Signal transducer and activator of transcription 3 (STAT3) protein suppresses adenoma-to-carcinoma transition in Apcmin/+ mice via regulation of Snail-1 (SNAI) protein stability

An oncogenic enhancer promotes melanoma progression via regulating ETV4 expression

BACKGROUND

Enhancers are important gene regulatory elements that promote the expression of critical genes in development and disease. Aberrant enhancer can modulate cancer risk and activate oncogenes that lead to the occurrence of various cancers. However, the underlying mechanism of most enhancers in cancer remains unclear. Here, we aim to explore the function and mechanism of a crucial enhancer in melanoma.

METHODS

Multi-omics data were applied to identify an enhancer (enh17) involved in melanoma progression. To evaluate the function of enh17, CRISPR/Cas9 technology were applied to knockout enh17 in melanoma cell line A375. RNA-seq, ChIP-seq and Hi-C data analysis integrated with luciferase reporter assay were performed to identify the potential target gene of enh17. Functional experiments were conducted to further validate the function of the target gene ETV4. Multi-omics data integrated with CUT&Tag sequencing were performed to validate the binding profile of the inferred transcription factor STAT3.

RESULTS

An enhancer, named enh17 here, was found to be aberrantly activated and involved in melanoma progression. CRISPR/Cas9-mediated deletion of enh17 inhibited cell proliferation, migration, and tumor growth of melanoma both in vitro and in vivo. Mechanistically, we identified ETV4 as a target gene regulated by enh17, and functional experiments further support ETV4 as a target gene that is involved in cancer-associated phenotypes. In addition, STAT3 acts as a transcription factor binding with enh17 to regulate the transcription of ETV4.

CONCLUSIONS

Our findings revealed that enh17 plays an oncogenic role and promotes tumor progression in melanoma, and its transcriptional regulatory mechanisms were fully elucidated, which may open a promising window for melanoma prevention and treatment.

Exploring Novel Frontiers: Leveraging STAT3 Signaling for Advanced Cancer Therapeutics

Signal Transducer and Activator of Transcription 3 (STAT3) plays a significant role in diverse physiologic processes, including cell proliferation, differentiation, angiogenesis, and survival. STAT3 activation via phosphorylation of tyrosine and serine residues is a complex and tightly regulated process initiated by upstream signaling pathways with ligand binding to receptor and non-receptor-linked kinases. Through downstream deregulation of target genes, aberrations in STAT3 activation are implicated in tumorigenesis, metastasis, and recurrence in multiple cancers. While there have been extensive efforts to develop direct and indirect STAT3 inhibitors using novel drugs as a therapeutic strategy, direct clinical application remains in evolution. In this review, we outline the mechanisms of STAT3 activation, the resulting downstream effects in physiologic and malignant settings, and therapeutic strategies for targeting STAT3. We also summarize the pre-clinical and clinical evidence of novel drug therapies targeting STAT3 and discuss the challenges of establishing their therapeutic efficacy in the current clinical landscape.

Bacterial Lipopolysaccharide Induces PD-L1 Expression and an Invasive Phenotype of Oral Squamous Cell Carcinoma Cells

BACKGROUND

Expression of programmed death ligand-1 (PD-L1) is related to the prognosis of many solid malignancies, including oral squamous cell carcinoma (OSCC), but the mechanism of PD-L1 induction remains obscure. In this study, we examined the expression of PD-L1 and partial epithelial-mesenchymal transition (pEMT) induced by bacterial lipopolysaccharide (LPS) in OSCC.

METHODS

The expression of Toll-like receptor 4 (TLR4) recognizing LPS in OSCC cell lines was analyzed. Moreover, the induction of PD-L1 expression by Porphyromonas gingivalis (P.g) or Escherichia coli (E. coli) LPS and EMT was analyzed by western blotting and RT-PCR. Morphology, proliferation, migration, and invasion capacities were examined upon addition of LPS. PD-L1 within EXOs was examined.

RESULTS

PD-L1 expression and pEMT induced by LPS of P.g or E. coli in TLR4-expressing OSCC cell lines were observed. Addition of LPS did not change migration, proliferation, or cell morphology, but increased invasive ability. Moreover, higher expression of PD-L1 was observed in OSCC EXOs with LPS.

CONCLUSION

Oral bacterial LPS is involved in enhanced invasive potential in OSCC cells, causing PD-L1 expression and induction of pEMT. The enhancement of PD-L1 expression after addition of LPS may be mediated by EXOs.

Vortioxetine hydrobromide inhibits the growth of gastric cancer cells in vivo and in vitro by targeting JAK2 and SRC

Gastric cancer is the fourth leading cause of cancer deaths worldwide. Most patients are diagnosed in the advanced stage. Inadequate therapeutic strategies and the high recurrence rate lead to the poor 5-year survival rate. Therefore, effective chemopreventive drugs for gastric cancer are urgently needed. Repurposing clinical drugs is an effective strategy for discovering cancer chemopreventive drugs. In this study, we find that vortioxetine hydrobromide, an FDA-approved drug, is a dual JAK2/SRC inhibitor, and has inhibitory effects on cell proliferation of gastric cancer. Computational docking analysis, pull-down assay, cellular thermal shift assay (CETSA) and in vitro kinase assays are used to illustrate vortioxetine hydrobromide directly binds to JAK2 and SRC kinases and inhibits their kinase activities. The results of non-reducing SDS-PAGE and Western blotting indicate that vortioxetine hydrobromide suppresses STAT3 dimerization and nuclear translocation activity. Furthermore, vortioxetine hydrobromide inhibits the cell proliferation dependent on JAK2 and SRC and suppresses the growth of gastric cancer PDX model in vivo. These data demonstrate that vortioxetine hydrobromide, as a novel dual JAK2/SRC inhibitor, curbs the growth of gastric cancer in vitro and in vivo by JAK2/SRC-STAT3 signaling pathways. Our results highlight that vortioxetine hydrobromide has the potential application in the chemoprevention of gastric cancer.

Role of STAT3 and NRF2 in Tumors: Potential Targets for Antitumor Therapy

Signal transducer and activator of transcription 3 (STAT3) and nuclear factor erythroid-derived 2-like 2 (NRF2, also known as NFE2L2), are two of the most complicated transcription regulators, which participate in a variety of physiological processes. Numerous studies have shown that they are overactivated in multiple types of tumors. Interestingly, STAT3 and NRF2 can also interact with each other to regulate tumor progression. Hence, these two important transcription factors are considered key targets for developing a new class of antitumor drugs. This review summarizes the pivotal roles of the two transcription regulators and their interactions in the tumor microenvironment to identify potential antitumor drug targets and, ultimately, improve patients' health and survival.

