Structure and functional analysis of the human STAT3 gene promoter: alteration of chromatin structure as a possible mechanism for the upregulation in cisplatin-resistant cells

Targeting STAT3 signaling pathway by curcumin and its analogues for breast cancer: A narrative review

BACKGROUND

Breast cancer (BC) continues to be a significant global health issue, with a rising number of cases requiring ongoing research and innovation in treatment strategies. Curcumin (CUR), a natural compound derived from Curcuma longa, and similar compounds have shown potential in targeting the STAT3 signaling pathway, which plays a crucial role in BC progression.

AIMS

The aim of this study was to investigate the effects of curcumin and its analogues on BC based on cellular and molecular mechanisms.

MATERIALS & METHODS

The literature search conducted for this study involved utilizing the Scopus, ScienceDirect, PubMed, and Google Scholar databases in order to identify pertinent articles.

RESULTS

This narrative review explores the potential of CUR and similar compounds in inhibiting STAT3 activation, thereby suppressing the proliferation of cancer cells, inducing apoptosis, and inhibiting metastasis. The review demonstrates that CUR directly inhibits the phosphorylation of STAT3, preventing its movement into the nucleus and its ability to bind to DNA, thereby hindering the survival and proliferation of cancer cells. CUR also enhances the effectiveness of other therapeutic agents and modulates the tumor microenvironment by affecting tumor-associated macrophages (TAMs). CUR analogues, such as hydrazinocurcumin (HC), FLLL11, FLLL12, and GO-Y030, show improved bioavailability and potency in inhibiting STAT3, resulting in reduced cell proliferation and increased apoptosis.

CONCLUSION

CUR and its analogues hold promise as effective adjuvant treatments for BC by targeting the STAT3 signaling pathway. These compounds provide new insights into the mechanisms of action of CUR and its potential to enhance the effectiveness of BC therapies.

Proteomics screening uncovers HMGA1 as a promising negative regulator for γ-globin expression in response to decreased β-globin levels

Reactivation of fetal hemoglobin (HbF) is a critical goal for the treatment of patients with hemoglobinopathies. β-globin disorders can trigger stress erythropoiesis in red blood cells (RBCs). Cell-intrinsic erythroid stress signals promote erythroid precursors to express high levels of fetal hemoglobin, which is also known as γ-globin. However, the molecular mechanism underlying γ-globin production during cell-intrinsic erythroid stress remains to be elucidated. Here, we utilized CRISPR-Cas9 to model a stressed state caused by reduced levels of adult β-globin in HUDEP2 human erythroid progenitor cells. We found that a decrease in β-globin expression correlates with the upregulation of γ-globin expression. We also identified transcription factor high-mobility group A1 (HMGA1; formerly HMG-I/Y) as a potential γ-globin regulator that responds to reduced β-globin levels. Upon erythroid stress, there is a downregulation of HMGA1, which normally binds -626 to -610 base pairs upstream from the STAT3 promoter, to downregulate STAT3 expression. STAT3 is a known γ-globin repressor, so the downregulation of HMGA1 ultimately upregulates γ-globin expression. SIGNIFICANCE: This study demonstrated HMGA1 as a potential regulator in the poorly understood phenomenon of stress-induced globin compensation, and after further validation these results might inform new strategies to treat patients with sickle cell disease and β-thalassemia.

Dual-Acting Cholinesterase-Human Cannabinoid Receptor 2 Ligands Show Pronounced Neuroprotection in Vitro and Overadditive and Disease-Modifying Neuroprotective Effects in Vivo

We have designed and synthesized a series of 14 hybrid molecules out of the cholinesterase (ChE) inhibitor tacrine and a benzimidazole-based human cannabinoid receptor subtype 2 (hCB2R) agonist and investigated them in vitro and in vivo. The compounds are potent ChE inhibitors, and for the most promising hybrids, the mechanism of human acetylcholinesterase (hAChE) inhibition as well as their ability to interfere with AChE-induced aggregation of β-amyloid (Aβ), and Aβ self-aggregation was assessed. All hybrids were evaluated for affinity and selectivity for hCB1R and hCB2R. To ensure that the hybrids retained their agonist character, the expression of cAMP-regulated genes was quantified, and potency and efficacy were determined. Additionally, the effects of the hybrids on microglia activation and neuroprotection on HT-22 cells were investigated. The most promising in vitro hybrids showed pronounced neuroprotection in an Alzheimer's mouse model at low dosage (0.1 mg/kg, i.p.), lacking hepatotoxicity even at high dose (3 mg/kg, i.p.).

Mineralocorticoid receptor negatively regulates angiogenesis through repression of STAT3 activity in endothelial cells

The mineralocorticoid receptor (MR) plays important roles in cardiovascular pathogenesis. The function of MR in angiogenesis is still controversial. This study aimed to explore the role of endothelial MR in angiogenesis and to delineate the underlying mechanism. Endothelial-hematopoietic MR knockout (EMRKO) mice were generated and subjected to hindlimb ischemia and injection of melanoma cells. Laser Doppler measurements showed that EMRKO mice had improved blood flow recovery and increased vessel density in ischemic limbs. In addition, EMRKO accelerated growth and increased the vessel density of tumors. Matrigel implantation, aortic ring assays, and tube formation assays demonstrated that MRKO endothelial cells (ECs) manifested increased angiogenic potential. MRKO ECs also displayed increased migration ability and proliferation. MRKO and MR knockdown both upregulated gene expression, protein level, and phosphorylation of signal transducer and activator of transcription 3 (STAT3). Stattic, a selective STAT3 inhibitor, attenuated the effects of MRKO on tube formation, migration, and proliferation of ECs. At the molecular level, MR interacted with CCAAT enhancer-binding protein beta (C/EBPβ) to suppress the transcription of STAT3. Furthermore, interactions between MR and STAT3 blocked the phosphorylation of STAT3. Finally, stattic abolished the pro-angiogenic phenotype of EMRKO mice. Taken together, endothelial MR is a negative regulator of angiogenesis, likely in a ligand-independent manner. Mechanistically, MR downregulates STAT3 that mediates the impacts of MR deficiency on the angiogenic activity of ECs and angiogenesis. Targeting endothelial MR may be a potential pro-angiogenic strategy for ischemic diseases. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

