DNp73 exerts function in metastasis initiation by disconnecting the inhibitory role of EPLIN on IGF1R-AKT/STAT3 signaling

AF1q Mediates Tumor Progression in Colorectal Cancer by Regulating AKT Signaling

The up-regulation of ALL1-fused gene from chromosome 1q (AF1q) is commonly seen in aggressive hematologic malignancies as well as in several solid tumor tissues. However, its expression and intrinsic function in human colorectal cancer (CRC) remains largely undefined. To explore the role of AF1q in human CRC progression, AF1q expression was analyzed in human CRC tissue samples and CRC cell lines. Clinical specimens revealed that AF1q was up-regulated in human CRC tissues, and that this up-regulation was associated with tumor metastasis and late tumor, lymph node, metastasis (TNM) stage. AF1q knockdown by shRNA inhibited tumor cell proliferation, migration, invasion, and epithelial-mesenchymal transition in vitro, as well as tumorigenesis and liver metastasis in vivo, whereas these effects were reversed following AF1q overexpression. These AF1q-mediated effects were modulated by the protein kinase B (AKT) signaling pathway, and inhibition of AKT signaling attenuated AF1q-induced tumor promotion. Thus, AF1q contributes to CRC tumorigenesis and progression through the activation of the AKT signaling pathway. AF1q might therefore serve as a promising new target in the treatment of CRC.

Human phosphatase CDC14A regulates actin organization through dephosphorylation of epithelial protein lost in neoplasm

CDC14 is an essential dual-specificity phosphatase that counteracts CDK1 activity during anaphase to promote mitotic exit in Saccharomyces cerevisiae Surprisingly, human CDC14A is not essential for cell cycle progression. Instead, it regulates cell migration and cell adhesion. Little is known about the substrates of hCDC14A and the counteracting kinases. Here, we combine phospho-proteome profiling and proximity-dependent biotin identification to identify hCDC14A substrates. Among these targets were actin regulators, including the tumor suppressor eplin. hCDC14A counteracts EGF-induced rearrangements of actin cytoskeleton by dephosphorylating eplin at two known extracellular signal-regulated kinase sites, serine 362 and 604. hCDC14A^PD and eplin knockout cell lines exhibited down-regulation of E-cadherin and a reduction in α/β-catenin at cell-cell adhesions. Reduction in the levels of hCDC14A and eplin mRNA is frequently associated with colorectal carcinoma and is correlated with poor prognosis. We therefore propose that eplin dephosphorylation by hCDC14A reduces actin dynamics to restrict tumor malignancy.

Epithelial protein lost in neoplasm (EPLIN): Beyond a tumor suppressor

The majority of cancer-related deaths are caused by tumor recurrence, metastasis and therapeutic resistance. During the late stages of tumor progression, multiple factors are involved, including the downregulation and/or loss of function of metastasis suppressors. Epithelial protein lost in neoplasm (EPLIN), an actin-binding protein, was initially identified as a putative tumor suppressor that is frequently downregulated in epithelial tumors. Recent evidence indicates that EPLIN may negatively regulate epithelia-to-mesenchymal transition (EMT), a crucial process by which cancer cells acquire invasive capabilities and therapeutic resistance. Importantly, downregulation of EPLIN is associated with clinical metastasis in a variety of solid tumors, suggesting that EPLIN could be a suppressor of metastasis. In this review, I will discuss the regulation and function of EPLIN in human cancer cells and explore the clinical significance of EPLIN in metastatic disease.

For robust big data analyses: a collection of 150 important pro-metastatic genes

Metastasis is the greatest contributor to cancer-related death. In the era of precision medicine, it is essential to predict and to prevent the spread of cancer cells to significantly improve patient survival. Thanks to the application of a variety of high-throughput technologies, accumulating big data enables researchers and clinicians to identify aggressive tumors as well as patients with a high risk of cancer metastasis. However, there have been few large-scale gene collection studies to enable metastasis-related analyses. In the last several years, emerging efforts have identified pro-metastatic genes in a variety of cancers, providing us the ability to generate a pro-metastatic gene cluster for big data analyses. We carefully selected 285 genes with in vivo evidence of promoting metastasis reported in the literature. These genes have been investigated in different tumor types. We used two datasets downloaded from The Cancer Genome Atlas database, specifically, datasets of clear cell renal cell carcinoma and hepatocellular carcinoma, for validation tests, and excluded any genes for which elevated expression level correlated with longer overall survival in any of the datasets. Ultimately, 150 pro-metastatic genes remained in our analyses. We believe this collection of pro-metastatic genes will be helpful for big data analyses, and eventually will accelerate anti-metastasis research and clinical intervention.

