STAT3 In Cancer Research Articles

APC/C CDH1 ubiquitinates STAT3 in mitosis.

STAT3, an oncogene drives tumor growth and is associated with poor prognosis. However, small molecule-based STAT3 inhibitors were unsuccessful in clinics. Recently, STAT3 degraders that ubiquitinate STAT3 were found to elicit long-lasting anti-tumor responses. Thus, triggering STAT3 ubiquitination in cancers is a better strategy than STAT3 inhibition. However, not much is known about the identity of E3-ligases that ubiquitinate STAT3 in cancers. Therefore, to design better therapies to degrade STAT3, we sought to identify E3-ligases that ubiquitinate STAT3 in cancer cells. To answer this question, we determined the cell cycle-dependent ubiquitination of STAT3 in HEK293T cells and examined the link between STAT3 dephosphorylation and ubiquitination. We found that STAT3 is more strongly ubiquitinated in mitosis than in other phases of the cell cycle. We observed that APC/C CDH1 binds and ubiquitinates STAT3 in mitosis. Further, we also found that inhibiting phosphatases decreases STAT3 ubiquitination. We conclude that APC/C CDH1 ubiquitinates STAT3 in mitosis. We suggest that mitosis can be a potential therapeutic window for treating STAT3-activated cancers.

Lycorine Ameliorates Thioacetamide-Induced Hepatic Fibrosis in Rats: Emphasis on Antioxidant, Anti-Inflammatory, and STAT3 Inhibition Effects.

Liver fibrosis is a foremost medical concern worldwide. In Saudi Arabia, numerous risk factors contribute to its high rates. Lycorine—a natural alkaloid—has antioxidant, anti-inflammatory, and antitumor activates. It has been reported to inhibit STAT3 in cancer. Therefore, this study aimed at investigating the possible antifibrotic effect of lycorine against thioacetamide (TAA)-induced liver fibrosis in rats and at elucidating the possible mechanisms. Liver fibrosis was induced by TAA (200 mg/kg i.p.), three per week for four weeks. Treatment with lycorine (0.5 and 1 mg/kg/d) amended TAA-induced rise of serum transaminases that was confirmed histopathologically. Moreover, it ameliorated liver fibrosis in a dose-dependent manner, as indicated by hindering the TAA-induced increase of hepatic hydroxyproline content, α-smooth muscle actin (α-SMA) and transforming growth factor (TGF-β1) expressions. TAA-induced oxidative stress was amended by lycorine treatment via restoring reduced glutathione and diminishing lipid peroxidation. Moreover, lycorine ameliorated hepatic inflammation by preventing the rise of inflammatory cytokines. Notably, lycorine inhibited STAT3 activity, as evidenced by the decreased phospho-STAT3 expression, accompanied by the elevation of the hepatic Bax/Bcl-2 ratio. In conclusion, lycorine hinders TAA-induced liver fibrosis in rats, due to—at least partly—its antioxidative and anti-inflammatory properties, along with its ability to inhibit STAT3 signaling.

The Multifaced Role of STAT3 in Cancer and Its Implication for Anticancer Therapy.

Signal transducer and activator of transcription (STAT) 3 is one of the most complex regulators of transcription. Constitutive activation of STAT3 has been reported in many types of tumors and depends on mechanisms such as hyperactivation of receptors for pro-oncogenic cytokines and growth factors, loss of negative regulation, and excessive cytokine stimulation. In contrast, somatic STAT3 mutations are less frequent in cancer. Several oncogenic targets of STAT3 have been recently identified such as c-myc, c-Jun, PLK-1, Pim1/2, Bcl-2, VEGF, bFGF, and Cten, and inhibitors of STAT3 have been developed for cancer prevention and treatment. However, despite the oncogenic role of STAT3 having been widely demonstrated, an increasing amount of data indicate that STAT3 functions are multifaced and not easy to classify. In fact, the specific cellular role of STAT3 seems to be determined by the integration of multiple signals, by the oncogenic environment, and by the alternative splicing into two distinct isoforms, STAT3α and STAT3β. On the basis of these different conditions, STAT3 can act both as a potent tumor promoter or tumor suppressor factor. This implies that the therapies based on STAT3 modulators should be performed considering the pleiotropic functions of this transcription factor and tailored to the specific tumor type.