ZNF341 controls STAT3 expression and thereby immunocompetence

Signal transducer and activator of transcription 3 (STAT3) is a central regulator of immune homeostasis. STAT3 levels are strictly controlled, and STAT3 impairment contributes to several diseases including the monogenic autosomal-dominant hyper-immunoglobulin E (IgE) syndrome (AD-HIES). We investigated patients of four consanguineous families with an autosomal-recessive disorder resembling the phenotype of AD-HIES, with symptoms of immunodeficiency, recurrent infections, skeletal abnormalities, and elevated IgE. Patients presented with reduced STAT3 expression and diminished T helper 17 cell numbers, in absence of STAT3 mutations. We identified two distinct homozygous nonsense mutations in ZNF341, which encodes a zinc finger transcription factor. Wild-type ZNF341 bound to and activated the STAT3 promoter, whereas the mutant variants showed impaired transcriptional activation, partly due to nuclear translocation failure. In summary, nonsense mutations in ZNF341 account for the STAT3-like phenotype in four autosomal-recessive kindreds. Thus, ZNF341 is a previously unrecognized regulator of immune homeostasis.

Targeting Upstream Kinases of STAT3 in Human Medulloblastoma Cells

BACKGROUND

Medulloblastoma is the most common malignant brain tumor in children. Despite improvement in overall survival rate, it still lacks an effective targeted treatment strategy. The Janus family of cytoplasmic tyrosine kinases (JAKs) and Src kinases, upstream protein kinases of signal transducer and activator of transcription 3 (STAT3), play important roles in medulloblastoma pathogenesis and therefore represent potential therapeutic targets.

METHODS

In this report, we examined the inhibitory efficacy of the JAK1/2 inhibitor, ruxolitinib, the JAK3 inhibitor, tofacitinib and two Src inhibitors, KX2-391 and dasatinib.

RESULTS

These small molecule drugs significantly reduce cell viability and inhibit cell migration and colony formation in human medulloblastoma cells in vitro. Src inhibitors have more potent efficacy than JAK inhibitors in inhibiting medulloblastoma cell migration ability. The Src inhibitors can inhibit both phosphorylation of STAT3 and Src while JAK inhibitors reduce JAK/STAT3 phosphorylation. We also investigated the combined effect of the Src inhibitor, dasatinib with cisplatin. The results show that dasatinib exerts synergistic effects with cisplatin in human medulloblastoma cells through the inhibition of STAT3 and Src.

CONCLUSION

Our results suggest that the small molecule inhibitors of STAT3 upstream kinases, ruxolitinib, tofacitinib, KX2-391, and dasatinib could be novel and attractive candidate drugs for the treatment of human medulloblastoma.

ATF3 Sustains IL-22-Induced STAT3 Phosphorylation to Maintain Mucosal Immunity Through Inhibiting Phosphatases

In gut epithelium, IL-22 transmits signals through STAT3 phosphorylation (pSTAT3) which provides intestinal immunity. Many components in the IL-22-pSTAT3 pathway have been identified as risk factors for inflammatory bowel disease (IBD) and some of them are considered as promising therapeutic targets. However, new perspectives are still needed to understand IL-22-pSTAT3 signaling for effective clinical interventions in IBD patients. Here, we revealed activating transcription factor 3 (ATF3), recently identified to be upregulated in patients with active IBD, as a crucial player in the epithelial IL-22-pSTAT3 signaling cascade. We found ATF3 is central to intestinal homeostasis and provides protection during colitis. Loss of ATF3 led to decreased crypt numbers, more shortened colon length, impaired ileal fucosylation at the steady state, and lethal disease activity during DSS-induced colitis which can be effectively ameliorated by rectal transplantation of wild-type colonic organoids. Epithelial stem cells and Paneth cells form a niche to orchestrate epithelial regeneration and host-microbe interactions, and IL-22-pSTAT3 signaling is a key guardian for this niche. We found ATF3 is critical for niche maintenance as ATF3 deficiency caused compromised stem cell growth and regeneration, as well as Paneth cell degeneration and loss of anti-microbial peptide (AMP)-producing granules, indicative of malfunction of Paneth/stem cell network. Mechanistically, we found IL-22 upregulates ATF3, which is required to relay IL-22 signaling leading to STAT3 phosphorylation and subsequent AMP induction. Intriguingly, ATF3 itself does not act on STAT3 directly, instead ATF3 regulates pSTAT3 by negatively targeting protein tyrosine phosphatases (PTPs) including SHP2 and PTP-Meg2. Furthermore, we identified ATF3 is also involved in IL-6-mediated STAT3 activation in T cells and loss of ATF3 leads to reduced capacity of Th17 cells to produce their signature cytokine IL-22 and IL-17A. Collectively, our results suggest that via IL-22-pSTAT3 signaling in the epithelium and IL-6-pSTAT3 signaling in Th17 cells, ATF3 mediates a cross-regulation in the barrier to maintain mucosal homeostasis and immunity.

