JAB1 regulates unphosphorylated STAT3 DNA-binding activity through protein–protein interaction in human colon cancer cells

Integrative analysis of cancer multimodality data identifying COPS5 as a novel biomarker of diffuse large B-cell lymphoma

Preventing, diagnosing, and treating diseases requires accurate clinical biomarkers, which remains challenging. Recently, advanced computational approaches have accelerated the discovery of promising biomarkers from high-dimensional multimodal data. Although machine-learning methods have greatly contributed to the research fields, handling data sparseness, which is not unusual in research settings, is still an issue as it leads to limited interpretability and performance in the presence of missing information. Here, we propose a novel pipeline integrating joint non-negative matrix factorization (JNMF), identifying key features within sparse high-dimensional heterogeneous data, and a biological pathway analysis, interpreting the functionality of features by detecting activated signaling pathways. By applying our pipeline to large-scale public cancer datasets, we identified sets of genomic features relevant to specific cancer types as common pattern modules (CPMs) of JNMF. We further detected COPS5 as a potential upstream regulator of pathways associated with diffuse large B-cell lymphoma (DLBCL). COPS5 exhibited co-overexpression with MYC, TP53, and BCL2, known DLBCL marker genes, and its high expression was correlated with a lower survival probability of DLBCL patients. Using the CRISPR-Cas9 system, we confirmed the tumor growth effect of COPS5, which suggests it as a novel prognostic biomarker for DLBCL. Our results highlight that integrating multiple high-dimensional data and effectively decomposing them to interpretable dimensions unravels hidden biological importance, which enhances the discovery of clinical biomarkers.

NRN1 interacts with Notch to increase oncogenic STAT3 signaling in melanoma

BACKGROUND

Melanoma is a highly heterogeneous cancer, in which frequent changes in activation of signaling pathways lead to a high adaptability to ever changing tumor microenvironments. The elucidation of cancer specific signaling pathways is of great importance, as demonstrated by the inhibitor of the common BrafV600E mutation PLX4032 in melanoma treatment. We therefore investigated signaling pathways that were influenced by neurotrophin NRN1, which has been shown to be upregulated in melanoma.

METHODS

Using a cell culture model system with an NRN1 overexpression, we investigated the influence of NRN1 on melanoma cells' functionality and signaling. We employed real time cell analysis and spheroid formation assays, while for investigation of molecular mechanisms we used a kinase phosphorylation kit as well as promotor activity analysis followed by mRNA and protein analysis.

RESULTS

We revealed that NRN1 interacts directly with the cleaved intracellular domain (NICD) of Notch1 and Notch3, causing a potential retention of NICD in the cytoplasm and thereby reducing the expression of its direct downstream target Hes1. This leads to decreased sequestration of JAK and STAT3 in a Hes1-driven phosphorylation complex. Consequently, our data shows less phosphorylation of STAT3 while presenting an accumulation of total protein levels of STAT3 in association with NRN1 overexpression. The potential of the STAT3 signaling pathway to act in both a tumor suppressive and oncogenic manner led us to investigate specific downstream targets - namely Vegf A, Mdr1, cMet - which were found to be upregulated under oncogenic levels of NRN1.

CONCLUSIONS

In summary, we were able to show that NRN1 links oncogenic signaling events between Notch and STAT3 in melanoma. We also suggest that in future research more attention should be payed to cellular regulation of signaling molecules outside of the classically known phosphorylation events.

Endogenous sulfur dioxide deficiency as a driver of cardiomyocyte senescence through abolishing sulphenylation of STAT3 at cysteine 259

OBJECTIVE

Cardiomyocyte senescence is an important contributor to cardiovascular diseases and can be induced by stressors including DNA damage, oxidative stress, mitochondrial dysfunction, epigenetic regulation, etc. However, the underlying mechanisms for the development of cardiomyocyte senescence remain largely unknown. Sulfur dioxide (SO2) is produced endogenously by aspartate aminotransferase 2 (AAT2) catalysis and plays an important regulatory role in the development of cardiovascular diseases. The present study aimed to explore the effect of endogenous SO2 on cardiomyocyte senescence and the underlying molecular mechanisms.

