IL-6R/STAT3/miR-34a feedback loop promotes EMT-mediated colorectal cancer invasion and metastasis

Cancer stem cells and tumor-associated macrophages: a roadmap for multitargeting strategies

The idea that tumor initiation and progression are driven by a subset of cells endowed with stem-like properties was first described by Rudolf Virchow in 1855. 'Cancer stem cells', as they were termed more than a century later, represent a subset of tumor cells that are able to generate all tumorigenic and nontumorigenic cell types within the malignancy. Although their existence was hypothesized >150 years ago, it was only recently that stem-like cells started to be isolated from different neoplastic malignancies. Interestingly, Virchow, in suggesting a correlation between cancer and the inflammatory microenvironment, also paved the way for the 'Seed and Soil' theory proposed by Paget a few years later. Despite the time that has passed since these two important concepts were suggested, the relationships between Virchow's 'stem-like cells' and Paget's 'soil' are far from being fully understood. One emerging topic is the importance of a stem-like niche in modulating the biological properties of stem-like cancer cells and thus in affecting the response of the tumor to drugs. This review aims to summarize the recent molecular data concerning the multilayered relationship between cancer stem cells and tumor-associated macrophages that form a key component of the tumor microenvironment. We also discuss the therapeutic implications of targeting this synergistic interplay.

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.

Glutamate dehydrogenase is a novel prognostic marker and predicts metastases in colorectal cancer patients

Background

Glutamate dehydrogenase (GDH) is a key enzyme that catalyzes the final reaction of the glutamine metabolic pathway, and has been reported implicated in tumor growth and metastasis. However, it’s clinical significance and role in colorectal cancer (CRC) pathogenesis is largely unknown.

Methods

The expression of GDH was determined by qPCR, western blot and immunohistochemistry in CRC cells and samples. The correlation of GDH expression with clinicopathologic features and prognosis was analyzed. The functional role of GDH in CRC cell proliferation, motility and metastasis was evaluated.

Results

We found that GDH was up-regulated both in colorectal cancer and metastatic lesions (n = 104). Patients with high GDH expression had poorer overall survival (HR 2.32; 95% CI 1.26-4.26; P = 0.007) and poorer disease-free survival rates (HR 2.48; 95% CI 1.25-4.92; P = 0.009) than those with low GDH expression. Furthermore, we showed that GDH expression was an independent prognostic factor for CRC. In addition, over-expression of GDH promoted cell proliferation, migration and invasion in vitro, whereas loss function of GDH did the opposite. Finally, we demonstrated that the promotion of CRC progression by GDH correlated with activation of STAT3 mediated epithelial-mesenchymal transition (EMT) induction.

Conclusions

These results indicate that GDH plays a critical role in CRC progression, and may provide a novel metabolism therapeutic target for CRC treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0500-6) contains supplementary material, which is available to authorized users.

G-CSF Promotes Neuroblastoma Tumorigenicity and Metastasis via STAT3-Dependent Cancer Stem Cell Activation

Increasing evidence suggests that inflammatory cytokines play a critical role in tumor initiation and progression. A cancer stem cell (CSC)-like subpopulation in neuroblastoma is known to be marked by expression of the G-CSF receptor (G-CSFR). Here, we report on the mechanistic contributions of the G-CSFR in neuroblastoma CSCs. Specifically, we demonstrate that the receptor ligand G-CSF selectively activates STAT3 within neuroblastoma CSC subpopulations, promoting their expansion in vitro and in vivo. Exogenous G-CSF enhances tumor growth and metastasis in human xenograft and murine neuroblastoma tumor models. In response to G-CSF, STAT3 acts in a feed-forward loop to transcriptionally activate the G-CSFR and sustain neuroblastoma CSCs. Blockade of this G-CSF-STAT3 signaling loop with either anti-G-CSF antibody or STAT3 inhibitor depleted the CSC subpopulation within tumors, driving correlated tumor growth inhibition, decreased metastasis, and increased chemosensitivity. Taken together, our results define G-CSF as a CSC-activating factor in neuroblastoma, suggest a comprehensive reevaluation of the clinical use of G-CSF in these patients to support white blood cell counts, and suggest that direct targeting of the G-CSF-STAT3 signaling represents a novel therapeutic approach for neuroblastoma.