Structure-Activity Relationships and Computational Investigations into the Development of Potent and Balanced Dual-Acting Butyrylcholinesterase Inhibitors and Human Cannabinoid Receptor 2 Ligands with Pro-Cognitive in Vivo Profiles

The enzyme butyrylcholinesterase (BChE) and the human cannabinoid receptor 2 (hCB₂R) represent promising targets for pharmacotherapy in the later stages of Alzheimer's disease. We merged pharmacophores for both targets into small benzimidazole-based molecules, investigated SARs, and identified several dual-acting ligands with a balanced affinity/inhibitory activity and an excellent selectivity over both hCB₁R and hAChE. A homology model for the hCB₂R was developed based on the hCB₁R crystal structure and used for molecular dynamics studies to investigate binding modes. In vitro studies proved hCB₂R agonism. Unwanted μ-opioid receptor affinity could be designed out. One well-balanced dual-acting and selective hBChE inhibitor/hCB₂R agonist showed superior in vivo activity over the lead CB₂ agonist with regards to cognition improvement. The data shows the possibility to combine a small molecule with selective and balanced GPCR-activity/enzyme inhibition and in vivo activity for the therapy of AD and may help to rationalize the development of other dual-acting ligands.

A homolog of teleostean signal transducer and activator of transcription 3 (STAT3) from rock bream, Oplegnathus fasciatus: Structural insights, transcriptional modulation, and subcellular localization

Signal transducer and activator of transcription 3 (STAT3) is one of the crucial transcription factors in the Janus kinase (JAK)/STAT signaling pathway, and it was previously considered as acute phase response factor. A number of interleukins (ILs) such as IL-5, IL-6, IL-9, IL-10, IL-12, and IL-22 are known to be involved in activation of STAT3. In addition, various growth factors and pathogenic or oxidative stresses mediate the activation of a wide range of functions via STAT3. In this study, a STAT3 homolog was identified and functionally characterized from rock bream (RbSTAT3), Oplegnathus fasciatus. In silico characterization revealed that the RbSTAT3 amino acid sequence shares highly conserved common domain architectural features including N-terminal domain, coiled coil domain, DNA binding domain, linker domain, and Src homology 2 (SH2) domains. In addition, a fairly conserved transcriptional activation domain (TAD) was located at the C-terminus. Comparison of RbSTAT3 with other counterparts revealed higher identities (>90%) with fish orthologs. The genomic sequence of RbSTAT3 was obtained from a bacterial artificial chromosome (BAC) library, and was identified as a multi-exonic gene (24 exons), as found in other vertebrates. Genomic structural comparison and phylogenetic studies have showed that the evolutionary routes of teleostean and non-teleostean vertebrates were distinct. Quantitative real time PCR (qPCR) analysis revealed that the spatial distribution of RbSTAT3 mRNA expression was ubiquitous and highly detectable in blood, heart, and liver tissues. Transcriptional modulation of RbSTAT3 was examined in blood and liver tissues after challenges with bacteria (Edwardsiella tarda and Streptococcus iniae), rock bream irido virus (RBIV), and immune stimulants (LPS and poly (I:C)). Significant changes in RbSTAT3 transcription were also observed in response to tissue injury. In addition, the transcriptional up-regulation of RbSTAT3 was detected in rock bream heart cells upon recombinant rock bream IL-10 (rRbIL-10) treatment. Subcellular localization and nuclear translocation of rock bream STAT3 following poly (I:C) treatment were also demonstrated. Taken together, the results of the current study provide important evidence for potential roles of rock bream STAT3 in the immune system and wound healing processes.

Benzyl Isothiocyanate (BITC) Induces Reactive Oxygen Species-dependent Repression of STAT3 Protein by Down-regulation of Specificity Proteins in Pancreatic Cancer

The antineoplastic agent benzyl isothiocyanate (BITC) acts by targeting multiple pro-oncogenic pathways/genes, including signal transducer and activator of transcription 3 (STAT3); however, the mechanism of action is not well known. As reported previously, BITC induced reactive oxygen species (ROS) in Panc1, MiaPaCa2, and L3.6pL pancreatic cancer cells. This was accompanied by induction of apoptosis and inhibition of cell growth and migration, and these responses were attenuated in cells cotreated with BITC plus glutathione (GSH). BITC also decreased expression of specificity proteins (Sp) Sp1, Sp3, and Sp4 transcription factors (TFs) and several pro-oncogenic Sp-regulated genes, including STAT3 and phospho-STAT3 (pSTAT3), and GSH attenuated these responses. Knockdown of Sp TFs by RNA interference also decreased STAT3/pSTAT3 expression. BITC-induced ROS activated a cascade of events that included down-regulation of c-Myc, and it was also demonstrated that c-Myc knockdown decreased expression of Sp TFs and STAT3 These results demonstrate that in pancreatic cancer cells, STAT3 is an Sp-regulated gene that can be targeted by BITC and other ROS inducers, thereby identifying a novel therapeutic approach for targeting STAT3.

Specific immunotherapy generates CD8(+) CD196(+) T cells to suppress lung cancer growth in mice

That specific immunotherapy can inhibit cancer growth has been recognized; its efficiency is to be improved. This study aimed to inhibit lung cancer (LC) growth in a mouse model by using an LC-specific vaccination. In this study, a LC mouse model was created by adoptive transplantation with LC cells. The tumor-bearing mice were vaccinated with LC cell extracts plus adjuvant TNBS or adoptive transplantation with specific CD8(+) CD196(+) T cells. The results showed that the vaccination with LC extracts (LCE)/TNBS markedly inhibited the LC growth and induced CD8(+) CD196(+) T cells in LC tissue and the spleen. These CD8(+) CD196(+) T cells proliferated and produce high levels of perforin upon exposure to LCE and specifically induced LC cell apoptosis. Exposure to TNBS induced RAW264.7 cells to produce macrophage inflammatory protein-3α; the latter activated signal transducer and activator of transcription 3 and further induced perforin expression in the CD8(+) CD196(+) T cells. Adoptive transfer with specific CD8(+) CD196(+) T cells suppressed LC growth in mice. In conclusion, immunization with LC extracts and TNBS can induce LC-specific CD8(+) CD196(+) T cells in LC-bearing mice and inhibit LC growth.