APPROACH AND RESULTS

We interestingly found a substantial reduction in the expression of AAT2 in the heart of aged mice in comparison to young mice. AAT2-knockdowned cardiomyocytes exhibited reduced SO2 content, elevated expression levels of Tp53, p21Cip/Waf, and p16INk4a, enhanced SA-β-Gal activity, and elevated level of γ-H2AX foci. Notably, supplementation with a SO2 donor ameliorated the spontaneous senescence phenotype and DNA damage caused by AAT2 deficiency in cardiomyocytes. Mechanistically, AAT2 deficiency suppressed the sulphenylation of signal transducer and activator of transcription 3 (STAT3) facilitated its nuclear translocation and DNA-binding capacity. Conversely, a mutation in the cysteine (Cys) 259 residue of STAT3 blocked SO2-induced STAT3 sulphenylation and subsequently prevented the inhibitory effect of SO2 on STAT3-DNA-binding capacity, DNA damage, and cardiomyocyte senescence. Additionally, cardiomyocyte (cm)-specific AAT2 knockout (AAT2cmKO) mice exhibited a deterioration in cardiac function, cardiomegaly, and cardiac aging, whereas supplementation with SO2 donors mitigated the cardiac aging and remodeling phenotypes in AAT2cmKO mice.

CONCLUSION

Downregulation of the endogenous SO2/AAT2 pathway is a crucial pathogenic mechanism underlying cardiomyocyte senescence. Endogenous SO2 modifies STAT3 by sulphenylating Cys259, leading to the inhibition of DNA damage and the protection against cardiomyocyte senescence.

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.

Emerging Role of Plant-Based Dietary Components in Post-Translational Modifications Associated with Colorectal Cancer

Colorectal cancer (CRC) is one of the most common cancers worldwide. Its main modifiable risk factors are diet, alcohol consumption, and smoking. Thus, the right approach through lifestyle changes may lead to its prevention. In fact, some natural dietary components have exhibited chemopreventive activity through modulation of cellular processes involved in CRC development. Although cancer is a multi-factorial process, the study of post-translational modifications (PTMs) of proteins associated with CRC has recently gained interest, as inappropriate modification is closely related to the activation of cell signalling pathways involved in carcinogenesis. Therefore, this review aimed to collect the main PTMs associated with CRC, analyse the relationship between different proteins that are susceptible to inappropriate PTMs, and review the available scientific literature on the role of plant-based dietary compounds in modulating CRC-associated PTMs. In summary, this review suggested that some plant-based dietary components such as phenols, flavonoids, lignans, terpenoids, and alkaloids may be able to correct the inappropriate PTMs associated with CRC and promote apoptosis in tumour cells.

Prognostic value of CSN5 in patients with digestive system cancers: a systematic review and meta-analysis

Background

Despite the understanding of the COP9 signalosome subunit 5 (CSN5) in tumor genesis, there is no conclusive evidence on its value to predict the survival and prognosis of digestive system tumor patients. Hence this study aimed to evaluate the impact of CSN5 levels on the survival and clinicopathological parameters of digestive system neoplasm patients.

Methods

First, a comprehensive search was conducted in four databases. We utilized the Hazard Ratio (HR) with a 95% confidence interval (CI) to evaluate the prognostic value of CSN5 for the overall survival (OS) and recurrence-free survival (RFS) of patients. Then, we estimated the connection between CSN5 and the clinicopathological parameters based on the Odds Ratio (OR) with the corresponding 95% CI.

Results

This meta-analysis included 22 studies and 2193 patients diagnosed with digestive system tumors. High expression of CSN5 was correlated to poorer OS (HR = 2.28, 95% CI: 1.71–3.03; p < 0.00001). Additionally, high CSN5 levels were correlated with worse invasion depth (OR = 0.49, 95% CI: 0.25–0.96, p = 0.04), positive lymphatic metastasis (OR = 0.28, 95% CI: 0.16–0.47, p = 0.00001), positive distant metastasis (OR = 0.32, 95% CI: 0.13–0.76, p = 0.01) and poorer differentiation degree (OR = 0.34, 95% CI: 0.19–0.60, p = 0.0003). However, we did not detect a correlation between CSN5 expression and age, gender, tumor stage, tumor size or vascular invasion. Furthermore, no significant publication bias was detected.

