STAT3beta, a distinct isoform from STAT3

The "Heater" of "Cold" Tumors-Blocking IL-6

The resolution of inflammation is not simply the end of the inflammatory response but rather a complex process that involves various cells, inflammatory factors, and specialized proresolving mediators following the occurrence of inflammation. Once inflammation cannot be cleared by the body, malignant tumors may be induced. Among them, IL-6, as an immunosuppressive factor, activates a variety of signal transduction pathways and induces tumorigenesis. Monitoring IL-6 can be used for the diagnosis, efficacy evaluation and prognosis of tumor patients. In terms of treatment, improving the efficacy of targeted and immunotherapy remains a major challenge. Blocking IL-6 and its mediated signaling pathways can regulate the tumor immune microenvironment and enhance immunotherapy responses by activating immune cells. Even transform "cold" tumors that are difficult to respond to immunotherapy into immunogenic "hot" tumors, acting as a "heater" for "cold" tumors, restarting the tumor immune cycle, and reducing immunotherapy-related toxic reactions and drug resistance. In clinical practice, the combined application of IL-6 inhibition with targeted therapy and immunotherapy may produce synergistic results. Nevertheless, additional clinical trials are imperative to further validate the safety and efficacy of this therapeutic approach.

Asymmetric post-translational modifications regulate the nuclear translocation of STAT3 homodimers in response to leukemia inhibitory factor

STAT3 is a pleiotropic transcription factor overactivated in 70% of solid tumours. We have recently reported that inactivating mutations on residues susceptible to post-translational modifications (PTMs) in only one of the monomers (i.e. asymmetric) caused changes in the cellular distribution of STAT3 homodimers. Here, we used more controlled experimental conditions, i.e. without the interference of endogenous STAT3 (STAT3-/- HeLa cells) and in the presence of a defined cytokine stimulus (Leukemia Inhibitory Factor, LIF), to provide further evidence that asymmetric PTMs affect the nuclear translocation of STAT3 homodimers. Time-lapse microscopy for 20 min after LIF stimulation showed that S727 dephosphorylation (S727A) and K685 inactivation (K685R) slightly enhanced the nuclear translocation of STAT3 homodimers, while K49 inactivation (K49R) delayed STAT3 nuclear translocation. Our findings suggest that asymmetrically modified STAT3 homodimers could be a new level of STAT3 regulation and, therefore, a potential target for cancer therapy.

Widespread variation in molecular interactions and regulatory properties among transcription factor isoforms

Most human Transcription factors (TFs) genes encode multiple protein isoforms differing in DNA binding domains, effector domains, or other protein regions. The global extent to which this results in functional differences between isoforms remains unknown. Here, we systematically compared 693 isoforms of 246 TF genes, assessing DNA binding, protein binding, transcriptional activation, subcellular localization, and condensate formation. Relative to reference isoforms, two-thirds of alternative TF isoforms exhibit differences in one or more molecular activities, which often could not be predicted from sequence. We observed two primary categories of alternative TF isoforms: "rewirers" and "negative regulators", both of which were associated with differentiation and cancer. Our results support a model wherein the relative expression levels of, and interactions involving, TF isoforms add an understudied layer of complexity to gene regulatory networks, demonstrating the importance of isoform-aware characterization of TF functions and providing a rich resource for further studies.

Unraveling the complexity of STAT3 in cancer: molecular understanding and drug discovery

Signal transducer and activator of transcription 3 (STAT3) is a transcriptional factor involved in almost all cancer hallmark features including tumor proliferation, metastasis, angiogenesis, immunosuppression, tumor inflammation, metabolism reprogramming, drug resistance, cancer stemness. Therefore, STAT3 has become a promising therapeutic target in a wide range of cancers. This review focuses on the up-to-date knowledge of STAT3 signaling in cancer. We summarize both the positive and negative modulators of STAT3 together with the cancer hallmarks involving activities regulated by STAT3 and highlight its extremely sophisticated regulation on immunosuppression in tumor microenvironment and metabolic reprogramming. Direct and indirect inhibitors of STAT3 in preclinical and clinical studies also have been summarized and discussed. Additionally, we highlight and propose new strategies of targeting STAT3 and STAT3-based combinations with established chemotherapy, targeted therapy, immunotherapy and combination therapy. These efforts may provide new perspectives for STAT3-based target therapy in cancer.