p53 mediates the suppression of cancer cell invasion by inducing LIMA1/EPLIN

The tumor suppressor gene p53 is frequently mutated in human cancer. p53 executes various functions, such as apoptosis induction and cell cycle arrest, by modulating transcriptional regulation. In this study, LIM domain and Actin-binding protein 1 (LIMA1) was identified as a target of the p53 family using a cDNA microarray. We also evaluated genome-wide occupancy of the p53 protein by performing chromatin immunoprecipitation-sequencing (ChIP-seq) and identified two p53 response elements in the LIMA1 gene. LIMA1 protein levels were increased by treatment with nutlin-3a, a small molecule that activates endogenous p53. In addition, LIMA1 expression was significantly downregulated in cancers compared with normal tissues. Knockdown of LIMA1 significantly enhanced cancer cell invasion and partially inhibited p53-induced suppression of cell invasion. Furthermore, low expression of LIMA1 in cancer patients correlated with decreased survival and poor prognosis. Thus, p53-induced LIMA1 inhibits cell invasion, and the downregulation of LIMA1 caused by p53 mutation results in decreased survival in cancer patients. Collectively, this study reveals the molecular mechanism of LIMA1 downregulation in various cancers and suggests that LIMA1 may be a novel prognostic predictor and a therapeutic target for cancer.

EPLIN: a fundamental actin regulator in cancer metastasis?

Treatment of malignant disease is of paramount importance in modern medicine. In 2012, it was estimated that 162,000 people died from cancer in the UK which illustrates a fundamental problem. Traditional treatments for cancer have various drawbacks, and this creates a considerable need for specific, molecular targets to overcome cancer spread. Epithelial protein lost in neoplasm (EPLIN) is an actin-associated molecule which has been implicated in the development and progression of various cancers including breast, prostate, oesophageal and lung where EPLIN expression is frequently lost as the cancer progresses. EPLIN is important in the regulation of actin dynamics and has multiple associations at epithelial cells junctions. Thus, EPLIN loss in cancer may have significant effects on cancer cell migration and invasion, increasing metastatic potential. Overexpression of EPLIN has proved to be an effective tool for manipulating cancerous traits such as reducing cell growth and cell motility and rendering cells less invasive illustrating the therapeutic potential of EPLIN. Here, we review the current state of knowledge of EPLIN, highlighting EPLIN involvement in regulating cytoskeletal dynamics, signalling pathways and implications in cancer and metastasis.

Pooling-Based Genome-Wide Association Study Identifies Risk Loci in the Pathogenesis of Ovarian Endometrioma in Chinese Han Women

Endometriosis, regarded as a complex disease, is influenced by multiple genetic factors. Recent genome-wide association studies (GWASs) in endometriosis have identified several susceptibility loci in Caucasian and Japanese populations. However, the overlapped susceptible loci were few. This case-control study tried to identify risk loci-related genes for ovarian endometrioma in Chinese Han women from central China using DNA pooling-based GWAS. Genome DNA samples were extracted from 3038 participants in central China. Pooling-based genome-wide scan and individual genotyping were performed using Affymetrix Genome-Wide Human SNP Array 6.0 and IPLEX Gold system, which demonstrated 10 ovarian endometrioma-related novel risk loci. There were 3 of them with P value < 5 × 10^-06, separately locating in intron of insulin-like growth factor 1 receptor, chromosome 7 open reading frame 50, and Meis homeobox 1. In conclusion, the pooling-based GWAS for ovarian endometrioma identified some novel single-nucleotide polymorphisms in Chinese Han women of central China. Further assessment in other samples will be crucial to confirm the susceptibility of these results and explore the mechanisms of the related genes in the pathogenesis of ovarian endometrioma.