Conclusion

This meta-analysis demonstrated that the overexpression of CSN5 level might foresee poorer OS in digestive system cancer patients. Additionally, CSN5 levels might be related to the prognosis of digestive system tumors.

STAT proteins: a kaleidoscope of canonical and non-canonical functions in immunity and cancer

STAT proteins represent an important family of evolutionarily conserved transcription factors that play key roles in diverse biological processes, notably including blood and immune cell development and function. Classically, STAT proteins have been viewed as inducible activators of transcription that mediate cellular responses to extracellular signals, particularly cytokines. In this 'canonical' paradigm, latent STAT proteins become tyrosine phosphorylated following receptor activation, typically via downstream JAK proteins, facilitating their dimerization and translocation into the nucleus where they bind to specific sequences in the regulatory region of target genes to activate transcription. However, growing evidence has challenged this paradigm and identified alternate 'non-canonical' functions, such as transcriptional repression and roles outside the nucleus, with both phosphorylated and unphosphorylated STATs involved. This review provides a revised framework for understanding the diverse kaleidoscope of STAT protein functional modalities. It further discusses the implications of this framework for our understanding of STAT proteins in normal blood and immune cell biology and diseases such as cancer, and also provides an evolutionary context to place the origins of these alternative functional modalities.

Recent Update on Development of Small-Molecule STAT3 Inhibitors for Cancer Therapy: From Phosphorylation Inhibition to Protein Degradation

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that regulates various biological processes, including proliferation, metastasis, angiogenesis, immune response, and chemoresistance. In normal cells, STAT3 is tightly regulated to maintain a transiently active state, while persistent STAT3 activation occurs frequently in cancers, associating with a poor prognosis and tumor progression. Targeting the STAT3 protein is a potentially promising therapeutic strategy for tumors. Although none of the STAT3 inhibitors has been marketed yet, a few of them have succeeded in entering clinical trials. This Review aims to systematically summarize the progress of the last 5 years in the discovery of directive STAT3 small-molecule inhibitors and degraders, focusing primarily on their structural features, design strategies, and bioactivities. We hope this Review will shed light on future drug design and inhibitor optimization to accelerate the discovery process of STAT3 inhibitors or degraders.

Nuclear β-catenin expression is positively regulated by JAB1 in human colorectal cancer cells

Wnt/β-catenin signaling is important for development and progression of colorectal cancer (CRC). The degradation complex for β-catenin is functionally impaired in CRC cells, thereby resulting in the accumulation of β-catenin and its translocation into the nucleus. Nuclear β-catenin interacts with and co-activates T cell factor4 (TCF4), resulting in β-catenin/TCF4-dependent transcription. Therefore, nuclear β-catenin has been categorized as the main driving force in the tumorigenesis of CRC. Recent studies reveal that Jun activation domain-binding protein 1 (JAB1) enhances the degradation of seven in absentia homolog-1 (SIAH-1), a putative E3 ubiquitin ligase of β-catenin, and positively regulates the expression of total β-catenin in human CRC cells. An another recent study also shows that nuclear β-catenin is ubiquitinated and degraded by an E3 ubiquitin ligase, tripartite motif-containing protein 33 (TRIM33). However, the regulatory mechanism for the expression of nuclear β-catenin remains to be fully understood. In this study, we have demonstrated that JAB1 positively regulates the expression of nuclear β-catenin, c-MYC as a β-catenin/TCF4 target, and cell cycle regulators, such as Ki-67 and topoisomerase IIα, in human CRC cells. Taken together, these results suggest that JAB1 is considered as a promising target for novel CRC therapy.