Targeting STAT3 Enzyme for Cancer Treatment

A category of cytoplasmic transcription factors called STATs mediates intracellular signaling, which is frequently generated at receptors on cell surfaces and subsequently sent to the nucleus. STAT3 is a member of a responsible for a variety of human tumor forms, including lymphomas, hematological malignancies, leukemias, multiple myeloma and several solid tumor types. Numerous investigations have demonstrated constitutive STAT3 activation lead to cancer development such as breast, head and neck, lung, colorectal, ovarian, gastric, hepatocellular, and prostate cancers. It's possible to get a hold of the book here. Tumor cells undergo apoptosis when STAT3 activation is suppressed. This review highlights the STAT3 activation and inhibition which can be used for further studies.

Novel insights into STAT3 in renal diseases

Signal transducer and activator of transcription 3 (STAT3) is a cell-signal transcription factor that has attracted considerable attention in recent years. The stimulation of cytokines and growth factors can result in the transcription of a wide range of genes that are crucial for several cellular biological processes involved in pro- and anti-inflammatory responses. STAT3 has attracted considerable interest as a result of a recent upsurge in study because of their role in directing the innate immune response and sustaining inflammatory pathways, which is a key feature in the pathogenesis of many diseases, including renal disorders. Several pathological conditions which may involve STAT3 include diabetic nephropathy, acute kidney injury, lupus nephritis, polycystic kidney disease, and renal cell carcinoma. STAT3 is expressed in various renal tissues under these pathological conditions. To better understand the role of STAT3 in the kidney and provide a theoretical foundation for STAT3-targeted therapy for renal disorders, this review covers the current work on the activities of STAT3 and its mechanisms in the pathophysiological processes of various types of renal diseases.

Identification of potential necroinflammation-associated necroptosis-related biomarkers for delayed graft function and renal allograft failure: a machine learning-based exploration in the framework of predictive, preventive, and personalized medicine

Delayed graft function (DGF) is one of the key post-operative challenges for a subset of kidney transplantation (KTx) patients. Graft survival is significantly lower in recipients who have experienced DGF than in those who have not. Assessing the risk of chronic graft injury, predicting graft rejection, providing personalized treatment, and improving graft survival are major strategies for predictive, preventive, and personalized medicine (PPPM/3PM) to promote the development of transplant medicine. However, since PPPM aims to accurately identify disease by integrating multiple omics, current methods to predict DGF and graft survival can still be improved. Renal ischemia/reperfusion injury (IRI) is a pathological process experienced by all KTx recipients that can result in varying occurrences of DGF, chronic rejection, and allograft failure depending on its severity. During this process, a necroinflammation-mediated necroptosis-dependent secondary wave of cell death significantly contributes to post-IRI tubular cell loss. In this article, we obtained the expression matrices and corresponding clinical data from the GEO database. Subsequently, nine differentially expressed necroinflammation-associated necroptosis-related genes (NiNRGs) were identified by correlation and differential expression analysis. The subtyping of post-KTx IRI samples relied on consensus clustering; the grouping of prognostic risks and the construction of predictive models for DGF (the area under the receiver operating characteristic curve (AUC) of the internal validation set and the external validation set were 0.730 and 0.773, respectively) and expected graft survival after a biopsy (the internal validation set's 1-year AUC: 0.770; 2-year AUC: 0.702; and 3-year AUC: 0.735) were based on the least absolute shrinkage and selection operator regression algorithms. The results of the immune infiltration analysis showed a higher infiltration abundance of myeloid immune cells, especially neutrophils, macrophages, and dendritic cells, in the cluster A subtype and prognostic high-risk groups. Therefore, in the framework of PPPM, this work provides a comprehensive exploration of the early expression landscape, related pathways, immune features, and prognostic impact of NiNRGs in post-KTx patients and assesses their capabilities as.predictors of post-KTx DGF and graft loss,targets of the vicious loop between regulated tubular cell necrosis and necroinflammation for targeted secondary and tertiary prevention, andreferences for personalized immunotherapy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13167-023-00320-w.

