Expression Of Signal Transducer And Activator Of Transcription 3 Target Genes Research Articles

STAT3 palmitoylation initiates a positive feedback loop that promotes the malignancy of hepatocellular carcinoma cells in mice.

Constitutive activation of the transcription factor STAT3 (signal transducer and activator of transcription 3) contributes to the malignancy of many cancers such as hepatocellular carcinoma (HCC) and is associated with poor prognosis. STAT3 activity is increased by the reversible palmitoylation of Cys108 by the palmitoyltransferase DHHC7 (encoded by ZDHHC7). Here, we investigated the consequences of S-palmitoylation of STAT3 in HCC. Increased ZDHHC7 abundance in HCC cases was associated with poor prognosis, as revealed by bioinformatics analysis of patient data. In HepG2 cells in vitro, DHHC7-mediated palmitoylation enhanced the expression of STAT3 target genes, including HIF1A, which encodes the hypoxia-inducible transcription factor HIF1α. Inhibiting DHHC7 decreased the S-palmitoylation of STAT3 and decreased HIF1α abundance. Furthermore, stabilization of HIF1α by cyclin-dependent kinase 5 (CDK5) enabled it to promote the expression of ZDHHC7, which generated a positive feedback loop between DHHC7, STAT3, and HIF1α. Perturbing this loop reduced the growth of HCC cells in vivo. Moreover, DHHC7, STAT3, and HIF1α were all abundant in human HCC tissues. Our study identifies a pathway connecting these proteins that is initiated by S-palmitoylation, which may be broadly applicable to understanding the role of this modification in cancer.

Selectively Targeting STAT3 Using a Small Molecule Inhibitor is a Potential Therapeutic Strategy for Pancreatic Cancer.

Pancreatic cancer is the worst prognosis among all human cancers, and novel effective treatments are urgently needed. Signal transducer and activator of transcription 3 (STAT3) has been demonstrated as a promising target for pancreatic cancer. Meanwhile, selectively targeted STAT3 with small molecule remains been challenging. To specifically identify STAT3 inhibitors, more than 1.3 million compounds were screened by structure-based virtual screening and confirmed with the direct binding assay. The amino acid residues that WB436B bound to were verified by induced-fit molecular docking simulation, RosettaLigand computations, and site-directed mutagenesis. On-target effects of WB436B were examined by microscale thermophoresis, surface plasmon resonance, in vitro kinase assay, RNA sequencing, and selective cell growth inhibition assessment. In vivo studies were performed in four animal models to evaluate effects of WB436B on tumor growth and metastasis. Kaplan-Meier analyses were used to assess survival. WB436B selectively bound to STAT3 over other STAT families protein, and in vitro antitumor activities were improved by 10 to 1,000 fold than the representative STAT3 inhibitors. WB436B selectively inhibits STAT3-Tyr705 phosphorylation, STAT3 target gene expression, and the viability of STAT3-dependent pancreatic cancer cells. WB436B significantly suppresses tumor growth and metastasis in vivo and prolongs survival of tumor-bearing mice. Mechanistic studies showed that WB436B have unique binding sites located in STAT3 Src homology 2 domain. Our work presents the first-in-class selective STAT3 inhibitor WB436B as a potential therapeutic candidate for the treatment of pancreatic cancer.

The Root Extract of Peucedanum praeruptorum Dunn Exerts Anticancer Effects in Human Non-Small-Cell Lung Cancer Cells with Different EGFR Mutation Statuses by Suppressing MET Activity.