Ailanthone: A novel potential drug for treating human cancer

Cancer is the second leading cause of death after cardiovascular disease. In 2015, >8.7 million people died worldwide due to cancer, and by 2030 this figure is expected to increase to ~13.1 million. Tumor chemotherapy drugs have specific toxicity and side effects, and patients can also develop secondary drug resistance. To prevent and treat cancer, scientists have developed novel drugs with improved antitumor effects and decreased toxicity. Ailanthone (AIL) is a quassinoid extract from the traditional Chinese medicine plant Ailanthus altissima, which is known to have anti-inflammatory and antimalarial effects. An increasing number of studies have focused on AIL due to its antitumor activity. AIL can inhibit cell proliferation and induce apoptosis by up- or downregulating cancer-associated molecules, which ultimately leads to cancer cell death. Antitumor effects of AIL have been observed in melanoma, acute myeloid leukemia, bladder, lung, breast, gastric and prostate cancer and vestibular neurilemmoma. To the best of our knowledge, the present study is the first review to describe the antitumor mechanisms of AIL.

Overexpression of JAB1 promotes malignant behavior and predicts poor prognosis in esophageal squamous cell carcinoma

BACKGROUND

This study investigated the expression and biological function of JAB1 in esophageal squamous cell carcinoma (ESCC).

METHODS

The expression of JAB1 in ESCC tissues and cells was measured using reverse transcriptase-polymerase chain reaction (RT-PCR), immunohistochemistry (IHC), and western blot analysis. Kaplan-Meier survival analysis was performed to explore the effect of JAB1 expression on the prognosis of ESCC patients. Furthermore, experiments were conducted in vivo and in vitro to determine the effect of JAB1 expression on the malignant behavior of ESCC cells.

RESULTS

Compared with adjacent tissues, JAB1 was highly overexpressed in cancer tissues (P = 0.01). Univariate and multivariate analyses of clinical data indicated that patients with JAB1 overexpression had a worse prognosis (P = 0.001 and P = 0.049, respectively). Cell function experiments and tumorigenesis experiments in nude mice showed that the upregulation of JAB1 might promote malignant behavior, and vice versa.

CONCLUSIONS

Overexpression of JAB1 promoted the proliferation, migration, and invasion of ESCC cells, and was significantly associated with poor prognosis of ESCC patients. Therefore, JAB1 could be considered as a promising prognostic factor and a possible target for the specific therapy of ESCC.

KEY POINTS

In this study, we found that JAB1 was highly overexpressed in cancer tissues, which could influence the malignant behavior of ESCC cells, and was significantly associated with poor prognosis of ESCC patients.

The pivotal oncogenic role of Jab1/CSN5 and its therapeutic implications in human cancer

Jab1/CSN5 is a conserved multifunctional protein involved in ubiquitin-mediated protein degradation. Deregulation of Jab1/CSN5 can exert dramatic effects on diverse cellular functions, including DNA repair, cell cycle control, apoptosis, angiogenesis, and signal transduction, all of which are critical for tumor development. Although increasing evidence has demonstrated that Jab1/CSN5 was overexpressed in a variety of human cancers and usually correlated with poor prognosis, little was known about the underlying regulatory principles that coordinated its function. In this review, we highlight recent advances of the oncogenic role of Jab1/CSN5 and its potential as a therapeutic target for anticancer intervention.

Nucleus, Mitochondrion, or Reticulum? STAT3 à La Carte

The transcription factor signal transducer and activator of transcription (STAT)3 mediates the functions of cytokines, growth factors, and oncogenes under both physiological and pathological conditions. Uncontrolled/constitutive STAT3 activity is often detected in tumors of different types, where its role is mostly that of an oncogene, contributing in multiple ways to tumor transformation, growth, and progression. For this reason, many laboratories and pharmaceutical companies are making efforts to develop specific inhibitors. However, STAT3 has also been shown to act as a tumor suppressor in a number of cases, suggesting that its activity is strongly context-specific. Here, we discuss the bases that can explain the multiple roles of this factor in both physiological and pathological contexts. In particular, we focus on the following four features: (i) the distinct properties of the STAT3α and β isoforms; (ii) the multiple post-translational modifications (phosphorylation on tyrosine or serine, acetylation and methylation on different residues, and oxidation and glutathionylation) that can affect its activities downstream of multiple different signals; (iii) the non-canonical functions in the mitochondria, contributing to the maintenance of energy homeostasis under stress conditions; and (iv) the recently discovered functions in the endoplasmic reticulum, where STAT3 contributes to the regulation of calcium homeostasis, energy production, and apoptosis.

