The microRNA miR-21 is overexpressed in many human cancers, wherein accumulating evidence indicates that it functions as an oncogene. Here, we report that the cytokine IFN rapidly induces miR-21 expression in human and mouse cells. Signal transducer and activator of transcription 3 (STAT3) was implicated in this pathway based on the lack of IFN effect on miR-21 expression in prostate cancer cells with a deletion in the STAT3 gene. STAT3 ablation abrogated IFN induction of miR-21, confirming the important role of STAT3 in regulating miR-21. Chromatin immunoprecipitation analysis showed that STAT3 directly bound the miR-21 promoter in response to IFN. Experiments in mouse embryo fibroblasts with a genetic deletion of the p65 NF-κB subunit showed that IFN-induced miR-21 expression was also dependent on NF-κB. STAT3 silencing blocked both IFN-induced p65 binding to the miR-21 promoter and p65 nuclear translocation. Thus, IFN-induced miR-21 expression is coregulated by STAT3 and NF-κB at the level of the miR-21 promoter. Several cell death regulators were identified as downstream targets of miR-21, including PTEN and Akt. Functional experiments in prostate cancer cells directly showed that miR-21 plays a critical role in suppressing IFN-induced apoptosis. Our results identify miR-21 as a novel IFN target gene that functions as a key feedback regulator of IFN-induced apoptosis.

The side chain of vitamin D3 is hydroxylated in a sequential manner by cytochrome P450scc (CYP11A1) to form 20-hydroxycholecalciferol, which can induce growth arrest and differentiation of both primary and immortalized epidermal keratinocytes. Since nuclear factor-κB (NF-κB) plays a pivotal role in the regulation of cell proliferation, differentiation and apoptosis, we examined the capability of 20-hydroxycholecalciferol to modulate the activity of NF-κB, using 1,25-dihydroxycholecalciferol (calcitriol) as a positive control. 20-hydroxycholecalciferol inhibits the activation of NFκB DNA binding activity as well as NF-κB-driven reporter gene activity in keratinocytes. Also, 20-hydroxycholecalciferol induced significant increases in the mRNA and protein levels of the NF-κB inhibitor protein, IκBα, in a time dependent manner, while no changes in total NF-κB-p65 mRNA or protein levels were observed. Another measure of NF-κB activity, p65 translocation from the cytoplasm into the nucleus was also inhibited in extracts of 20-hydroxycholecalciferol treated keratinocytes. Increased IκBα was concomitantly observed in cytosolic extracts of 20-hydroxycholecalciferol treated keratinocytes, as determined by immunoblotting and immunofluorescent staining. In keratinocytes lacking vitamin D receptor (VDR), 20-hydroxycholecalciferol did not affect IκBα mRNA levels, indicating that it requires VDR for its action on NF-κB activity. Comparison of the effects of calcitrol, hormonally active form of vitamin D3, with 20-hydrocholecalciferol show that both agents have a similar potency in inhibiting NF-κB. Since NF-κB is a major transcription factor for the induction of inflammatory mediators, our findings indicate that 20-hydroxycholecalciferol may be an effective therapeutic agent for inflammatory and hyperproliferative skin diseases.

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Background: DNA damage response and miRNAs have been linked to cancer progression. Results: Genotoxic drug induces up-regulation of miR-21 in a NF-B-and STAT3-dependent manner, which correlates with enhanced breast cancer cell invasion. Conclusion: Genotoxic NF-B activation promotes breast cancer invasion via miR-21 induction. Significance: Genotoxic NF-B signaling pathway may serve as a drug target to reduce therapeutic resistance and metastasis in breast cancer.

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The nuclear factor kB (NF-kB) transcription factor regulates the expression of genes involved in cell survival and immune responses. We have identified a novel interferon (IFN)-activated signaling pathway that leads to NF-kB activation and demonstrate that a subset of IFN-stimulated genes and microRNAs that play key roles in cellular response to IFN is regulated by NF-kB. This review focuses on the IFN-induced NF-kB activation pathway and the role of NF-kB in the expression of IFN-induced coding and noncoding genes, antiviral activity and apoptosis, and the therapeutic application of IFN in cancer and infectious disease.