The aim of this study was to investigate the anticancer effects of the root extract of Peucedanum praeruptorum Dunn (EPP) in human non-small-cell lung cancer (NSCLC) cells and explore the mechanisms of action. We used four types of human lung cancer cell lines, including H1299 (epidermal growth factor receptor (EGFR) wild-type), PC9 (EGFR Glu746-Ala750 deletion mutation in exon 19; EGFR tyrosine kinase inhibitor (TKI)-sensitive), H1975 (EGFR L858R/T790M double-mutant; EGFR TKI-resistant), and PC9/ER (erlotinib-resistant) cells. EPP suppressed cell growth and the colony formation of NSCLC cells in a concentration-dependent manner. EPP stimulated chromatin condensation, increased the percentage of sub-G1 phase cells, and enhanced the proportion of annexin V-positive cells, demonstrating that EPP triggered apoptosis in NSCLC cells regardless of the EGFR mutation and EGFR TKI resistance status. The phosphorylation level of the signal transducer and activator of transcription 3 (STAT3) and AKT was decreased by EPP. The expression of STAT3 target genes was also downregulated by EPP. EPP reversed hepatocyte growth factor (HGF)-induced MET phosphorylation and gefitinib resistance. Taken together, our results demonstrate that EPP exerted anticancer effects not only in EGFR TKI-sensitive NSCLC cells, but also in EGFR TKI-resistant NSCLC cells, by suppressing MET activity.

Selected Articles from This Issue

Despite previous assumptions that constitutively high Wnt signaling promotes colorectal cancer in each stage of disease, recent studies have demonstrated that reduced Wnt signaling is associated with colorectal cancer invasiveness and poor prognoses. However, little work has been done to elucidate how diminished Wnt signaling underlies aggressive colorectal cancer phenotypes. Chen and colleagues used genetic manipulation strategies and orthotopic mouse models to show that abrogating Wnt signaling increases colorectal cancer invasiveness and decreases immune responsiveness in vivo. Disrupting Wnt signaling by targeting Wnt coreceptor LDL receptor-related protein 6 (LRP6) with CRISPR/Cas9 or transducing a dominant negative version of Wnt transcriptional effector lymphoid enhancer binding factor 1 (LEF1) increases tumor submucosal invasion and dissemination in mice. Using RNA-Seq, the authors revealed that reducing Wnt signaling elevates expression of markers associated with stemness and a mesenchymal phenotype, while repressing expression of immune-stimulatory molecules and collagens. The authors used TCGA data to demonstrate that the low Wnt signaling expression profile corresponds with poor survival in colorectal cancer patients, underscoring the potential clinical relevance of dampened Wnt signaling in colorectal cancer progression.Cholangiocarcinoma (CCA) is an aggressive biliary tract cancer for which effective therapeutics are lacking. Prostaglandin E2 (PGE2)-mediated inflammation is a critical component of CCA carcinogenesis and progression. 15-hydroxyprostaglandin dehydrogenase (15-PGDH) chemically modifies and inactivates PGE2, but its expression is often diminished in CCA. In their work, Zhang and colleagues leveraged public data to show that expression of histone methyltransferase G9a negatively correlates with 15-PGDH expression. The authors validated the G9a-15-PGDH relationship in a mouse model of CCA in which the Notch intracellular domain and constitutively active Akt are expressed via hydrodynamic injection of sleeping beauty transposase-based plasmids. shRNA-mediated G9a silencing increases 15-PGDH expression in CCA cell lines, limiting cell proliferation in vitro and tumor growth in vivo. ChIP assays demonstrated that G9a is recruited to the 15-PGDH promoter by the Myc/Max/E-box complex, which prevents signal transducer and activator of transcription 4 (STAT4) from binding the promoter and inducing 15-PGDH expression. The work presented elucidates a previously unknown mechanism underlying CCA development and progression and reveals a novel potential target for CCA therapeutic strategies.Neurofibromatosis type 2 is characterized by growth of benign nervous system tumors, such as schwannomas, which can lead to deafness, brain stem compression, and death. Neurofibromatosis type 2 is caused by mutations in tumor suppressor gene NF2. Previously, Cho and colleagues demonstrated that NF2 loss promotes elevated TβR1 signaling, resulting in phosphorylation and degradation of tumor suppressor Raf kinase inhibitor protein (RKIP). While TGF-β inhibitors halt schwannoma growth, they are not ideal therapeutics given schwannomas occur around adolescence and TGF-β is required for development. Here, Cho and colleagues developed a novel TβR1 inhibitor, Nf18001, that abrogates TβR1-mediated RKIP degradation while maintaining canonical TGF-β signaling. The authors used human and mouse schwannoma cell lines to demonstrate that Nf18001 disrupts TβR1-RKIP interactions to sustain RKIP expression and lower NF2-mutant cell viability while not influencing normal fibroblast survival. Nf18001 arrests cell cycle progression in schwannoma cells, and augments Schwann cell differentiation marker expression while diminishing expression of markers associated with cell stemness. Nf18001 also displayed efficacy in a schwannoma allograft mouse model, where treatment slowed tumor growth.The pro-tumorigenic role of signal transducer and activator of transcription 3 (STAT3) in multiple myeloma has been established, but therapeutically targeting STAT3 has proven challenging. Similarly, given its canonical role in DNA damage repair, checkpoint kinase 1 (Chk1) inhibition has been tested in anti-cancer therapeutic regimens, but with ambiguous results. In their study, Zhou and colleagues employed a gene expression array to demonstrate that Chk1 inhibition diminishes expression of oncogenic STAT3 target genes in multiple myeloma cells, suggesting Chk1 inhibition may also effectively inhibit STAT3 activity. Subsequent work showed that Chk1 directly binds to STAT3 and phosphorylates it at tyrosine 705, enabling STAT3 dimerization and DNA binding. Chk1 inhibition — pharmacologically and via shRNA silencing — diminishes STAT3 tyrosine 705 phosphorylation and inhibits STAT3 DNA binding, reducing expression of STAT3 transcriptional targets. Chk1 inhibition abrogates STAT3 tyrosine 705 phosphorylation in IL-6–dependent, -independent, and bortezomib-resistant cells, as well as in patient primary myeloma mononuclear cells and multiple myeloma cells implanted into mice, suggesting Chk1 inhibition may provide therapeutic efficacy against multiple myeloma through a STAT3-related mechanism.

