the Cell ◽

10.1091/mbc.e11-07-0592 ◽

2011 ◽

Vol 22 (24) ◽

pp. 4854-4867 ◽

Cited By ~ 46

Author(s):

Jennifer Larimore ◽

Karine Tornieri ◽

Pearl V. Ryder ◽

Avanti Gokhale ◽

Stephanie A. Zlatic ◽

...

Keyword(s):

Membrane Protein ◽

Cortical Neurons ◽

Neuronal Cells ◽

Neuronal Cell ◽

Adaptor Protein ◽

Nerve Terminals ◽

Endosome Trafficking ◽

Neuronal Cell Bodies ◽

Cultured Cortical Neurons ◽

Lysosome Related Organelles

Dysbindin assembles into the biogenesis of lysosome-related organelles complex 1 (BLOC-1), which interacts with the adaptor protein complex 3 (AP-3), mediating a common endosome-trafficking route. Deficiencies in AP-3 and BLOC-1 affect synaptic vesicle composition. However, whether AP-3-BLOC-1–dependent sorting events that control synapse membrane protein content take place in cell bodies upstream of nerve terminals remains unknown. We tested this hypothesis by analyzing the targeting of phosphatidylinositol-4-kinase type II α (PI4KIIα), a membrane protein present in presynaptic and postsynaptic compartments. PI4KIIα copurified with BLOC-1 and AP-3 in neuronal cells. These interactions translated into a decreased PI4KIIα content in the dentate gyrus of dysbindin-null BLOC-1 deficiency and AP-3–null mice. Reduction of PI4KIIα in the dentate reflects a failure to traffic from the cell body. PI4KIIα was targeted to processes in wild-type primary cultured cortical neurons and PC12 cells but failed to reach neurites in cells lacking either AP-3 or BLOC-1. Similarly, disruption of an AP-3–sorting motif in PI4KIIα impaired its sorting into processes of PC12 and primary cultured cortical neuronal cells. Our findings indicate a novel vesicle transport mechanism requiring BLOC-1 and AP-3 complexes for cargo sorting from neuronal cell bodies to neurites and nerve terminals.

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Defects in the cappuccino (cno) gene on mouse chromosome 5 and human 4p cause Hermansky-Pudlak syndrome by an AP-3–independent mechanism

Blood ◽

10.1182/blood.v96.13.4227.h8004227_4227_4235 ◽

2000 ◽

Vol 96 (13) ◽

pp. 4227-4235 ◽

Cited By ~ 5

Author(s):

Babette Gwynn ◽

Steven L. Ciciotte ◽

Susan J. Hunter ◽

Linda L. Washburn ◽

Richard S. Smith ◽

...

Keyword(s):

Mouse Chromosome ◽

Protein Trafficking ◽

Dense Body ◽

Spontaneous Mutation ◽

Oculocutaneous Albinism ◽

Chromosome 5 ◽

Prolonged Bleeding ◽

Independent Mechanism ◽

Hermansky Pudlak Syndrome ◽

Lysosome Related Organelles

Defects in a triad of organelles (melanosomes, platelet granules, and lysosomes) result in albinism, prolonged bleeding, and lysosome abnormalities in Hermansky-Pudlak syndrome (HPS). Defects in HPS1, a protein of unknown function, and in components of the AP-3 complex cause some, but not all, cases of HPS in humans. There have been 15 inherited models of HPS described in the mouse, underscoring its marked genetic heterogeneity. Here we characterize a new spontaneous mutation in the mouse, cappuccino (cno), that maps to mouse chromosome 5 in a region conserved with human 4p15-p16. Melanosomes ofcno/cno mice are immature and dramatically decreased in number in the eye and skin, resulting in severe oculocutaneous albinism. Platelet dense body contents (adenosine triphosphate, serotonin) are markedly deficient, leading to defective aggregation and prolonged bleeding. Lysosomal enzyme concentrations are significantly elevated in the kidney and liver. Genetic, immunofluorescence microscopy, and lysosomal protein trafficking studies indicate that the AP-3 complex is intact in cno/cno mice. It was concluded that the cappuccino gene encodes a product involved in an AP-3–independent mechanism critical to the biogenesis of lysosome-related organelles.

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The WASH complex, an endosomal Arp2/3 activator, interacts with the Hermansky–Pudlak syndrome complex BLOC-1 and its cargo phosphatidylinositol-4-kinase type IIα

Molecular Biology of the Cell ◽

10.1091/mbc.e13-02-0088 ◽

2013 ◽

Vol 24 (14) ◽

pp. 2269-2284 ◽

Cited By ~ 52

Author(s):

P. V. Ryder ◽

R. Vistein ◽

A. Gokhale ◽

M. N. Seaman ◽

M. A. Puthenveedu ◽

...