Central Roles of STAT3-Mediated Signals in Onset and Development of Cancers: Tumorigenesis and Immunosurveillance

Since the time of Rudolf Virchow in the 19th century, it has been well-known that cancer-associated inflammation contributes to tumor initiation and progression. However, it remains unclear whether a collapse of the balance between the antitumor immune response via the immunological surveillance system and protumor immunity due to cancer-related inflammation is responsible for cancer malignancy. The majority of inflammatory signals affect tumorigenesis by activating signal transducer and activation of transcription 3 (STAT3) and nuclear factor-κB. Persistent STAT3 activation in malignant cancer cells mediates extremely widespread functions, including cell growth, survival, angiogenesis, and invasion and contributes to an increase in inflammation-associated tumorigenesis. In addition, intracellular STAT3 activation in immune cells causes suppressive effects on antitumor immunity and leads to the differentiation and mobilization of immature myeloid-derived cells and tumor-associated macrophages. In many cancer types, STAT3 does not directly rely on its activation by oncogenic mutations but has important oncogenic and malignant transformation-associated functions in both cancer and stromal cells in the tumor microenvironment (TME). We have reported a series of studies aiming towards understanding the molecular mechanisms underlying the proliferation of various types of tumors involving signal-transducing adaptor protein-2 as an adaptor molecule that modulates STAT3 activity, and we recently found that AT-rich interactive domain-containing protein 5a functions as an mRNA stabilizer that orchestrates an immunosuppressive TME in malignant mesenchymal tumors. In this review, we summarize recent advances in our understanding of the functional role of STAT3 in tumor progression and introduce novel molecular mechanisms of cancer development and malignant transformation involving STAT3 activation that we have identified to date. Finally, we discuss potential therapeutic strategies for cancer that target the signaling pathway to augment STAT3 activity.

Potential Refinement of Recurrence Score by pSTAT3 Status

The likelihood of recurrence in breast cancer patients with hormone receptor-positive (HR-positive) tumors is influenced by clinical, histopathological, and molecular features. Recent studies suggested that activated STAT3 (pSTAT3) might serve as a biomarker of outcome in breast cancer patients. In the present work, we have analyzed the added value of pSTAT3 to OncotypeDx Recurrence Score (RS) in patient prognostication. We have found that patients with low RS (<26) and low pSTAT3 might represent a population at a higher risk for cancer recurrence. Furthermore, we have observed that a positive pSTAT3 score alone can be a favorable marker for patients with HR-positive breast cancer under the age of 50. In an era of personalized medicine, these findings warrant further appraisal of chemotherapy benefit in this population.

Targeting STAT3 Signaling Pathway in Colorectal Cancer

Signal transducer and activator of transcription 3 (STAT3) is a critical transcription factor that has been firmly associated with colorectal cancer (CRC) initiation and development. STAT3 mediates key inflammatory mechanisms in colitis-associated cancer, becomes excessively activated in CRC, and enhances cancer cell proliferation, tumor growth, angiogenesis, invasion, and migration. STAT3 hyperactivation in malignant cells, surrounding immune cells and cancer-associated fibroblasts, mediates inhibition of the innate and adaptive immunity of the tumor microenvironment, and, therefore, tumor evasion from the immune system. These features highlight STAT3 as a promising therapeutic target; however, the mechanisms underlying these features have not been fully elucidated yet and STAT3 inhibitors have not reached the clinic in everyday practice. In the present article, we review the STAT3 signaling network in CRC and highlight the current notion for the design of STAT3-focused treatment approaches. We also discuss recent breakthroughs in combination immunotherapy regimens containing STAT3 inhibitors, therefore providing a new perception for the clinical application of STAT3 in CRC.

The two facets of gp130 signalling in liver tumorigenesis

The liver is a vital organ with multiple functions and a large regenerative capacity. Tumours of the liver are the second most frequently cause of cancer-related death and develop in chronically inflamed livers. IL-6-type cytokines are mediators of inflammation and almost all members signal via the receptor subunit gp130 and the downstream signalling molecule STAT3. We here summarize current knowledge on how gp130 signalling and STAT3 in tumour cells and cells of the tumour micro-environment drives hepatic tumorigenesis. We furthermore discuss very recent findings describing also anti-tumorigenic roles of gp130/STAT3 and important considerations for therapeutic interventions.

GNAQ knockdown promotes bone metastasis through epithelial-mesenchymal transition in lung cancer cells

AIMS

Bone metastasis ultimately occurs due to a complex multistep process, during which the interactions between cancer cells and bone microenvironment play important roles. Prior to colonization of the bone, cancer cells must succeed through a series of steps that will allow them to gain migratory and invasive properties; epithelial-to-mesenchymal transition (EMT) is known to be integral here. The aim of this study was to determine the effects of G protein subunit alpha Q (GNAQ) on the mechanisms underlying bone metastasis through EMT pathway.

METHODS

A total of 80 tissue samples from patients who were surgically treated during January 2012 to December 2014 were used in the present study. Comparative gene analysis revealed that the GNAQ was more frequently altered in metastatic bone lesions than in primary tumour sites in lung cancer patients. We investigated the effects of GNAQ on cell proliferation, migration, EMT, and stem cell transformation using lung cancer cells with GNAQ-knockdown. A xenograft mouse model tested the effect of GNAQ using micro-CT analyses and histological analyses.

RESULTS

GNAQ-knockdown showed down-regulation of tumour growth through mitogen-activated protein kinase (MAPK) signalling in lung cancer cells, but not increased apoptosis. We found that GNAQ-knockdown induced EMT and promoted invasiveness. GNAQ-knockdown cells injected into the bone marrow of murine tibia induced tumour growth and bone-to-lung metastasis, whereas it did not in control mice. Moreover, the knockdown of GNAQ enhanced cancer stem cell-like properties in lung cancer cells, which resulted in the development of resistance to chemotherapy.

CONCLUSION

The present study reveals that the GNAQ-knockdown induced cancer stem cell-like properties. Cite this article: Bone Joint Res 2021;10(5):310-320.

IL-6 promotes MYC-induced B cell lymphomagenesis independent of STAT3

The inflammatory cytokine IL-6 is known to play a causal role in the promotion of cancer, although the underlying mechanisms remain to be completely understood. Interplay between endogenous and environmental cues determines the fate of cancer development. The Eμ-myc transgenic mouse expresses elevated levels of c-Myc in the B cell lineage and develops B cell lymphomas with associated mutations in p53 or other genes linked to apoptosis. We generated Eμ-myc mice that either lacked the IL-6 gene, or lacked the STAT3 gene specifically in B cells to determine the role of the IL-6/JAK/STAT3 pathway in tumor development. Using the Eμ-myc lymphoma mouse model, we demonstrate that IL-6 is a critical tumor promoter during early stages of B cell lymphomagenesis. IL-6 is shown to inhibit the expression of tumor suppressors, notably BIM and PTEN, and this may contribute to advancing MYC-driven B cell tumorigenesis. Several miRNAs known to target BIM and PTEN are upregulated by IL-6 and likely lead to the stable suppression of pro-apoptotic pathways early during the tumorigenic process. STAT3, a classical downstream effector of IL-6, appears dispensable for Eμ-myc driven lymphomagenesis. We conclude that the growth-promoting and anti-apoptotic mechanisms activated by IL-6 are critically involved in Eμ-myc driven tumor initiation and progression, but the B cell intrinsic expression of STAT3 is not required.