8-Epi-xanthatin induces the apoptosis of DU145 prostate carcinoma cells through signal transducer and activator of transcription 3 inhibition and reactive oxygen species generation.

Signal transducer and activator of transcription 3 (STAT3) is aberrantly activated in many human cancers. We tried to find STAT3 inhibitors from natural sources and found that Xanthium fruit extracts decreased phosphorylation of STAT3-Y705. 8-Epi-xanthatin (EXT) was isolated from the extracts. When DU145 cancer cells were treated with EXT, p-STAT3-Y705 was decreased with an IC50 of 3.2 μM. EXT decreased the expression of STAT3 target genes, such as cyclin A, cyclin D1, and BCL-2, and induced PARP cleavage, indicating apoptotic cell death. Downregulation of EXT-induced p-STAT3-Y705 was rescued by pretreating DU145 cells with antioxidants, such as N-acetyl-L-cysteine (NAC), indicating that reactive oxygen species (ROS) were involved in the EXT-induced inhibition of STAT3 activation. Furthermore, we proved the association of EXT with STAT3 protein by using a drug affinity responsive target stability (DARTS) assay and a cellular thermal shift assay (CETSA). EXT inhibited proliferation of DU145 cells with a GI50 of 6 μM and reduced tumor growth in mice xenografted with DU145 cells. Immunoblotting showed that phosphorylation of STAT3-Y705 was lower in EXT-treated tumor tissue than in control tissues. Collectively, we found that EXT binds to, and inhibits, STAT3 activation and could be a lead compound for anticancer therapy.

Napabucasin, a novel inhibitor of STAT3, inhibits growth and synergises with doxorubicin in diffuse large B-cell lymphoma.

Diffuse large B-cell lymphoma (DLBCL), the most common type of aggressive non-Hodgkin lymphoma (NHL), has highly heterogeneous molecular characteristics. Although some patients initially respond to standard R-CHOP therapy, 30-40% develop refractory disease or suffer relapse. Signal transducer and activator of transcription 3 (STAT3), which regulates multiple oncogenic processes, has been found to be constitutively activated in various cancers, including DLBCL, suggesting its potential as a therapeutic target. In this study, we determined that 34% (23/69) of DLBCL patients expressed pSTAT3 (Y705) in tumour tissues. Napabucasin, a novel STAT3 inhibitor, exhibited potent cytotoxicity against NHL cell lines in a dose-dependent manner. Mechanistic studies demonstrated that napabucasin induced intrinsic and extrinsic cell apoptosis, downregulated the expression of STAT3 target genes, including the antiapoptotic protein Mcl-1, and regulated the ROS-mediated mitogen-activated protein kinase (MAPK) pathway. Most importantly, in vivo studies revealed the suppressive efficacy of napabucasin as a monotherapy without obvious toxicity. Furthermore, preliminary combination studies of napabucasin with doxorubicin showed significant synergism both in vitro and in vivo. Thus, our studies provide evidence that napabucasin alone or in combination is a promising therapeutic candidate for DLBCL patients.