JAKs and STATs from a Clinical Perspective: Loss-of-Function Mutations, Gain-of-Function Mutations, and Their Multidimensional Consequences

The JAK/STAT signaling pathway plays a key role in cytokine signaling and is involved in development, immunity, and tumorigenesis for nearly any cell. At first glance, the JAK/STAT signaling pathway appears to be straightforward. However, on closer examination, the factors influencing the JAK/STAT signaling activity, such as cytokine diversity, receptor profile, overlapping JAK and STAT specificity among non-redundant functions of the JAK/STAT complexes, positive regulators (e.g., cooperating transcription factors), and negative regulators (e.g., SOCS, PIAS, PTP), demonstrate the complexity of the pathway's architecture, which can be quickly disturbed by mutations. The JAK/STAT signaling pathway has been, and still is, subject of basic research and offers an enormous potential for the development of new methods of personalized medicine and thus the translation of basic molecular research into clinical practice beyond the use of JAK inhibitors. Gain-of-function and loss-of-function mutations in the three immunologically particularly relevant signal transducers STAT1, STAT3, and STAT6 as well as JAK1 and JAK3 present themselves through individual phenotypic clinical pictures. The established, traditional paradigm of loss-of-function mutations leading to immunodeficiency and gain-of-function mutation leading to autoimmunity breaks down and a more differentiated picture of disease patterns evolve. This review is intended to provide an overview of these specific syndromes from a clinical perspective and to summarize current findings on pathomechanism, symptoms, immunological features, and therapeutic options of STAT1, STAT3, STAT6, JAK1, and JAK3 loss-of-function and gain-of-function diseases.

Differential silencing of STAT3 isoforms leads to changes in STAT3 activation

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor involved in multiple fundamental biological processes and a key player in cancer development and progression. STAT3 is activated upon tyrosine phosphorylation and is constitutively active in various malignancies; therefore, the expression of pSTAT3 has been recognized as a predictor of poor survival. STAT3 encodes two alternatively-spliced STAT3 isoforms: the full-length STAT3α isoform and the truncated STAT3β isoform. These isoforms have been suggested as the reason for the occasionally observed opposing roles of STAT3 in cancer: an oncogene, on one hand, and a tumor suppressor on the other. To investigate their roles in aggressive breast cancer, we separately silenced each isoform and found that they affect each other's activation, impacting cell viability, cytokine expression, and migration. Silencing specific isoforms can lead to a more favorable balance of activated STAT3 proteins in the cell. Distinguishing between the two isoforms and their active forms is crucial for STAT3-related cancer diagnosis and therapy.

Increased STAT expression in Reed-Sternberg cells as a potential positive prognostication biomarker in Hodgkin lymphoma

Classic Hodgkin lymphoma (cHL) prognostication primarily relies on clinical and radiological factors. Despite this, a subset of patients still progress. Immunohistochemistry (IHC) based biomarkers on diagnostic tissue have not been routinely used for prognostication. A multicentre retrospective analysis identified 62 patients with cHL. IHC on diagnostic tissues was used to stain Reed-Sternberg cells (RS) cells for STAT1, pSTAT3, p53 and tumour microenvironment for CD68 and PD-1. IHC stains were scored by anatomical pathologists blinded to patients and their outcomes and correlated with survival. Strong intensity of STAT1 and pSTAT3 staining correlated with improved overall survival (OS), with hazard ratios (HR) of 0.21 [95% confidence interval (CI) 0.06-0.76] and 0.22 (95% CI 0.06-0.84), respectively. Similarly, the median OS for weak versus strong STAT1 or pSTAT3 staining was 8.8 years versus not reached. Other IHC stains did not correlate with prognosis. In this cohort of cHL patients, downregulation of immunohistochemical STAT1 or pSTAT3 in RS cells is associated with inferior OS, suggesting STAT transcription within the pathognomonic RS cells may have tumour suppressor function and may be a potential biomarker for cHL prognosis.

E-prostanoid 3 receptor deficiency on myeloid cells protects against ischemic acute kidney injury via breaking the auto-amplification loop of necroinflammation

Necroinflammation plays an important role in disease settings such as acute kidney injury (AKI). We and others have elucidated that prostaglandins, which are critically involved in inflammation, may activate E-prostanoid 3 receptor (EP3) at low concentrations. However, how EP3 blockade interacts with regulated cell death and affects AKI remains unknown. In this study, AKI was induced by ischemia-reperfusion (30 minutes/24 hours) in Ep3 knockout (Ep3-/-), bone marrow chimeric, myeloid conditional EP3 knockout and corresponding control mice. The production of prostaglandins E2 and I2 was markedly increased after ischemia-reperfusion, and either abrogation or antagonism of EP3 ameliorated the injury. EP3 deficiency curbed inflammatory cytokine release, neutrophil infiltration and serum high-mobility group box 1 levels, but additional TLR4 inhibition with TAK-242 did not offer further protection against the injury and inflammation. The protection of Ep3-/- was predominantly mediated by suppressing Mixed Lineage Kinase domain-Like-dependent necroptosis, resulting from the inhibition of cytokine generation and the switching of cell death modality from necroptosis to apoptosis through caspase-8 up-regulation, in part due to the restraint of IL-6/JAK2/STAT3 signaling. EP3 deficiency failed to further alleviate the injury when necroptosis was inhibited. Ep3-/- in bone marrow-derived cells, particularly that in myeloid cells, protected kidneys to the same extent as that of global EP3 deletion. Thus, our results demonstrate that EP3 deficiency especially that on myeloid cells, ameliorates ischemic AKI via curbing inflammation and breaking the auto-amplification loop of necroinflammation. Hence, EP3 may be a promising target for the prevention and/or treatment of AKI.

