A Novel Mutation in LEPRE1 That Eliminates Only the KDEL ER- Retrieval Sequence Causes Non-Lethal Osteogenesis Imperfecta

Ryuji Fukuzawa,Naoko Amano,Tomonobu Hasegawa,Tomohiro Ishii,Mamoru Tanaka,Eugene A Permyakov,David R Eyre,Masaki Takagi,Joan C Marini,Gen Nishimura,Aileen M Barnes,Maryann Weis

doi:10.1371/journal.pone.0036809

Abstract

Prolyl 3-hydroxylase 1 (P3H1), encoded by the LEPRE1 gene, forms a molecular complex with cartilage-associated protein (CRTAP) and cyclophilin B (encoded by PPIB) in the endoplasmic reticulum (ER). This complex is responsible for one step in collagen post-translational modification, the prolyl 3-hydroxylation of specific proline residues, specifically α1(I) Pro986. P3H1 provides the enzymatic activity of the complex and has a Lys-Asp-Glu-Leu (KDEL) ER-retrieval sequence at the carboxyl terminus. Loss of function mutations in LEPRE1 lead to the Pro986 residue remaining unmodified and lead to slow folding and excessive helical post-translational modification of type I collagen, which is seen in both dominant and recessive osteogenesis imperfecta (OI). Here, we present the case of siblings with non-lethal OI due to novel compound heterozygous mutations in LEPRE1 (c.484delG and c.2155dupC). The results of RNA analysis and real-time PCR suggest that mRNA with c.2155dupC escapes from nonsense-mediated RNA decay. Without the KDEL ER- retrieval sequence, the product of the c.2155dupC variant cannot be retained in the ER. This is the first report of a mutation in LEPRE1 that eliminates only the KDEL ER-retrieval sequence, whereas other functional domains remain intact. Our study shows, for the first time, that the KDEL ER- retrieval sequence is essential for P3H1 functionality and that a defect in KDEL is sufficient for disease onset.

Highlights

Osteogenesis imperfecta (OI; MIM #166200, #166210, #259420, #166220, #610967, #610968, #610682, #610915, #259440, #613848 and #613982) comprises a heterogeneous group of connective tissue disorders characterized by fragile bones with susceptibility to fractures
LEPRE1 encodes prolyl 3-hydroxylase 1 (P3H1), which forms a molecular complex with cartilageassociated protein (CRTAP) and cyclophilin B (CypB, encoded by PPIB) in the endoplasmic reticulum (ER) that is responsible for one step in collagen post-translational modification, the prolyl 3hydroxylation of specific proline residues, a1(I) Pro986 [19]
ER-resident proteins must be distinguished from newly synthesized secretory proteins, which pass through this compartment as they transit the secretory pathway toward the extracellular space

Summary

Introduction

Osteogenesis imperfecta (OI; MIM #166200, #166210, #259420, #166220, #610967, #610968, #610682, #610915, #259440, #613848 and #613982) comprises a heterogeneous group of connective tissue disorders characterized by fragile bones with susceptibility to fractures. Most cases of OI are caused by heterozygous mutations in COL1A1 or COL1A2, the genes encoding the two type I procollagen alpha chains, proa (I) and proa (I) [1]. Recent investigations have discovered several genes responsible for OI inherited as an autosomal recessive trait [8,9,10,11,12,13,14,15,16,17,18] Among these genes, LEPRE1 encodes prolyl 3-hydroxylase 1 (P3H1), which forms a molecular complex with cartilageassociated protein (CRTAP) and cyclophilin B (CypB, encoded by PPIB) in the endoplasmic reticulum (ER) that is responsible for one step in collagen post-translational modification, the prolyl 3hydroxylation of specific proline residues, a1(I) Pro986 [19]. Loss of function mutations in either LEPRE1 or CRTAP lead to loss of both proteins in the cell, leave the Pro986 residue unmodified, and lead to slow folding and excessive helical post-translational modification of type I collagen [21]

Methods

Results

Conclusion