Cytotoxic T Lymphocyte Antigen-4 Down-Regulates T Helper 1 Cells by Increasing Expression of Signal Transducer and Activator of Transcription 3 in Acute Graft-versus-Host Disease

Numerous previous studies have suggested that cytotoxic T lymphocyte antigen-4 (CTLA-4) plays an important role in acute graft-versus-host disease (GVHD). How CTLA-4 acts in regulating acute GVHD remains unknown, however. In the present study, we found that, compared with healthy controls, CTLA-4 plasma and relative mRNA levels in patients with acute GVHD were initially decreased and then markedly elevated after 28 days of treatment. CTLA-4 levels were higher in patients with grade I-II acute GVHD compared with those with grade III-IV acute GVHD both before and after treatment. Up-regulation of CTLA-4 significantly increased the luciferase activity and degree of phosphorylation of signal transducer and activator of transcription 3 (STAT3). Meanwhile, T cell activation was significantly inhibited, and levels of IFN-γ, IL-17, and IL-22 decreased. These findings suggest that CTLA-4 might be involved in the pathogenesis of acute GVHD, and may down-regulate T helper 1 cells by increasing STAT3 expression in acute GVHD.

Nuclear matrix protein SMAR1 control regulatory T-cell fate during inflammatory bowel disease (IBD)

Regulatory T (Treg) cells are essential for self-tolerance and immune homeostasis. Transcription factor Foxp3, a positive regulator of Treg cell differentiation, has been studied to some extent. Signal transducer and activator of transcription factor 3 (STAT3) is known to negatively regulate Foxp3. It is not clear how STAT3 is regulated during Treg differentiation. We show that SMAR1, a known transcription factor and tumor suppressor, is directly involved in maintaining Treg cell fate decision. T-cell-specific conditional knockdown of SMAR1 exhibits increased susceptibility towards inflammatory disorders, such as colitis. The suppressive function of Treg cells is compromised in the absence of SMAR1 leading to increased T helper type 17 (Th17) differentiation and inflammation. Compared with wild-type, the SMAR1(-/-) Treg cells showed increased susceptibility of inflammatory bowel disease in Rag1(-/ -) mice, indicating the role of SMAR1 in compromising Treg cell differentiation resulting in severe colitis. We show that SMAR1 negatively regulate STAT3 expression favoring Foxp3 expression and Treg cell differentiation. SMAR1 binds to the MAR element of STAT3 promoter, present adjacent to interleukin-6 response elements. Thus Foxp3, a major driver of Treg cell differentiation, is regulated by SMAR1 via STAT3 and a fine-tune balance between Treg and Th17 phenotype is maintained.

MiR-7, inhibited indirectly by lincRNA HOTAIR, directly inhibits SETDB1 and reverses the EMT of breast cancer stem cells by downregulating the STAT3 pathway

Epithelial-mesenchymal transition (EMT) contributes to tumor invasion and metastasis in many cancers and correlates highly with the acquisition of cancer stem cell (CSC) characteristics. EMT also correlates with changes in specific microRNAs (miRNAs) that have already been integrated into tumorigenic programs as either oncogenes or tumor suppressor genes. Here, we show that miR-7, which was downregulated in breast CSCs (BCSCs) isolated from the human MCF-7 and MDA-MB-231 cell lines, inhibited cell invasion and metastasis, decreased the BCSC population and partially reversed EMT in MDA-MB-231 cells by directly targeting the oncogene, SETDB1. The conspicuous epigenetic transition induced by miR-7 overexpression was found not only in MDA-MB-231 cells but also in BCSC xenograft tumors. MiR-7 inhibited the metastasis of BCSCs in lungs, kidneys, and adrenal glands of NOD/SCID mice. ChIP-polymerase chain reaction result suggested that the SETDB1 induced STAT3 expression by binding to the promoter of STAT3. MiR-7-mediated downregulation of SETDB1 resulted in the suppression of STAT3, which led to the downregulation of c-myc, twist, and mir-9. In addition, the downregulation of miR-7 in BCSCs may be indirectly attributed to lincRNA HOTAIR by modulating the expression of HoxD10 that promotes the expression of miR-7. These findings demonstrate that miR-7 was a tumor suppressor and that the overexpression of miR-7 might serve as a good strategy for treating highly invasive breast cancer.

A novel small molecular STAT3 inhibitor, LY5, inhibits cell viability, cell migration, and angiogenesis in medulloblastoma cells

Signal transducers and activators of transcription 3 (STAT3) signaling is persistently activated and could contribute to tumorigenesis of medulloblastoma. Numerous studies have demonstrated that inhibition of the persistent STAT3 signaling pathway results in decreased proliferation and increased apoptosis in human cancer cells, indicating that STAT3 is a viable molecular target for cancer therapy. In this study, we investigated a novel non-peptide, cell-permeable small molecule, named LY5, to target STAT3 in medulloblastoma cells. LY5 inhibited persistent STAT3 phosphorylation and induced apoptosis in human medulloblastoma cell lines expressing constitutive STAT3 phosphorylation. The inhibition of STAT3 signaling by LY5 was confirmed by down-regulating the expression of the downstream targets of STAT3, including cyclin D1, bcl-XL, survivin, and micro-RNA-21. LY5 also inhibited the induction of STAT3 phosphorylation by interleukin-6 (IL-6), insulin-like growth factor (IGF)-1, IGF-2, and leukemia inhibitory factor in medulloblastoma cells, but did not inhibit STAT1 and STAT5 phosphorylation stimulated by interferon-γ (IFN-γ) and EGF, respectively. In addition, LY5 blocked the STAT3 nuclear localization induced by IL-6, but did not block STAT1 and STAT5 nuclear translocation mediated by IFN-γ and EGF, respectively. A combination of LY5 with cisplatin or x-ray radiation also showed more potent effects than single treatment alone in the inhibition of cell viability in human medulloblastoma cells. Furthermore, LY5 demonstrated a potent inhibitory activity on cell migration and angiogenesis. Taken together, these findings indicate LY5 inhibits persistent and inducible STAT3 phosphorylation and suggest that LY5 is a promising therapeutic drug candidate for medulloblastoma by inhibiting persistent STAT3 signaling.