Adipose-derived stem cells promote tumor initiation and accelerate tumor growth by interleukin-6 production

Adipose-derived stem cells (ADSCs) are multipotent cells that have attracted much recent attention. Here, we show that ADSCs enhance sphere formation and in vivo tumor initiation of breast and colon cancer cells. In co-culture, ADSCs induced several stem cell markers in cancer cells. ADSCs also accelerated tumor growth. Interaction of ADSCs and cancer cells stimulated secretion of interlukin-6 in ADSCs, which in turn acted in a paracrine manner on cancer cells to enhance their malignant properties. Interleukin-6 regulated stem cell-related genes and activated JAK2/STAT3 in cancer cells. We suggest that ADSCs may enhance tumor initiation and promotion.

Aberrantly expressed Fra-1 by IL-6/STAT3 transactivation promotes colorectal cancer aggressiveness through epithelial-mesenchymal transition

The pro-inflammatory cytokine interleukin-6 (IL-6) in tumor microenvironment has been suggested to promote development and progression of colorectal cancer (CRC). However, the underlying molecular mechanisms remain elusive. In this study, we demonstrate that fos-related antigen-1 (Fra-1) plays a critical role in IL-6 induced CRC aggressiveness and epithelial-mesenchymal transition (EMT). In CRC cell lines, the expression of Fra-1 gene was found significantly upregulated during IL-6-driven EMT process. The Fra-1 induction occurred at transcriptional level in a manner dependent on signal transducer and activator of transcription 3 (STAT3), during which both phosphorylated and acetylated post-translational modifications were required for STAT3 activation to directly bind to the Fra-1 promoter. Importantly, RNA interference-based attenuation of either STAT3 or Fra-1 prevented IL-6-induced EMT, cell migration and invasion, whereas ectopic expression of Fra-1 markedly reversed the STAT3-knockdown effect and enhanced CRC cell aggressiveness by regulating the expression of EMT-promoting factors (ZEB1, Snail, Slug, MMP-2 and MMP-9). Furthermore, Fra-1 levels were positively correlated with the local invasion depth as well as lymph node and liver metastasis in a total of 229 CRC patients. Intense immunohistochemical staining of Fra-1 was observed at the tumor marginal area adjacent to inflammatory cells and in parallel with IL-6 secretion and STAT3 activation in CRC tissues. Together, this study proposes the existence of an aberrant IL-6/STAT3/Fra-1 signaling axis leading to CRC aggressiveness through EMT induction, which suggests novel therapeutic opportunities for the malignant disease.

MicroRNA-33b, upregulated by EF24, a curcumin analog, suppresses the epithelial-to-mesenchymal transition (EMT) and migratory potential of melanoma cells by targeting HMGA2

Diphenyl difluoroketone (EF24), a curcumin analog, exhibits potent anti-tumor activities by arresting cell cycle and inducing apoptosis. However, the efficacy and modes of action of EF24 on melanoma metastasis remain elusive. In this study, we found that at non-cytotoxic concentrations, EF24 suppressed cell motility and epithelial-to-mesenchymal Transition (EMT) of melanoma cell lines, Lu1205 and A375. EF24 also suppressed HMGA2 expression at mRNA and protein levels. miR-33b directly bound to HMGA2 3' untranslated region (3'-UTR) to suppress its expression as measured by dual-luciferase assay. EF24 increased expression of E-cadherin and decreased STAT3 phosphorylation and expression of the mesenchymal markers, vimentin and N-cadherin. miR-33b inhibition or HMGA2 overexpression reverted EF24-mediated suppression of EMT phenotypes. In addition, EF24 modulated the HMGA2-dependent actin stress fiber formation, focal adhesion assembly and FAK, Src and RhoA activation by targeting miR-33b. Thus, the results suggest that EF24 suppresses melanoma metastasis via upregulating miR-33b and concomitantly reducing HMGA2 expression. The observed activities of EF24 support its further evaluation as an anti-metastatic agent in melanoma therapy.

