Lipopolysaccharide (LPS) induces expression of tumor necrosis factor ␣ (TNF␣) and other pro-inflammatory cytokines in macrophages. Following its induction, TNF␣ gene transcription is rapidly attenuated, in part due to the accumulation of NF-B p50 homodimers that bind to three B sites in the TNF␣ promoter. Here we have investigated the inhibitory role of BCL-3, an IBlike protein that interacts exclusively with p50 and p52 homodimers. BCL-3 was induced by LPS with delayed kinetics and was associated with p50 in the nucleus. Forced expression of BCL-3 suppressed LPS-induced transcription from the TNF␣ promoter and inhibited two artificial promoters composed of TNF␣ B sites that preferentially bind p50 dimers. BCL-3-mediated repression was reversed by trichostatin A and was enhanced by overexpression of HDAC-1, indicating that transcriptional attenuation involves recruitment of histone deacetylase. Analysis of macrophages from p50 and BCL-3 knock-out mice revealed that both transcription factors negatively regulate TNF␣ expression and that BCL-3 inhibits IL-1␣ and IL-1␤. In contrast, induction of the anti-inflammatory cytokine IL-10 was reduced in BCL-3 null macrophages. BCL-3 was not required for the production of p50 homodimers but BCL-3 expression was severely diminished in p50-deficient cells. Together, these findings indicate that p50 and BCL-3 function as anti-inflammatory regulators in macrophages by attenuating transcription of pro-inflammatory cytokines and activating IL-10 expression.

PSG1, PSG6, PSG6N, and PSG11 induce dose-dependent secretion of anti-inflammatory cytokines by human monocytes. Human and murine PSGs exhibit cross-species activity. Our results are consistent with a role for PSGs in modulation of the innate immune system.

Pregnancy-specific glycoproteins (PSGs) are a family of secreted proteins produced by the placenta, which are believed to have a critical role in pregnancy success. Treatment of monocytes with three members of the human PSGs induces interleukin (IL)-10, IL-6, and transforming growth factor-beta(1) (TGF-beta(1)) secretion. To determine whether human and murine PSGs have similar functions and use the same receptor, we treated wild-type and CD9-deficient macrophages with murine PSG17N and human PSG1 and -11. Our data show that murine PSG17N induced secretion of IL-10, IL-6, prostaglandin E(2), and TGF-beta(1) and that CD9 expression is required for the observed induction of cytokines. Therefore, the ability of PSG17 to induce anti-inflammatory cytokines parallels that of members of the human PSG family, albeit human and murine PSGs use different receptors, as CD9-deficient and wild-type macrophages responded equally to human PSGs. We then proceeded to examine the signaling mechanisms responsible for the CD9-mediated response to PSG17. Inhibition of cyclooxygenase 2 significantly reduced the PSG17N-mediated increase in IL-10 and IL-6. Further characterization of the response to PSG17 indicated that cyclic adenosine monophosphate-dependent protein kinase A (PKA) is involved in the up-regulation of IL-10 and IL-6, and it is not required for the induction of TGF-beta(1). Conversely, treatment of macrophages with a PKC inhibitor reduced the PSG17-mediated induction of TGF-beta(1), IL-6, and IL-10 significantly. The induction of anti-inflammatory cytokines by various PSGs supports the hypothesis that these glycoproteins have an essential role in the regulation of the maternal immune response in species with hemochorial placentation.

No abstract

One of the hallmarks of leukemic cells is their ability to proliferate and survive in the absence of exogenous growth factors (GFs). However, the molecular mechanisms used by myeloid tumor cells to escape apoptosis are not fully understood. Here we report that Myc/Raf-transformed macrophages require the transcription factor C/EBP␤ to prevent cell death. In contrast to wild-type cells, C/EBP␤ ؊/؊ macrophages were completely dependent on macrophage colony-stimulating factor or granulocyte-macrophage colony-stimulating factor for survival and displayed impaired tumorigenicity in vivo. Microarray analysis revealed that C/EBP␤-deficient cells expressed significantly reduced levels of the prosurvival factor insulin-like growth factor I (IGF-I). Overexpression of C/EBP␤ stimulated transcription from the IGF-I promoter, indicating that IGF-I is a direct transcriptional target of C/EBP␤. Serological neutralization of IGF-I in C/EBP␤