Excessive Tnf-Alpha Production Results From Reduction Of C-Fos Via Aberrant Expression Of Mir-34a In Neutrophils From Myelodysplastic Syndrome Patients

The molecular basis of ineffective hematopoiesis in myelodysplastic syndromes (MDS) has yet to be defined. Elevation of tumor necrosis factor (TNF)-α in bone marrow plasma has been considered to be a cause of apoptosis of hematopoietic progenitor cells, and this could result in ineffective hematopoiesis in MDS. However, the mechanism of TNF-α elevation has not been elucidated. We recently found aberrant regulation of c-fos mRNA stability in neutrophils isolated from MDS patients (Feng et al, PLoS ONE, 2013). Since the expression levels of RNA-binding proteins that regulated c-fos mRNA stability were not altered in the majority of the patients and no mutations were detected in c-fos mRNA, microRNAs were possibly involved in the insufficient stabilization of c-fos mRNA. In this study, we chose 20 microRNAs targeting c-fos according to four different databases and compared their expression levels in neutrophils between MDS patients and healthy volunteers. Among them, miR-34a and miR-155 were significantly increased in MDS (p Recently, it was reported that c-fos physically interacted with nuclear factor κB (NF-κB) p65 to inhibit transcription of TNF-α in response to pro-inflammatory cytokines such as lipopolysaccharide (LPS) in monocytic cells (Koga et al, Immunity, 2009). Therefore, we hypothesized that neutrophils with reduced c-fos would overproduce TNF-α in response to inflammatory stimuli in MDS. To test our hypothesis, siRNA for c-fos was introduced into HL60 cells that were differentiated toward a neutrophil-like phenotype by 1.25% DMSO. The treatment with siRNA decreased c-fos protein levels to 58.8 ± 19.6-fold of that in the control cells. When stimulated with 1 μM LPS for 3 hours, the increase rates of TNF-α mRNA were greater in c-fos siRNA-treated cells (41.2 ± 25.7-fold, p Disclosures No relevant conflicts of interest to declare.