Transcriptional regulation of STAT3 by SPTBN1 and SMAD3 in HCC through cAMP-response element-binding proteins ATF3 and CREB2

The cytoskeletal protein Spectrin, beta, non-erythrocytic 1 (SPTBN1), an adapter protein to SMAD3 in TGF-β signaling, may prevent hepatocellular carcinoma (HCC) development by downregulating the expression of signal transducer and activator of transcription 3 (STAT3). To elucidate the as yet undefined mechanisms that regulate this process, we demonstrate that higher levels of STAT3 transcription are found in livers of heterozygous SPTBN1(+/-) mice as compared to that of wild type mice. We also found increased levels of STAT3 mRNA, STAT3 protein, and p-STAT3 in human HCC cell-lines after knockdown of SPTBN1 or SMAD3, which promoted cell colony formation. Inhibition of STAT3 overrode the increase in cell colony formation due to knockdown of SPTBN1 or SMAD3. We also found that inhibition of SPTBN1 or SMAD3 upregulated STAT3 promoter activity in HCC cell-lines, which is dependent upon the cAMP-response element (CRE) and STAT-binding element (SBE) sites of the STAT3 promoter. Mechanistically, suppression of SPTBN1 and SMAD3 augmented the transcription of STAT3 by upregulating the CRE-binding proteins ATF3 and CREB2 and augmented the binding of those proteins to the regions within or upstream of the CRE site of the STAT3 promoter. Finally, in human HCC tissues, SPTBN1 expression correlated negatively with expression levels of STAT3, ATF3, and CREB2; SMAD3 expression correlated negatively with STAT3 expression; and the level of phosphorylated SMAD3 (p-SMAD3) correlated negatively with ATF3 and CREB2 protein levels. SPTBN1 and SMAD3 collaborate with CRE-binding transcription factors to inhibit STAT3, thereby preventing HCC development.

Preclinical therapeutic potential of a nitrosylating agent in the treatment of ovarian cancer

This study examines the role of s-nitrosylation in the growth of ovarian cancer using cell culture based and in vivo approaches. Using the nitrosylating agent, S-nitrosoglutathione (GSNO), a physiological nitric oxide molecule, we show that GSNO treatment inhibited proliferation of chemoresponsive and chemoresistant ovarian cancer cell lines (A2780, C200, SKVO3, ID8, OVCAR3, OVCAR4, OVCAR5, OVCAR7, OVCAR8, OVCAR10, PE01 and PE04) in a dose dependent manner. GSNO treatment abrogated growth factor (HB-EGF) induced signal transduction including phosphorylation of Akt, p42/44 and STAT3, which are known to play critical roles in ovarian cancer growth and progression. To examine the therapeutic potential of GSNO in vivo, nude mice bearing intra-peritoneal xenografts of human A2780 ovarian carcinoma cell line (2×10⁶) were orally administered GSNO at the dose of 1 mg/kg body weight. Daily oral administration of GSNO significantly attenuated tumor mass (p<0.001) in the peritoneal cavity compared to vehicle (phosphate buffered saline) treated group at 4 weeks. GSNO also potentiated cisplatin mediated tumor toxicity in an A2780 ovarian carcinoma nude mouse model. GSNO’s nitrosylating ability was reflected in the induced nitrosylation of various known proteins including NFκB p65, Akt and EGFR. As a novel finding, we observed that GSNO also induced nitrosylation with inverse relationship at tyrosine 705 phosphorylation of STAT3, an established player in chemoresistance and cell proliferation in ovarian cancer and in cancer in general. Overall, our study underlines the significance of S-nitrosylation of key cancer promoting proteins in modulating ovarian cancer and proposes the therapeutic potential of nitrosylating agents (like GSNO) for the treatment of ovarian cancer alone or in combination with chemotherapeutic drugs.

Protein quantitative trait loci identify novel candidates modulating cellular response to chemotherapy

Annotating and interpreting the results of genome-wide association studies (GWAS) remains challenging. Assigning function to genetic variants as expression quantitative trait loci is an expanding and useful approach, but focuses exclusively on mRNA rather than protein levels. Many variants remain without annotation. To address this problem, we measured the steady state abundance of 441 human signaling and transcription factor proteins from 68 Yoruba HapMap lymphoblastoid cell lines to identify novel relationships between inter-individual protein levels, genetic variants, and sensitivity to chemotherapeutic agents. Proteins were measured using micro-western and reverse phase protein arrays from three independent cell line thaws to permit mixed effect modeling of protein biological replicates. We observed enrichment of protein quantitative trait loci (pQTLs) for cellular sensitivity to two commonly used chemotherapeutics: cisplatin and paclitaxel. We functionally validated the target protein of a genome-wide significant trans-pQTL for its relevance in paclitaxel-induced apoptosis. GWAS overlap results of drug-induced apoptosis and cytotoxicity for paclitaxel and cisplatin revealed unique SNPs associated with the pharmacologic traits (at p<0.001). Interestingly, GWAS SNPs from various regions of the genome implicated the same target protein (p<0.0001) that correlated with drug induced cytotoxicity or apoptosis (p≤0.05). Two genes were functionally validated for association with drug response using siRNA: SMC1A with cisplatin response and ZNF569 with paclitaxel response. This work allows pharmacogenomic discovery to progress from the transcriptome to the proteome and offers potential for identification of new therapeutic targets. This approach, linking targeted proteomic data to variation in pharmacologic response, can be generalized to other studies evaluating genotype-phenotype relationships and provide insight into chemotherapeutic mechanisms.