Advances in the role of STAT3 in macrophage polarization

The physiological processes of cell growth, proliferation, differentiation, and apoptosis are closely related to STAT3, and it has been demonstrated that aberrant STAT3 expression has an impact on the onset and progression of a number of inflammatory immunological disorders, fibrotic diseases, and malignancies. In order to produce the necessary biological effects, macrophages (M0) can be polarized into pro-inflammatory (M1) and anti-inflammatory (M2) types in response to various microenvironmental stimuli. STAT3 signaling is involved in macrophage polarization, and the research of the effect of STAT3 on macrophage polarization has gained attention in recent years. In order to provide references for the treatment and investigation of disorders related to macrophage polarization, this review compiles the pertinent signaling pathways associated with STAT3 and macrophage polarization from many fundamental studies.

The Role of IL-6 in Cancer Cell Invasiveness and Metastasis-Overview and Therapeutic Opportunities

Interleukin 6 (IL-6) belongs to a broad class of cytokines involved in the regulation of various homeostatic and pathological processes. These activities range from regulating embryonic development, wound healing and ageing, inflammation, and immunity, including COVID-19. In this review, we summarise the role of IL-6 signalling pathways in cancer biology, with particular emphasis on cancer cell invasiveness and metastasis formation. Targeting principal components of IL-6 signalling (e.g., IL-6Rs, gp130, STAT3, NF-κB) is an intensively studied approach in preclinical cancer research. It is of significant translational potential; numerous studies strongly imply the remarkable potential of IL-6 signalling inhibitors, especially in metastasis suppression.

A Narrative Review of STAT Proteins in Diabetic Retinopathy: From Mechanisms to Therapeutic Prospects

Diabetic retinopathy (DR), a blinding disease, is one of the high-incidence chronic complications of diabetes. However, the current treatment for DR is mainly based on advanced pathological changes, which cannot reverse pre-existing retinal tissue damage and visual impairment. Signal transducer and activator of transcription (STAT) proteins are essential in DR through early and late stages. They participate in the early stage of DR through multiple mechanisms and have a strong proangiogenic effect in the late stage. Inhibiting STAT proteins activity has also achieved a significant effect in reversing the pathological changes of DR. Thus, STAT proteins are expected to be an effective therapeutic target in the early stage of DR and can make up for inadequate late treatment. This review introduces the structure, signal transduction mode, and biological functions of STAT proteins in detail and focuses on their role in the mechanism of DR. We also summarize the current research on STAT-related biological agents in DR, aiming to provide a theoretical basis for the treatment of DR.

Identification of four STAT3 isoforms and functional investigation of IL-6/JAK2/STAT3 pathway in blunt snout bream (Megalobrama amblycephala)

Signal transducer and activator of transcription 3 (STAT3) is a major regulator of immune response and chronic inflammatory, which can be activated by interleukin-6 (IL-6). In mammals, STAT3 has multiple isoforms, and its function has been well studied. In teleost, a single stat3 has been cloned and identified in several species, but studies on its function are limited. In the present study, four stat3 isoforms including mastat3α1, mastat3α2, mastat3β1 and mastat3β2 were identified from blunt snout bream (Megalobrama amblycephala). The results of quantitative PCR (qPCR) showed that four mastat3 transcripts were ubiquitously expressed in all 10 tissues examined. After Aeromonas hydrophila challenge, the expression patterns of mastat3a1, mastat3a2 and mastat3β2 were similar, but significantly different from that of mastat3β1. In addition, western blot showed that rmaIL-6+rmasIL-6R (IL-6 trans-signaling) significantly up-regulated phosphorylation levels of the four maSTAT3 isoforms and mRNA levels of the il-10, il-11, tnf-a, socs3a and socs3b genes, while rmaIL-6 (IL-6 classical signaling) only significantly up-regulated phosphorylation levels of the two maSTAT3α isoforms and mRNA levels of the il-10, socs3a and socs3b genes. Meanwhile, overexpression or inhibition of JAK2 could significantly change the STAT3 phosphorylation. Finally, JAK2 and STAT3 inhibitors could significantly inhibit the up-regulation of il-10, il-11, tnf-a, socs3a and socs3b induced by rmaIL-6+rmasIL-6R or rmaIL-6. To sum up, this study reveals the functional distinctions and overlaps among the four maSTAT3 isoforms in blunt snout bream and reveals the differential regulation of IL-6 classical signaling and trans-signaling on downstream immune genes via the JAK2/STAT3 pathway, enriching our knowledge of fish's defense mechanisms against pathogens.