WITHDRAWN: Hypoxia-induced STAT3 contributes to chemoresistance and epithelial-mesenchymal transition in prostate cancer cells

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Radiation promotes invasiveness of non-small-cell lung cancer cells through granulocyte-colony-stimulating factor

Despite ionizing radiation (IR) is being widely used as a standard treatment for lung cancer, many evidences suggest that IR paradoxically promotes cancer malignancy. However, its molecular mechanisms underlying radiation-induced cancer progression remain obscure. Here, we report that exposure to fractionated radiation (2 Gy per day for 3 days) induces the secretion of granulocyte-colony-stimulating factor (G-CSF) that has been commonly used in cancer therapies to ameliorate neutropenia. Intriguingly, radiation-induced G-CSF promoted the migratory and invasive properties by triggering the epithelial-mesenchymal cell transition (EMT) in non-small-cell lung cancer cells (NSCLCs). By irradiation, G-CSF was upregulated transcriptionally by β-catenin/TCF4 complex that binds to the promoter region of G-CSF as a transcription factor. Importantly, irradiation increased the stability of β-catenin through the activation of PI3K/AKT (phosphatidylinositol 3-kinase/AKT), thereby upregulating the expression of G-CSF. Radiation-induced G-CSF is recognized by G-CSFR and transduced its intracellular signaling JAK/STAT3 (Janus kinase/signal transducers and activators of transcription), thereby triggering EMT program in NSCLCs. Taken together, our findings suggest that the application of G-CSF in cancer therapies to ameliorate neutropenia should be reconsidered owing to its effect on cancer progression, and G-CSF could be a novel therapeutic target to mitigate the harmful effect of radiotherapy for the treatment of NSCLC.

MiR-34a inhibits oral cancer progression partially by repression of interleukin-6-receptor

Previous reports revealed that a significant decrease of miR-34a in oral cancer. But the role of miR-34a in oral cancer needs further research. In the present study, we will investigate the effect of miR-34a on oral cancer cell phenotypes. First, it was verified that miR-34a expression was lower in oral cancer tissues compared with their normal controls, so did the oral cancer cells. Next, it was showed that miR-34a overexpression in oral cancer cells could inhibit cell proliferation, G1 phase arrest, metastasis and epithelial mesenchymal transition. It was predicted that interleukin-6-receptor (IL6R) was a potential target gene of miR-34a by bioinformatics analysis and identified by luciferase assay. It was further showed that miR-34a inhibited oral cancer progression via IL6R. Collectively, our findings suggested that miR-34a may function as a tumor suppressor in oral cancer by targeting IL6R.

SHP-1 is a negative regulator of epithelial-mesenchymal transition in hepatocellular carcinoma

Epithelial-to-mesenchymal transition (EMT) is well known to involve in tumor invasion and metastasis. Src homology region 2 domain-containing phosphatase 1 (SHP-1) functions as a potent tumor suppressor and also acts as a negative regulator of p-STAT3(Tyr705) oncogenic signaling. However, little is known about the molecular mechanism(s) through which SHP-1 regulates EMT during hepatocellular carcinoma (HCC) progression. Here we first reported that endogenous SHP-1 protein levels were significantly downregulated in cells with mesenchymal characteristics and negatively correlated with p-STAT3(Tyr705) and vimentin but positively correlated with E-cadherin. SHP-1 overexpression abolished transforming growth factor-β1 (TGF-β1)-induced p-STAT3(Tyr705) and EMT, as well inhibited migration and invasion but further rescued by signal transducer and activator of transcription factor 3 (STAT3) overexpression. Depletion of SHP-1 could induce a more increase in TGF-β1-induced p-STAT3(Tyr-705) and EMT characteristics, further supporting the mechanism that suppression of TGF-β1-induced EMT is dependent on SHP-1-mediated STAT3 inactivation. Constitutively overexpressed SHP-1 tyrosine phosphatase activity by D61A-mutated SHP-1 markedly reduced TGF-β1-induced p-STAT3(Tyr705) and EMT features but was not altered by C453S catalytic-dead mutant SHP-1. Consequently, SHP-1 acted as a powerful suppressor in preventing EMT by exerting its tyrosine phosphatase activity that directly downregulated p-STAT3(Tyr705). Most notably, we discovered a novel SHP-1 agonist SC-43 better than sorafenib to exert more potent anti-EMT effects in vitro as well as anti-metastatic growth in vivo. In conclusion, SHP-1 is a potent suppressor of HCC EMT and metastasis, thus highlighting that SC-43-SHP-1 axis may serve as a potential therapeutic target that antagonized p-STAT3(Tyr705) and thereby prevented HCC EMT and metastasis.