The central dogma of biology explains that DNA is transcribed to mRNA that is further translated into protein. Many genome-wide studies have implicated genetic variation that influences gene expression and that ultimately affect downstream complex traits including response to drugs. However, because of technical limitations, few studies have evaluated the contribution of genetic variation on protein expression and ensuing effects on downstream phenotypes. To overcome this challenge, we used a novel technology to simultaneously measure the baseline expression of 441 proteins in lymphoblastoid cell lines and compared them with publicly available genetic data. To further illustrate the utility of this approach, we compared protein-level measurements with chemotherapeutic induced apoptosis and cell-growth inhibition data. This study demonstrates the importance of using protein information to understand the functional consequences of genetic variants identified in genome-wide association studies. This protein data set will also have broad utility for understanding the relationship between other genome-wide studies of complex traits.

MTA1 promotes STAT3 transcription and pulmonary metastasis in breast cancer

Overexpression of the prometastatic chromatin modifier protein metastasis tumor antigen 1 (MTA1) in human cancer contributes to tumor aggressiveness, but the role of endogenous MTA1 in cancer has not been explored. Here, we report the effects of selective genetic depletion of MTA1 in a physiologically relevant spontaneous mouse model of breast cancer pulmonary metastasis. We found that MTA1 acts as a mandatory modifier of breast-to-lung metastasis without effects on primary tumor formation. The underlying mechanism involved MTA1-dependent stimulation of STAT3 transcription through action on the MTA1/STAT3/Pol II coactivator complex, and, in turn, on the expression and functions of STAT3 target genes including Twist1. Accordingly, we documented a positive correlation between levels of MTA1 and STAT3 in publicly available breast cancer data sets. Together, our findings reveal an essential modifying role of the physiologic level of MTA1 in supporting pulmonary metastasis of breast cancer.

Cisplatin resistance: a cellular self-defense mechanism resulting from multiple epigenetic and genetic changes

Cisplatin is one of the most effective broad-spectrum anticancer drugs. Its effectiveness seems to be due to the unique properties of cisplatin, which enters cells via multiple pathways and forms multiple different DNA-platinum adducts while initiating a cellular self-defense system by activating or silencing a variety of different genes, resulting in dramatic epigenetic and/or genetic alternations. As a result, the development of cisplatin resistance in human cancer cells in vivo and in vitro by necessity stems from bewilderingly complex genetic and epigenetic changes in gene expression and alterations in protein localization. Extensive published evidence has demonstrated that pleiotropic alterations are frequently detected during development of resistance to this toxic metal compound. Changes occur in almost every mechanism supporting cell survival, including cell growth-promoting pathways, apoptosis, developmental pathways, DNA damage repair, and endocytosis. In general, dozens of genes are affected in cisplatin-resistant cells, including pathways involved in copper metabolism as well as transcription pathways that alter the cytoskeleton, change cell surface presentation of proteins, and regulate epithelial-to-mesenchymal transition. Decreased accumulation is one of the most common features resulting in cisplatin resistance. This seems to be a consequence of numerous epigenetic and genetic changes leading to the loss of cell-surface binding sites and/or transporters for cisplatin, and decreased fluid phase endocytosis.

Chromatin immunoprecipitation to verify or to identify in vivo protein-DNA interactions

Chromatin immunoprecipitation (ChIP) is a valuable tool to detect the interaction in vivo between a DNA-associated protein and DNA fragments. Combined with approaches to assess gene expression in response to accumulation of a transcription factor, it is possible to identify direct responsive targets from targets that are indirectly responsive to accumulation of the transcription factor. ChIP may be used to confirm in vivo association of a transcriptional regulator with suspected target DNA fragments. ChIP may also be used to discover new targets, and when combined with high-throughput approaches to identify DNA fragments associated with a transcription factor, it may provide a tool to study the gene regulatory networks active during plant development and/or response to the environment. Furthermore, ChIP is also a powerful means to map epigenetic modifications within a genome.

Role of ZNF143 in tumor growth through transcriptional regulation of DNA replication and cell-cycle-associated genes

The cell cycle is strictly regulated by numerous mechanisms to ensure cell division. The transcriptional regulation of cell-cycle-related genes is poorly understood, with the exception of the E2F family that governs the cell cycle. Here, we show that a transcription factor, zinc finger protein 143 (ZNF143), positively regulates many cell-cycle-associated genes and is highly expressed in multiple solid tumors. RNA-interference (RNAi)-mediated knockdown of ZNF143 showed that expression of 152 genes was downregulated in human prostate cancer PC3 cells. Among these ZNF143 targets, 41 genes (27%) were associated with cell cycle and DNA replication including cell division cycle 6 homolog (CDC6), polo-like kinase 1 (PLK1) and minichromosome maintenance complex component (MCM) DNA replication proteins. Furthermore, RNAi of ZNF143 induced apoptosis following G2/M cell cycle arrest. Cell growth of 10 lung cancer cell lines was significantly correlated with cellular expression of ZNF143. Our data suggest that ZNF143 might be a master regulator of the cell cycle. Our findings also indicate that ZNF143 is a member of the growing list of non-oncogenes that are promising cancer drug targets.