Keyword(s):

Actin Cytoskeleton ◽

Adaptor Protein ◽

Coat Proteins ◽

Lipid Kinase ◽

Rho Family Gtpases ◽

Vesicle Biogenesis ◽

Hermansky Pudlak Syndrome ◽

Rho Family ◽

Lysosome Related Organelles ◽

Phosphatidylinositol 4

Vesicle biogenesis machinery components such as coat proteins can interact with the actin cytoskeleton for cargo sorting into multiple pathways. It is unknown, however, whether these interactions are a general requirement for the diverse endosome traffic routes. In this study, we identify actin cytoskeleton regulators as previously unrecognized interactors of complexes associated with the Hermansky–Pudlak syndrome. Two complexes mutated in the Hermansky–Pudlak syndrome, adaptor protein complex-3 and biogenesis of lysosome-related organelles complex-1 (BLOC-1), interact with and are regulated by the lipid kinase phosphatidylinositol-4-kinase type IIα (PI4KIIα). We therefore hypothesized that PI4KIIα interacts with novel regulators of these complexes. To test this hypothesis, we immunoaffinity purified PI4KIIα from isotope-labeled cell lysates to quantitatively identify interactors. Strikingly, PI4KIIα isolation preferentially coenriched proteins that regulate the actin cytoskeleton, including guanine exchange factors for Rho family GTPases such as RhoGEF1 and several subunits of the WASH complex. We biochemically confirmed several of these PI4KIIα interactions. Of importance, BLOC-1 complex, WASH complex, RhoGEF1, or PI4KIIα depletions altered the content and/or subcellular distribution of the BLOC-1–sensitive cargoes PI4KIIα, ATP7A, and VAMP7. We conclude that the Hermansky–Pudlak syndrome complex BLOC-1 and its cargo PI4KIIα interact with regulators of the actin cytoskeleton.

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A Novel Likely Pathogenic Variant in the BLOC1S5 Gene Associated with Hermansky-Pudlak Syndrome Type 11 and an Overview of Human BLOC-1 Deficiencies

Cells ◽

10.3390/cells10102630 ◽

2021 ◽

Vol 10 (10) ◽

pp. 2630

Author(s):

Doris Boeckelmann ◽

Mira Wolter ◽

Barbara Käsmann-Kellner ◽

Udo Koehler ◽

Lea Schieber-Nakamura ◽

...

Keyword(s):

Genetic Defect ◽

Adaptor Protein ◽

Genetic Alterations ◽

Oculocutaneous Albinism ◽

Pathogenic Variants ◽

New Type ◽

Hermansky Pudlak Syndrome ◽

Lysosome Related Organelles ◽

Next Generation Sequencing Ngs ◽

Generation Sequencing

Hermansky-Pudlak syndrome (HPS) is a heterogeneous disorder combining oculocutaneous albinism (OCA) and a platelet function disorder of varying severity as its most prominent features. The genes associated with HPS encode for different BLOC- (biogenesis of lysosome-related organelles complex) complexes and for the AP-3 (adaptor protein-3) complex, respectively. These proteins are involved in maturation, trafficking, and the function of lysosome-related organelles (LROs) such as melanosomes and platelet δ-granules. Some patients with different types of HPS can develop additional complications and symptoms like pulmonary fibrosis, granulomatous colitis, and immunodeficiency. A new type of HPS has recently been identified associated with genetic alterations in the BLOC1S5 gene, which encodes the subunit Muted of the BLOC-1 complex. Our aim was to unravel the genetic defect in two siblings with a suspected HPS diagnosis (because of OCA and bleeding symptoms) using next generation sequencing (NGS). Platelet functional analysis revealed reduced platelet aggregation after stimulation with ADP and a severe secretion defect in platelet δ-granules. NGS identified a novel homozygous essential splice site variant in the BLOC1S5 gene present in both affected siblings who are descendants of a consanguine marriage. The patients exhibited no additional symptoms. Our study confirms that pathogenic variants of BLOC1S5 cause the recently described HPS type 11.

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Defects in the cappuccino (cno) gene on mouse chromosome 5 and human 4p cause Hermansky-Pudlak syndrome by an AP-3–independent mechanism

Blood ◽

10.1182/blood.v96.13.4227 ◽

2000 ◽

Vol 96 (13) ◽

pp. 4227-4235 ◽

Cited By ~ 27

Author(s):

Babette Gwynn ◽

Steven L. Ciciotte ◽

Susan J. Hunter ◽

Linda L. Washburn ◽

Richard S. Smith ◽

...

Keyword(s):

Mouse Chromosome ◽

Protein Trafficking ◽

Dense Body ◽

Spontaneous Mutation ◽

Oculocutaneous Albinism ◽

Chromosome 5 ◽

Prolonged Bleeding ◽

Independent Mechanism ◽

Hermansky Pudlak Syndrome ◽

Lysosome Related Organelles

Abstract Defects in a triad of organelles (melanosomes, platelet granules, and lysosomes) result in albinism, prolonged bleeding, and lysosome abnormalities in Hermansky-Pudlak syndrome (HPS). Defects in HPS1, a protein of unknown function, and in components of the AP-3 complex cause some, but not all, cases of HPS in humans. There have been 15 inherited models of HPS described in the mouse, underscoring its marked genetic heterogeneity. Here we characterize a new spontaneous mutation in the mouse, cappuccino (cno), that maps to mouse chromosome 5 in a region conserved with human 4p15-p16. Melanosomes ofcno/cno mice are immature and dramatically decreased in number in the eye and skin, resulting in severe oculocutaneous albinism. Platelet dense body contents (adenosine triphosphate, serotonin) are markedly deficient, leading to defective aggregation and prolonged bleeding. Lysosomal enzyme concentrations are significantly elevated in the kidney and liver. Genetic, immunofluorescence microscopy, and lysosomal protein trafficking studies indicate that the AP-3 complex is intact in cno/cno mice. It was concluded that the cappuccino gene encodes a product involved in an AP-3–independent mechanism critical to the biogenesis of lysosome-related organelles.

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