6-Shogaol has been shown to possess many antitumor properties including inhibition of cancer cell growth, inhibition of cancer metastasis, induction of apoptosis in cancer cells and induction of cancer cell differentiation. Despite its prominent antitumor effects, the direct molecular target of 6-shogaol has remained elusive. To identify the direct targets of 6-shogaol, a comprehensive antitumor profile of 6-shogaol (NSC752389) was tested in the NCI-60 cell line in an in vitro screen. The results show that 6-shogaol is COMPARE negative suggesting that it functions via a mechanism of action distinct from existing classes of therapeutic agents. Further analysis using microarray gene profiling and Connectivity Map analysis showed that MCF-7 cells treated with 6-shogaol display gene expression signatures characteristic of peroxisome proliferator activated receptor γ (PPARγ) agonists, suggesting that 6-shogaol may activate the PPARγ signaling pathway for its antitumor effects. Indeed, treatment of MCF-7 and HT29 cells with 6-shogaol induced PPARγ transcriptional activity, suppressed NFκB activity, and induced apoptosis in breast and colon cancer cells in a PPARγ-dependent manner. Furthermore, 6-shogaol is capable of binding to PPARγ with a binding affinity comparable to 15-delta prostaglandin J2, a natural ligand for PPARγ. Together, our findings suggest that the antitumor effects of 6-shogaol are mediated through activation of PPARγ and imply that activation of PPARγ might be beneficial for breast and colon cancer treatment.
Interleukin-6 (IL-6) is the major activator of the acute phase response (APR). One important regulator of IL-6-activated APR is peroxisome proliferator-activated receptor alpha (PPARα). Currently, there is a growing interest in determining the role of PPARα in regulating APR; however, studies on the molecular mechanisms and signaling pathways implicated in mediating the effects of IL-6 on the expression of PPARα are limited. We previously revealed that IL-6 inhibits PPARα gene expression through CAAT/enhancer-binding protein transcription factors in hepatocytes. In this study, we determined that STAT1/3 was the direct downstream molecules that mediated the Janus kinase 2 (JAK2) and phosphatidylinositol-3 kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathways in IL-6-induced repression of PPARα. Treatment of cells with pharmacological inhibitors of JAK2, PI3K, AKT, and mTOR attenuated the inhibitory effect of IL-6 on PPARα protein in a dose-dependent manner. These inhibitors also decreased the IL-6-induced repression of PPARα mRNA expression and promoter activity. Overexpression of STAT1 and STAT3 in HepG2 cells cotransfected with a reporter vector containing this PPARα promoter region revealed that both the expression plasmids inhibited the IL-6-induced repression of PPARα promoter activity. In the presence of inhibitors of JAK2 and mTOR (AG490 and rapamycin, respectively), IL-6-regulated protein expression and DNA binding of STAT1 and STAT3 were either completely or partially inhibited simultaneously, and the IL-6-induced repression of PPARα protein and mRNA was also inhibited. This study has unraveled novel pathways by which IL-6 inhibits PPARα gene transcription, involving the modulation of JAK2/STAT1-3 and PI3K/AKT/mTOR by inducing the binding of STAT1 and STAT3 to STAT-binding sites on the PPARα promoter. Together, these findings represent a new model of IL-6-induced suppression of PPARα expression by inducing STAT1 and STAT3 phosphorylation and subsequent down-regulation of PPARα mRNA expression.
H3K4 trimethylation is strongly associated with active transcription. The deposition of this mark is catalyzed by SET-domain methyltransferases, which consist of a subcomplex containing WDR5, ASH2L, and RBBP5 (the WAR subcomplex); a catalytic SET-domain protein; and additional complexspecific subunits. The ERK MAPK pathway also plays an important role in gene regulation via phosphorylation of transcription factors, co-regulators, or histone modifier complexes. However, the potential interactions between these two pathways remain largely unexplored. We investigated their potential interplay in terms of the regulation of the immediate early gene (IEG) regulatory network. We found that depletion of components of the WAR subcomplex led to increased levels of unspliced transcripts of IEGs that did not necessarily reflect changes in their mature transcripts. This occurs in a manner independent from changes in the H3K4me3 levels at the promoter region. We focused on FOS and found that the depletion of WAR subcomplex components affected the efficiency of FOS transcript processing. Our findings show a new aspect of WAR subcomplex function in coordinating active transcription with efficient pre-mRNA processing.
To investigate the mechanistic action of brewers' rice in regulating the Wnt/nuclear factor-kappa B (NF-κB)/Nrf2-signaling pathways during colon carcinogenesis in male Sprague-Dawley rats.