Upregulation of STAT3 marks Burkitt lymphoma cells refractory to Epstein-Barr virus lytic cycle induction by HDAC inhibitors

A fundamental problem in studying the latent-to-lytic switch of Epstein-Barr virus (EBV) and the viral lytic cycle itself is the lack of a culture system fully permissive to lytic cycle induction. Strategies to target EBV-positive tumors by inducing the viral lytic cycle with chemical agents are hindered by inefficient responses to stimuli. In vitro, even in the most susceptible cell lines, more than 50% of cells latently infected with EBV are refractory to induction of the lytic cycle. The mechanisms underlying the refractory state are not understood. We separated lytic from refractory Burkitt lymphoma-derived HH514-16 cells after treatment with an HDAC inhibitor, sodium butyrate. Both refractory- and lytic-cell populations responded to the inducing stimulus by hyperacetylation of histone H3. However, analysis of host cell gene expression showed that specific cellular transcripts Stat3, Fos, and interleukin-8 (IL-8) were preferentially upregulated in the refractory-cell population, while IL-6 was upregulated in the lytic population. STAT3 protein levels were also substantially increased in refractory cells relative to untreated or lytic cells. This increase in de novo expression resulted primarily in unphosphorylated STAT3. Examination of single cells revealed that high levels of STAT3 were strongly associated with the refractory state. The refractory state is manifest in a unique subpopulation of cells that exhibits different cellular responses than do lytic cells exposed to the same stimulus. Identifying characteristics of cells refractory to lytic induction relative to cells that undergo lytic activation will be an important step in developing a better understanding of the regulation of the EBV latent to lytic switch.

The high-mobility group A1a/signal transducer and activator of transcription-3 axis: an achilles heel for hematopoietic malignancies?

Although HMGA1 (high-mobility group A1; formerly HMG-I/Y) is an oncogene that is widely overexpressed in aggressive cancers, the molecular mechanisms underlying transformation by HMGA1 are only beginning to emerge. HMGA1 encodes the HMGA1a and HMGA1b protein isoforms, which function in regulating gene expression. To determine how HMGA1 leads to neoplastic transformation, we looked for genes regulated by HMGA1 using gene expression profile analysis. Here, we show that the STAT3 gene, which encodes the signaling molecule signal transducer and activator of transcription 3 (STAT3), is a critical downstream target of HMGA1a. STAT3 mRNA and protein are up-regulated in fibroblasts overexpressing HMGA1a and activated STAT3 recapitulates the transforming activity of HMGA1a in fibroblasts. HMGA1a also binds directly to a conserved region of the STAT3 promoter in vivo in human leukemia cells by chromatin immunoprecipitation and activates transcription of the STAT3 promoter in transfection experiments. To determine if this pathway contributes to HMGA1-mediated transformation, we investigated STAT3 expression in our HMGA1a transgenic mice, all of which developed aggressive lymphoid malignancy. STAT3 expression was increased in the leukemia cells from our transgenics but not in control cells. Blocking STAT3 function induced apoptosis in the transgenic leukemia cells but not in controls. In primary human leukemia samples, there was a positive correlation between HMGA1a and STAT3 mRNA. Moreover, blocking STAT3 function in human leukemia or lymphoma cells led to decreased cellular motility and foci formation. Our results show that the HMGA1a-STAT3 axis is a potential Achilles heel that could be exploited therapeutically in hematopoietic and other malignancies overexpressing HMGA1a.

Transcriptional activation of signal transducer and activator of transcription (STAT) 3 and STAT5B partially mediate homeobox A1-stimulated oncogenic transformation of the immortalized human mammary epithelial cell

We have previously demonstrated that the p44/42 MAPK pathway is one pathway involved in homeobox (HOX) A1-stimulated oncogenesis. However, inhibition of MAPK kinase 1 does not completely prevent HOXA1-stimulated oncogenic transformation, suggesting the involvement of additional signal transduction pathways. Here, we report that forced expression of HOXA1 in immortalized human mammary epithelial cells significantly increased levels of signal transducer and activator of transcription (STAT) 3, 5A, and 5B mRNA by transcriptional up-regulation. The protein levels of STAT3 and 5B, but not STAT5A, and protein phosphorylation levels of STAT3 and 5B were significantly increased by forced expression of HOXA1. Forced expression of STAT3 or STAT5B was sufficient to transform oncogenically an immortalized human mammary epithelial cell line. Accordingly, inhibition of STAT3 or STAT5B activity with dominant negative STAT3 or STAT5B abrogated the ability of HOXA1 to stimulate cell proliferation, survival, oncogenic transformation, and generation of large disorganized multiacinar structures in three-dimensional culture. These results suggest that HOXA1 partially mediates oncogenic transformation of the immortalized human mammary epithelial cell through modulation of the STAT3 and STAT5B pathways.

Oncogenic Ras-induced morphologic change is through MEK/ERK signaling pathway to downregulate Stat3 at a posttranslational level in NIH3T3 cells

Ras is a key regulator of the MAP kinase-signaling cascade and may cause morphologic change of Ras-transformed cells. Signal transducer and activator of transcription 3 (Stat3) can be activated by cytokine stimulation. In this study, we unravel that Ha-ras(V12) overexpression can downregulate the expression of Stat3 protein at a posttranslational level in NIH3T3 cells. Furthermore, we demonstrate that Stat3 expression downregulated by Ha-ras(V12) overexpression is through proteosome degradation and not through a mTOR/p70S6K-related signaling pathway. The suppression of Stat3 accompanied by the morphologic change induced by Ha-ras(V12) was through mitogen extracellular kinase (MEK)/extracellular-regulated kinase (ERK) signaling pathway. Microtubule disruption is involved in Ha-ras(V12)-induced morphologic change, which could be reversed by overexpression of Stat3. Taken together, we are the first to demonstrate that Stat3 protein plays a critical role in Ha-ras(V12)-induced morphologic change. Oncogenic Ras-triggered morphologic change is through the activation of MEK/ERK to posttranslationally downregulate Stat3 expression. Our finding may shed light on developing novel therapeutic strategies against Ras-related tumorigenesis.