TYK2 in Tumor Immunosurveillance.

We review the history of the tyrosine kinase 2 (TYK2) as the founding member of the Janus kinase (JAK) family and outline its structure-function relation. Gene-targeted mice and hereditary defects of TYK2 in men have established the biological and pathological functions of TYK2 in innate and adaptive immune responses to infection and cancer and in (auto-)inflammation. We describe the architecture of the main cytokine receptor families associated with TYK2, which activate signal transducers and activators of transcription (STATs). We summarize the cytokine receptor activities with well characterized dependency on TYK2, the types of cells that respond to cytokines and TYK2 signaling-induced cytokine production. TYK2 may drive beneficial or detrimental activities, which we explain based on the concepts of tumor immunoediting and the cancer-immunity cycle in the tumor microenvironment. Finally, we summarize current knowledge of TYK2 functions in mouse models of tumor surveillance. The biology and biochemistry of JAKs, TYK2-dependent cytokines and cytokine signaling in tumor surveillance are well covered in recent reviews and the oncogenic properties of TYK2 are reviewed in the recent Special Issue ‘Targeting STAT3 and STAT5 in Cancer’ of Cancers.

Direct Targeting Options for STAT3 and STAT5 in Cancer.

Signal transducer and activator of transcription (STAT)3 and STAT5 are important transcription factors that are able to mediate or even drive cancer progression through hyperactivation or gain-of-function mutations. Mutated STAT3 is mainly associated with large granular lymphocytic T-cell leukemia, whereas mutated STAT5B is associated with T-cell prolymphocytic leukemia, T-cell acute lymphoblastic leukemia and γδ T-cell-derived lymphomas. Hyperactive STAT3 and STAT5 are also implicated in various hematopoietic and solid malignancies, such as chronic and acute myeloid leukemia, melanoma or prostate cancer. Classical understanding of STAT functions is linked to their phosphorylated parallel dimer conformation, in which they induce gene transcription. However, the functions of STAT proteins are not limited to their phosphorylated dimerization form. In this review, we discuss the functions and the roles of unphosphorylated STAT3/5 in the context of chromatin remodeling, as well as the impact of STAT5 oligomerization on differential gene expression in hematopoietic neoplasms. The central involvement of STAT3/5 in cancer has made these molecules attractive targets for small-molecule drug development, but currently there are no direct STAT3/5 inhibitors of clinical grade available. We summarize the development of inhibitors against the SH2 domains of STAT3/5 and discuss their applicability as cancer therapeutics.

STAT1 inhibits STAT3 activation in esophageal squamous cell carcinoma.

BackgroundSignal transducer and activator of transcription (STAT) 1 is an important transcription factor and has been reported to be a tumor suppressor in many types of cancer. However, another STAT family member, STAT3, is considered to be an oncogene. The cross-talk between STAT1 and STAT3 in cancer has not been fully demonstrated.Materials and methodsEsophageal squamous cell carcinoma (ESCC) was used as a model to examine STAT1-STAT3 cross-regulation in cancer. We detected STAT1-STAT3 binding by co-immunoprecipitation (co-IP) and measured the transcription activity by using a luciferase reporter gene. DNA binding was detected by a DNA probe. Expression of STAT1 and STAT3 in ESCC was detected by immunohistochemistry.ResultsWe found that STAT1 attenuated STAT3 activity upon oncostatin M treatment by decreasing STAT3 transcription activity and DNA binding ability of STAT3. Furthermore STAT3 downregulation increased the phosphorylation and transcriptional activation of STAT1. Finally, STAT1 expression and STAT3 expression were negatively correlated in ESCC cases.ConclusionAltogether, this paper demonstrated STAT1 and STAT3 cross-regulation in ESCC and proposed that STAT3 downregulation and/or STAT1 accumulation may be a therapeutic approach to treat ESCC.