Regulation of cancer metastasis by microRNAs

MicroRNAs (miRNAs) are a class of endogenous small non-coding RNAs that have been found highly conserved among species. MiRNAs are able to negatively regulate gene expression through base pairing of 3' UTRs of their target genes. Therefore, miRNAs have been shown to play an important role in regulating various cellular activities. Over the past decade, substantial evidences have been obtained to show that miRNAs are aberrantly expressed in human malignancies and could act as "OncomiRs" or "Tumor suppressor miRs". In recent years, increasing number of studies have demonstrated the involvement of miRNAs in cancer metastasis. Many studies have shown that microRNAs could directly target genes playing a central role in epithelia-mesenchymal-transition (EMT), a cellular transformation process that allows cancer cells to acquire motility and invasiveness. EMT is considered an essential step driving the early phase of cancer metastasis. This review will summarize the recent findings and characterization of miRNAs that are involved in the regulation of EMT, migration, invasion and metastasis of cancer cells. Lastly, we will discuss potential use of miRNAs as diagnostic and prognostic biomarkers as well as therapeutic targets for cancer.

LEF1 Targeting EMT in Prostate Cancer Invasion Is Regulated by miR-34a

The microRNA-34a (miR-34a), a tumor-suppressive microRNA (miRNA), is implicated in epithelial-mesenchymal transition (EMT) and cancer stem cells. Lymphoid enhancer-binding factor-1 (LEF1) is a key transcription factor in the Wnt signaling pathway, and has been suggested to be involved in regulation of cell proliferation and invasion. Here, the molecular mechanism of miR-34a and LEF1 in cooperatively regulating prostate cancer cell invasion is described. Molecular profiling analysis of miRNA levels in prostate cancer cells revealed a negative correlation between miR-34a and LEF1 expression, and the downregulation of LEF1 by miR-34a was confirmed by luciferase assays. Furthermore, miR-34a specifically repressed LEF1 expression through direct binding to its 3'-untranslated regions (3'-UTR). miR-34a modulated the levels of LEF1 to regulate EMT in prostate cancer cells. Functionally, miR-34a negatively correlated with the migration and invasion of prostate cancer cells through LEF1. An analysis of miR-34a expression levels in matched human tumor and benign tissues demonstrated consistent and statistically significant downregulation of miR-34a in primary prostate cancer specimens. These data strongly suggest that miR-34a/LEF1 regulation of EMT plays an important role in prostate cancer migration and invasion.

IMPLICATIONS

The miR-34a-LEF1 axis represents a potential molecular target for novel therapeutic strategies in prostate cancer.

An update on miRNAs as biological and clinical determinants in colorectal cancer: a bench-to-bedside approach

Colorectal carcinogenesis represents a sequential progression of normal colonic mucosa from adenoma to carcinoma. It has become apparent that miRNA deregulation contributes to the initiation and progression of colorectal cancer (CRC). These oncogenic or tumor-suppressive miRNAs interact with intracellular signaling networks and lead to alteration of cell proliferation, apoptosis, metastasis and even response to chemotherapeutic treatments. This article aims to review the cutting edge progress in the discovery of the role of novel mechanisms for miRNAs in the development of CRC. We will also discuss the potential use of miRNAs as biomarkers for early diagnosis and prognosis of CRC. Furthermore, with advancements in RNA delivery technology, it is anticipated that manipulation of miRNAs may offer an alternative therapy for CRC treatment.