STAT proteins play critical roles in the signal transduction pathways for various cytokines. The type I interferons (IFN␣͞␤) promote the DNA-binding activity of the transcription factors STAT1, STAT2, and STAT3. Although the requirement for STAT1 and STAT2 in IFN␣͞␤ signaling and action is well documented, the biological importance of STAT3 to IFN action has not yet been addressed. We found that STAT3 plays a critical role in signal transduction by IFN␣͞␤. A human cell line that is resistant to the antiviral and antiproliferative activities of IFN but is still IFN-responsive by virtue of STAT1 and STAT2 activation was found to be defective in STAT3 activation and in induction of NF-B DNA-binding activity. Expression of STAT3 in these resistant cells complemented these signaling defects and also markedly increased cellular sensitivity to the antiviral and antiproliferative effects of IFN. Because STAT3 is involved in the induction of NF-B DNA-binding activity and in the induction of antiviral and antiproliferative activity, our results place STAT3 as an important upstream element in type I IFN signal transduction and in the induction of biological activities. Therefore, our results indicate that STAT1 and STAT2 are not the only STATs required for the expression of the key biological activities of IFN␣͞␤.Interferons (IFNs) are cytokines that block the viral infection of cells, inhibit cell proliferation, and modulate cell differentiation. Type I IFNs (IFN ␣, ␤, and ) compete with each other for binding to a common cell surface receptor, whereas the receptor for type II IFN (IFN␥) is a distinct entity (1). The type I IFN receptor is composed of IFNAR1 and IFNAR2 chains (2-4), which undergo rapid, ligand-dependent tyrosine phosphorylation. Although IFNAR2 is the ligand-binding subunit, IFNAR1 acts as a species-specific transducer for the actions of type I IFN (5-7). IFNs transduce signals from the cell surface resulting in selective gene activation (8-10) through the activation of JAK tyrosine kinases and signal transducers and activators of transcription (STAT) factors (11,12). Upon their tyrosine phosphorylation, IFN-activated STATs (STAT1, STAT2, and STAT3) dimerize and translocate to the nucleus.The crucial role that STAT1 and STAT2 play in the transcriptional response to IFN␣͞␤ and in the induction of antiviral activity has been demonstrated in knockout mice and in mutant human cell lines deficient in these proteins. However, the importance of STAT3 in IFN␣͞␤ action has been unresolved. For example, knockout of the STAT3 gene in mice leads to early embryonic lethality and STAT3-deficient cell lines could not be isolated (13). We recently reported that STAT3 acts as a bridge (adapter) for the IFN-dependent interaction of the IFNAR1 receptor chain and the regulatory 85-kDa (p85) subunit of phosphatidylinositol-3Ј (PI-3) kinase (14). PI-3 kinase is important in the regulation of many cellular events involving protein tyrosine kinases and is an upstream element in a serine kinase transduction cascade (15, 1...

EF24 is a curcumin analog that has improved anticancer activity over curcumin, but its therapeutic potential and mechanism of action is unknown, which is important to address as curcumin targets multiple signaling pathways. EF24 inhibits the NF-κB but not the JAK-STAT signaling pathway in DU145 human prostate cancer cells and B16 murine melanoma cells. EF24 induces apoptosis in these cells apparently by inhibiting miR-21 expression, and also enhances the expression of several miR-21 target genes, PTEN and PDCD4. EF24 treatment significantly suppressed the growth of DU145 prostate cancer xenografts in immunocompromised mice and resulted in tumor regression. EF24 enhanced the expression of the miR-21 target PTEN in DU145 tumor tissue, but suppressed the expression of markers of proliferating cells (cyclin D1 and Ki67). In syngeneic mice injected with B16 cells, EF24 treatment inhibited the formation of lung metastasis, prolonged animal survival, inhibited miR-21 expression and increased the expression of miR-21 target genes. Expression profiling of miRNAs regulated by EF24 in vitro and in vivo showed that the antitumor activity of EF24 reflected the enhanced expression of potential tumor suppressor miRNAs as well as the suppressed expression of oncogenic miRNAs, including miR-21. Taken together, our data suggest that EF24 is a potent anticancer agent and selectively targets NF-κB signaling and miRNA expression, indicating that EF24 has significant potential as a therapeutic agent in various cancers.