Cytoplasmic Terminus of Vacuolar Type Proton Pump Accessory Subunit Ac45 Is Required for Proper Interaction with V0 Domain Subunits and Efficient Osteoclastic Bone Resorption

• Published in: The Journal of biological chemistry Vol. 283; no. 19; pp. 13194 - 13204
• Main Authors: Feng, Haotian, Cheng, Taksum, Pavlos, Nathan J., Yip, Kirk H.M., Carrello, Amerigo, Seeber, Ruth, Eidne, Karin, Zheng, Ming H., Xu, Jiake
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 09.05.2008; American Society for Biochemistry and Molecular Biology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M709712200

Solubilization of mineralized bone by osteoclasts is largely dependent on the acidification of the extracellular resorption lacuna driven by the vacuolar (H+)-ATPases (V-ATPases) polarized within the ruffled border membranes. V-ATPases consist of two functionally and structurally distinct domains, V1 and V0. The peripheral cytoplasmically oriented V1 domain drives ATP hydrolysis, which necessitates the translocation of protons across the integral membrane bound V0 domain. Here, we demonstrate that an accessory subunit, Ac45, interacts with the V0 domain and contributes to the vacuolar type proton pump-mediated function in osteoclasts. Consistent with its role in intracellular acidification, Ac45 was found to be localized to the ruffled border region of polarized resorbing osteoclasts and enriched in pH-dependent endosomal compartments that polarized to the ruffled border region of actively resorbing osteoclasts. Interestingly, truncation of the 26-amino acid residue cytoplasmic tail of Ac45, which encodes an autonomous internalization signal, was found to impair bone resorption in vitro. Furthermore, biochemical analysis revealed that although both wild type Ac45 and mutant were capable of associating with subunits a3, c, c″, and d, deletion of the cytoplasmic tail altered its binding proximity with a3, c″, and d. In all, our data suggest that the cytoplasmic terminus of Ac45 contains elements necessary for its proper interaction with V0 domain and efficient osteoclastic bone resorption.