Meprin β expression modulates the interleukin-6 mediated JAK2-STAT3 signaling pathway in ischemia/reperfusion-induced kidney injury

Meprin metalloproteinases have been implicated in the pathophysiology of ischemia/reperfusion (IR)-induced kidney injury. Previous in vitro data showed that meprin β proteolytically processes interleukin-6 (IL-6) resulting in its inactivation. Recently, meprin-β was also shown to cleave the IL-6 receptor. The goal of this study was to determine how meprin β expression impacts IL-6 and downstream modulators of the JAK2-STAT3-mediated signaling pathway in IR-induced kidney injury. IR was induced in 12-week-old male wild-type (WT) and meprin β knockout (βKO) mice and kidneys obtained at 24 h post-IR. Real-time PCR, western blot, and immunostaining/microscopy approaches were used to quantify mRNA and protein levels respectively, and immunofluorescence counterstaining with proximal tubule (PT) markers to determine protein localization. The mRNA levels for IL-6, CASP3 and BCL-2 increased significantly in both genotypes. Interestingly, western blot data showed increases in protein levels for IL-6, CASP3, and BCL-2 in the βKO but not in WT kidneys. However, immunohistochemical data showed increases in IL-6, CASP3, and BCL-2 proteins in select kidney tubules in both genotypes, shown to be PTs by immunofluorescence counterstaining. IR-induced increases in p-STAT-3 and p-JAK-2 in βKO at a global level but immunoflourescence counterstaining demonstrated p-JAK2 and p-STAT3 increases in select PT for both genotypes. BCL-2 increased only in the renal corpuscle of WT kidneys, suggesting a role for meprins expressed in leukocytes. Immunohistochemical analysis confirmed higher levels of leukocyte infiltration in WT kidneys when compared to βKO kidneys. The present data demonstrate that meprin β modulates IR-induced kidney injury in part via IL-6/JAK2/STAT3-mediated signaling.

Preliminary study on the role and mechanism of KIRREL3 in the development of esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is a common malignant tumor of the digestive tract, which is very harmful to human health. The JAK-STAT signaling pathway is a recognized carcinogenic pathway that plays a role in the proliferation, apoptosis, migration, and invasion of a variety of cancer cells. Some studies have shown that the activation status of STAT3 affects the expression of KIRREL3. However, the expression of KIRREL3 in ESCC and its relationship with KIRREL3 or the JAK-STAT signaling pathway is still unclear.

METHODS

In this study, we used immunohistochemistry and western blotting to analyze the protein expression levels of KIRREL3 in tumor tissues and ESCC cell lines. We applied proliferation assays, plate clone formation assays, Transwell assays, flow cytometry analysis, and CDX animal models to examine the role of KIRREL3 in ESCC.

RESULTS

The results indicate that KIRREL3 is highly expressed to varying degrees in ESCC tissues and cell lines. Knocking down KIRREL3 expression in ESCC cells could correspondingly inhibit cell proliferation, colony formation, invasion, and migration, and had some effects on cell cycle progression and apoptosis. In addition, overexpressing KIRREL3 in these cells had opposite effects. Tumor formation in nude mice experiments also confirmed that KIRREL3 is involved in the growth of ESCC cells in vivo.

CONCLUSIONS

These data suggest that KIRREL3 plays a key role in the development of ESCC, and KIRREL3 is a potential new target for the early diagnosis and clinical treatment of this disease.

