A BLOC‐1 mutation screen reveals a novel BLOC1S3 mutation in Hermansky–Pudlak Syndrome type 8

Abstract

Summary Hermansky-Pudlak Syndrome (HPS) is a genetically heterogeneous disorder of lysosome-related organelle biogenesis and is characterized by oculocutaneous albinism and a bleeding diathesis. Over the past decade, we screened 250 patients with HPS-like symptoms for mutations in the genes responsible for HPS subtypes 1–6. We identified 38 individuals with no functional mutations, and therefore, we analyzed all 8 genes encoding the Biogenesis of Lysosome-related Organelles Complex-1 (BLOC-1) proteins in these individuals. Here we describe the identification of a novel nonsense mutation in BLOC1S3 (HPS-8) in a 6 year-old Iranian boy. This mutation caused nonsense mediated decay of BLOC1S3 mRNA and destabilized the BLOC-1 complex. Our patient’s melanocytes showed aberrant localization of TYRP1, with increased plasma-membrane trafficking. These findings confirm a common cellular defect for HPS patients with defects in BLOC-1 subunits. We identified only 2 patients with BLOC-1 defects in our cohort, suggesting that other HPS genes remain to be identified.

Clinical and molecular phenotyping of a child with Hermansky-Pudlak syndrome-7, an uncommon genetic type of HPS

“…We found that the Dysbindin protein level was also reduced in HPS-8 fibroblasts compared to normal control cells, which provides further evidence that Dysbindin protein expression is sensitive to BLOC-1 stability. Of note, we previously reported absent (instead of greatly reduced) Dysbindin protein expression in fibroblasts from this patient with HPS-8 [12]; differences in these data are likely due to use of different anti-Dysbindin primary antibodies for immunoblotting. It is established in HPS human and mouse cells that a defect in one subunit affects stability of the entire complex, which can lead to degradation of other subunits in the same complex.…”

“…It is established in HPS human and mouse cells that a defect in one subunit affects stability of the entire complex, which can lead to degradation of other subunits in the same complex. This phenomenon at the protein level was shown for HPS defects in BLOC-1 [10, 12, 24], BLOC-2 [25, 26], BLOC-3 [27, 28], and the Adaptor-Protein-3 complex [8, 29]. …”

“…3.4.1 To study the cellular effect of the DTNBP1 nonsense mutation, studies were performed in fibroblasts from the HPS-7 patient, a normal control and a previously published HPS-8 patient [12]. HPS-8 is another HPS type with a BLOC-1 defect due to mutation in BLOC1S3 [12].…”

In vitro functional correction of Hermansky–Pudlak Syndrome type-1 by lentiviral-mediated gene transfer

“…All HPS patient cells used in this study were homozygous for a 16-bp duplication in exon 15 of the HPS1 gene (c.1472_1487dup16) and cultured as previously described [9]. Patients were enrolled in protocol NCT00001456, “Clinical and Basic Investigations Into Hermansky-Pudlak Syndrome”, approved by the NHGRI Institutional Review Board, and gave written informed consent.…”

“…Immunofluorescence microscopy was performed as described [9], using a mouse monoclonal antibody against TYRP1 obtained from BioLegend (Dedham, MA, USA), a sheep polyclonal antibody against TGN46 from AbD Serotec (Raleigh, NC, USA), and the DAPI nuclear stain (Vector Laboratories, Burlingame, CA, USA). All imaging was performed on a Zeiss 510 META confocal laser-scanning microscope (Carl Zeiss, Thornwood, NY, USA).…”