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PLoS Genet. 2019 Feb 1;15(2):e1007917. doi: 10.1371/journal.pgen.1007917. eCollection 2019 Feb.

Mammalian Hbs1L deficiency causes congenital anomalies and developmental delay associated with Pelota depletion and 80S monosome accumulation.

Author information

1
Division of Newborn Medicine, Boston Children's Hospital, Boston, Massachusetts, United States of America.
2
Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, United States of America.
3
Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, United States of America.
4
Laboratoire de Biologie Moléculaire Eucaryote, Centre de Biologie Intégrative, Université de Toulouse, CNRS, UPS, Toulouse, France.
5
Division of Genetics and Genomics, Boston Children's Hospital, Boston, Massachusetts, United States of America.
6
The Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, Massachusetts, United States of America.
7
Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.
8
Université de Strasbourg, Centre National de La Recherche Scientifique UMR 7104, INSERM U964, Strasbourg, France.
9
Wellcome Sanger Institute, Cambridge, United Kingdom.
10
Broad Institute of MIT and Harvard, Cambridge, Massachusetts, United States of America.

Abstract

Hbs1 has been established as a central component of the cell's translational quality control pathways in both yeast and prokaryotic models; however, the functional characteristics of its human ortholog (Hbs1L) have not been well-defined. We recently reported a novel human phenotype resulting from a mutation in the critical coding region of the HBS1L gene characterized by facial dysmorphism, severe growth restriction, axial hypotonia, global developmental delay and retinal pigmentary deposits. Here we further characterize downstream effects of the human HBS1L mutation. HBS1L has three transcripts in humans, and RT-PCR demonstrated reduced mRNA levels corresponding with transcripts V1 and V2 whereas V3 expression was unchanged. Western blot analyses revealed Hbs1L protein was absent in the patient cells. Additionally, polysome profiling revealed an abnormal aggregation of 80S monosomes in patient cells under baseline conditions. RNA and ribosomal sequencing demonstrated an increased translation efficiency of ribosomal RNA in Hbs1L-deficient fibroblasts, suggesting that there may be a compensatory increase in ribosome translation to accommodate the increased 80S monosome levels. This enhanced translation was accompanied by upregulation of mTOR and 4-EBP protein expression, suggesting an mTOR-dependent phenomenon. Furthermore, lack of Hbs1L caused depletion of Pelota protein in both patient cells and mouse tissues, while PELO mRNA levels were unaffected. Inhibition of proteasomal function partially restored Pelota expression in human Hbs1L-deficient cells. We also describe a mouse model harboring a knockdown mutation in the murine Hbs1l gene that shared several of the phenotypic elements observed in the Hbs1L-deficient human including facial dysmorphism, growth restriction and retinal deposits. The Hbs1lKO mice similarly demonstrate diminished Pelota levels that were rescued by proteasome inhibition.

PMID:
30707697
DOI:
10.1371/journal.pgen.1007917
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