The Multifaceted Role of STAT3 in NK-Cell Tumor Surveillance

Signal transducer and activator of transcription 3 (STAT3) is a member of the Janus kinase (JAK)-STAT pathway, which is one of the key pathways contributing to cancer. STAT3 regulates transcription downstream of many cytokines including interleukin (IL)-6 and IL-10. In cancer, STAT3 is mainly described as a tumor promoter driving tumor cell proliferation, resistance to apoptosis, angiogenesis and metastasis and aberrant activation of STAT3 is associated with poor prognosis. STAT3 is also an important driver of immune evasion. Among many other immunosuppressive mechanisms, STAT3 aids tumor cells to escape natural killer (NK) cell-mediated immune surveillance. NK cells are innate lymphocytes, which can directly kill malignant cells but also regulate adaptive immune responses and contribute to the composition of the tumor microenvironment. The inborn ability to lyse transformed cells renders NK cells an attractive tool for cancer immunotherapy. Here, we provide an overview of the role of STAT3 in the dynamic interplay between NK cells and tumor cells. On the one hand, we summarize the current knowledge on how tumor cell-intrinsic STAT3 drives the evasion from NK cells. On the other hand, we describe the multiple functions of STAT3 in regulating NK-cell cytotoxicity, cytokine production and their anti-tumor responses in vivo. In light of the ongoing research on STAT3 inhibitors, we also discuss how targeting STAT3 would affect the two arms of STAT3-dependent regulation of NK cell-mediated anti-tumor immunity. Understanding the complexity of this interplay in the tumor microenvironment is crucial for future implementation of NK cell-based immunotherapies.

STAT3-EMT axis in tumors: modulation of cancer metastasis, stemness and therapy response

Epithelial-to-mesenchymal transition (EMT) mechanism is responsible for metastasis of tumor cells and their spread to various organs and tissues of body, providing undesirable prognosis. In addition to migration, EMT increases stemness and mediates therapy resistance. Hence, pathways involved in EMT regulation should be highlighted. STAT3 is an oncogenic pathway that can elevate growth rate and migratory ability of cancer cells and induce drug resistance. The inhibition of STAT3 signaling impairs cancer progression and promotes chemotherapy-mediated cell death. Present review focuses on STAT3 and EMT interaction in modulating cancer migration. First of all, STAT3 is an upstream mediator of EMT and is able to induce EMT-mediated metastasis in brain tumors, thoracic cancers and gastrointestinal cancers. Therefore, STAT3 inhibition significantly suppresses cancer metastasis and improves prognosis of patients. EMT regulators such as ZEB1/2 proteins, TGF-β, Twist, Snail and Slug are affected by STAT3 signaling to stimulate cancer migration and invasion. Different molecular pathways such as miRNAs, lncRNAs and circRNAs modulate STAT3/EMT axis. Furthermore, we discuss how STAT3 and EMT interaction affects therapy response of cancer cells. Finally, we demonstrate targeting STAT3/EMT axis by anti-tumor agents and clinical application of this axis for improving patient prognosis.

STAT3β disrupted mitochondrial electron transport chain enhances chemosensitivity by inducing pyroptosis in esophageal squamous cell carcinoma

The clinical efficacy of cisplatin in the treatment of esophageal squamous cell carcinoma (ESCC) is undesirable. Signal transducer and activator of transcription 3β (STAT3β), a splice variant of STAT3, restrains STAT3α activity and enhances chemosensitivity in ESCC. However, the underlying molecular mechanisms remain poorly understood. Here, we found that high expression of STAT3β contributes to cisplatin sensitivity and enhances Gasdermin E (GSDME) dependent pyroptosis in ESCC cells after exposure to cisplatin. Mechanistically, STAT3β was located into the mitochondria and its high expression disrupts the activity of the electron transport chain, resulting in an increase of ROS in cisplatin treatment cells. While high levels of ROS caused activation of caspase-3 and GSDME, and induced cell pyroptosis. STAT3β blocked the phosphorylation of STAT3α S727 in mitochondria by interacting with ERK1/2 following cisplatin treatment, disrupting electron transport chain and inducing activation of GSDME. Clinically, high expression of both STAT3β and GSDME was strongly associated with better overall survival and disease-free survival of ESCC patients. Overall, our study reveals that STAT3β sensitizes ESCC cells to cisplatin by disrupting mitochondrial electron transport chain and enhancing pyroptosis, which demonstrates the prognostic significance of STAT3β in ESCC therapy.

Nelfinavir restricts A549 cell growth by inhibiting STAT3 signaling

Objective

To investigate the anticancer effect of nelfinavir (NFV) on human A549 cells.