Systematic analysis of gene expression alterations and clinical outcomes of STAT3 in cancer.

Accumulated studies have provided controversial evidences of prognostic value for signal transducer and activator of transcription proteins 3 (STAT3) in cancers. To address this inconsistency, we performed a systematic analysis to determine whether STAT3 can serve as a prognostic marker in human cancers. STAT3 expression was assessed using Oncomine analysis. cBioPortal, Kaplan-Meier Plotter, and Prognoscan were performed to identify the prognostic roles of STAT3 in human cancers. The copy number alteration, mutation, interactive analysis, and visualize the altered networks were performed by cBioPortal. We found that STAT3 was more frequently overexpressed in lung, ovarian, gastric, blood and brain cancers than their normal tissues and its expression might be negatively related with the prognosis. In addition, STAT3 mutation mainly occurred in uterine cancer and existed in a hotspot in SH2 domain. Those findings suggest that STAT3 might serve as a diagnostic and therapeutic target for certain types of cancer, such as lung, ovarian, gastric, blood and brain cancers. However, future research is required to validate our findings and thus promote the clinical utility of STAT3 in those cancers prognosis evaluation.

STAT3 in cancer: A double edged sword

The transcription factor signal transducer and activator of transcription (STAT) 3 is activated downstream of cytokines, growth factors and oncogenes to mediate their functions under both physiological and pathological conditions. In particular, aberrant/unrestrained STAT3 activity is detected in a wide variety of tumors, driving multiple pro-oncogenic functions. For that, STAT3 is widely considered as an oncogene and is the object of intense translational studies. One of the distinctive features of this factor is however, its ability to elicit different and sometimes contrasting effects under different conditions. In particular, STAT3 activities have been shown to be either pro-oncogenic or tumor-suppressive according to the tumor aetiology/mutational landscape, suggesting that the molecular bases underlining its functions are still incompletely understood. Here we discuss some of the properties that may provide the bases to explain STAT3 heterogeneous functions, and in particular how post-translational modifications contribute shaping its sub-cellular localization and activities, the cross talk between these activities and cell metabolic conditions, and finally how its functions can control the behaviour of both tumor and tumor microenvironment cell populations.

The Opposing Function of STAT3 as an Oncoprotein and Tumor Suppressor Is Dictated by the Expression Status of STAT3β in Esophageal Squamous Cell Carcinoma

STAT3 is known to have both oncogenic and tumor suppressive effects, but the regulation of these opposing effects is elusive. We hypothesized that STAT3β, one of the two STAT3 isoforms, is the key determinant in this context. The prognostic significance of STAT3β and phospho-STAT3α(Y705) (pSTAT3α(Y705)) was evaluated in 286 cases of patients with esophageal squamous cell carcinoma (ESCC). STAT3β-induced changes in the chemosensitivity to cisplatin and 5-fluorouracil were assessed both in vitro and in vivo. STAT3β-induced changes in the frequency of cancer stem cells were evaluated using Hoechst and CD44 staining. How STAT3β regulates STAT3α was determined using immunoprecipitation, confocal microscopy, DNA-binding, and chromatin immunoprecipitation-PCR. STAT3β expression is an independent protective prognostic marker in patients with ESCC, which strongly correlated with longer overall survival (P = 0.0009) and recurrence-free survival (P = 0.0001). STAT3β significantly decreased the cancer stem cell population, and sensitized ESCC cells to cisplatin and 5-fluorouracil in tumor xenografts. Mechanistically, STAT3β markedly attenuated the transcription activity of STAT3α via inducing STAT3α:STAT3β heterodimers. However, the heterodimer formation decreased the binding between STAT3α and PTPN9 (better known as PTP-MEG2), a protein tyrosine phosphatase, thereby promoting the phosphorylation of STAT3α(Y705) and enhancing its nuclear translocation and DNA binding. Correlating with this, high STAT3β expression converts the prognostic value of pSTAT3α(Y705) from unfavorable to favorable in patients with ESCC. STAT3β suppresses chemoresistance and cancer stemness by blocking the transcriptional activity of STAT3α. The paradoxical increase in pSTAT3α(Y705) induced by STAT3β carries important implications as to how the biologic and prognostic significance of STAT3 in cancers should be interpreted.

