Human disease-causing NOG missense mutations: Effects on noggin secretion, dimer formation, and bone morphogenetic protein binding

Department of Genetics and Center for Human Genetics, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, OH 44106, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 10/2001; 98(20):11353-8. DOI: 10.1073/pnas.201367598
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Secreted noggin protein regulates bone morphogenetic protein activity during development. In mice, a complete loss of noggin protein leads to multiple malformations including joint fusion, whereas mice heterozygous for Nog loss-of-function mutations are normal. In humans, heterozygous NOG missense mutations have been found in patients with two autosomal dominant disorders of joint development, multiple synostosis syndrome (SYNS1) and a milder disorder proximal symphalangism (SYM1). This study investigated the effect of one SYNS1 and two SYM1 disease-causing missense mutations on the structure and function of noggin. The SYNS1 mutation abolished, and the SYM1 mutations reduced, the secretion of functional noggin dimers in transiently transfected COS-7 cells. Coexpression of mutant noggin with wild-type noggin, to resemble the heterozygous state, did not interfere with wild-type noggin secretion. These data indicate that the human disease-causing mutations are hypomorphic alleles that reduce secretion of functional dimeric noggin. Therefore, we conclude that noggin has both species-specific and joint-specific dosage-dependent roles during joint formation. Surprisingly, in contrast to the COS-7 cell studies, the SYNS1 mutant was able to form dimers in Xenopus laevis oocytes. This finding indicates that there also exist species-specific differences in the ability to process mutant noggin polypeptides.

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    • "We then examined whether the TGF-β or BMP ligands were required for the activation of their respective signaling pathways in cells treated with recombinant Wnt3a, by using ligand traps in the form of a TGF-β neutralizing antibody or noggin, a secreted inhibitor of BMPs (Marcelino et al., 2001). Incubation of recombinant Wnt3a or TGF-β (control) with the TGF-β neutralizing antibody for 1 h prior to treating cells was sufficient to block the phosphorylation of Smad3 (Figure 4A). "
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    • "However, the anti-GFP antibody revealed only minor amounts (about 6%) of BMP7-2A-Venus and BMP2-2A-Venus full-length proteins but no Noggin-2A-Venus fusion. This suggests that the 53-kDa immunosignal for Noggin in the supernatant represents Noggin dimers that can be detected under low stringent reducing conditions during electrophoresis [34]. Thus, the ribosomal skipping and the secretion of the target proteins encoded by the rAAVs were very efficient. "
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    • "Nucleotide and amino acid sequence similarities are more than 90% among humans, mice, and other mammals (Valenzuela et al. 1995). In humans, several point mutations in the NOG gene have been linked to congenital skeletal malformations, for example, proximal symphalangism or multiple synostoses syndrome (Gong et al. 1999; Marcelino et al. 2001; Hirshoren et al. 2008). Therefore, the NOG gene is a potential candidate for involvement in congenital skeletal malformations in domesticated dogs. "
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