Chemerin reverses the malignant phenotype and induces differentiation of human hepatoma SMMC7721 cells

Chemerin exhibits an inhibitory effect on hepatocellular carcinoma; however, the underlying mechanism is unclear. Here, low chemerin expression was confirmed in samples of liver cancer patients and hepatoma cells. Chemerin altered hepatoma cell morphology but had no effect on normal hepatocytes. Chemerin inhibited proliferation of several human hepatoma cell lines. Real-time PCR detection of hepatocellular carcinoma markers showed that mRNA levels of albumin and A-type gamma-glutamyl transferase increased whereas those of alpha-fetoprotein, alkaline phosphatase, B-type gamma-glutamyl transferase, insulin-like growth factor II, and human telomerase reverse transcriptase decreased in chemerin-treated SMMC7721 cells. Western blotting revealed that chemerin up-regulated albumin and vimentin expressions, and downregulated alpha-fetoprotein expression. Phosphorylated STAT3 was significantly up-regulated, whereas phosphorylated ERK and AKT were significantly downregulated by chemerin. Chemerin decreased phosphorylated ERK and AKT expression and the cell proliferation induced by PI3K activator 740 Y-P but could not significantly alter phosphorylated STAT3 expression and the cell growth induced by STAT3 inhibitor NSC74859. In conclusion, chemerin reversed the malignant phenotype and induced SMMC7721 cell differentiation by inhibiting MAPK/ERK and PI3K/AKT signaling; growth inhibition by chemerin is not directly related to the JAK/STAT signaling pathway. Our study provides novel evidence that chemerin could be utilized for liver cancer treatment.

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.

Significance of STAT3 in Immune Infiltration and Drug Response in Cancer

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor and regulates tumorigenesis. However, the functions of STAT3 in immune and drug response in cancer remain elusive. Hence, we aim to reveal the impact of STAT3 in immune infiltration and drug response comprehensively by bioinformatics analysis. The expression of STAT3 and its relationship with tumor stage were explored by Tumor Immune Estimation Resource (TIMER), Human Protein Altas (HPA), and UALCAN databases. The correlations between STAT3 and immune infiltration, gene markers of immune cells were analyzed by TIMER. Moreover, the association between STAT3 and drug response was evaluated by the Cancer Cell Line Encyclopedia (CCLE) and Cancer Therapeutics Response Portal (CTRP). The results suggested that the mRNA transcriptional level of STAT3 was lower in tumors than normal tissues and mostly unrelated to tumor stage. Besides, the protein expression of STAT3 decreased in colorectal and renal cancer compared with normal tissues. Importantly, STAT3 was correlated with immune infiltration and particularly regulated tumor-associated macrophage (TAM), M2 macrophage, T-helper 1 (Th1), follicular helper T (Treg), and exhausted T-cells. Remarkably, STAT3 was closely correlated with the response to specified inhibitors and natural compounds in cancer. Furthermore, the association between STAT3 and drug response was highly cell line type dependent. Significantly, the study provides thorough insight that STAT3 is associated with immunosuppression, as well as drug response in clinical treatment.

STAT3: Versatile Functions in Non-Small Cell Lung Cancer

Signal Transducer and Activator of Transcription 3 (STAT3) activation is frequently found in non-small cell lung cancer (NSCLC) patient samples/cell lines and STAT3 inhibition in NSCLC cell lines markedly impairs their survival. STAT3 also plays a pivotal role in driving tumor-promoting inflammation and evasion of anti-tumor immunity. Consequently, targeting STAT3 either directly or by inhibition of upstream regulators such as Interleukin-6 (IL-6) or Janus kinase 1/2 (JAK1/2) is considered as a promising treatment strategy for the management of NSCLC. In contrast, some studies also report STAT3 being a tumor suppressor in a variety of solid malignancies, including lung cancer. Here, we provide a concise overview of STAT3‘s versatile roles in NSCLC and discuss the yins and yangs of STAT3 targeting therapies.

Unphosphorylated STAT3 in heterochromatin formation and tumor suppression in lung cancer

BACKGROUND

Aberrant JAK/STAT activation has been detected in many types of human cancers. The role of JAK/STAT activation in cancer has been mostly attributed to direct transcriptional regulation of target genes by phosphorylated STAT (pSTAT), while the unphosphorylated STAT (uSTAT) is believed to be dormant and reside in the cytoplasm. However, several studies have shown that uSTATs can be found in the nucleus. In addition, it has been shown that tissue-specific loss of STAT3 or STAT5 in mice promotes cancer growth in certain tissues, and thus these STAT proteins can act as tumor suppressors. However, no unifying mechanism has been shown for the tumor suppressor function of STATs to date. We have previously demonstrated a non-canonical mode of JAK/STAT signaling for Drosophila STAT and human STAT5A, where a fraction of uSTAT is in the nucleus and associated with Heterochromatin Protein 1 (HP1); STAT activation (by phosphorylation) causes its dispersal, leading to HP1 delocalization and heterochromatin loss.

METHODS

We used a combination of imaging, cell biological assays, and mouse xenografts to investigate the role of STAT3 in lung cancer development.

RESULTS

We found that uSTAT3 has a function in promoting heterochromatin formation in lung cancer cells, suppressing cell proliferation in vitro, and suppressing tumor growth in mouse xenografts.

CONCLUSIONS

Thus, uSTAT3 possesses noncanonical function in promoting heterochromatin formation, and the tumor suppressor function of STAT3 is likely attributable to the heterochromatin-promoting activity of uSTAT3 in the non-canonical JAK/STAT pathway.

STAT3 and STAT5 Activation in Solid Cancers

The Signal Transducer and Activator of Transcription (STAT)3 and 5 proteins are activated by many cytokine receptors to regulate specific gene expression and mitochondrial functions. Their role in cancer is largely context-dependent as they can both act as oncogenes and tumor suppressors. We review here the role of STAT3/5 activation in solid cancers and summarize their association with survival in cancer patients. The molecular mechanisms that underpin the oncogenic activity of STAT3/5 signaling include the regulation of genes that control cell cycle and cell death. However, recent advances also highlight the critical role of STAT3/5 target genes mediating inflammation and stemness. In addition, STAT3 mitochondrial functions are required for transformation. On the other hand, several tumor suppressor pathways act on or are activated by STAT3/5 signaling, including tyrosine phosphatases, the sumo ligase Protein Inhibitor of Activated STAT3 (PIAS3), the E3 ubiquitin ligase TATA Element Modulatory Factor/Androgen Receptor-Coactivator of 160 kDa (TMF/ARA160), the miRNAs miR-124 and miR-1181, the Protein of alternative reading frame 19 (p19ARF)/p53 pathway and the Suppressor of Cytokine Signaling 1 and 3 (SOCS1/3) proteins. Cancer mutations and epigenetic alterations may alter the balance between pro-oncogenic and tumor suppressor activities associated with STAT3/5 signaling, explaining their context-dependent association with tumor progression both in human cancers and animal models.