STAT3 Interactors as Potential Therapeutic Targets for Cancer Treatment

Signal transducers and activators of transcription (STATs) mediate essential signaling pathways in different biological processes, including immune responses, hematopoiesis, and neurogenesis. Among the STAT members, STAT3 plays crucial roles in cell proliferation, survival, and differentiation. While STAT3 activation is transient in physiological conditions, STAT3 becomes persistently activated in a high percentage of solid and hematopoietic malignancies (e.g., melanoma, multiple myeloma, breast, prostate, ovarian, and colon cancers), thus contributing to malignant transformation and progression. This makes STAT3 an attractive therapeutic target for cancers. Initial strategies aimed at inhibiting STAT3 functions have focused on blocking the action of its activating kinases or sequestering its DNA binding ability. More recently, the diffusion of proteomic-based techniques, which have allowed for the identification and characterization of novel STAT3-interacting proteins able to modulate STAT3 activity via its subcellular localization, interact with upstream kinases, and recruit transcriptional machinery, has raised the possibility to target such cofactors to specifically restrain STAT3 oncogenic functions. In this article, we summarize the available data about the function of STAT3 interactors in malignant cells and discuss their role as potential therapeutic targets for cancer treatment.

Jab1/COPS5 as a Novel Biomarker for Diagnosis, Prognosis, Therapy Prediction and Therapeutic Tools for Human Cancer

C-Jun activation domain-binding protein-1 (Jab1) involves in controlling cellular proliferation, cell cycle, apoptosis, affecting a series of pathways, as well as regulating genomic instability and DNA damage response (DDR). Jab1/COPS5 dysregulation contributes to oncogenesis by deactivating several tumor suppressors and activating oncogenes. Jab1 overexpression was found in many tumor types, illuminating its important role in cancer initiation, progression, and prognosis. Jab1/COPS5 has spurred a strong research interest in developing inhibitors of oncogenes/oncoproteins for cancer therapy. In this paper, we present evidences demonstrating the importance of Jab1/COPS5 overexpression in several cancer types and recent advances in dissecting the Jab1/COPS5 upstream and downstream signaling pathways. By conducting ingenuity pathway analysis (IPA) based on the Ingenuity Knowledge Base, we investigated signaling network that interacts with Jab1/COPS5. The data confirmed the important role of Jab1/COPS5 in tumorigenesis, demonstrating the potential of Jab1/COPS5 to be used as a biomarker for cancer patients, and further support that Jab1/COPS5 may serve as a potential therapeutic target in different cancers.

JAB1-STAT3 activation loop is associated with recurrence following 5-fluorouracil-based adjuvant chemotherapy in human colorectal cancer

Jun activation domain-binding protein 1 (JAB1) has been shown to have multiple roles in tumorigenesis, including the degradation of tumor suppressor proteins such as p53, Smad7, Runx3 and the cyclin-dependent kinase inhibitor p27^Kip1, and the activation of oncogenic transcription factors, such as c-Jun and hypoxia-inducible factor-1α. In addition, our previous study revealed that JAB1 positively regulates signal transducer and activator of transcription 3 (STAT3) DNA-binding activity in human colon cancer cells. In turn, the oncogenic transcription factor STAT3 positively regulates JAB1 expression, indicative of a positive feedback loop. Furthermore, high JAB1 expression is associated with a poor prognosis in numerous malignant carcinomas. However, the association between JAB1 expression and prognosis in colorectal cancer remains unclear. The aim of the present study was to elucidate the association between JAB1 and STAT3 expression and recurrence in colorectal cancer. In the present study, it was found that high JAB1 expression in primary colorectal cancer tissues is an independent predictor of recurrence following 5-fluorouracil (5-FU)-based adjuvant chemotherapy in colorectal cancer patients, and that high expression of both JAB1 and STAT3 in primary colorectal cancer tissues is associated with a lower recurrence-free survival rate following 5-FU-based adjuvant chemotherapy compared to high expression of only JAB1 or STAT3. Overall, these results suggest that JAB1 is a novel predictive marker of recurrence following 5-FU-based adjuvant chemotherapy in colorectal cancer patients, and that the JAB1-STAT3 activation loop may be a potential therapeutic target in recurrent colorectal cancer following 5-FU-based adjuvant chemotherapy.