Research progress in multiple regulation pathways of STAT3 in cancer

Research progress in multiple regulation pathways of STAT3 in cancer

STAT5 in Cancer and Immunity.

Signal transducers and activators of transcription 5 (STAT5a and STAT5b) are highly homologous proteins that are encoded by 2 separate genes and are activated by Janus-activated kinases (JAK) downstream of cytokine receptors. STAT5 proteins are activated by a wide variety of hematopoietic and nonhematopoietic cytokines and growth factors, all of which use the JAK-STAT signalling pathway as their main mode of signal transduction. STAT5 proteins critically regulate vital cellular functions such as proliferation, differentiation, and survival. The physiological importance of STAT5 proteins is underscored by the plethora of primary human tumors that have aberrant constitutive activation of these proteins, which significantly contributes to tumor cell survival and malignant progression of disease. STAT5 plays an important role in the maintenance of normal immune function and homeostasis, both of which are regulated by specific members of IL-2 family of cytokines, which share a common gamma chain (γ(c)) in their receptor complex. STAT5 critically mediates the biological actions of members of the γ(c) family of cytokines in the immune system. Essentially, STAT5 plays a critical role in the function and development of Tregs, and consistently activated STAT5 is associated with a suppression in antitumor immunity and an increase in proliferation, invasion, and survival of tumor cells. Thus, therapeutic targeting of STAT5 is promising in cancer.

Multiple regulation pathways and pivotal biological functions of STAT3 in cancer.

STAT3 is both a transcription activator and an oncogene that is tightly regulated under normal physiological conditions. However, abundant evidence indicates that STAT3 is persistently activated in several cancers, with a crucial position in tumor onset and progression. In addition to its traditional role in cancer cell proliferation, invasion, and migration, STAT3 also promotes cancer through altering gene expression via epigenetic modification, inducing epithelial–mesenchymal transition (EMT) phenotypes in cancer cells, regulating the tumor microenvironment, and promoting cancer stem cells (CSCs) self-renewal and differentiation. STAT3 is regulated not only by the canonical cytokines and growth factors, but also by the G-protein-coupled receptors, cadherin engagement, Toll-like receptors (TLRs), and microRNA (miRNA). Despite the presence of diverse regulators and pivotal biological functions in cancer, no effective therapeutic inventions are available for inhibiting STAT3 and acquiring potent antitumor effects in the clinic. An improved understanding of the complex roles of STAT3 in cancer is required to achieve optimal therapeutic effects.

Inactivating STAT3: bad for tumor, good for muscle

The Signal Transducer and Activator of Transcription 3, also known as STAT3, is a transcription factor originally identified as downstream effector of IL6-, IFNγ- and IFNα-mediated inflammatory pathways, and it is undesirably activated in multiple types of cancer.1 STAT3 plays a role in tumor cell proliferation, survival, angiogenesis, metastasis and immune responses. As a consequence, an active research to inhibit STAT3 and generate anti-tumor effects is underway. Unfortunately, the high complexity of the signaling cascades wherein STAT3 is interdigitated hardens the possibility of selectively inhibiting cancer growth without deleterious side effects (i.e. immunosuppression). Upstream activators of STAT3, as the Janus Tyrosine Kinase (JAK), are therefore regarded as better inhibitory targets also because STAT3 lacks its own enzimatic activity, a preferential pre-requisite for drug targets. Interestingly, recent studies have recognized Toll-like receptors (i.e. TLR4) as well as G-protein-coupled receptors (i.e. S1PR1) as additional activators of the JAK/STAT3 pathway, thus pointing to new directions for targeting STAT3 in cancer.

