Tumor necrosis factor‐α enhances the transcription of smad ubiquitination regulatory factor 1 in an activating protein‐1‐ and runx2‐dependent manner

Abstract

Smad ubiquitination regulatory factor 1 (Smurf1) is an E3 ubiquitin ligase that negatively regulates osteoblast differentiation. Although tumor necrosis factor-α (TNF-α) has been shown to increase Smurf1 expression, the details of the regulatory mechanisms remain unclear. Here, we investigated the molecular mechanism by which TNF-α stimulates Smurf1 expression in C2C12 and primary cultured mouse calvarial cells. TNF-α treatment rapidly induced the activation of NF-κB and MAPKs. Smurf1 induction by TNF-α was blocked by the inhibition of JNK or ERK, while the inhibition of NF-κB and p38 MAPK had no effect on Smurf1 induction. TNF-α treatment or c-Jun overexpression enhanced the activity of a luciferase reporter that contained a 2.7 kb mouse Smurf1 promoter sequence. Site-directed mutagenesis of the Smurf1 reporter and chromatin immunoprecipitation analysis demonstrated that the activating protein-1 (AP-1) binding motif at -922 bp on the mouse Smurf1 promoter mediated TNF-α/JNK/AP-1-stimulated Smurf1 transcription. Interestingly, Smurf1 expression was not observed in Runx2-null mouse calvarial cells. When Runx2 was ectopically expressed in these cells, the basal and TNF-α-induced expression of Smurf1 was restored. Overexpression of Runx2 transactivated the Smurf1 promoter in a dose-dependent manner. Reporter and chromatin immunoprecipitation assays demonstrated that the Runx2-binding motif at -202 bp functioned in Runx2-mediated Smurf1 expression. ERK activation by TNF-α treatment or constitutively active MEK1 overexpression increased Smurf1 expression in a Runx2-dependent manner. These results suggest that the JNK/AP-1 and ERK/Runx2 signaling pathways mediate TNF-α-dependent Smurf1 transcription.

On-Chip Evaluation of Neutrophil Activation and Neutrophil–Endothelial Cell Interaction during Neutrophil Chemotaxis

“…The same trend, down-regulation of these adhesion molecules, was found in our previous study where neutrophils were stimulated by CXC-motif chemokine 8 (CXCL8); 20 however, as multiple literature precedents also reported up-regulation of those molecules from neutrophils after stimulation, 41–43 this unexpected down-regulation was unexplained in the previous study. Upon close examination of precedent work done in co-culture, 41–43 we see that CD11b and CD66b expressions were up-regulated in EC-treated cells.…”

Melatonin reversed tumor necrosis factor‐alpha‐inhibited osteogenesis of human mesenchymal stem cells by stabilizing SMAD1 protein

“…Tumor necrosis factor‐alpha has been documented to regulate bone remodeling by suppressing osteogenesis and activating osteoclastogenesis . Quite a few signaling pathways are involved in mediating the effects of TNFα on osteogenesis as reported . Among them, SMURF1 seems particularly notable because SMURF1 itself is a well‐known negative regulator of bone formation.…”

“…TNF transgenic mice, which exhibited significantly decreased bone volume, had significantly lower SMAD1 protein level than wild‐type mice . In vitro studies demonstrated that TNFα suppressed both osteoblast function and MSCs osteogenesis via upregulating SMURF1, which may target SMAD1/5 or RUNX2 . Additionally, BMP2‐induced osteogenic differentiation and bone formation were dramatically inhibited in inflammatory environment .…”

Effect of sclerostin removal <i>in vivo</i> on experimental periodontitis in mice

“…This may occur through activation of MAPK signaling, which is induced by tumor necrosis factor (TNF)-α and TNF-related weak inducer of apoptosis (TWEAK) (22). In addition, Ras/ERK1/2 MAPK signaling, as the probable pathway in inflammatory bone resorption, is activated by TNF-α via the enhanced transcription of Smad ubiquitination regulatory factor 1 and is dependent on Runx2, which activates bone formation-related cytokines (23,24). ERK1/2-Runx2 signaling is also related to mechanical stress (25), which may explain why periodontitis frequently occurs during orthodontic treatment.…”