Methods

The inhibitory effects of NFV on the proliferation of human A549 cells were assessed using a MTT assay. Apoptotic cells were observed by fluorescence microscopy following Hoechst 33342 staining. Apoptosis of A549 cells was assessed using Annexin-V/propidium iodide staining and flow cytometry. Expression levels of signal transducer and activator of transcription 3 (STAT3) and p-STAT3 were measured by western blotting. STAT3 RNA silencing was used to investigate the pro-apoptotic mechanism of NFV in A549 cells.

Results

NFV dose-dependently suppressed proliferation of human A549 cells and induced significant apoptosis. Western blotting showed that the antitumor function of NFV might be mediated by STAT3 inhibition. A549 cell apoptosis in response to 20 µM NFV was significantly increased following STAT3 silencing. NFV significantly impeded the expression of the anti-apoptotic proteins Bcl-xL and Bcl-2, by increased the expression of the pro-apoptotic protein Cle-PARP.

Conclusions

Our findings highlight STAT3 as a promising therapeutic target. NFV is a novel anti-cancer drug for the treatment of non-small-cell lung cancer.

STAT3 phosphorylation in central leptin resistance

Mechanism exploitation of energy homeostasis is urgently required because of the worldwide prevailing of obesity-related metabolic disorders in human being. Although it is well known that leptin plays a central role in regulating energy balance by suppressing food intake and promoting energy expenditure, the existence of leptin resistance in majority of obese individuals hampers the utilization of leptin therapy against these disorders. However, the mechanism of leptin resistance is largely unknown in spite of the globally enormous endeavors. Current theories to interpret leptin resistance include the impairment of leptin transport, attenuation of leptin signaling, chronic inflammation, ER tress, deficiency of autophagy, as well as leptin itself. Leptin-activated leptin receptor (LepRb) signals in hypothalamus via several pathways, in which JAK2-STAT3 pathway, the most extensively investigated one, is considered to mediate the major action of leptin in energy regulation. Upon leptin stimulation the phosphorylation of STAT3 is one of the key events in JAK2-STAT3 pathway, followed by the dimerization and nuclear translocation of this molecule. Phosphorylated STAT3 (p-STAT3), as a transcription factor, binds to and regulates its target gene such as POMC gene, playing the physiological function of leptin. Regarding POMC gene in hypothalamus however little is known about the detail of its interaction with STAT3. Moreover the status of p-STAT3 and its significance in hypothalamus of DIO mice needs to be well elucidated. This review comprehends literatures on leptin and leptin resistance and especially discusses what STAT3 phosphorylation would contribute to central leptin resistance.

STAT3β Enhances Sensitivity to Concurrent Chemoradiotherapy by Inducing Cellular Necroptosis in Esophageal Squamous Cell Carcinoma

Concurrent chemoradiotherapy (CCRT), especially platinum plus radiotherapy, is considered to be one of the most promising treatment modalities for patients with advanced esophageal cancer. STAT3β regulates specific target genes and inhibits the process of tumorigenesis and development. It is also a good prognostic marker and a potential marker for response to adjuvant chemoradiotherapy (ACRT). We aimed to investigate the relationship between STAT3β and CCRT. We examined the expression of STAT3α and STAT3β in pretreatment tumor biopsies of 105 ESCC patients who received CCRT by immunohistochemistry. The data showed that ESCC patients who demonstrate both high STAT3α expression and high STAT3β expression in the cytoplasm have a significantly better survival rate, and STAT3β expression is an independent protective factor (HR = 0.424, p = 0.003). Meanwhile, ESCC patients with high STAT3β expression demonstrated a complete response to CCRT in 65 patients who received platinum plus radiation therapy (p = 0.014). In ESCC cells, high STAT3β expression significantly inhibits the ability of colony formation and cell proliferation, suggesting that STAT3β enhances sensitivity to CCRT (platinum plus radiation therapy). Mechanistically, through RNA-seq analysis, we found that the TNF signaling pathway and necrotic cell death pathway were significantly upregulated in highly expressed STAT3β cells after CCRT treatment. Overall, our study highlights that STAT3β could potentially be used to predict the response to platinum plus radiation therapy, which may provide an important insight into the treatment of ESCC.