Combination of microRNA therapeutics with small-molecule anticancer drugs: mechanism of action and co-delivery nanocarriers

MicroRNAs (miRNAs) regulate multiple molecular pathways vital for the hallmarks of cancer with a high degree of biochemical specificity and potency. By restoring tumor suppressive miRNAs or ablating oncomiRs, miRNA-based therapies can sensitize cancer cells to conventional cytotoxins and the molecularly targeted drugs by promoting apoptosis and autophagy, reverting epithelial-to-mesenchymal transition, suppressing tumor angiogenesis, and downregulating efflux transporters. The development of miRNA-based therapeutics in combination with small-molecule anticancer drugs provides an unprecedented opportunity to counteract chemoresistance and improve treatment outcome in a broad range of human cancers. This review summarizes the mechanisms and advantages for the combination therapies involving miRNAs and small-molecule drugs, as well as the recent advances in the co-delivery nanocarriers for these agents.

Mechanisms of Immune Signaling in Colitis-Associated Cancer

The inflammatory bowel diseases ulcerative colitis and Crohn's disease are associated with an increased risk for the development of colorectal cancer. During recent years, several immune signaling pathways have been linked to colitis-associated cancer (CAC), largely owing to the availability of suitable preclinical models. Among these, chronic intestinal inflammation has been shown to support tumor initiation through oxidative stress-induced mutations. A proinflammatory microenvironment that develops, possibly as a result of defective intestinal barrier function and host-microbial interactions, enables tumor promotion. Several molecular pathways such as tumor necrosis factor/nuclear factor-κB or interleukin 6/signal transducer and activator of transcription 3 signaling have been identified as important contributors to CAC development and could be promising therapeutic targets for the prevention and treatment of CAC.

Molecular functions and significance of the MTA family in hormone-independent cancer

The members of the metastasis-associated protein (MTA) family play pivotal roles in both physiological and pathophysiological processes, especially in cancer development and metastasis, and their role as master regulators has come to light. Due to the fact that they were first identified as crucial factors in estrogen receptor-mediated breast cancer metastasis, most of the early studies focused on their hormone-dependent functions. However, the accumulating evidence shows that the members of MTA family are deregulated in most, if not all, the cancers studied so far. Therefore, the levels as well as the activities of the MTA family members are widely accepted as potential biomarkers for diagnosis, prognosis, and predictors of overall survival. They function differently in different cancers with specific mechanisms. p53 and HIF-1α appear to be the respectively common upstream and downstream regulator of the MTA family in both development and metastasis of a wide spectrum of cancers. Here, we review the expression and clinical significance of the MTA family, focusing on hormone-independent cancers. To illustrate the molecular mechanisms, we analyze the MTA family-related signaling pathways in different cancers. Finally, targeting the MTA family directly or the pathways involved in the MTA family indirectly could be invaluable strategies in the development of cancer therapeutics.

Stat3: friend or foe in colitis and colitis-associated cancer?

Chronic inflammation predisposes tissue to cancer development. Individuals afflicted with inflammatory bowel diseases are at an increased risk of developing colorectal cancer depending on disease severity, duration, and management. The intestinal epithelium exhibits mitochondrial dysfunction during colitis and colitis-associated cancer. Signal Transducer and Activator of Transcription (Stat)-3 is a transcription factor involved in growth-promoting and antiapoptotic signaling pathways. In addition to its activities as a transcription factor, Stat3 resides in the mitochondria of cells where it is required for optimal electron transport chain activity and protects against stress-induced mitochondrial dysfunction. The function of mitochondrial Stat3 is not completely understood; dichotomous roles include protecting against cellular injury but also supporting malignant transformation. This review discusses the roles of Stat3 in the regulation of intestinal epithelial cell fate during colitis and colorectal cancer with an emphasis on mitochondrial dysfunction and the potential involvement of mitochondrial Stat3 during disease progression.

