Bril: A Novel Bone-Specific Modulator of Mineralization§

Authors


  • Parts of this work were previously published in abstract form in the Proceedings of the 2006 Annual Meeting of the American Society of Bone and Mineral Research, September 15–19, 2006, Philadelphia, PA, USA, and the 2006 Annual Meeting of the Australian and New Zealand Bone and Mineral Society, October 22–26, 2006, Port Douglas, Queensland, Australia.

  • Drs Salois, Sellin, Bessette, and Godin are employees of Phenogene Therapeutics. All other authors state that they have no conflicts of interest.

  • §

    Published online on April 21, 2008

Abstract

In the course of attempting to define the bone “secretome” using a signal-trap screening approach, we identified a gene encoding a small membrane protein novel to osteoblasts. Although previously identified in silico as ifitm5, no localization or functional studies had been undertaken on this gene. We characterized the expression patterns and localization of this gene in vitro and in vivo and assessed its role in matrix mineralization in vitro. The bone specificity and shown role in mineralization led us to rename the gene bone restricted ifitm-like protein (Bril). Bril encodes a 14.8-kDa 134 amino acid protein with two transmembrane domains. Northern blot analysis showed bone-specific expression with no expression in other embryonic or adult tissues. In situ hybridization and immunohistochemistry in mouse embryos showed expression localized on the developing bone. Screening of cell lines showed Bril expression to be highest in osteoblasts, associated with the onset of matrix maturation/mineralization, suggesting a role in bone formation. Functional evidence of a role in mineralization was shown by adenovirus-mediated Bril overexpression and lentivirus-mediated Bril shRNA knockdown in vitro. Elevated Bril resulted in dose-dependent increases in mineralization in UMR106 and rat primary osteoblasts. Conversely, knockdown of Bril in MC3T3 osteoblasts resulted in reduced mineralization. Thus, we identified Bril as a novel osteoblast protein and showed a role in mineralization, possibly identifying a new regulatory pathway in bone formation.

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