C/EBP Mediates Synergistic Upregulation of Gene Expression by Interferon- and Tumor Necrosis Factor- in Bone Marrow-Derived Mesenchymal Stem Cells

摘要

Mesenchymal stem cells (MSCs) are potent immunoregulators and have shown clinical utility in suppressing immunity. MSC function is modulated by cytokines, since inflammatory cytokines, such as interferon- (IFN) concomitant with tumor necrosis factor- (TNF), induce their immunoregulatory capability. Here, we show that IFN and TNF act synergistically to induce high levels of expression of interleukin-6 (IL-6) and several other immune-related molecules in MSCs in vitro. We further found that, while either IFN or TNF alone induced minor expression of C/EBP in MSCs, this transcription factor was dramatically upregulated when these cytokines were added together. A causal relationship between C/EBP upregulation and IL-6 expression was demonstrated by small interfering RNA knockdown of C/EBP. C/EBP knockdown also inhibited the synergistic expression of CXCL1, inducible nitric oxide synthase, and CCL5 in response to concomitant IFN and TNF. We conclude that C/EBP is a key transcription factor in synergistic gene upregulation by IFN and TNF. Importantly, C/EBP similarly mediated synergistic gene induction in response to IFN accompanied by IL-1 or lipopolysaccharide, suggesting that synergy between IFN and other stimuli share C/EBP as common mechanism. Furthermore, while STAT1 is critical in IFN signaling, we found that STAT1 knockdown in MSCs did not affect C/EBP expression or the synergistic induction of IL-6 and CXCL1 by IFN and TNF. Thus, C/EBP is not regulated by STAT1. These results demonstrate the importance of cytokine interactions in MSC immunobiology, a better understanding of which will allow improved clinical application of these cells. STEM CELLS 2009;27:942-948