The STAT3 inhibitor Stattic acts independently of STAT3 to decrease histone acetylation and modulate gene expression.

Signal transducer and activator of transcription 3 (STAT3) is an important transcription factor involved in many physiological functions including embryonic development and immune responses and is often activated under pathological conditions such as cancer. Strategies to inactivate STAT3 are being pursued as potential anticancer therapies and have led to the identification of Stattic (6-nitrobenzo[b]thiophene-1,1-dioxide) as a "specific" STAT3 inhibitor that is often used to interrogate STAT3-mediated gene expression in vitro and in vivo. Here, we show that Stattic exerts many STAT3-independent effects on cancer cells, calling for reassessment of results previously ascribed to STAT3 functions. Studies of the STAT3-deficient prostate cancer cell line PC-3 (PC3) along with STAT3-proficient breast cancer cell lines (MDA-MB-231, SUM149) revealed that Stattic attenuated histone acetylation and neutralized effects of the histone deacetylase (HDAC) inhibitor romidepsin. In PC3 cells, Stattic alone inhibited gene expression of CCL20 and CCL2, but activated expression of TNFA, CEBPD, SOX2, and MYC. In addition, we found that Stattic promoted autophagy and caused cell death. These data point to profound epigenetic effects of Stattic that are independent of its function as a STAT3 inhibitor. Our results demonstrate that Stattic directly or indirectly reduces histone acetylation and suggest reevaluation of Stattic and related compounds as polypharmacological agents through multipronged cytotoxic effects on cancer cells.

Reprogramming factors induce proliferation and inhibit apoptosis of melanoma cells by changing the expression of particular genes.

Uncontrolled proliferation and defective apoptosis are two major factors responsible for maintaining the malignant properties of melanoma cells. Our previous study demonstrated that induced expression of four reprogramming factors remodeled the phenotype of B16­F10 mouse melanoma cells into melanoma stem cells. The present study was conducted to investigate the effect of the four Yamanaka reprogramming factors, namely Oct4, Sox2, Klf4 and c­Myc (OSKM), on the proliferation and apoptosis of melanoma cells, and to identify the responsible molecular signals. The results identified that expression of the four reprogramming factors was highly induced by doxycycline treatment in the stable melanoma cell clone that was transfected with a plasmid expressing these factors, driven by the Tet­On element. It was further confirmed that induced expression of these factors enhanced the proliferation and suppressed the apoptosis of the melanoma cells. In addition, induced OSKM expression increased cell proliferation, accelerated the progression of the cell cycle, and upregulated the mRNA expression levels of Janus kinase 2 (JAK2) and Cyclin­B1. Induced expression of these factors also decreased the apoptosis, as well as upregulated B­cell lymphoma 2 (BCL­2) and downregulated BCL­2­associated X (BAX) mRNA expression levels. Taken together, the results suggested that upregulated JAK2 and Cyclin­B1 may be responsible for the enhanced proliferation of melanoma cells, and that BCL­2 upregulation and BAX downregulation may account for the suppressed apoptosis of these cells.

Hepatitis C virus ARFP/F protein interacts with cellular MM-1 protein and enhances the gene trans-activation activity of c-Myc.

The ARFP/F protein is synthesized from the +1 reading frame of the hepatitis C virus (HCV) core protein gene. The function of this protein remains unknown. To study the function of the HCV ARFP/F protein, we have conducted the yeast two-hybrid screening experiment to identify cellular proteins that may interact with the ARFP/F protein. MM-1, a c-Myc interacting protein, was found to interact with HCV ARFP/F protein in this experiment. The physical interaction between ARFP/F and MM-1 proteins was further confirmed by the GST pull-down assay, the co-immunoprecipitation assay and confocal microscopy. As MM-1 can inhibit the gene transactivation activity of c-Myc, we have conducted further analysis to examine the possible effect of the ARFP/F protein on c-Myc. Our results indicate that the HCV ARFP/F protein can enhance the gene trans-activation activity of c-Myc, apparently by antagonizing the inhibitory effect of MM-1. The ability of the ARFP/F protein to enhance the activity of c-Myc raises the possibility that ARFP/F protein might play a role in hepatocellular transformation in HCV patients.

Down-regulation of 5S rRNA by miR-150 and miR-383 enhances c-Myc-rpL11 interaction and inhibits proliferation of esophageal squamous carcinoma cells.

5S rRNA plays an important part in ribosome biology and is over-expression in multiple cancers. In this study, we found that 5S rRNA is a direct target of miR-150 and miR-383 in esophageal squamous cell carcinoma (ESCC). Overexpression of miR-150 and miR-383 inhibited ESCC cell proliferation in vitro and in vivo. Moreover, 5S rRNA silencing by miR-150 and miR-383 might intensify rpL11-c-Myc interaction, which attenuated role of c-Myc as an oncogenic transcriptional factor and dysregulation of multiple c-Myc target genes. Taken together, our results highlight the involvement of miRNAs in ribosomal regulation during tumorigenesis.

Glucagon phosphorylates serine 552 of ß-catenin leading to increased expression of cyclin D1 and c-Myc in the isolated rat liver.

In the last 20 years the prevalence of metabolic disorders, in particular type 2 diabetes (T2D), has more than doubled. Recently, a strong link between T2D and cancer, in particularly liver cancer has been reported. However, the mechanism connecting the development of type 2 diabetes and cancer remains unknown. One of the biggest drivers of liver cancer is alterations in the Wnt/ß-catenin pathway. In this study, we aimed to identify the effect of glucagon on ß-catenin in the isolated rat liver. We found glucagon, which is substantially raised in patients with T2D, rapidly phosphorylates ß-catenin on serine 552 that is associated with increased expression of genes cyclin D1 (CCND1) and c-Myc (MYC), which are known to be involved in liver cancer. This finding may explain the increased risk of liver cancer in people with T2D.