Expression of Sox2 in breast cancer cells promotes the recruitment of M2 macrophages to tumor microenvironment

Transcriptional factor Sox2 promotes tumor metastasis; however its regulatory effect on tumor-associated macrophages (TAMs, M2 phenotype) has not been defined. This study disclosed concomitant expression of TAMs marker-CD163 with SOX2 in human breast cancer and showed that Sox2 in breast cancer cells promotes recruitment of TAMs with altered expression of multiple chemokines, including MIP-1α, ICAM-1 etc. and activation of Stat3 and NF-κB signalings. In addition, TAMs rescued the compromised lung metastasis induced by Sox2 silencing in breast cancer cells. Together, this study documented that Sox2 plays an important role in recruiting TAMs and promotes tumor metastasis in a TAMs dependent manner.

Epithelial-mesenchymal transition and cancer stem cells, mediated by a long non-coding RNA, HOTAIR, are involved in cell malignant transformation induced by cigarette smoke extract

The incidence of lung diseases, including cancer, caused by cigarette smoke is increasing, but the molecular mechanisms of gene regulation induced by cigarette smoke remain unclear. This report describes a long noncoding RNA (lncRNA) that is induced by cigarette smoke extract (CSE) and experiments utilizing lncRNAs to integrate inflammation with the epithelial-mesenchymal transition (EMT) in human bronchial epithelial (HBE) cells. The present study shows that, induced by CSE, IL-6, a pro-inflammatory cytokine, leads to activation of STAT3, a transcription activator. A ChIP assay determined that the interaction of STAT3 with the promoter regions of HOX transcript antisense RNA (HOTAIR) increased levels of HOTAIR. Blocking of IL-6 with anti-IL-6 antibody, decreasing STAT3, and inhibiting STAT3 activation reduced HOTAIR expression. Moreover, for HBE cells cultured in the presence of HOTAIR siRNA for 24h, the CSE-induced EMT, formation of cancer stem cells (CSCs), and malignant transformation were reversed. Thus, IL-6, acting on STAT3 signaling, which up-regulates HOTAIR in an autocrine manner, contributes to the EMT and to CSCs induced by CSE. These data define a link between inflammation and EMT, processes involved in the malignant transformation of cells caused by CSE. This link, mediated through lncRNAs, establishes a mechanism for CSE-induced lung carcinogenesis.

Inhibition of the Interleukin-11-STAT3 Axis Attenuates Hypoxia-Induced Migration and Invasion in MDA-MB-231 Breast Cancer Cells

Although interleukin-11 (IL-11) has been reported to be elevated in hypoxic tumors and has been associated with a poor prognosis in various cancers, little is known about its precise role in promoting metastasis in hypoxic tumors. In the present study, the molecular mechanism underlying the effects of IL-11 on MDA-MB-231 breast cancer cells migration and invasion in relation to metastasis under hypoxic conditions has been defined. Inhibition of IL-11 expression or function using small interfering RNA (siRNA) or a neutralizing antibody attenuated hypoxic MDA-MB-231 breast cancer cell migration and invasion through down-regulation of matrix metalloproteinases (MMPs) and activation of epithelial-to-mesenchymal transition (EMT) related gene expression. In addition, hypoxia-induced IL-11 increased STAT3 phosphorylation and STAT3 knockdown suppressed hypoxic MDA-MB-231 breast cancer cell invasion due to reduced MMP levels and reprogrammed EMT-related gene expression. These results suggest that one of the hypoxic metastasis pathways and the regulation of this pathway could be a potential target for novel cancer therapeutics.

