Metastasis-associated protein 1 (MTA1), a master chromatin modifier, has been shown to regulate cancer progression and is widely upregulated in human cancer including, hepatitis B virus-associated hepatocellular carcinomas (HCC). Here we provide evidence that hepatitis B virus transactivator protein HBx stimulates the expression of MTA1 but not MTA2 or MTA3. The underlying mechanism of HBx stimulation of MTA1 involves HBx targeting of transcription factor NF-κB and the recruitment of HBx/p65 complex to the NF-κB -consensus motif on the relaxed MTA1 gene chromatin. We also discovered that MTA1 depletion in HBx-expressing cells severely impairs the ability of HBx to stimulate NF-κB signaling and the expression of target pro-inflammatory molecules. Furthermore the presence of HBx in HBx-infected hepatocellular carcinomas correlated well with increased MTA1 and NF-κB-p65. Collectively, these findings revealed a previously unrecognized integral role of MTA1 in HBx stimulation of NF-κB signaling and consequently, the expression of NF-κB targets gene products with functions in inflammation and tumorigenesis.

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The MTA1 coregulator (metastatic tumor antigen 1), a component of the nucleosome remodeling and deacetylase (NuRD) complex, has been intimately linked with human cancer, but its role in inflammatory responses remains unknown. Here, we discovered that MTA1 is a target of inflammation, and stimulation of macrophages with Escherichia coli lipopolysaccharide (LPS) stimulates MTA1 transcription via the NF-B pathway. Unexpectedly, we found that MTA1 depletion in LPS-stimulated macrophages impairs NF-B signaling and expression of inflammatory molecules. MTA1 itself acts as a transcriptional coactivator of inflammatory cytokines in LPS-stimulated macrophages, and in contrast, it acts as a corepressor in resting primary macrophages as its depletion induced cytokine expression. LPS stimulates S-nitrosylation of histone deacetylase 2 (HDAC2) and interferes with its binding to MTA1, which, in turn, resulted in the loss of corepressor behavior of MTA1⅐HDAC complex in activated macrophages. Consequently, the net levels of inflammatory cytokines in LPSstimulated macrophages from MTA1 ؊/؊ mice were high compared with wild-type mice. Accordingly, MTA1 ؊/؊ mice were much more susceptible than control mice to septic shock induced by LPS, revealing that MTA1 protects mice from deregulated host inflammatory response. These findings reveal a previously unrecognized, critical homeostatic role of MTA1, both as a target and as a component of the NF-B circuitry, in the regulation of inflammatory responses.

Nitric oxide has been implicated in the pathogenesis of inflammatory disorders, including hepatitis B virus-associated hepatocellular carcinoma. Transactivator protein HBx, a major regulator of cellular responses of hepatitis B virus, is known to induce the expression of MTA1 (metastasis-associated protein 1) coregulator via NF-B signaling in hepatic cells. However, the underlying mechanism of HBx regulation of the inducible nitric-oxide synthase (iNOS) pathway remains unknown. Here we provide evidence that MTA1 is a positive regulator of iNOS transcription and plays a mechanistic role in HBx stimulation of iNOS expression and activity. We found that the HBx-MTA1 complexisrecruitedontothehumaniNOSpromoterinanNF-Bdependent manner. Pharmacological inhibition of the NF-B signaling prevented the ability of HBx to stimulate the transcription, the expression, and the activity of iNOS; nevertheless, these effects could be substantially rescued by MTA1 dysregulation. We further discovered that HBx-mediated stimulation of MTA1 is paralleled by the suppression of miR-661, a member of the small noncoding RNAs, recently shown to target MTA1. We observed that miR-661 controls of MTA1 expression contributed to the expression and activity of iNOS in HBx-expressing HepG2 cells. Accordingly, depletion of MTA1 by either miR-661 or siRNA in HBx-expressing cells severely impaired the ability of HBx to modulate the endogenous levels of iNOS and nitrite production. Together, these findings reveal an inherent role of MTA1 in HBx regulation of iNOS expression and consequently its function in the liver cancer cells.