Cucurbitacin B inhibits gastric cancer progression by suppressing STAT3 activity

Signal transducer and activator of transcription 3 (STAT3) is expressed aberrantly in multiple tumors, including gastric cancer (GC). STAT3 overexpression and excessive activation have been confirmed to play vital roles in tumorigenesis. Cucurbitacin B (CuB) is a natural product with potent anti-cancer activities in solid tumors. Here, we systematically studied the underlying molecular mechanisms of CuB inhibition of GC both in vitro and in vivo. In GC cell lines, nanomolar concentrations of CuB decreased the phosphorylation of TYR-705 in STAT3 and suppressed STAT3 target gene expression, including c-Myc and Bcl-xL. Computational docking analysis showed that CuB interacts with the DNA-binding domain of STAT3 at several hydrophobic residues. In addition, pull-down experiments showed that CuB is a direct inhibitor of STAT3. CuB in combination with the conventional chemotherapy drug cisplatin exerted enhanced cytotoxicity in GC cells, possibly due to the potentiated inhibition of STAT3 activation. Moreover, a xenograft mouse model confirmed the therapeutic effect of CuB in vivo. These characteristics render CuB a promising candidate drug for further development in the design of new effective STAT3 inhibitors for treating GC.

A Sesquiterpenoid from Farfarae Flos Induces Apoptosis of MDA-MB-231 Human Breast Cancer Cells through Inhibition of JAK-STAT3 Signaling.

Triple-negative breast cancers (TNBCs) are hard-to-treat breast tumors with poor prognosis, which need to be treated by chemotherapy. Signal transducer and activator of transcription 3 (STAT3) is a transcription factor involved in proliferation, metastasis, and invasion of cancer cells. Therefore, research on searching for promising compounds with metabolism that suppress phosphorylation or transcription of STAT3 in TNBC cells is important. Farfarae Flos is well known as a traditional medicine for treating inflammation. However, few studies have shown that sesquiterpenoids from Farfarae Flos have an anticancer effect. In this study, efficient separation methods and an MTT assay were conducted to isolate an anticancer compound from Farfarae Flos against TNBC MDA-MB-231 cells. Here, 7β-(3-Ethyl-cis-crotonoyloxy)-1α-(2-methylbutyryloxy)-3,14-dehydro-Z-notonipetranone (ECN), a compound isolated from Farfarae Flos showed a potent cytotoxic effect on MDA-MB-231 cells. ECN inhibited JAK–STAT3 signaling and suppressed the expression of STAT3 target genes. In addition, ECN induced apoptosis through both extrinsic and intrinsic pathways. Furthermore, we investigated that ECN inhibited the growth of tumors by intraperitoneal administration in mice injected with MDA-MB-231 cells. Therefore, ECN can be an effective chemotherapeutic agent for breast cancer treatment.

Triptolide exerts an anti-tumor effect on non‑small cell lung cancer cells by inhibiting activation of the IL‑6/STAT3 axis.

Lung cancer is the leading cause of cancer‑associated mortality and current treatments are not sufficiently effective. Numerous studies have revealed that triptolide (TP), a classical traditional Chinese medicine compound widely used as an anti‑inflammatory and antirheumatic drug, also has an antitumor effect. This effect is hypothesized to be mediated by multiple pathways, with signal transducer and activator of transcription 3 (STAT3) possibly one of them. Evidence indicates that STAT3 participates in the initiation and progression of lung cancer during cell proliferation, apoptosis and migration; however, whether and how TP affects STAT3 and its targets remain unclear. In this study, the potential role of TP in the proliferation, apoptosis, and migration of non‑small cell lung cancer cell lines was investigated and evaluated the impact of TP on the interleukin‑6 (IL‑6)/STAT3 axis. The results showed that TP inhibited cell proliferation and migration and induced apoptosis. TP decreased the phosphorylation of STAT3, inhibited STAT3 translocation into the nucleus, and reduced the expression of STAT3 target genes involved in cell survival, apoptosis and migration, e.g. C‑myc, BCL‑2, myeloid cell leukemia‑1 (MCL‑1), and matrix metallopeptidase 9 (MMP‑9). Additionally, IL‑6‑induced activation of STAT3 target genes (e.g. MCL‑1 and BCL‑2) was attenuated by TP and homoharringtonine. In conclusion, the effect of TP on STAT3 signaling points to a promising strategy for drug development.