High expression level of peptidylprolyl isomerase A is correlated with poor prognosis of liver hepatocellular carcinoma

Peptidylprolyl isomerase A (PPIA) has been reported to be correlated with cancer. The present study investigated the prognostic values of PPIA expression levels in cancer by comparing different types of cancer using databases. High expression levels of PPIA were observed in 17 out of 17 cancer types compared with normal adjacent tissues. High expression levels of PPIA were associated with decreased overall survival in low grade glioma, acute myeloid leukemia, lung adenocarcinoma, skin cutaneous melanoma and liver hepatocellular carcinoma (LIHC). The prognostic effect of PPIA expression in LIHC was independent of tumor grade. High expression levels of PPIA were of particular prognostic value in stage 3, American Joint Committee on Cancer Tumor 3, hepatitis B virus negative and sorafenib-administered subgroups in LIHC. The expression level of PPIA was significantly associated with levels of basigin and signal transducer and activator of transcription 3, which may be major effectors of PPIA in the progression of the cancer.

Epithelial-Mesenchymal Transition Promotes the Differentiation Potential of Xenopus tropicalis Immature Sertoli Cells

Epithelial-mesenchymal transition (EMT) is a fundamental process in embryonic development by which sessile epithelial cells are converted into migratory mesenchymal cells. Our laboratory has been successful in the establishment of Xenopus tropicalis immature Sertoli cells (XtiSCs) with the restricted differentiation potential. The aim of this study is the determination of factors responsible for EMT activation in XtiSCs and stemness window acquisition where cells possess the broadest differentiation potential. For this purpose, we tested three potent EMT inducers—GSK-3 inhibitor (CHIR99021), FGF2, and/or TGF-β1 ligand. XtiSCs underwent full EMT after 3-day treatment with CHIR99021 and partial EMT with FGF2 but not with TGF-β1. The morphological change of CHIR-treated XtiSCs to the typical spindle-like cell shape was associated with the upregulation of mesenchymal markers and the downregulation of epithelial markers. Moreover, only CHIR-treated XtiSCs were able to differentiate into chondrocytes in vitro and cardiomyocytes in vivo. Interestingly, EMT-shifted cells could migrate towards cancer cells (HeLa) in vitro and to the injury site in vivo. The results provide a better understanding of signaling pathways underlying the generation of testis-derived stem cells.

ZEB1 and IL-6/11-STAT3 signalling cooperate to define invasive potential of pancreatic cancer cells via differential regulation of the expression of S100 proteins

Background

S100 proteins have been implicated in various aspects of cancer, including epithelial-mesenchymal transitions (EMT), invasion and metastasis, and also in inflammatory disorders. Here we examined the impact of individual members of this family on the invasion of pancreatic ductal adenocarcinoma (PDAC) cells, and their regulation by EMT and inflammation.

Methods

Invasion of PDAC cells was analysed in zebrafish embryo xenografts and in transwell invasion assays. Expression and regulation of S100 proteins was studied in vitro by immunoblotting, quantitative PCR and immunofluorescence, and in pancreatic lesions by immunohistochemistry.

Results

Whereas the expression of most S100 proteins is characteristic for epithelial PDAC cell lines, S100A4 and S100A6 are strongly expressed in mesenchymal cells and upregulated by ZEB1. S100A4/A6 and epithelial protein S100A14 respectively promote and represses cell invasion. IL-6/11-STAT3 pathway stimulates expression of most S100 proteins. ZEB1 synergises with IL-6/11-STAT3 to upregulate S100A4/A6, but nullifies the effect of inflammation on S100A14 expression.

Conclusion

EMT/ZEB1 and IL-6/11-STAT3 signalling act independently and congregate to establish the expression pattern of S100 proteins, which drives invasion. Although ZEB1 regulates expression of S100 family members, these effects are masked by IL-6/11-STAT3 signalling, and S100 proteins cannot be considered as bona fide EMT markers in PDAC.

Control of Tyrosine Kinase Signalling by Small Adaptors in Colorectal Cancer

Tyrosine kinases (TKs) phosphorylate proteins on tyrosine residues as an intracellular signalling mechanism to coordinate intestinal epithelial cell communication and fate decision. Deregulation of their activity is ultimately connected with carcinogenesis. In colorectal cancer (CRC), it is still unclear how aberrant TK activities contribute to tumour formation because TK-encoding genes are not frequently mutated in this cancer. In vertebrates, several TKs are under the control of small adaptor proteins with potential important physiopathological roles. For instance, they can exert tumour suppressor functions in human cancer by targeting several components of the oncogenic TK signalling cascades. Here, we review how the Src-like adaptor protein (SLAP) and the suppressor of cytokine signalling (SOCS) adaptor proteins regulate the SRC and the Janus kinase (JAK) oncogenic pathways, respectively, and how their loss of function in the intestinal epithelium may influence tumour formation. We also discuss the potential therapeutic value of these adaptors in CRC.

A leucine-rich diet modulates the mTOR cell signalling pathway in the gastrocnemius muscle under different Walker-256 tumour growth conditions

Background

The exact signalling mechanism of the mTOR complex remains a subject of constant debate, even with some evidence that amino acids participate in the same pathway as used for insulin signalling during protein synthesis. Therefore, this work conducted further study of the actions of amino acids, especially leucine, in vivo, in an experimental model of cachexia. We analysed the effects of a leucine-rich diet on the signalling pathway of protein synthesis in muscle during a tumour growth time-course.

Methods

Wistar rats were distributed into groups based on Walker-256 tumour implant and subjected to a leucine-rich diet and euthanised at three different time points following tumour development (the 7th, 14th and 21st day). We assessed the mTOR pathway key-proteins in gastrocnemius muscle, such as RAG-A-GTPase, ERK/MAP4K3, PKB/Akt, mTOR, p70S6K1, Jnk, IRS-1, STAT3, and STAT6 comparing among the experimental groups. Serum WF (proteolysis-induced factor like from Walker-256 tumour) and muscle protein synthesis and degradation were assessed.

Results

The tumour-bearing group had increased serum WF content, and the skeletal-muscle showed a reduction in IRS-1 and RAG activation, increased PKB/Akt and Erk/MAP4K3 on the 21st day, and maintenance of p70S6K1, associated with increases in muscle STAT-3 and STAT-6 levels in these tumour-bearing rats.

Conclusion

Meanwhile, the leucine-rich diet modulated key steps of the mTOR pathway by triggering the increased activation of RAG and mTOR and maintaining JNK, STAT-3 and STAT-6 levels in muscle, leading to an increased muscle protein synthesis, reducing the degradation during tumour evolution in a host, minimising the cancer-induced damages in the cachectic state.