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.

Hepatitis B virus promotes cancer cell migration by downregulating miR-340-5p expression to induce STAT3 overexpression

Background

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related deaths worldwide, and infection with hepatitis B virus (HBV) is a leading cause of HCC. Previous studies have demonstrated that expression of the tumor inhibitor miR-340 is significantly downregulated in HCC tissues compared with normal liver tissues. However, the precise biological role of miR-340-5p in HBV–HCC and its molecular mechanism of action remain unknown.

Results

Expression of miR-340-5p was downregulated in HBV-associated HCC liver tissue and HBV-infected cells, facilitating migration of liver cancer cells. Signal transducer and activator of transcription (STAT)3 was found to be a direct functional target of miR-340-5p. The regulation of STAT3 expression by miR-340-5p was assessed using qRT-PCR and western blotting, and the effects of exogenous miR-340-5p and STAT3 on the migration of HBV-infected cells were evaluated in vitro using Transwell^® and wound-healing assays. The expression of E-cadherin and vimentin, associated with epithelial–mesenchymal transition, was also assessed using Western blotting after transfection of miR-340-5p mimics and/or STAT3 expression vectors. Overexpression of STAT3 resulted in rescue of HBV effects, decreased E-cadherin expression, increased vimentin expression, and ultimately, enhanced cell migration. Re-introduction of the STAT3 CDS led to marked reversal of the inhibition of cell migration in HBV-infected cells mediated by miR-340-5p.

Conclusions

Hepatitis B virus promotes the migration of liver cancer cells by downregulating miR-340-5p expression to induce STAT3 overexpression. Our results show that STAT3 plays a key role in regulating cell migration in HBV–HCC involving miR-340-5p.

Non-canonical Stat3 signaling in cancer

Stat3 is a member of the signal transducers and activators of transcription family and is a known regulator of essential biologic processes including angiogenesis, apoptosis, cell cycle progression, and cell migration. Canonical Stat3-mediated signaling involves tyrosine phosphorylation on specific residues that leads to homodimerization and translocation to the nucleus. For many years it was presumed that most, if not all, of the functions of Stat3, both normal and aberrant, were due to the canonical cytokine and growth factor signaling mechanisms. Recent studies suggest that Stat3 functions through alternate non-canonical pathways to bring about some of these biological functions both in normal cells as well as during cancer development and progression. A number of studies have now shown that Stat3 has a function in mitochondria and that unphosphorylated Stat3 (uStat3) can also function as a transcription factor broadening the potential mechanisms involved in Stat3 action. In this review article, we discuss these two main non-canonical functions of Stat3 and their potential roles in oncogenesis. Given the many facets of Stat3 signaling, additional comprehensive investigations are required to fully understand the role of non-canonical Stat3 signaling in cancer and whether these pathways can be targeted for cancer prevention and treatment. © 2015 Wiley Periodicals, Inc.

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.

The STAT3 inhibitor WP1066 synergizes with vorinostat to induce apoptosis of mantle cell lymphoma cells

Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin lymphoma (NHL) characterized by the translocation t (11; 14) (q13; q32). Drug resistance remains a formidable obstacle to treatment and the median survival for MCL patients is between 3 and 5 years. Thus, there is an urgent need to discover novel approaches to MCL therapy. The signal transducer and activation of transcription 3 (STAT3) has been found to be constitutively activated in several subtypes of MCL cell lines and MCL tumors. WP1066, a small-molecule inhibitor of STAT3, exerted antitumor activity in hematological and solid malignancies by inhibiting key survival and growth signaling pathways. In the present study, we evaluated the antiproliferative and proapoptotic activity of WP1066 combined with pan-histone deacetylase (HDAC) inhibitor vorinostat (SAHA) in a panel of MCL cell lines. In addition, potential mechanisms involved were also explored. The outcome showed that combination of WP1066 with SAHA resulted in synergistic growth inhibition and apoptosis induction in MCL cell lines in vitro. Furthermore, combination of WP1066 with SAHA inhibited the constitutive STAT3 activation and modulated mRNA expressions of anti- and pro-apoptotic genes. Our findings suggest that agents targeting the STAT3 pathway such as WP1066 may be useful therapeutic drugs for MCL when combined with SAHA.