STAT3 Signaling in Cancer

In recent years, signal transducers and activators of transcription (STAT) proteins have been recognized as cytoplasmic transcription factors that mediate extracellular signaling to the nucleus controlling fundamental functions, such as cell proliferation, apoptosis, differentiation, immune responses and angiogenesis. Among them, STAT3 is a major player, aberrant activation of which is involved in several diseases, including cancer. Among other upstream regulators, IL-6/Jak signaling can activate STAT3 and its role appears to be critical in various types of cancer. Although STAT3 has been traditionally recognized as amoncogene, more recently the dual role of STAT3 in cancer, either tumor inductive or suppressive, has been appreciated. The importance and differential effect of STAT3 on tyrosine or serine residues are also a matter of continuing debate. Interestingly, recent findings suggesting that STAT3 plays an important role in cancer stem cell regulation have gained significant attention. This review summarizes current literature focusing on the significance of STAT3 in several diseases as well as in cancer. Understanding the complexity of STAT3 function has the potential to elucidate important molecular aspects of cancer with significant therapeutic implications.

S-27 : STAT3: From fundamental discoveries to the clinic

STAT3 is a key transducer for various cytokine signaling and it plays a crucial role in tumor progression, enabling tumor cell proliferation/survival while turning off body’s anti-tumor immune response. Silencing STAT3 could therefore have significant implications for improved cancer therapy. However, as a transcription factor lacking its own enzymatic activity, STAT3 is a challenging target for conventional small molecule drugs. We recently identified new biology of STAT3 in cancer and developed novel approaches to target STAT3. While actively developing several new technologies capable of inhibiting STAT3 and other challenging targets, Dr. Yu and colleagues at City of Hope Comprehensive Cancer Center are moving one of the approaches towards clinical trials.

STAT3 in Cancer-Friend or Foe?

The roles and significance of STAT3 in cancer biology have been extensively studied for more than a decade. Mounting evidence has shown that constitutive activation of STAT3 is a frequent biochemical aberrancy in cancer cells, and this abnormality directly contributes to tumorigenesis and shapes many malignant phenotypes in cancer cells. Nevertheless, results from more recent experimental and clinicopathologic studies have suggested that STAT3 also can exert tumor suppressor effects under specific conditions. Importantly, some of these studies have demonstrated that STAT3 can function either as an oncoprotein or a tumor suppressor in the same cell type, depending on the specific genetic background or presence/absence of specific coexisting biochemical defects. Thus, in the context of cancer biology, STAT3 can be a friend or foe. In the first half of this review, we will highlight the “evil” features of STAT3 by summarizing its oncogenic functions and mechanisms. The differences between the canonical and non-canonical pathway will be highlighted. In the second half, we will summarize the evidence supporting that STAT3 can function as a tumor suppressor. To explain how STAT3 may mediate its tumor suppressor effects, we will discuss several possible mechanisms, one of which is linked to the role of STAT3β, one of the two STAT3 splicing isoforms. Taken together, it is clear that the roles of STAT3 in cancer are multi-faceted and far more complicated than one appreciated previously. The new knowledge has provided us with new approaches and strategies when we evaluate STAT3 as a prognostic biomarker or therapeutic target.

STAT3 in hepatocellular carcinoma: new perspectives.

Chronic liver damage and inflammation are strong promoters of hepatocellular carcinoma (HCC) formation. HCC cells communicate with inflammatory and stromal cells via cytokine/chemokine signals. These heterotypic interactions inhibit immunologic anticancer activities and promote protumorigenic activities, such as angiogenesis or invasiveness. STAT3 mediates several reciprocal interactions between liver cancer cells and stromal cells and modulates preconditions of tumor formation such as chronic inflammation. Therefore, activation of STAT3 is considered as a tumor-promoting event in HCC formation. However, the oncogenic role of STAT3 in cancers has been challenged by several reports that suggest a tumor-suppressive activity. Here we discuss tumor-promoting and tumor-suppressive effects of cytokine-activated STAT3 in HCC.