Therapeutically exploiting STAT3 activity in cancer - using tissue repair as a road map

The tightly orchestrated temporal and spatial control of signal transducer and activator of transcription 3 (STAT3) activity in epithelial, immune and stromal cells is critical for wound healing and tissue repair. Excessive STAT3 activation within cancer cells and cells of the tumour microenvironment can be viewed as a neoplastic mimic of an inflammation-driven repair response that collectively promotes tumour progression. In addition to the canonical transcriptional pathways by which STAT3 promotes stem cell-like characteristics, survival, proliferation, metastatic potential and immune evasion, cytoplasmic STAT3 activity fuels tumour growth by metabolic and other non-transcriptional mechanisms. Here, we review the tumour-modulating activities of STAT3 in light of its role as a signalling node integrating inflammatory responses during wound healing. Accordingly, many of the cytokines that contribute to the para-inflammatory state of most solid malignancies converge on and underpin dysregulated STAT3 activity. Targeting of these cytokines, their cognate receptors and associated signalling cascades in clinical trials is beginning to demonstrate therapeutic efficacy, given that interference with STAT3 activity is likely to simultaneously curb the growth of cancer cells and augment antitumour immunity.

Dual gene deficient models of ApcMin/+ mouse in assessing molecular mechanisms of intestinal carcinogenesis

The Apc^Min/+ mouse, carrying an inactivated allele of the adenomatous polyposis coli (Apc) gene, is a widely used animal model of human colorectal tumorigenesis. While crossed with other gene knockout or knock-in mice, these mice possess advantages in investigation of human intestinal tumorigenesis. Intestinal tumor pathogenesis involves multiple gene alterations; thus, various double gene deficiency models could provide novel insights into molecular mechanisms of tumor biology, as well as gene-gene interactions involved in intestinal tumor development and assessment of novel strategies for preventing and treating intestinal cancer. This review discusses approximately 100 double gene deficient mice and their associated intestinal tumor development and progression phenotypes. The dual gene knockouts based on the Apc mutation background consist of inflammation and immune-related, cell cycle-related, Wnt/β-catenin signaling-related, tumor growth factor (TGF)-signaling-related, drug metabolism-related, and transcription factor genes, as well as some oncogenes and tumor suppressors. Future studies should focus on conditional or inducible dual or multiple mouse gene knockout models to investigate the molecular mechanisms underlying intestinal tumor development, as well as potential drug targets.

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 is indispensable for damage-induced crypt regeneration but not for Wnt-driven intestinal tumorigenesis

Signal transducer and activator of transcription 3 (Stat3) has been shown to play a role in intestinal regeneration and colitis-associated colon carcinogenesis. However, the role of Stat3 in the Wnt-driven sporadic intestinal tumorigenesis remains poorly understood. We examined the roles of Stat3 in intestinal regeneration and tumorigenesis by organoid culture experiments using Stat3^∆IEC mouse–derived intestinal epithelial cells in which Stat3 was disrupted. The regeneration of intestinal mucosa and organoid formation were significantly suppressed by Stat3 disruption, which was compensated by Wnt activation. Furthermore, once organoids were recovered, Stat3 was no longer required for organoid growth. These results indicate that Stat3 and Wnt signaling cooperatively protect epithelial cells at the early phase of intestinal regeneration. In contrast, intestinal tumorigenesis was not suppressed by Stat3 disruption in adenomatous polyposis coli (Apc)^Δ716 and Apc^∆716 Tgfbr2^∆IEC mice, thus indicating that Stat3 is not required for Wnt activation–driven intestinal tumorigenesis. Mechanistically, Itga5 and Itga6 were down-regulated by Stat3 disruption, and focal adhesion kinase (FAK) activation was also suppressed. Notably, FAK inhibitor suppressed the organoid formation of wild-type epithelial cells. These results indicate that Stat3 is indispensable for the survival of epithelial cells through the activation of integrin signaling and the downstream FAK pathway; however, it is not required for the Wnt signaling-activated normal or tumor epithelial cells.—Oshima, H., Kok, S.-Y., Nakayama, M., Murakami, K., Voon, D. C.-C., Kimura, T., Oshima, M. Stat3 is indispensable for damage-induced crypt regeneration but not for Wnt-driven intestinal tumorigenesis.

STAT3 is a master regulator of epithelial identity and KRAS-driven tumorigenesis

A dichotomy exists regarding the role of signal transducer and activator of transcription 3 (STAT3) in cancer. Functional and genetic studies demonstrate either an intrinsic requirement for STAT3 or a suppressive effect on common types of cancer. These contrasting actions of STAT3 imply context dependency. To examine mechanisms that underlie STAT3 function in cancer, we evaluated the impact of STAT3 activity in KRAS-driven lung and pancreatic cancer. Our study defines a fundamental and previously unrecognized function of STAT3 in the maintenance of epithelial cell identity and differentiation. Loss of STAT3 preferentially associates with the acquisition of mesenchymal-like phenotypes and more aggressive tumor behavior. In contrast, persistent STAT3 activation through Tyr705 phosphorylation confers a differentiated epithelial morphology that impacts tumorigenic potential. Our results imply a mechanism in which quantitative differences of STAT3 Tyr705 phosphorylation, as compared with other activation modes, direct discrete outcomes in tumor progression.

STAT3: a multifaceted oncoprotein

Signal transducer and activator of transcription (STAT) 3 is a key signalling protein engaged by a multitude of growth factors and cytokines to elicit diverse biological outcomes including cellular growth, differentiation, and survival. The complete loss of STAT3 is not compatible with life and even partial loss of function mutations lead to debilitating pathologies like hyper IgE syndrome. Conversely, augmented STAT3 activity has been reported in as many as 50% of all human tumours. The dogma of STAT3 activity posits that it is a tyrosine phosphorylated transcription factor which modulates the expression of hundreds of genes. However, the regulation and biological consequences of STAT3 activation are far more complex. In addition to tyrosine phosphorylation, STAT3 is decorated with a plethora of post-translational modifications which regulate STAT3's nuclear function in addition to its non-genomic activities. In addition to these emerging complexities in the biochemical regulation of STAT3 activity, recent studies reveal that STAT3 is either oncogenic or a tumour suppressor. This review will explore these complexities.

Atrazine exposure improves the proliferation of H22 cellsin vitroandin vivo

Atrazine (ATZ), a widely used triazine herbicide, has been detected in the surface and ground water even far from where it is applied. Recently, the biotoxicity of atrazine to the immune, reproductive and endocrine systems has been preliminarily observed in laboratory experiments and epidemiological research studies. In order to further comprehend the carcinogenic nature of ATZ, in vitro and in vivo models were established in this study to explore the effects of ATZ exposure on hepatocellular carcinoma. The results showed that after being treated with ATZ, the proliferation of H22 cells increased, and the tumor volume and amount of ascites were significantly increased in an in situ transplantation tumor model established in C57BL/6 mice compared to the control group. The expression of p53 was down-regulated, while the expression of cyclin-D1, VEGF, MMP2, Stat3 and C-myc was up-regulated in the ATZ-treated groups compared to the control group. These results indicate that ATZ might activate the Stat3 signaling pathway and promote the proliferation and invasion of hepatocellular carcinoma cells.