The p53/microRNA connection in gastrointestinal cancer

The protein encoded by the TP53 gene is one of the most important suppressors of tumor formation, which is also frequently inactivated in gastrointestinal cancer. MicroRNAs (miRNAs) are small noncoding RNAs that inhibit translation and/or promote degradation of their target messenger RNAs. In recent years, several miRNAs have been identified as mediators and regulators of p53’s tumor suppressing functions. p53 induces expression and/or maturation of several miRNAs, which leads to the repression of critical effector proteins. Furthermore, certain miRNAs regulate the expression and activity of p53 through direct repression of p53 or its regulators. Experimental findings indicate that miRNAs are important components of the p53 network. In addition, the frequent genetic and epigenetic alterations of p53-regulated miRNAs in tumors indicate that they play an important role in cancer initiation and/or progression. Therefore, p53-regulated miRNAs may represent attractive diagnostic and/or prognostic biomarkers. Moreover, restoration of p53-induced miRNAs results in suppression of tumor growth and metastasis in mouse models of cancer. Thus, miRNA-based therapeutics may represent a feasible strategy for future cancer treatment. Here we summarize the current published state-of-the-art on the role of the p53-miRNA connection in gastrointestinal cancer.

IL-33/ST2 pathway contributes to metastasis of human colorectal cancer

Interleukin-33 (IL-33) was recently implicated in cancer pathogenesis. However, the possible effect of IL-33 on tumor progression of colorectal cancer (CRC), which is one of the most commonly diagnosed and lethal cancers worldwide, was still unclear. Here we evaluated the potential role of IL-33/ST2 pathway in metastasis of human CRC. We found an elevated expression of IL-33 and ST2 in tumor tissues of CRC patients. Higher expressions of IL-33 and ST2 were observed in poor-differentiated human CRC cells. Of note, IL-33 stimulation promoted the invasion of human CRC cells in a dose dependent manner. Enhanced IL-33/ST2 signaling promoted CRC metastasis, while attenuated IL-33/ST2 signaling decreased CRC metastasis. In consistent, enforced IL-33 expression in human CRC cells enhanced their growth, metastasis and reduced the survival time in nude mice, while decreased IL-33 expression in human CRC cells inhibited their growth, metastasis and prolonged the survival time in nude mice. Finally, we observed an increased expression of IL-6, CXCR4, MMP2 and MMP9 in response to IL-33/ST2 signaling in human CRC cells, which were crucial for the enhanced metastasis by IL-33 stimulation. Collectively, our findings demonstrated that IL-33/ST2 pathway could contribute to the metastasis of human CRC, which could enlarge the understanding of CRC pathogenesis and provide clues for developing new CRC therapeutics.

Mir-34: a new weapon against cancer?

The microRNA(miRNA)-34a is a key regulator of tumor suppression. It controls the expression of a plethora of target proteins involved in cell cycle, differentiation and apoptosis, and antagonizes processes that are necessary for basic cancer cell viability as well as cancer stemness, metastasis, and chemoresistance. In this review, we focus on the molecular mechanisms of miR-34a-mediated tumor suppression, giving emphasis on the main miR-34a targets, as well as on the principal regulators involved in the modulation of this miRNA. Moreover, we shed light on the miR-34a role in modulating responsiveness to chemotherapy and on the phytonutrients-mediated regulation of miR-34a expression and activity in cancer cells. Given the broad anti-oncogenic activity of miR-34a, we also discuss the substantial benefits of a new therapeutic concept based on nanotechnology delivery of miRNA mimics. In fact, the replacement of oncosuppressor miRNAs provides an effective strategy against tumor heterogeneity and the selective RNA-based delivery systems seems to be an excellent platform for a safe and effective targeting of the tumor.

