Post-translational modification by monoclonal nonspecific suppressor factor beta (MNSF beta) has been implicated in the regulation of a variety of cellular events. Previous studies have demonstrated that MNSF beta covalently binds to the intracellular pro-apoptotic protein Bcl-G in a macrophage cell line, Raw264.7, suggesting involvement of this ubiquitin-like protein in apoptosis. Most recently, we found that MNSF beta covalently conjugates to endophilin II, a member of the endophilin A family, and inhibits phagocytosis by macrophages. In this study, we further examined the mechanism of action of MNSF beta/endophilin II complex in the phagocytosis of zymosan. MNSF beta/endophilin II I mediated inhibition of phagocytosis in Raw264.7 cells was neutralized by anti-Decti-1, beta-glucan receptor, mAb, indicating that MNSF beta/endophilin II is a mediator of Dectin-1 signaling in regulating phagocytosis. The beta-glucan-dependent TNF alpha response to zymosan was significantly increased by the treatment with endophilin II siRNA and/or MNSF beta siRNA. Conversely, cotransfection of endophilin II and MNSF beta cDNAs inhibited the enhancement of zymosan-induced TNF alpha production. Interestingly, endophilin II siRNA did not affect Pam(3)CSK(4) (TLR2 specific ligand)-induced TNF alpha production. Endophilin II and/or MNSF beta siRNA enhanced zymosan-induced I kappa beta alpha degradation. Together, these results demonstrate that MNSF beta/endophilin II inhibits the signal path-way upstream of IKK activation, but not downstream of TLR2 signaling. (C) 2010 Elsevier Inc. All rights reserved.