Generation of Inhibitory NFκB Complexes and Phosphorylated cAMP Response Element-binding Protein Correlates with the Anti-inflammatory Activity of Complement Protein C1q in Human Monocytes

Abstract

The interaction of C1q with specific cells of the immune system induces activities, such as enhancement of phagocytosis in monocytes and stimulation of superoxide production in neutrophils. In contrast to some other monocyte activators, C1q itself does not induce pro-inflammatory cytokine production, but rather inhibits the lipopolysaccharide (LPS)-stimulated induction of certain pro-inflammatory cytokines and induces expression of interleukin-10. To investigate the molecular mechanism by which C1q exerts this effect on gene expression, the influence of C1q on the activation of transcription factors of the NFB family and cAMP response element-binding protein (CREB) was assessed. C1q treatment increased B binding activity in freshly isolated human monocytes in a time-dependent fashion as assessed by electrophoretic mobility shift assays. In antibody supershift experiments, anti-p50 antibody supershifted the C1q-induced NFB complex, whereas anti-p65 antibody had little effect, suggesting that C1q induced the translocation of NFB p50p50 homodimers. This is in contrast to the dominant induction of p65 containing complexes in parallel monocyte cultures stimulated with LPS. C1q treatment also induced cAMP response element (CRE)-binding activity as demonstrated by electrophoretic mobility shift assay, increased phosphorylation of CREB, and induction of CRE driven gene expression. In contrast, CREB activation was not detected in LPS-treated monocytes. These results suggest that C1q may modulate the cytokine profile expressed in response to inflammatory stimuli (e.g. LPS), by triggering inhibitory and/or competing signals. Because C1q and other defense collagens have been shown to enhance clearance of apoptotic cells, this regulatory pathway may be beneficial in avoiding autoimmunity and/or resolving inflammation.The transcription factor complexes of the NFB family have attracted widespread attention because of their rapid induction, the wide range of genes whose expression is influenced by these complexes, and the apparent consequences of its induction in several diseases (1). The NFB/Rel family of transcription factors, which include p65, p50, p52, RelB, and c-Rel, form homo-and heterodimers resulting in distinct transcription factor complexes that regulate expression of many different genes (2). In unstimulated cells, NFB is sequestered in the cytoplasm. Upon stimulation, the inhibitory protein IB␣ dissociates from specific pre-existing cytoplasmic NFB complexes, allowing the transcription factors to translocate to the nucleus and initiate the expression of target genes (1). Lipopolysaccharide (LPS) 5 and other pathogen-associated molecules have long been implicated in the inducible expression of many genes in monocytes, including pro-inflammatory cytokines such as tumor necrosis factor-␣, IL-1␣ and -␤, and IL-6 via specific NFB translocation (3). Prolonged LPS activation can also induce expression of anti-inflammatory IL-10 in monocytes, perhaps an important step in regulation of inflammation (4). Studies suggest t...

C1q and HMGB1 reciprocally regulate human macrophage polarization

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Autophosphorylation Docking Site Tyr-867 in Mer Receptor Tyrosine Kinase Allows for Dissociation of Multiple Signaling Pathways for Phagocytosis of Apoptotic Cells and Down-modulation of Lipopolysaccharide-inducible NF-κB Transcriptional Activation

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