Molecular analysis of DMP1 mutants causing autosomal recessive hypophosphatemic rickets

Emily G. Farrow, Siobhan I. Davis, Leanne M. Ward, Lelia J. Summers, Judith S. Bubbear, Richard Keen, Trevor C B Stamp, Laurence R I Baker, Lynda Bonewald, Kenneth White

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

We previously demonstrated that the mutations Met1Val (M1V) and the deletion of nucleotides 1484-1490 (1484-1490del) in Dentin matrix protein-1 (DMP1) cause the novel disorder autosomal recessive hypophosphatemic rickets (ARHR), which is associated with elevated fibroblast growth factor-23 (FGF23). To further understand the role of DMP1 in ARHR, we undertook molecular genetic and in vitro expression studies. First, we examined a kindred with a severe hypophosphatemic rickets phenotype and recessive inheritance. Analyses of this family demonstrated that the affected members had elevated serum FGF23 and carried a large, biallelic deletion that removed the majority of DMP1. At a minimum, this deletion encompassed 49 kb between DMP1 exon 3 and an intergenic region 5′ to the next telomeric gene, integrin-binding sialoprotein (IBSP). We next performed immunofluorescent studies in cells to understand the effects of the known ARHR mutations on DMP1 cellular processing. These analyses showed that the M1V DMP1 mutant was not sorted to the trans-Golgi network (TGN) and secretory pathway, but filled the entire cytoplasm. In contrast, the 1484-1490del mutant localized to the TGN and was secreted, similar to wild type DMP1. The 1484-1490del mutation replaces the DMP1 18 C-terminal amino acids with 33 non-native residues. Truncation of wild type DMP1 by these native 18 residues followed by Western blot and confocal microscopic analyses demonstrated a wild type expression pattern when compared with the 1484-1490del mutant, indicating that the last 18 residues are not critical for cellular trafficking, but that the 33 additional residues arising from the 1484-1490del mutation likely compromise DMP1 processing. The relationship between DMP1 and FGF23 is unclear. To test endogenous DMP1 response to serum metabolites that also regulate FGF23, UMR-106 cells were treated with 1,25(OH)2 vitamin D (1 × 10- 7 M) and showed a 12-fold increase in DMP1 mRNA and protein at 24 h. In summary, we have identified a novel DMP1 deletion as the cause of ARHR, as well as demonstrated that the ARHR mutations alter DMP1 cellular processing, and that DMP1 can be regulated by vitamin D. Taken together, this work expands our understanding of the genetic and molecular mechanisms associated with DMP1 alterations causing ARHR.

Original languageEnglish
Pages (from-to)287-294
Number of pages8
JournalBone
Volume44
Issue number2
DOIs
StatePublished - Feb 2009

Fingerprint

Hypophosphatemic Rickets
Mutant Proteins
Dentin
Proteins
trans-Golgi Network
Mutation
Molecular Biology
Integrin-Binding Sialoprotein
Ergocalciferols

Keywords

  • ARHR
  • FGF23
  • Hypophosphatemia
  • SIBLING
  • Vitamin D

ASJC Scopus subject areas

  • Physiology
  • Endocrinology, Diabetes and Metabolism
  • Histology

Cite this

Farrow, E. G., Davis, S. I., Ward, L. M., Summers, L. J., Bubbear, J. S., Keen, R., ... White, K. (2009). Molecular analysis of DMP1 mutants causing autosomal recessive hypophosphatemic rickets. Bone, 44(2), 287-294. https://doi.org/10.1016/j.bone.2008.10.040

Molecular analysis of DMP1 mutants causing autosomal recessive hypophosphatemic rickets. / Farrow, Emily G.; Davis, Siobhan I.; Ward, Leanne M.; Summers, Lelia J.; Bubbear, Judith S.; Keen, Richard; Stamp, Trevor C B; Baker, Laurence R I; Bonewald, Lynda; White, Kenneth.

In: Bone, Vol. 44, No. 2, 02.2009, p. 287-294.

Research output: Contribution to journalArticle

Farrow, EG, Davis, SI, Ward, LM, Summers, LJ, Bubbear, JS, Keen, R, Stamp, TCB, Baker, LRI, Bonewald, L & White, K 2009, 'Molecular analysis of DMP1 mutants causing autosomal recessive hypophosphatemic rickets', Bone, vol. 44, no. 2, pp. 287-294. https://doi.org/10.1016/j.bone.2008.10.040
Farrow EG, Davis SI, Ward LM, Summers LJ, Bubbear JS, Keen R et al. Molecular analysis of DMP1 mutants causing autosomal recessive hypophosphatemic rickets. Bone. 2009 Feb;44(2):287-294. https://doi.org/10.1016/j.bone.2008.10.040
Farrow, Emily G. ; Davis, Siobhan I. ; Ward, Leanne M. ; Summers, Lelia J. ; Bubbear, Judith S. ; Keen, Richard ; Stamp, Trevor C B ; Baker, Laurence R I ; Bonewald, Lynda ; White, Kenneth. / Molecular analysis of DMP1 mutants causing autosomal recessive hypophosphatemic rickets. In: Bone. 2009 ; Vol. 44, No. 2. pp. 287-294.
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