ATZ exposure promotes tumor proliferation and metastasis.

STAT3 is required for MiR-17-5p-mediated sensitization to chemotherapy-induced apoptosis in breast cancer cells

Signal transducer and activator of transcription 3 (STAT3) controls cell survival, growth, migration, and invasion. Here, we observed that STAT3 exerted anti-apoptotic effects in breast cancer cells. On the other hand, miR-17-5p induced apoptosis in breast cancer cells, and overexpression of miR-17-5p sensitized MCF-7 cells to paclitaxel-induced apoptosis via STAT3. Overexpression of STAT3 in MCF-7 cells decreased paclitaxel-induced apoptosis, but STAT3 knockout abolished the miR-17-5p-induced increases in apoptosis. Finally, miR-17-5p promoted apoptosis by increasing p53 expression, which was inhibited by STAT3. These results demonstrate a novel pathway via which miR-17-5p inhibits STAT3 and increases p53 expression to promote apoptosis in breast cancer cells.

Loss of claudin-3 expression induces IL6/gp130/Stat3 signaling to promote colon cancer malignancy by hyperactivating Wnt/β-catenin signaling

The Hyperactivated Wnt/β-catenin signaling acts as a switch to induce EMT and promote colorectal cancer. However, due to its essential role in gut homeostasis, therapeutic targeting of this pathway has proven challenging. Additionally, IL-6/Stat-3 signaling, activated by microbial translocation through the dysregulated mucosal barrier in colon adenomas, facilitates the adenoma to adenocarcinomas transition. However, inter-dependence between these signaling pathways and key mucosal barrier components in regulating colon tumorigenesis and cancer progression remains unclear. In current study, we have discovered, using a comprehensive investigative regimen, a novel and tissue specific role of claudin-3, a tight junction integral protein, in inhibiting colon cancer progression by serving as the common rheostat of Stat-3 and Wnt-signaling activation. Loss of claudin-3 also predicted poor patient survival. These findings however contrasted an upregulated claudin-3 expression in other cancer types and implicated role of the epigenetic regulation. Claudin-3−/− mice revealed dedifferentiated and leaky colonic epithelium, and developed invasive adenocarcinoma when subjected to colon cancer. Wnt-signaling hyperactivation, albeit in GSK-3β independent manner, differentiated colon cancer in claudin-3−/− mice versus WT-mice. Claudin-3 loss also upregulated the gp130/IL6/Stat3 signaling in colonic epithelium potentially assisted by infiltrating immune components. Genetic and pharmacological studies confirmed that claudin-3 loss induces Wnt/β-catenin activation, which is further exacerbated by Stat-3-activation and help promote colon cancer. Overall, these novel findings identify claudin-3 as a therapeutic target for inhibiting overactivation of Wnt-signaling to prevent CRC malignancy.

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.

MicroRNA-155 deletion promotes tumorigenesis in the azoxymethane-dextran sulfate sodium model of colon cancer

Clinical studies have linked microRNA-155 (miR-155) expression in the tumor microenvironment to poor prognosis. However, whether miR-155 upregulation is predictive of a pro- or antitumorigenic response is unclear, as the limited preclinical data available remain controversial. We examined miR-155 expression in tumor tissue from colon cancer patients. Furthermore, we investigated the role of this microRNA in proliferation and apoptosis, inflammatory processes, immune cell populations, and transforming growth factor-β/SMAD signaling in a chemically induced (azoxymethane-dextran sulfate sodium) mouse model of colitis-associated colon cancer. We found a higher expression of miR-155 in the tumor region than in nontumor colon tissue of patients with colon cancer. Deletion of miR-155 in mice resulted in a greater number of polyps/adenomas, an increased symptom severity score, a higher grade of epithelial dysplasia, and a decrease in survival. Surprisingly, these findings were associated with an increase in apoptosis in the normal mucosa, but there was no change in proliferation. The protumorigenic effects of miR-155 deletion do not appear to be driven solely by dysregulation of inflammation, as both genotypes had relatively similar levels of inflammatory mediators. The enhanced tumorigenic response in miR-155(-/-) mice was associated with alterations in macrophages and neutrophils, as markers for these populations were decreased and increased, respectively. Furthermore, we demonstrated a greater activation of the transforming growth factor-β/SMAD pathway in miR-155(-/-) mice, which was correlated with the increased tumorigenesis. Given the multiple targets of miR-155, careful evaluation of its role in tumorigenesis is necessary prior to any consideration of its potential as a biomarker and/or therapeutic target in colon cancer.

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

PURPOSE

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.

EXPERIMENTAL DESIGN

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.

RESULTS

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.

CONCLUSIONS

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.

Eriocalyxin B blocks human SW1116 colon cancer cell proliferation, migration, invasion, cell cycle progression and angiogenesis via the JAK2/STAT3 signaling pathway

Eriocalyxin B, a natural ent-kaurene diterpene compound, has been shown to prevent carcinogenesis and tumor development. However, little is known regarding the mechanism underlying the antitumor activity of Eriocalyxin B in human colon cancer. The aim of the present study was to examine the role of Eriocalyxin B in SW1116 cells, and to verify the hypothesis that the Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway may serve as a therapeutic target in human colon cancer treatment. Cell proliferation was measured with a Cell Counting kit‑8 assay, and the cell cycle was assessed by flow cytometry. Cell migration and invasion were measured by Transwell analysis. In addition, western blot analysis was performed to detect the protein expression levels in SW1116 cells treated with various concentrations of Eriocalyxin B. The results demonstrated that 1 µmol/l Eriocalyxin B was effective at inhibiting JAK2 and STAT3 phosphorylation, followed by the downregulation of JAK2 and STAT3 downstream target expression, which resulted in the inhibition of cell proliferation, migration, invasion and angiogenesis. Eriocalyxin B also suppressed the expression of proliferation‑associated protein (proliferating cell nuclear antigen) and angiogenesis‑associated proteins (vascular endothelial growth factor and vascular endothelial growth factor receptor 2), as well as that of migration- and invasion‑associated proteins (matrix metalloproteinase 2 and 9). These results suggested that Eriocalyxin B may suppress JAK2/STAT3 signaling, and thus act as a therapeutic or preventive agent in the treatment of human colon cancer.

