Tumor-derived cytokines dysregulate macrophage interferon-gamma responsiveness and interferon regulatory factor-8 expression

Tumors can evade immune responses through suppressor signals that dysregulate host effector cell function. In this study we demonstrate that tumor-derived suppressor molecules impede host antitumor immune activity through dysregulation of multiple macrophage (Mphi) pathways, including suppressed production of cytotoxic and immunostimulatory agents and impaired expression of the interferon regulatory factor-8 (IRF-8) protein, a critical transducer of interferon-gamma-mediated activation pathways. The tumor-derived immunosuppressive cytokines interleukin-10 and transforming growth factor-beta(1) constrain IRF-8 production by normal Mphis, regardless of priming, and IRF-8 is also dysregulated in primary Mphis from tumor-burdened hosts. Collectively, these data describe a new mechanism by which tumors disrupt immune function and suggest that abrogation of tumor-derived immunoregulatory factors in situ can restore immune function and enhance antitumor efficacy.     

Synergism of tumor necrosis factor and interferon-gamma in induction of differentiation of human myeloblastic leukemic ML-1 cells

Natural or recombinant human tumor necrosis factor (TNF) induced NBT-reducing activity of ML-1 cells in a dose-dependent manner. Interferon-gamma (IFN-gamma) induced NBT-reducing activity only marginally. However, when IFN-gamma was combined with TNF, induction of NBT-reducing activity was remarkably increased. IFN-alpha or -beta had almost no effect on the induction of NBT-reducing activity of ML-1 cells, either alone or in combination with TNF. Treatment with both TNF and IFN-gamma synergistically enhanced morphological changes, growth inhibition and activity of Fc receptors, and NBT reduction in ML-1 cells, but not phagocytic activity. The TNF treated cells were classified as macrophage-like by morphology, and by lineage-specific alpha-naphthyl acetate esterase stain. The results indicate that combinations of TNF and IFN-gamma act synergistically in the induction of differentiation of human myeloblastic ML-1 cells.     

Docking-dependent ubiquitination of the interferon regulatory factor-1 tumor suppressor protein by the ubiquitin ligase CHIP

Characteristically for a regulatory protein, the IRF-1 tumor suppressor turns over rapidly with a half-life of between 20-40 min. This allows IRF-1 to reach new steady state protein levels swiftly in response to changing environmental conditions. Whereas CHIP (C terminus of Hsc70-interacting protein), appears to chaperone IRF-1 in unstressed cells, formation of a stable IRF-1·CHIP complex is seen under specific stress conditions. Complex formation, in heat- or heavy metal-treated cells, is accompanied by a decrease in IRF-1 steady state levels and an increase in IRF-1 ubiquitination. CHIP binds directly to an intrinsically disordered domain in the central region of IRF-1 (residues 106-140), and this site is sufficient to form a stable complex with CHIP in cells and to compete in trans with full-length IRF-1, leading to a reduction in its ubiquitination. The study reveals a complex relationship between CHIP and IRF-1 and highlights the role that direct binding or "docking" of CHIP to its substrate(s) can play in its mechanism of action as an E3 ligase.