Interleukin-6 and its receptors: a highly regulated and dynamic system

Interleukin-6 (IL-6) is a multifunctional cytokine with well-defined pro- and anti-inflammatory properties. Although only small amounts in the picogram range can be detected in healthy humans, IL-6 expression is highly and transiently up-regulated in nearly all pathophysiological states. IL-6 induces intracellular signaling pathways after binding to its membrane-bound receptor (IL-6R), which is only expressed on hepatocytes and certain subpopulations of leukocytes (classic signaling). Transduction of the signal is mediated by the membrane-bound β-receptor glycoprotein 130 (gp130). In a second pathway, named trans-signaling, IL-6 binds to soluble forms of the IL-6R (sIL-6R), and this agonistic IL-6/sIL-6R complexes can in principle activate all cells due to the uniform expression of gp130. Importantly, several soluble forms of gp130 (sgp130) are found in the human blood, which are considered to be the natural inhibitors of IL-6 trans-signaling. Most pro-inflammatory roles of IL-6 have been attributed to the trans-signaling pathway, whereas anti-inflammatory and regenerative signaling, including the anti-bacterial acute phase response of the liver, is mediated by IL-6 classic signaling. In this simplistic view, only a minority of cell types expresses the IL-6R and is therefore responsive for IL-6 classic signaling, whereas gp130 is ubiquitously expressed throughout the human body. However, several reports point towards a much more complex situation. A plethora of factors, including proteases, cytokines, chemical drugs, and intracellular signaling pathways, are able to modulate the cellular expression of the membrane-bound and soluble forms of IL-6R and gp130. In this review, we summarize current knowledge of regulatory mechanisms that control and regulate the dynamic expression of IL-6 and its two receptors.

The architect who never sleeps: tumor-induced plasticity

Tumor cell plasticity is an event that has been observed in several malignancies. In fact, most of the solid tumors are characterized by cellular heterogeneity and undergo constant changes as the tumor develops. The increased plasticity displayed by these cells allows them to acquire additional properties, enabling epithelial-mesenchymal transitions, dedifferentiation and the acquisition of stem cell-like properties. Here we discuss the particular importance of an inflammatory microenvironment for the bidirectional control of cellular plasticity and the potential for therapeutic intervention.

ZNF281/ZBP-99: a new player in epithelial-mesenchymal transition, stemness, and cancer

Epithelial-mesenchymal transition (EMT) represents an important mechanism during development and wound healing, and its deregulation has been implicated in metastasis. Recently, the Krüppel-type zinc-finger transcription factor ZNF281 has been characterized as an EMT-inducing transcription factor (EMT-TF). Expression of ZNF281 is induced by the EMT-TF SNAIL and inhibited by the tumor suppressive microRNA miR-34a, which mediates repression of ZNF281 by the p53 tumor suppressor. Therefore, SNAIL, miR-34a and ZNF281 form a feed-forward regulatory loop, which controls EMT. Deregulation of this circuitry by mutational and epigenetic alterations in the p53/miR-34a axis promotes colorectal cancer (CRC) progression and metastasis formation. As ZNF281 physically interacts with the transcription factors NANOG, OCT4, SOX2, and c-MYC, it has been implicated in the regulation of pluripotency, stemness, and cancer. Accordingly, ectopic ZNF281 expression in CRC lines induces the stemness markers LGR5 and CD133 and promotes sphere formation, suggesting that the elevated expression of ZNF281 detected in cancer may enhance tumor stem cell formation and/or function. Here, we review the functional and organismal studies of ZNF281/ZBP-99 and its close relative ZBP-89/ZFP148 reported so far. Taken together, ZNF281 related biology has the potential to be translated into cancer diagnostic, prognostic, and therapeutic approaches.

Microenvironment-dependent cues trigger miRNA-regulated feedback loop to facilitate the EMT/MET switch

The metastatic spread of tumor epithelial cells accounts for over 90% of cancer-specific mortality; however, the molecular mechanisms that govern tumor spread and distant recolonization remain unclear. In this issue of JCI, Rokavec and colleagues shine light on this murky aspect of tumor biology by focusing through the lens of microenvironmental contributions, namely inflammation, as driving signals that set off a delicate, intracellular feedback loop among cytokine receptors, transcription factors and miRNAs. This study provides in vivo evidence and identifies molecular players behind the elusive switch that drives the epithelial-to-mesenchymal transition and the mesenchymal-to-epithelial transition.