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Abstract

Craniometaphyseal dysplasia (CMD) is a bone dysplasia characterized by overgrowth and sclerosis of the craniofacial bones and abnormal modeling of the metaphyses of the tubular bones. Hyperostosis and sclerosis of the skull may lead to cranial nerve compressions resulting in hearing loss and facial palsy. An autosomal dominant form of the disorder (MIM 123000) was linked to chromosome 5p15.2-p14.1 (ref. 3) within a region harboring the human homolog (ANKH) of the mouse progressive ankylosis (ank) gene. The ANK protein spans the outer cell membrane and shuttles inorganic pyrophosphate (PPi), a major inhibitor of physiologic and pathologic calcification, bone mineralization and bone resorption. Here we carry out mutation analysis of ANKH, revealing six different mutations in eight of nine families. The mutations predict single amino acid substitutions, deletions or insertions. Using a helix prediction program, we propose for the ANK molecule 12 membrane-spanning helices with an alternate inside/out orientation and a central channel permitting the passage of PPi. The mutations occur at highly conserved amino acid residues presumed to be located in the cytosolic portion of the protein. Our results link the PPi channel ANK with bone formation and remodeling.

Pyrophosphate Inhibits Mineralization of Osteoblast Cultures by Binding to Mineral, Up-regulating Osteopontin, and Inhibiting Alkaline Phosphatase Activity

“…Although the reason for this is not immediately obvious, we hypothesize that elevated P i produced by TNAP hydrolysis of free, unadsorbed (to mineral) PP i could be responsible because P i has been shown to elevate Ank expression in cementoblasts (31). Furthermore, the structure and function of Ank is not entirely clear (20,37), and Wang et al (21) have demonstrated that blocking Ank expression led to increases in both intra-and extracellular PP i levels, whereas Ank overexpression led to decreases in both intra-and extracellular PP i levels, suggesting a level of complexity in PPi handling and homeostasis that needs to be better clarified. Increased Ank expression as a result of increased exogenous PP i could simply be an attempt by the cells to return extracellular PP i levels to normal by as yet an unknown mechanism.…”

Progressive Ankylosis (Ank) Protein Is Expressed by Neurons and Ank Immunohistochemical Reactivity Is Increased by Limbic Seizures

“…Third, the antibody used for immunohistochemical staining was generated against the C-terminal 37 amino acid residues of the Ank protein. The topologic organization of Ank in the plasma membrane has not been experimentally determined, but a model proposed by Nurnberg et al (2001) indicates that this C-terminal region is located in the cytoplasm. Therefore, seizure activity could promote an increase in neuronal cell permeability, which would make the antibody epitope more accessible.…”

“…First, goat anti-Ank polyclonal antiserum was obtained using two synthetic peptides as the antigen. Together these peptides corresponded to the human Ank C-terminal 37 amino acid residues, a region with 100% sequence identity to the murine Ank protein (Ho et al, 2000;Nurnberg et al, 2001). Anti-Ank antibodies were purified and concentrated by passing the serum over an antigen column.…”

“…Ank/ank mutant mice also display a marked increase in cementum formation during tooth development (Nociti et al, 2002). Furthermore, it has been reported that mutations in the human Ank gene can cause autosomal dominant craniometaphyseal dysplasia (Nurnberg et al, 2001;Reichenberger et al, 2001) and some forms of chondrocalcinosis (Pendleton et al, 2002).…”

“…nk is a growth factor-regulated gene encoding an ‫-45ف‬kDa protein with 10 to 12 transmembrane domains, three potential glycosylation sites, and multiple putative phosphorylation sites (Guo et al, 2002;Ho et al, 2000;Nurnberg et al, 2001;Sohn et al, 2002). An autosomal recessive mutation at the Ank locus is the molecular basis for murine progressive ankylosis, a disease characterized by excessive mineralization of articular cartilage, bony outgrowths, and joint destruction (Ho et al, 2000).…”