The c-MYC-ABCB5 axis plays a pivotal role in 5-fluorouracil resistance in human colon cancer cells

c-MYC overexpression is frequently observed in various cancers including colon cancer and regulates many biological activities such as aberrant cell proliferation, apoptosis, genomic instability, immortalization and drug resistance. However, the mechanism by which c-MYC confers drug resistance remains to be fully elucidated. In this study, we found that the c-MYC expression level in primary colorectal cancer tissues correlated with the recurrence rate following 5-fluorouracil (5-FU)-based adjuvant chemotherapy. Supporting this finding, overexpression of exogenous c-MYC increased the survival rate following 5-FU treatment in human colon cancer cells, and knockdown of endogenous c-MYC decreased it. Furthermore, c-MYC knockdown decreased the expression level of ABCB5, which is involved in 5-FU resistance. Using a chromatin immunoprecipitation assay, we found that c-MYC bound to the ABCB5 promoter region. c-MYC inhibitor (10058-F4) treatment inhibited c-MYC binding to the ABCB5 promoter, leading to a decrease in ABCB5 expression level. ABCB5 knockdown decreased the survival rate following 5-FU treatment as expected, and the ABCB5 expression level was increased in 5-FU-resistant human colon cancer cells. Finally, using a human colon cancer xenograft murine model, we found that the combined 5-FU and 10058-F4 treatment significantly decreased tumorigenicity in nude mice compared with 5-FU or 10058-F4 treatment alone. 10058-F4 treatment decreased the ABCB5 expression level in the presence or absence of 5-FU. In contrast, 5-FU treatment alone increased the ABCB5 expression level. Taken together, these results suggest that c-MYC confers resistance to 5-FU through regulating ABCB5 expression in human colon cancer cells.

Aberrant expression of p-STAT3 in peripheral blood CD4+ and CD8+ T cells related to hepatocellular carcinoma development

Hepatocellular carcinoma (HCC) is one of the most common cancer types worldwide. The signal transducer and activator of transcription 3 (STAT3) protein is a member of the STAT transcription factor family. Oncogenesis, invasion, and metastasis of HCC are associated with activation of STAT3. However, whether aberrant expression of phosphorylated STAT3 (p-STAT3) in peripheral CD4+ and CD8+ T cells relates to HCC pathogenesis remains unclear. In this study, the expression of p-STAT3 in CD4+ and CD8+ T cells, and the levels of interferon-γ (IFN-γ), interleukin-4 (IL-4), IL-6 and IL-10 in the human hepatoma cell line Huh7 co-cultured with peripheral blood mononucleated cells (PBMCs) of healthy volunteers were measured. The correlations between p-STAT3 and IFN-γ/IL-4, IFN-γ, IL-4, IL-6 and IL-10 were then analyzed. Results showed that the p-STAT3 level is higher in CD4+ and CD8+ T cells in the peripheral blood of HCC patients, and in PBMCs co-cultured with Huh7 cells compared to controls. The cytokine (IL-4, IL-6 and IL-10) levels were increased and the IFN-γ level was decreased in the serum of HCC patients and in supernatants of PBMCs co-cultured with Huh7 cells. Correlation analyses demonstrated that the IFN-γ/IL-4 ratio and the IFN-γ level negatively correlate to the p-STAT3 level in CD4+ and CD8+ T cells in samples from patients and in cells cultured in vitro. By contrast, the levels of IL-4, IL-6 and IL-10 positively correlated to the p-STAT3 level. This study indicated that the expression of p-STAT3 is upregulated in peripheral CD4+ and CD8+ T cells of HCC patients, and which may result in abnormal immune surveillance and thereby, contribute to HCC pathogenesis.