Suppression of EGFR/STAT3 activity by lupeol contributes to the induction of the apoptosis of human non‑small cell lung cancer cells.

The aim of this study was to investigate the underlying mechanisms responsible for the anticancer effects of lupeol on human non‑small cell lung cancer(NSCLC). MTT assay and Trypan blue exclusion assay were used to evaluate the cell viability. DAPI staining and flow cytometric analysis were used to detect apoptosis. Molecular docking and western blot analysis were performed to determine the target of lupeol. We found that lupeol suppressed the proliferation and colony formation of NSCLC cells in a dose‑dependent manner. In addition, lupeol increased chromatin condensation, poly(ADP‑ribose) polymerase (PARP) cleavage, sub‑G1 cell populations, and the proportion of AnnexinV‑positive cells, indicating that lupeol triggered the apoptosis of NSCLC cells. Notably, lupeol inhibited the phosphorylation of epithelial growth factor receptor(EGFR). A docking experiment revealed that lupeol directly bound to the tyrosine kinase domain of EGFR. We observed that the signal transducer and activator of transcription3 (STAT3), a downstream molecule of EGFR, was also dephosphorylated by lupeol. Lupeol suppressed the nuclear translocation and transcriptional activity of STAT3 and downregulated the expression of STAT3 target genes. The constitutive activation of STAT3 by STAT3 Y705D overexpression suppressed lupeol‑induced apoptosis, demonstrating that the inhibition of STAT3 activity contributed to the induction of apoptosis. The anticancer effects of lupeol were consistently observed in EGFR tyrosine kinase inhibitor (TKI)‑resistant H1975 cells (EGFR L858R/T790M). Taken together, the findings of this study suggest that lupeol may be used, not only for EGFRTKI‑naïve NSCLC, but also for advanced NSCLC with acquired resistance to EGFRTKIs.

YL064 directly inhibits STAT3 activity to induce apoptosis of multiple myeloma cells

Aberrant activation of signal transducer and activator of transcription 3 (STAT3) plays a critical role in the proliferation and survival of multiple myeloma. And inactivation of STAT3 is considered a promising strategy for the treatment of multiple myeloma. Here we show that the sinomenine derivative YL064 could selectively reduce the cell viability of multiple myeloma cell lines and primary multiple myeloma cells. Moreover, YL064 also induces cell death of myeloma cells in the presence of stromal cells. Western blot analysis showed that YL064 inhibited the constitutive activation and IL-6-induced activation of STAT3, reflected by the decreased phosphorylation of STAT3 on Tyr705. Consistent with this, YL064 inhibited the nuclear translocation of STAT3 and the expression of STAT3 target genes, such as cyclin D1 and Mcl-1. Using biotin- and FITC-labeled YL064, we found that YL064 could pull-down STAT3 from myeloma cells and colocalized with STAT3, suggesting that YL064 directly targets STAT3. Cellular thermal shift assay further demonstrated the engagement of YL064 to STAT3 in cells. Molecular docking studies indicated that YL064 may interact with STAT3 in its SH2 domain, thereby inhibiting the dimerization of STAT3. Finally, YL064 inhibited the growth of human myeloma xenograft in vivo. Taken together, this study demonstrated that YL064 may be a promising candidate compound for the treatment of multiple myeloma by directly targeting STAT3.