Physiologically achievable concentrations of genistein enhance telomerase activity in prostate cancer cells via the activation of STAT3

Telomerase contributes to the infinite replicative potential of cancer cells by conferring proliferation and survival through the regulation of growth factors and apoptotic proteins. Although it is generally known that the phytoestrogen, genistein, has telomerase-repressing and anti-proliferative effects on various cancer cells at pharmacological concentrations, we report here that physiologically achievable concentrations of genistein enhance telomerase activity, the proliferation of human prostate cancer cells and tumor growth in the transgenic adenocarcinoma mouse prostate model. In determining the mechanism for enhanced telomerase activity, we observed that physiological concentrations of genistein activated signal transducers and activators of transcription 3 (STAT3) both in vitro and in vivo and increased STAT3 binding to the telomerase reverse transcriptase promoter in human prostate cancer cells. These results demonstrate for the first time that physiologically achievable concentrations of genistein enhance telomerase reverse transcriptase transcriptional activity in prostate cancer cells via the activation of STAT3. Consequently, these concentrations of genistein will augment the growth of prostate cancer cells that could be detrimental to individuals with prostate cancer and therefore, caution should be exercised when genistein is considered for chemotherapeutic purposes.

Mechanisms of resistance to cisplatin and carboplatin

While cisplatin and carboplatin are active versus most common cancers, epithelial malignancies are incurable when metastatic. Even if an initial response occurs, acquired resistance due to mutations and epigenetic events limits efficacy. Resistance may be due to excess of a resistance factor, to saturation of factors required for tumor cell killing, or to mutation or alteration of a factor required for tumor cell killing. Platinum resistance could arise from decreased tumor blood flow, extracellular conditions, reduced platinum uptake, increased efflux, intracellular detoxification by glutathione, etc., decreased binding (e.g., due to high intracellular pH), DNA repair, decreased mismatch repair, defective apoptosis, antiapoptotic factors, effects of several signaling pathways, or presence of quiescent non-cycling cells. In lung cancer, flattening of dose-response curves at higher doses suggests that efficacy is limited by exhaustion of something required for cell killing, and several clinical observations suggest epigenetic events may play a major role in resistance.

The broad-range cyclin-dependent kinase inhibitor UCN-01 induces apoptosis in colon carcinoma cells through transcriptional suppression of the Bcl-x(L) protein

The broad-range cyclin-dependent kinase inhibitor 7-hydroxystaurosporine (UCN-01) is known to induce both a G1 cell cycle arrest and apoptosis. The mechanism of UCN-01-induced apoptosis is largely unknown. We analysed the mechanism of cytotoxicity of UCN-01 in four established colon carcinoma cell lines. The cell lines SW48 and LS513 responded to UCN-01 treatment by undergoing apoptosis in a concentration-dependent manner while the cell lines HT-29 and WiDr were completely resistant. Apoptosis in LS513 and SW48 cell lines was concomitant with the suppression of Bcl-x(L) on mRNA and protein level. In contrast, in the apoptosis-resistant cell lines, Bcl-x(L) expression was not affected by UCN-01. Stable overexpression of the Bcl-x(L) protein abrogated UCN-01-triggered apoptosis, but only partially restored growth, indicating that both cell cycle arrest and apoptosis exert the anticancer effect in a coordinated manner. The inhibition of Akt phosphorylation did not correlate with the apoptotic phenotype. UCN-01 inhibited the activating STAT3 phosphorylations on Ser727 and, notably, on Tyr705, but STAT3 did not contribute to Bcl-x(L) expression in colon carcinoma cells. Moreover, we show for the first time that UCN-01 induces apoptosis by suppression of Bcl-x(L) expression. The inhibition of this pathway is a new aspect of cytotoxic and modulatory potential of UCN-01.

Structural and functional characterization of two human V-ATPase subunit gene promoters

The vacuolar-ATPase (V-ATPase) is a multi-subunit enzyme that couples ATP hydrolysis to proton pumping across membranes. V-ATPase genes are considered to be housekeeping genes and are expressed in human neoplastic tissue and in cell lines. We have isolated and characterized several genomic clones containing the 5'-end of the human V-ATPase genes. DNA sequence analysis of the promoters of two V-ATPase subunit genes, encoding C (ATP6C) and c (ATP6F), reveals GC-rich regions in the region of the first exon. Neither TATA- nor CCAAT-boxes were found in these promoters, but both GC-boxes and E-boxes were identified. Transient transfection analysis, using a series of 5' nested deletions of promoter-luciferase constructs in human cancer cells, demonstrated that a positive cis-acting regulatory region was present in these TATA-less promoters. The regions between -79 and -40 of the ATP6C promoter and between -245 and -99 of the ATP6F promoter were identified as being likely to be extremely important for basal promoter activity. Electrophoretic mobility shift assays (EMSA) of these cis-regulatory regions revealed the basal promoter to be highly complex, with cooperative binding of several transcription factors, including Sp family members. These data identify the critical regulatory regions for both the ATP6C and ATP6F basal promoters and stress the functional importance of multiple protein complexes, involving the Sp family of transcription factors, in regulating gene expression.

Relations between clusters of oxidatively damaged nucleotides and active or open nucleosomes in the rat Nth 1 gene

The distribution of oxidative damage to bases such as 8-hydroxyguanine (8-OH-Gua), was determined at the nucleotide level of resolution using the ligation-mediated PCR technique. Administration of a renal carcinogen, ferric nitrilotriacetate (Fe-NTA), is known to induce oxidative stress and subsequent formation of 8-OH-Gua in the kidney. Whole genomic DNA was isolated from the rat kidney with or without Fe-NTA treatment and then digested with formamidopyrimidine-DNA glycosylase (Fpg). As a target, we focused on the gene of a DNA repair enzyme for thymine glycol, Nth 1. Cleaved signals were found in exon 1 and exon 3, but not exon 5. Nucleosomes in these regions, enriched in damaged nucleotides, were highly accessible to micrococcal nuclease, especially in the kidney. Taking into account the function of the protein segment encoded by these regions, we discussed the molecular mechanism of the restricted formation of the damaged nucleotides.