4-protein signature predicting tamoxifen treatment outcome in recurrent breast cancer

Estrogen receptor (ER) positive tumors represent the majority of breast malignancies, and are effectively treated with hormonal therapies, such as tamoxifen. However, in the recurrent disease resistance to tamoxifen therapy is common and a major cause of death. In recent years, in-depth proteome analyses have enabled identification of clinically useful biomarkers, particularly, when heterogeneity in complex tumor tissue was reduced using laser capture microdissection (LCM). In the current study, we performed high resolution proteomic analysis on two cohorts of ER positive breast tumors derived from patients who either manifested good or poor outcome to tamoxifen treatment upon recurrence. A total of 112 fresh frozen tumors were collected from multiple medical centers and divided into two sets: an in-house training and a multi-center test set. Epithelial tumor cells were enriched with LCM and analyzed by nano-LC Orbitrap mass spectrometry (MS), which yielded >3000 and >4000 quantified proteins in the training and test sets, respectively. Raw data are available via ProteomeXchange with identifiers PXD000484 and PXD000485. Statistical analysis showed differential abundance of 99 proteins, of which a subset of 4 proteins was selected through a multivariate step-down to develop a predictor for tamoxifen treatment outcome. The 4-protein signature significantly predicted poor outcome patients in the test set, independent of predictive histopathological characteristics (hazard ratio [HR] = 2.17; 95% confidence interval [CI] = 1.15 to 4.17; multivariate Cox regression p value = 0.017). Immunohistochemical (IHC) staining of PDCD4, one of the signature proteins, on an independent set of formalin-fixed paraffin-embedded tumor tissues provided and independent technical validation (HR = 0.72; 95% CI = 0.57 to 0.92; multivariate Cox regression p value = 0.009). We hereby report the first validated protein predictor for tamoxifen treatment outcome in recurrent ER-positive breast cancer. IHC further showed that PDCD4 is an independent marker.

Synthetic investigation on chirally pure Mannich derivatives of pseudophenylpropanolamine and their anticancer properties against HepG-2 cells with inhibition of JAK2/STAT3

In vitro and in vivo anticancer activity of compound 3a was proved as a novel blocker of JAK2/STAT3 signaling pathway and exerts both anti-proliferative and apoptotic activities in HepG-2 cells with xenograft mice model.

Naringin, a natural dietary compound, prevents intestinal tumorigenesis in Apc (Min/+) mouse model

PURPOSE

Naringin is a natural dietary flavonoid compound. We aimed to evaluate the effects of naringin on intestinal tumorigenesis in the adenomatous polyposis coli multiple intestinal neoplasia (Apc (Min/+)) mouse model.

METHODS

Apc (Min/+) mice were given either naringin (150 mg/kg) or vehicle by p.o. gavage daily for 12 consecutive weeks. Mice were killed with ether, and blood samples were collected to assess the concentrations of IL-6 and PGE2. Total intestines were removed, and the number of polyps was examined. Tissue samples of intestinal polyps were subjected to the assays of histopathology, immunohistochemical analysis and Western blotting analysis.

RESULTS

Apc (Min/+) mice fed with naringin developed less and smaller polyps in total intestines. Naringin prevented intestinal tumorigenesis without adverse effects. Histopathologic analysis revealed the reduction of dysplastic cells and dysplasia in the adenomatous polyps. The treatments' effects might arise from its anti-proliferation, induction of apoptosis and modulation of GSK-3β and APC/β-catenin signaling pathways. Naringin also exerted its effects on tumorigenesis through anti-chronic inflammation.

CONCLUSION

Naringin prevented intestinal tumorigenesis likely through a collection of activities including anti-proliferation, induction of apoptosis, modulation of GSK-3β and APC/β-catenin pathways and anti-inflammation. Naringin is a potential chemopreventive agent for reducing the risk of colonic cancers.

STAT3 integrates cooperative Ras and TGF-β signals that induce Snail expression

The epithelial-mesenchymal transition (EMT) is a crucial morphological event that occurs during the progression of epithelial tumors. EMT can be induced by transforming growth factor β (TGF-β) in certain kinds of cancer cells through the induction of Snail, a key regulator of EMT. We have previously found that TGF-β remarkably induces Snail expression in cooperation with Ras signals; however, the underlying mechanism of this synergism has not yet been determined. Here, we demonstrate that signal transducer and activator of transcription 3 (STAT3) acts as a mediator that synergizes TGF-β and Ras signals. The overexpression of STAT3 enhanced Snail induction, whereas siRNA-mediated knockdown of STAT3 inhibited it. The STAT3-YF mutant, which has Tyr 705 substituted with Phe, did not enhance Snail induction. Several STAT3 mutants lacking transcriptional activity also failed to enhance it; however, the putative STAT3-binding elements in the Snail promoter regions were not required for STAT3-mediated Snail induction. Protein inhibitor of activated STAT3 (PIAS3) inhibited the enhanced Snail promoter activity induced by TGF-β and Ras. The interaction between PIAS3 and STAT3 was reduced by TGF-β in cells harboring oncogenic Ras, whereas TGF-β promoted the binding of PIAS3 to Smad3, a crucial mediator of TGF-β signaling. Therefore, these findings suggest that STAT3 enhances Snail induction when it is dissociated from PIAS3 by TGF-β in cooperation with Ras signals.

Signal transducers and activators of transcription 3-induced metastatic potential in gastric cancer cells is enhanced by glycogen synthase kinase-3β

The transcription factor signal transducers and activators of transcription 3 (STAT3) can promote cancer metastasis, but its underlying regulatory mechanisms in gastric cancer cell invasiveness still remain obscure. We investigated the relationship between STAT3 and glycogen synthase kinase-3β (GSK-3β) and its significance in metastatic potential in gastric cancer cells. Immunohistochemical tissue array analysis of 267 human gastric carcinoma specimens showed that the expressions of active forms of STAT3 (pSTAT3) and GSK-3β (pGSK-3β) were found in 68 (25%) and 124 (46%) of 267 gastric cancer cases, respectively, showing a positive correlation (p < 0.001). Cell culture experiments using gastric cancer cell lines SNU-638 and SNU-668 revealed that STAT3 suppression did not affect pGSK-3β expression, whereas GSK-3β inhibition reduced pSTAT3 expression. With respect to metastatic potential in gastric cancer cells, both STAT3 suppression and GSK-3β inhibition decreased cell migration, invasion, and mesenchymal marker (Snail, Vimentin, and MMP9) expression. Moreover, the inhibitory effects of STAT3 and GSK-3β on cell migration were synergistic. These results demonstrated that STAT3 and GSK-3β are positively associated and synergistically contribute to metastatic potential in gastric cancer cells. Thus, dual use of STAT3 and GSK-3β inhibitors may enhance the efficacy of the anti-metastatic treatment of gastric cancer.

Disruption of STAT3 signalling promotes KRAS-induced lung tumorigenesis

STAT3 is considered to play an oncogenic role in several malignancies including lung cancer; consequently, targeting STAT3 is currently proposed as therapeutic intervention. Here we demonstrate that STAT3 plays an unexpected tumour-suppressive role in KRAS mutant lung adenocarcinoma (AC). Indeed, lung tissue-specific inactivation of Stat3 in mice results in increased Kras^G12D-driven AC initiation and malignant progression leading to markedly reduced survival. Knockdown of STAT3 in xenografted human AC cells increases tumour growth. Clinically, low STAT3 expression levels correlate with poor survival and advanced malignancy in human lung AC patients with smoking history, which are prone to KRAS mutations. Consistently, KRAS mutant lung tumours exhibit reduced STAT3 levels. Mechanistically, we demonstrate that STAT3 controls NF-κB-induced IL-8 expression by sequestering NF-κB within the cytoplasm, thereby inhibiting IL-8-mediated myeloid tumour infiltration and tumour vascularization and hence tumour progression. These results elucidate a novel STAT3–NF-κB–IL-8 axis in KRAS mutant AC with therapeutic and prognostic relevance.