Induction of apoptosis by morusin in human non-small cell lung cancer cells by suppression of EGFR/STAT3 activation

This study was designed to validate the anticancer effects of morusin in human non-small cell lung cancer (NSCLC) cells. Morusin suppressed the cell growth and colony formation in a concentration-dependent manner in H1299, H460 and H292 cells. These anticancer activities were related with apoptosis induction proved by the accumulation of chromatin condensation, PARP cleavage, increase of sub-G1 phage and annexin V-positive cell population. Interestingly, signal transducer and activator of transcription 3 (STAT3) was dephosphorylated by morusin. Morusin suppressed the transcriptional activity of STAT3 and down-regulated the expression of STAT3 target genes. In addition, morusin inhibited the phosphorylation of epithelial growth factor receptor (EGFR), an upstream regulator of STAT3. The docking study showed that morusin directly binds to the tyrosine kinase domain of EGFR. Furthermore, the anticancer effects of morusin were consistently observed in erlotinib-resistant H1975 cells expressing L858R and T790 M mutant EGFR, suggesting that morusin can be used for the advanced NSCLC with acquired resistance to EGFR TKI. Taken together, our results demonstrate that morusin induced apoptosis in human NSCLC cells regardless of EGFR mutation status through inhibition of EGFR/STAT3 activation.

Stattic enhances the anti-proliferative effect of docetaxel via the Bax/Bcl-2/cyclin B axis in human cancer cells

Abstract We investigated the effects of Stattic, an important signal transducer and activator of transcription 3 (STAT3) inhibitor, on enhancing the anti-proliferative and apoptotic effects of docetaxel in lung A549 and prostate cancer DU145 cells. Cell proliferation, cellular apoptosis and expression of STAT3 target genes were evaluated by DAPI staining, Annexin V/PI staining, cell cycle analysis and Real Time PCR. The anticancer effects of docetaxel and Stattic combination therapy induced synergistic effects in A549 and DU145 cells with combination indices of 0.71 and 0.52, respectively. Annexin V/PI demonstrated that there was a 2-fold increase in the proportion of apoptotic cells in cells treated with docetaxel and Stattic in A549 and DU145 cell lines, compared with control groups. Compared with cells treated with either docetaxel or Stattic alone, the results of the current study identified a significant decrease in the transcript levels of the anti-apoptotic proteins Bcl-2 and Bcl-xl and a marked increase in the level of the pro-apoptotic protein, Bax in cells that underwent combination therapy with docetaxel and Stattic combination (P

GRIM-19 represses the proliferation and invasion of cutaneous squamous cell carcinoma cells associated with downregulation of STAT3 signaling

The gene associated with retinoid-interferon-induced mortality-19 (GRIM-19) has been identified as a tumor suppressor in many human cancers. However, little is known about the role of GRIM-19 in cutaneous squamous cell carcinoma (CSCC). Here, we aimed to investigate the potential function of GRIM-19 in CSCC and explore the underlying molecular mechanisms. We found that GRIM-19 protein and transcript levels were significantly decreased in CSCC cell lines. Overexpression of GRIM-19 suppressed the proliferation and invasion of CSCC cells, whereas knockdown of GRIM-19 promoted the proliferation and invasion of CSCC cells. Also, we found that overexpression of GRIM-19 inhibited the phosphorylation and transcription activity of the signal transducer and activator of transcription 3 (STAT3). Overexpression of GRIM-19 also suppressed the expression of STAT3 target genes, including cyclin D1, Bcl-2 and metal matrix proteinase 2. By contrast, knockdown of GRIM-19 showed the opposite effect. Moreover, suppression of STAT3 significantly attenuated the effect of GRIM-19 knockdown on induction of proliferation, invasion, and STAT3 target genes in CSCC cells. Taken together, our data show that GRIM-19 suppresses the proliferation and invasion of CSCC cells associated with downregulation of STAT3 signaling, suggesting a tumor suppressive role of GRIM-19 in CSCC. Our study suggests that decreased expression of GRIM-19 may contribute to the development and progression of CSCC and that GRIM-19 may serve as a potential therapeutic target for CSCC treatment.

Analysis of STAT3 post-translational modifications (PTMs) in human prostate cancer with different Gleason Score.

