title: Dysregulation of PLDN (pallidin) is a mechanism for platelet dense granule deficiency in RUNX1 haplodeficiency.
abstract: Essentials Platelet dense granule (DG) deficiency is a major abnormality in RUNX1 haplodeficiency patients. The molecular mechanisms leading to the platelet DG deficiency are unknown. Platelet expression of PLDN (BLOC1S6, pallidin), involved in DG biogenesis, is regulated by RUNX1. Downregulation of PLDN is a mechanism for DG deficiency in RUNX1 haplodeficiency.
  
  
  
  Background Inherited RUNX1 haplodeficiency is associated with thrombocytopenia and platelet dysfunction. Dense granule (DG) deficiency has been reported in patients with RUNX1 haplodeficiency, but the molecular mechanisms are unknown. Platelet mRNA expression profiling in a patient previously reported by us with a RUNX1 mutation and platelet dysfunction showed decreased expression of PLDN (BLOC1S6), which encodes pallidin, a subunit of biogenesis of lysosome-related organelles complex-1 (BLOC-1) involved in DG biogenesis. PLDN mutations in the pallid mouse and Hermansky-Pudlak syndrome-9 are associated with platelet DG deficiency. Objectives We postulated that PLDN is a RUNX1 target, and that its decreased expression leads to platelet DG deficiency in RUNX1 haplodeficiency. Results Platelet pallidin and DG levels were decreased in our patient. This was also observed in two siblings from a different family with a RUNX1 mutation. Chromatin immunoprecipitation and electrophoretic mobility shift assays with phorbol ester-treated human erythroleukemia (HEL) cells showed RUNX1 binding to RUNX1 consensus sites in the PLDN1 5' upstream region. In luciferase reporter studies, mutation of RUNX1 sites in the PLDN promoter reduced activity. RUNX1 overexpression enhanced and RUNX1 downregulation decreased PLDN1 promoter activity and protein expression. RUNX1 downregulation resulted in impaired handling of mepacrine and mislocalization of the DG marker CD63 in HEL cells, indicating impaired DG formation, recapitulating findings on PLDN downregulation. Conclusions These studies provide the first evidence that PLDN is a direct target of RUNX1 and that its dysregulation is a mechanism for platelet DG deficiency associated with RUNX1 haplodeficiency.
authors.affiliation: Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA, USA.
authors.forename: G F
authors.initials: GF
authors.lastname: Mao
authors.affiliation: Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA, USA.|Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, PA, USA.
authors.forename: L E
authors.initials: LE
authors.lastname: Goldfinger
authors.affiliation: Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Fan
authors.affiliation: Division of Hematology, The Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.|Children's Hospital of Philadelphia and Department of Pediatrics, The Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: M P
authors.initials: MP
authors.lastname: Lambert
authors.affiliation: Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA, USA.
authors.forename: G
authors.initials: G
authors.lastname: Jalagadugula
authors.affiliation: Department of Pediatrics, Children's National Medical Center, Washington, DC, USA.
authors.forename: R
authors.initials: R
authors.lastname: Freishtat
authors.affiliation: Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA, USA.|Department of Medicine, Temple University School of Medicine, Philadelphia, PA, USA.
authors.forename: A K
authors.initials: AK
authors.lastname: Rao
mesh_terms: D000818:Animals; D001665:Binding Sites; D001791:Blood Platelet Disorders / Q000235:genetics; D001792:Blood Platelets / Q000166:cytology*; D002352:Carrier Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D002648:Child; D002675:Child, Preschool; D050676:Core Binding Factor Alpha 2 Subunit / Q000235:genetics / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D015536:Down-Regulation; D005260:Female; D005786:Gene Expression Regulation; D057895:Haploinsufficiency; D022861:Hermanski-Pudlak Syndrome / Q000235:genetics; D006801:Humans; D037102:Lectins / Q000378:metabolism; D008297:Male; D051379:Mice; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism*; D060149:Tetraspanin 30 / Q000378:metabolism; D013921:Thrombocytopenia / Q000235:genetics
chemical_list: C104378:BLOC1S1 protein, human; C400284:BLOC1S6 protein, human; C554586:CD63 protein, human; D002352:Carrier Proteins; D050676:Core Binding Factor Alpha 2 Subunit; D003598:Cytoskeletal Proteins; D037102:Lectins; D009419:Nerve Tissue Proteins; C412722:PALLD protein, human; D010750:Phosphoproteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C493728:RUNX1 protein, human; D060149:Tetraspanin 30
keywords: PLDN protein, human; RUNX1; blood platelets; platelet storage pool deficiency; thrombocytopenia