The ubiquitin-like protein monoclonal nonspecific suppressor factor beta conjugates to endophilin II and regulates phagocytosis.
Monoclonal nonspecific suppressor factor beta (MNSFbeta) is a ubiquitously expressed member of the ubiquitin-like family that has been implicated in various biological functions. Previous studies have demonstrated that MNSFbeta covalently binds to the intracellular proapoptotic protein Bcl-G in cells of the macrophage cell line Raw264.7, suggesting involvement of this ubiquitin-like protein in apoptosis. In this study, we purified a 62 kDa MNSFbeta adduct from murine liver lysates by sequential chromatography on DEAE and anti-MNSFbeta IgG-conjugated Sepharose. MALDI-TOF MS fingerprinting revealed that this MNSFbeta adduct consists of an 8.5 kDa MNSFbeta and endophilin II, a member of the endophilin A family. MNSFbeta may conjugate to endophilin II with a linkage between the C-terminal Gly74 and Lys294. We confirmed this result by immunoprecipitation/western blot studies. Endophilin II was ubiquitously expressed in various tissues, although a truncated form was observed in liver. The 62 kDa MNSFbeta-endophilin II was specifically expressed in liver and macrophages. Small interfering RNA-mediated knockdown of endophilin II and/or MNSFbeta promoted phagocytosis of zymosan in Raw264.7 cells. Conversely, cotransfection of endophilin II and MNSFbeta cDNAs inhibited the phagocytosis of zymosan. Such inhibition was not observed in cells expressing a mutant of endophilin II in which Lys294 was replaced by arginine. These results suggest that the post-translational modification of endophilin II by MNSFbeta might be implicated in phagocytosis by macrophages.
Nakamura
Morihiko
M
Department of Cooperative Medical Research, Collaboration Center, Shimane University, Izumo 693-8501, Japan. nkmr0515@med.shimane-u.ac.jp
Shimosaki
Shunsuke
S
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000502:physiology*; D008099:Liver / Q000737:chemistry; D051379:Mice; D008969:Molecular Sequence Data; D010587:Phagocytosis; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013491:Suppressor Factors, Immunologic / Q000737:chemistry / Q000302:isolation & purification / Q000502:physiology*
D047908:Intracellular Signaling Peptides and Proteins; D013491:Suppressor Factors, Immunologic; C528010:endophilin II, mouse; C072169:monoclonal nonspecific suppressor factor