Targeting Blockage of STAT3 in Hepatocellular Carcinoma Cells Augments NK Cell Functions via Reverse Hepatocellular Carcinoma–Induced Immune Suppression

STAT3 is an important transcriptional factor for cell growth, differentiation, and apoptosis. Although evidence suggests a positive role for STAT3 in cancer, the inhibitory effects of tumor STAT3 on natural killer (NK) cell functions in human hepatocellular carcinoma are unclear. In this study, we found that blocking STAT3 in hepatocellular carcinoma cells enhanced NK-cell antitumor function. In the case of STAT3-blocked hepatocellular carcinoma cells, NKG2D ligands were upregulated, which promoted recognition by NK cells. Importantly, the cytokine profile of hepatocellular carcinoma cells was altered; in particular, TGF-β and interleukin 10 (IL-10) expression was reduced, and type I interferon (IFN) was induced, thus facilitating NK-cell activation. Indeed, the cytotoxicity of NK cells treated with supernatant from STAT3-blocked hepatocellular carcinoma cells was augmented, with a concomitant elevation of molecules associated with NK cytolysis. Further experiments confirmed that the recovery of NK cells depended on the downregulation of TGF-β and upregulation of type I IFN derived from STAT3-blocked hepatocellular carcinoma cells. These findings demonstrated a pivotal role for STAT3 in hepatocellular carcinoma-mediated NK-cell dysfunction, and highlighted the importance of STAT3 blockade for hepatocellular carcinoma immunotherapy, which could restore NK-cell cytotoxicity in addition to its direct influence on tumor cells.

Critical analysis of the potential for targeting STAT3 in human malignancy

The signal transducer and activator of transcription (STAT) family of proteins was originally discovered in the context of normal cell biology where they function to transduce intracellular and extracellular signals to the nucleus, ultimately leading to transcription of specific target genes and downstream phenotypic effects. It was quickly appreciated that the STATs, especially STAT3, play a fundamental role in human malignancy. In contrast to normal biology in which transient STAT3 signaling is strictly regulated by a tightly coordinated network of activators and deactivators, STAT3 is constitutively activated in human malignancies. Constitutive STAT3 signaling has been associated with many cancerous phenotypes across nearly all human cancers, including the upregulation of cell growth, proliferation, survival, and motility, among others. Studies involving candidate preclinical STAT3 inhibitors have further demonstrated that the reversal of these phenotypes results from pharmacologic or genetic inhibition of STAT3, suggesting that STAT3 may be a promising target for clinical interventions. Indeed, a Phase 0 clinical trial involving a STAT3 decoy oligonucleotide demonstrated that STAT3 is a drug-gable target in human tumors. Because of the ubiquity of overactive STAT3 in cancer, its role in promoting a wide variety of cancerous phenotypes, and the strong clinical and preclinical studies performed to date, STAT3 represents a promising target for the development of inhibitors for the treatment of human cancers.

STAT3 suppresses transcription of proapoptotic genes in cancer cells with the involvement of its N-terminal domain

Activation of STAT3 in cancers leads to gene expression promoting cell proliferation and resistance to apoptosis, as well as tumor angiogenesis, invasion, and migration. In the characterization of effects of ST3-H2A2, a selective inhibitor of the STAT3 N-terminal domain (ND), we observed that the compound induced apoptotic death in cancer cells associated with robust activation of proapoptotic genes. Using ChIP and tiling human promoter arrays, we found that activation of gene expression in response to ST3-H2A2 is accompanied by altered STAT3 chromatin binding. Using inhibitors of STAT3 phosphorylation and a dominant-negative STAT3 mutant, we found that the unphosphorylated form of STAT3 binds to regulatory regions of proapoptotic genes and prevents their expression in tumor cells but not normal cells. siRNA knockdown confirmed the effects of ST3-HA2A on gene expression and chromatin binding to be STAT3 dependent. The STAT3-binding region of the C/EBP-homologous protein (CHOP) promoter was found to be localized in DNaseI hypersensitive site of chromatin in cancer cells but not in nontransformed cells, suggesting that STAT3 binding and suppressive action can be chromatin structure dependent. These data demonstrate a suppressive role for the STAT3 ND in the regulation of proapoptotic gene expression in cancer cells, providing further support for targeting STAT3 ND for cancer therapy.