STAT3 is an intracellular transducer of cytokine signals that cooperates with Ras in tumour formation and is often activated in lung cancer. Here the authors show that STAT3 acts as a tumour suppressor in a mouse model of Kras-driven lung adenocarcinoma.

Myeloid STAT3 promotes formation of colitis-associated colorectal cancer in mice

Myeloid cells lacking STAT3 promote antitumor responses of NK and T cells but it is unknown if this crosstalk affects development of autochthonous tumors. We deleted STAT3 in murine myeloid cells (STAT3^Δm) and examined the effect on the development of autochthonous colorectal cancers (CRCs). Formation of Azoxymethane/Dextransulfate (AOM/DSS)-induced CRCs was strongly suppressed in STAT3^Δm mice. Gene expression profiling showed strong activation of T cells in the stroma of STAT3^Δm CRCs. Moreover, STAT3^Δm host mice were better able to control the growth of transplanted MC38 colorectal tumor cells which are known to be killed in a T cell-dependent manner. These data suggest that myeloid cells lacking STAT3 control formation of CRCs mainly via cross activation of T cells. Interestingly, the few CRCs that formed in STAT3^Δm mice displayed enhanced stromalization but appeared normal in size indicating that they have acquired ways to escape enhanced tumor surveillance. We found that CRCs in STAT3^Δm mice consistently activate STAT3 signaling which is implicated in immune evasion and might be a target to prevent tumor relapse.

Role of STAT3 in lung cancer

Lung cancer remains a challenging disease. It is responsible for the high cancer mortality rates in the US and worldwide. Elucidation of the molecular mechanisms operative in lung cancer is an important first step in developing effective therapies. Accumulating evidence over the last 2 decades suggests a critical role for Signal Transducer and Activator of Transcription 3 (STAT3) as a point of convergence for various signaling pathways that are dysregulated in the disease. In this review, we discuss possible molecular mechanisms involving STAT3 in lung tumorigenesis based on recent literature. We consider possible roles of STAT3 in cancer cell proliferation and survival, in the tumor immune environment, and in epigenetic regulation and interaction of STAT3 with other transcription factors. We also discuss the potential role of STAT3 in tumor suppression, which complicates strategies of targeting STAT3 in cancer therapy.

Neutral Phosphate-Affinity SDS-PAGE system for profiling of protein phosphorylation

In this chapter, we describe a standard protocol for phosphate-affinity SDS-PAGE that uses a dizinc(II) complex of the phosphate-binding molecule Phos-tag in conjunction with a neutral-pH gel system (Zn(2+-)Phos-tag SDS-PAGE) to detect shifts in the mobilities of phosphoproteins. A previous protocol for affinity electrophoresis that uses polyacrylamide-bound Mn(2+)-Phos-tag and Laemmli's buffer system under conditions of alkaline pH has limitations in separating certain phosphoproteins. The current protocol provides major improvements in separation and detection of various phosphorylated protein species. We here introduce two neutral-pH gel systems buffered with Bis-Tris-HCl and Tris-AcOH, respectively, for Zn(2+)-Phos-tag SDS-PAGE, and we also discuss their characteristics on the basis of comparative studies on phosphorylation profiling of proteins with a wide range of molecular masses. Each analytical procedure, from the beginning of gel preparation to the end of electrophoresis, requires 2.5-5 h with either buffer system.

Ion channel TRPV1-dependent activation of PTP1B suppresses EGFR-associated intestinal tumorigenesis

The intestinal epithelium has a high rate of turnover, and dysregulation of pathways that regulate regeneration can lead to tumor development; however, the negative regulators of oncogenic events in the intestinal epithelium are not fully understood. Here we identified a feedback loop between the epidermal growth factor receptor (EGFR), a known mediator of proliferation, and the transient receptor potential cation channel, subfamily V, member 1 (TRPV1), in intestinal epithelial cells (IECs). We found that TRPV1 was expressed by IECs and was intrinsically activated upon EGFR stimulation. Subsequently, TRPV1 activation inhibited EGFR-induced epithelial cell proliferation via activation of Ca2+/calpain and resulting activation of protein tyrosine phosphatase 1B (PTP1B). In a murine model of multiple intestinal neoplasia (Apc(Min/+) mice), TRPV1 deficiency increased adenoma formation, and treatment of these animals with an EGFR kinase inhibitor reversed protumorigenic phenotypes, supporting a functional association between TRPV1 and EGFR signaling in IECs. Administration of a TRPV1 agonist suppressed intestinal tumorigenesis in Apc(Min/+) mice, similar to--as well as in conjunction with--a cyclooxygenase-2 (COX-2) inhibitor, which suggests that targeting both TRPV1 and COX-2 has potential as a therapeutic approach for tumor prevention. Our findings implicate TRPV1 as a regulator of growth factor signaling in the intestinal epithelium through activation of PTP1B and subsequent suppression of intestinal tumorigenesis.

STAT3: An Anti-Invasive Factor in Colorectal Cancer?

Signal Transducer and Activator of Transcription 3 (STAT3) is activated in a majority of cancers, and promotes tumorigenesis and even metastasis through transcriptional activation of its target genes. Recently, we discovered that STAT3 suppresses epithelial-to-mesenchymal transition (EMT) and thus metastasis in a mouse model of colorectal cancer (CRC), while it did not affect the overall tumor burden. Furthermore, we found that STAT3 in intestinal epithelial cells (IEC) suppresses EMT by regulating stability of an EMT inducer, SNAI-1 (Snail-1). Here, STAT3 functions as an adaptor rather than a transcription factor in the post-translational modification of SNAI-1. In this review, we discuss the unexpected and contradictory role of STAT3 in metastasis of CRC and its clinical implications.

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.

Genomic profiling of hepatocellular adenomas reveals recurrent FRK-activating mutations and the mechanisms of malignant transformation

Hepatocellular adenomas (HCA) are benign liver tumors predominantly developed in women using oral contraceptives. Here, exome sequencing identified recurrent somatic FRK mutations that induce constitutive kinase activity, STAT3 activation, and cell proliferation sensitive to Src inhibitors. We also found uncommon recurrent mutations activating JAK1, gp130, or β-catenin. Chromosome copy number and methylation profiling revealed patterns that correlated with specific gene mutations and tumor phenotypes. Finally, integrative analysis of HCAs transformed to hepatocellular carcinoma revealed β-catenin mutation as an early alteration and TERT promoter mutations as associated with the last step of the adenoma-carcinoma transition. In conclusion, we identified the genomic diversity in benign hepatocyte proliferation, several therapeutic targets, and the key genomic determinants of the adenoma-carcinoma transformation sequence.