Ubiquitin-like protein MNSFß noncovalently binds to molecular chaperone HSPA8 and regulates osteoclastogenesis.

ABSTRACT

MNSFß, a ubiquitin-like protein, covalently binds to various target proteins including proapoptotic Bcl-G. During the course of isolation of MNSFß-conjugating enzyme(s), we identified a novel target protein for MNSFß. MALDI-TOF MS fingerprinting revealed that the MNSFß-interacting protein is HSPA8 (heat shock 70-kDa protein 8). We observed that MNSFß noncovalently binds to HSPA8 in the presence of ATP in vitro. Double knockdown of MNSFß and HSPA8 strongly inhibited RANKL-induced osteoclastogenesis from Raw264.7 macrophage-like cells. The same treatment inhibited RANKL-induced ERK1/2 and p38 phosphorylation and TNFα production, suggesting that the association of MNSFß with HSPA8 may promote RANKL-induced osteoclastogenesis. This is the first report that MNSFß binds to a protein substrate via the noncovalent association and exerts biological effects.