Prostate Cancer (PCa) is a complex and heterogeneous disease. The androgen receptor (AR) and the signal transducer and activator of transcription 3 (STAT3) could be effective targets for PCa therapy. STAT3, a cytoplasmatic latent transcription factor, is a hub protein for several oncogenic signalling pathways and up-regulates the expression of numerous genes involved in tumor cell proliferation, angiogenesis, metastasis and cell survival. STAT3 activity can be modulated by several Post-Translational Modifications (PTMs) which reflect particular cell conditions and may be implicated in PCa development and progression. The aim of this work was to analyze STAT3 PTMs at different tumor stages and their relationship with STAT3 cellular functions. For this purpose, sixty-five prostatectomy, Formalin-fixed paraffin-embedded (FFPE) specimens, classified with different Gleason Scores, were subjected to immunoblotting, immunofluorescence staining and RT-PCR analysis. All experiments were carried out in matched non-neoplastic and neoplastic tissues. Data obtained showed different STAT3 PTMs profiles among the analyzed tumor grades which correlate with differences in the amount and distribution of specific STAT3 interactors as well as the expression of STAT3 target genes. These results highlight the importance of PTMs as an additional biomarker for the exactly evaluation of the PCa stage and the optimal treatment of this disease.

Gene expression–based discovery of atovaquone as a STAT3 inhibitor and anticancer agent

AbstractThe oncogenic transcription factor signal transducer and activator of transcription 3 (STAT3) is frequently activated inappropriately in a wide range of hematological and solid cancers, but clinically available therapies targeting STAT3 are lacking. Using a computational strategy to identify compounds opposing the gene expression signature of STAT3, we discovered atovaquone (Mepron), an antimicrobial approved by the US Food and Drug Administration, to be a potent STAT3 inhibitor. We show that, at drug concentrations routinely achieved clinically in human plasma, atovaquone inhibits STAT3 phosphorylation, the expression of STAT3 target genes, and the viability of STAT3-dependent hematological cancer cells. These effects were also observed with atovaquone treatment of primary blasts isolated from patients with acute myelogenous leukemia or acute lymphocytic leukemia. Atovaquone is not a kinase inhibitor but instead rapidly and specifically downregulates cell-surface expression of glycoprotein 130, which is required for STAT3 activation in multiple contexts. The administration of oral atovaquone to mice inhibited tumor growth and prolonged survival in a murine model of multiple myeloma. Finally, in patients with acute myelogenous leukemia treated with hematopoietic stem cell transplantation, extended use of atovaquone for Pneumocystis prophylaxis was associated with improved relapse-free survival. These findings establish atovaquone as a novel, clinically accessible STAT3 inhibitor with evidence of anticancer efficacy in both animal models and humans.

Hepatitis C virus and its protein NS4B activate the cancer-related STAT3 pathway via the endoplasmic reticulum overload response

Oxidative stress induces the activation of signal transducer and activator of transcription 3 (STAT3), which plays an important role in hepatocellular carcinoma (HCC). We have previously reported that hepatitis C virus (HCV) and its protein NS4B induce the production of reactive oxygen species (ROS) via the endoplasmic reticulum overload response (EOR) in human hepatocytes. Here, we found that NS4B and HCV induce STAT3 activation and stimulate the expression of cancer-related STAT3 target genes, including VEGF, c-myc, MMP-9 and Mcl-1, by EOR in human hepatocytes. Moreover, the cancer-related STAT3 pathway activated by NS4B and HCV via EOR were found to promote human hepatocyte viability. Taken together, these findings revealed that HCV NS4B might contribute to HCC by activating the EOR-mediated cancer-related STAT3 pathway, and this could provide novel insights into HCV-induced HCC.

Honokiol Inhibits Constitutive and Inducible STAT3 Signaling via PU.1-Induced SHP1 Expression in Acute Myeloid Leukemia Cells.

