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A homozygous pathogenic missense variant broadens the phenotypic and mutational
spectrum of CREB3L1-related osteogenesis imperfecta
Guillemyn B, Kayserili H, Demuynck L, Sips P, De Paepe A, Syx D, Coucke PJ, Malfait F,
Symoens S
Human Molecular Genetics, 28 (11), 1801-1809, 2019.
This is a pre-copyedited, author-produced version of an article accepted for publication in
Human Molecular Genetics following peer review. The version of record is available online
at: https://doi.org/10.1093/hmg/ddz017.
To refer to or to cite this work, please use the citation to the published version:
Guillemyn B, Kayserili H, Demuynck L, Sips P, De Paepe A, Syx D, Coucke PJ, Malfait F, and
Symoens S (2019). A homozygous pathogenic missense variant broadens the phenotypic
and mutational spectrum of CREB3L1-related osteogenesis imperfecta. Hum Mol Genet
28(11) 1801-1809. doi: 10.1093/hmg/ddz017
For Peer Review
1
A homozygous pathogenic missense variant broadens the
phenotypic and mutational spectrum of CREB3L1-related
osteogenesis imperfecta
Brecht Guillemyn
1
, Hülya Kayserili
2
, Lynn Demuynck
1
, Patrick Sips
1
, Anne De Paepe
1
,
Delfien Syx
1
, Paul J. Coucke
1
, Fransiska Malfait
1
, Sofie Symoens
1,*
1
Center for Medical Genetics Ghent, Ghent University Hospital, Department of Biomolecular
Medicine, Ghent 9000, Belgium
2
KOÇ University School of Medicine (KUSoM) Medical Genetics Department, Topkapi
Zeytinburnu, 34010 Istanbul, Turkey
*To whom correspondence should be addressed: Department of Biomolecular Medicine,
Center for Medical Genetics Ghent, Ghent University Hospital, Corneel Heymanslaan 10,
Medical Research Building 1, 9000 Ghent, Belgium. Tel: 0032/9 332 02 33; Email:
Sofie.Symoens@UGent.be
Page 1 of 28 Human Molecular Genetics
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Abstract
The cyclic AMP responsive element binding protein 3-like 1 (CREB3L1) gene codes for the
endoplasmic reticulum stress transducer old astrocyte specifically induced substance (OASIS),
which has an important role in osteoblast differentiation during bone development. Deficiency
of OASIS is linked to a severe form of autosomal recessive osteogenesis imperfecta (OI), but
only few patients have been reported. We identified the first homozygous pathogenic missense
variant (p.(Ala304Val)) in a patient with lethal OI, which is located within the highly conserved
basic leucine zipper domain, four amino acids upstream of the DNA binding domain. In vitro
structural modeling and luciferase assays demonstrate that this missense variant affects a
critical residue in this functional domain, thereby decreasing the type I collagen transcriptional
binding ability. In addition, overexpression of the mutant OASIS protein leads to decreased
transcription of the SEC23A and SEC24D genes, which code for components of the coat protein
complex type II (COPII), and aberrant OASIS signaling also results in decreased protein levels
of SEC24D. Our findings therefore provide additional proof of the potential involvement of the
COPII secretory complex in the context of bone-associated disease.
Page 2 of 28Human Molecular Genetics
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Introduction
Osteogenesis imperfecta (OI) is a clinically and genetically heterogeneous group of heritable
bone dysplasias, with the severity of symptoms ranging from perinatal lethality to generalized
osteopenia (1). This brittle bone disease affects one in 15,000-20,000 births and is characterized
by typical clinical manifestations such as bone fragility, skeletal deformities, low bone mass
and short stature. Extraskeletal features, including blue sclerae, dentinogenesis imperfecta,
adult-onset hearing loss, joint hypermobility, restrictive pulmonary disease, cardiovascular
abnormalities and easy bruising, contribute to the multisystemic disorder (1-3). The
predominant autosomal dominant (AD) forms are caused by mutations in either COL1A1 (MIM
120150) or COL1A2 (MIM 120160), encoding the α1- and α2-chains of type I procollagen
respectively. Another rare AD OI subtype is associated with mutations in interferon–induced
transmembrane protein 5 (IFITM5, MIM 614757), which is involved in bone mineralization. In
approximately 10% of OI cases, the disease has an autosomal recessive (AR) inheritance.
Several genes have been associated with these AR forms of OI, and they are classified according
to their mechanism and pathophysiology: collagen post-translational modification (CRTAP,
MIM 605497; P3H1, MIM 610339; PPIB, MIM 123841), collagen processing and crosslinking
(SERPINH1, MIM 600943; FKBP10, MIM 607063; PLOD2, MIM 601865; BMP1, MIM
112264), bone mineralization (SERPINF1, MIM 172860) and osteoblast
differentiation/function (SP7, MIM 606633; TMEM38B, MIM 611236; WNT1, MIM 164820;
CREB3L1, MIM 616215; SPARC, MIM 182120; MBTPS2, MIM 300294; TAPT1, MIM
616897) (1, 2, 4-18).
The CREB3L1 gene (cAMP Responsive Element Binding Protein 3 Like 1) encodes the
endoplasmic reticulum (ER)-stress transducer ‘old astrocyte specifically induced substance’
(OASIS), a basic leucine zipper (bZIP) transcription factor which belongs to the well-conserved
family of the cyclic AMP responsive element binding protein/activating transcription factor
(CREB/ATF) genes. OASIS is processed by regulated intramembrane proteolysis (RIP) in
response to ER stress, and is highly expressed in osteoblasts (19, 20). OASIS
-/-
mice exhibit
severe osteopenia and spontaneous fractures, resulting from a decrease in type I collagen in the
bone matrix and a decline in the activity of osteoblasts. More recently, Col1a1 was identified
as a target of OASIS, and Murakami et al. demonstrated with murine studies that OASIS
activates the transcription of Col1a1 through an unfolded protein response element (UPRE)-
Page 3 of 28 Human Molecular Genetics
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like sequence in the Col1a1 promoter region, thereby revealing its critical role in bone
formation (19-21).
Hitherto, only 3 reports have associated homozygous CREB3L1 defects to an AR form of OI (a
whole gene deletion, the in-frame deletion (c.934_936delAAG, p.(Lys312del)) and the
nonsense variant (c.1284C>A, p.(Tyr428*))), which is currently classified as OI type XVI (2,
15, 22, 23).
Here, we present a Turkish family, in which molecular analysis of the proband revealed a
previously unreported homozygous missense variant (c.911C>T, p.(Ala304Val)).
We applied structural modeling to study the effects of this missense variant on the OASIS
protein. We then performed further in vitro studies to investigate the functional consequences
regarding regulation of type I collagen and COPII component gene expression.
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