Format

Send to

Choose Destination
J Thromb Haemost. 2017 Apr;15(4):792-801. doi: 10.1111/jth.13619. Epub 2017 Feb 23.

Dysregulation of PLDN (pallidin) is a mechanism for platelet dense granule deficiency in RUNX1 haplodeficiency.

Author information

1
Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA, USA.
2
Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, PA, USA.
3
Division of Hematology, The Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
4
Children's Hospital of Philadelphia and Department of Pediatrics, The Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
5
Department of Pediatrics, Children's National Medical Center, Washington, DC, USA.
6
Department of Medicine, Temple University School of Medicine, Philadelphia, PA, USA.

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.

SUMMARY:

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.

KEYWORDS:

PLDN protein, human; RUNX1; blood platelets; platelet storage pool deficiency; thrombocytopenia

PMID:
28075530
PMCID:
PMC5378588
DOI:
10.1111/jth.13619
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for Wiley Icon for PubMed Central
Loading ...
Support Center