Constitutive and inducible activation of signal transducer and activator of transcription 3 (STAT3) signaling facilitates the carcinogenesis in most human cancers including acute myeloid leukemia (AML). Negative regulators, such as protein tyrosine phosphatases SHP1, inhibit the activated STAT3 signaling. In this study, we investigated the effect of honokiol (HNK), a constituent of Magnolia officinalis, on the STAT3 signaling. STAT3 signaling and SHP1 expression were measured by quantitative real-time PCR and western blotting in leukemic cell lines and primary AML blasts treated with HNK. HNK decreased the phosphorylated STAT3 but not the total STAT3 through increasing the expression of SHP1. In addition, HNK inhibited transcription activity of STAT3, reduced nuclear translocation of STAT3, and decreased the expression of STAT3 target genes. Knockdown of SHP1 by small hairpin RNA (shRNA) or treatment with vanadate, a protein tyrosine phosphatases inhibitor, abolished HNK-induced STAT3 inhibition, suggesting that SHP1 plays an important role in the inhibition of STAT3 signaling by HNK. Further, HNK increased the expression of transcript factor PU.1, which had been reported to activate the expression of SHP1 via binding SHP1 promoter region. Knockdown of PU.1 reversed HNK-induced upregulation of SHP1 and inactivation of STAT3 signaling. Finally, HNK increased the expression of PU.1 and SHP1 in hematopoietic progenitors isolated from patients with AML. In conclusion, our data have shown a regulatory mechanism underlying the inhibition of STAT3 signaling by HNK. Therefore, as a relative non-toxic compound, HNK may offer a therapeutic advantage in the clinical treatment for AML.

Alantolactone selectively suppresses STAT3 activation and exhibits potent anticancer activity in MDA-MB-231 cells

The important goal of cancer drug discovery is to develop therapeutic agents that are effective, safe, and affordable. In the present study, we demonstrated that alantolactone, which is a sesquiterpene lactone, has potential activity against triple-negative breast cancer MDA-MB-231 cells by suppressing the signal transducer and activator of transcription 3 (STAT3) signaling pathway. Alantolactone effectively suppressed both constitutive and inducible STAT3 activation at tyrosine 705. Alantolactone decreased STAT3 translocation to the nucleus, its DNA-binding, and STAT3 target gene expression. Alantolactone significantly inhibits STAT3 activation with a marginal effect on MAPKs and on NF-κB transcription; however, this effect is not mediated by inhibiting STAT3 upstream kinases. Although SHP-1, SHP-2, and PTEN, which are protein tyrosine phosphatases (PTPs), were not affected by alantolactone, the treatment with a PTP inhibitor reversed the alantolactone-induced suppression of STAT3 activation, indicating that PTP plays an important role in the action of alantolactone. Finally, alantolactone treatment resulted in the inhibition of migration, invasion, adhesion, and colony formation. The in vivo administration of alantolactone inhibited the growth of human breast xenograft tumors. These results provide preclinical evidence to continue the development of alantolactone as a STAT3 inhibitor and as a potential therapeutic agent against breast cancer.

Role of Transcription Factor Acetylation in Diabetic Kidney Disease

Nuclear factor (NF)-κB and signal transducer and activator of transcription 3 (STAT3) play a critical role in diabetic nephropathy (DN). Sirtuin-1 (SIRT1) regulates transcriptional activation of target genes through protein deacetylation. Here, we determined the roles of Sirt1 and the effect of NF-κB (p65) and STAT3 acetylation in DN. We found that acetylation of p65 and STAT3 was increased in both mouse and human diabetic kidneys. In human podocytes, advanced glycation end products (AGEs) induced p65 and STAT3 acetylation and overexpression of acetylation-incompetent mutants of p65 and STAT3 abrogated AGE-induced expression of NF-κB and STAT3 target genes. Inhibition of AGE formation in db/db mice by pyridoxamine treatment attenuated proteinuria and podocyte injury, restored SIRT1 expression, and reduced p65 and STAT3 acetylation. Diabetic db/db mice with conditional deletion of SIRT1 in podocytes developed more proteinuria, kidney injury, and acetylation of p65 and STAT3 compared with db/db mice without SIRT1 deletion. Treatment of db/db mice with a bromodomain and extraterminal (BET)-specific bromodomain inhibitor (MS417) which blocks acetylation-mediated association of p65 and STAT3 with BET proteins, attenuated proteinuria, and kidney injury. Our findings strongly support a critical role for p65 and STAT3 acetylation in DN. Targeting protein acetylation could be a potential new therapy for DN.