STAT3 isoforms differentially affect ACE2 expression: A potential target for COVID-19 therapy

The SARS‐coronavirus 2 is the aetiologic agent COVID‐19. ACE2 has been identified as a cell entry receptor for the virus. Therefore, trying to understand how the gene is controlled has become a major goal. We silenced the expression of STAT3α and STAT3β, and found that while silencing STAT3α causes an increase in ACE2 expression, silencing STAT3β causes the opposite effect. Studying the role of STAT3 in ACE2 expression will shed light on the molecular events that contribute to the progression of the disease and that the different roles of STAT3α and STAT3β in that context must be taken in consideration. Our results place STAT3 in line with additional potential therapeutic targets for treating COVID‐19 patients.

STAT3, the Challenge for Chemotherapeutic and Radiotherapeutic Efficacy

Chemoradiotherapy is one of the most effective and extensively used strategies for cancer treatment. Signal transducer and activator of transcription 3 (STAT3) regulates vital biological processes, such as cell proliferation and cell growth. It is constitutively activated in various cancers and limits the application of chemoradiotherapy. Accumulating evidence suggests that STAT3 regulates resistance to chemotherapy and radiotherapy and thereby impairs therapeutic efficacy by mediating its feedback loop and several target genes. The alternative splicing product STAT3β is often identified as a dominant-negative regulator, but it enhances sensitivity to chemotherapy and offers a new and challenging approach to reverse therapeutic resistance. We focus here on exploring the role of STAT3 in resistance to receptor tyrosine kinase (RTK) inhibitors and radiotherapy, outlining the potential of targeting STAT3 to overcome chemo(radio)resistance for improving clinical outcomes, and evaluating the importance of STAT3β as a potential therapeutic approach to overcomes chemo(radio)resistance. In this review, we discuss some new insights into the effect of STAT3 and its subtype STAT3β on chemoradiotherapy sensitivity, and we explore how these insights influence clinical treatment and drug development for cancer.

Repurposing of drugs as STAT3 inhibitors for cancer therapy

Drug repurposing is a valuable approach in delivering new cancer therapeutics rapidly into the clinic. Existing safety and patient tolerability data for drugs already in clinical use represent an untapped resource in terms of identifying therapeutic agents for off-label protein targets. The multicellular effects of STAT3 mediated by a range of various upstream signaling pathways make it an attractive therapeutic target with utility in a range of diseases including cancer, and has led to the development of a variety of STAT3 inhibitors. Moreover, heightened STAT3 transcriptional activation in tumor cells and within the cells of the tumor microenvironment contribute to disease progression. Consequently, there are many STAT3 inhibitors in preclinical development or under evaluation in clinical trials for their therapeutic efficacy predominantly in inflammatory diseases and cancer. Despite these advances, many challenges remain in ultimately providing STAT3 inhibitors to patients as cancer treatments, highlighting the need not only for a better understanding of the mechanisms associated with STAT3 activation, but also how various pharmaceutical agents suppress STAT3 activity in various cancers. In this review we discuss the importance of STAT3-dependent functions in cancer, review the status of compounds designed as direct-acting STAT3 inhibitors, and describe some of the strategies for repurposing of drugs as STAT3 inhibitors for cancer therapy.

Marek's Disease Virus Regulates the Ubiquitylome of Chicken CD4+ T Cells to Promote Tumorigenesis

Ubiquitination and deubiquitination of cellular proteins are reciprocal reactions catalyzed by ubiquitination-related enzymes and deubiquitinase (DUB) which regulate almost all cellular processes. Marek's disease virus (MDV) encodes a viral DUB that plays an important role in the MDV pathogenicity. Chicken CD4+ T-cell lymphoma induced by MDV is a key contributor to multiple visceral tumors and immunosuppression of chickens with Marek's disease (MD). However, alterations in the ubiquitylome of MDV-induced T lymphoma cells are still unclear. In this study, a specific antibody against K-ε-GG was used to isolate ubiquitinated peptides from CD4+ T cells and MD T lymphoma cells. Mass spectrometry was used to compare and analyze alterations in the ubiquitylome. Our results showed that the ubiquitination of 717 and 778 proteins was significantly up- and downregulated, respectively, in T lymphoma cells. MDV up- and downregulated ubiquitination of a similar percentage of proteins. The ubiquitination of transferases, especially serine/threonine kinases, was the main regulatory target of MDV. Compared with CD4+ T cells of the control group, MDV mainly altered the ubiquitylome associated with the signal transduction, immune system, cancer, and infectious disease pathways in T lymphoma cells. In these pathways, the ubiquitination of CDK1, IL-18, PRKCB, ETV6, and EST1 proteins was significantly up- or downregulated as shown by immunoblotting. The current study revealed that the MDV infection could exert a significant influence on the ubiquitylome of CD4+ T cells.