Histone demethylase RBP2 promotes malignant progression of gastric cancer through TGF-β1-(p-Smad3)-RBP2-E-cadherin-Smad3 feedback circuit

Some feedback pathways are critical in the process of tumor development or malignant progression. However the mechanisms through which these pathways are epigenetically regulated have not been fully elucidated. Here, we demonstrated that the histone demethylase RBP2 was crucial for TGF-β1-(p-Smad3)-RBP2-E-cadherin-Smad3 feedback circuit that was implicated in malignant progression of tumors and its knockdown significantly inhibited gastric cancer (GC) metastasis both in vitro and in vivo. Mechanistically, RBP2 can directly bind to E-cadherin promoter and suppress its expression, facilitating EMT and distant metastasis of GC. RBP2 can also be induced by TGF-β1, a key inducer of EMT, through phosphorylated Smad3 (p-Smad3) pathway in GC. The upregulated RBP2 can be recruited by p-smad3 to E-cadherin promoter and enhance its suppression, contributing to the promotion of metastasis of GC. In addition, the suppression of E-cadherin by RBP2 attenuated inhibition of Smad3 phosphorylation (exerted by E-cadherin), resulting further induction of RBP2 expression, and thus constituting positive feedback regulation during GC malignant progression. This TGF-β1-(p-Smad3)-RBP2- E-cadherin-Smad3 feedback circuit may be a novel mechanism for GC malignant progression and suppression of RBP2 expression may serve as a new strategy for the prevention of tumor distant metastasis.

CRNDE Promotes Malignant Progression of Glioma by Attenuating miR-384/PIWIL4/STAT3 Axis

Colorectal neoplasia differentially expressed (CRNDE) is the most upregulated long noncoding RNA (lncRNA) in glioma. Herein, the function and potential molecular mechanisms of CRNDE and miR-384 were illustrated in glioma cells. CRNDE overexpression facilitated cell proliferation, migration, and invasion, while inhibited glioma cells apoptosis. Quantitative real-time polymerase chain reaction (PCR) demonstrated that miR-384 was downregulated in human glioma tissues and glioma cell lines. Moreover, restoration of miR-384 exerted tumor-suppressive functions. In addition, the expression of miR-384 was negatively correlated with CRNDE expression. A binding region between CRNDE and miR-384 was confirmed using luciferase assays. Moreover, CRNDE promoted cell malignant behavior by decreasing miR-384 expression. At the molecular level, treatment by CRNDE knockdown or miR-384 overexpression resulted in a decrease of piwi-like RNA-mediated gene silencing 4 (PIWIL4) protein. Besides, PIWIL4 was identified as a target of miR-384 and plays an oncogenic role in glioma. Similarly, downstream proteins of PIWIL4 such as STAT3, cyclin D1, VEGFA, SLUG, MMP-9, caspase 3, Bcl-2, and bcl-xL were modulated when treated with miR-384 and PIWIL4. Remarkably, CRNDE knockdown combined with miR-384 overexpression led to tumor regression in vivo. Overall, these results depicted a novel pathway mediated by CRNDE in glioma, which may be a potential application for glioma therapy.

Epithelial protein lost in neoplasm-α (EPLIN-α) is a potential prognostic marker for the progression of epithelial ovarian cancer

Epithelial protein lost in neoplasm-α (EPLIN-α) is a cytoskeletal protein whose expression is often lost or is aberrant in cancerous cells and tissues and whose loss is believed to be involved in aggressive phenotypes. This study examined this molecule in human epithelial ovarian tissues and investigated the cellular impact of EPLIN-α on ovarian cancer cells (EOC), SKOV3 and COV504. The expression of EPLIN-α in human ovarian tissues and EOC was assessed at both the mRNA and protein levels using reverse transcription-PCR (RT-PCR) and immunohistochemistry, respectively. In vitro assays for cellular matrix adhesion and migration (confirmed by an electrical cell substrate impedance sensing (ECIS) based method), invasion and cell growth were employed in order to assess the biological influence of EPLIN-α expression on EOC cells. Immunohistochemical analysis of ovarian cancer samples demonstrated that only a small number expressed EPLIN-α protein. Downregulation of EPLIN-α protein in EOC cell lines increased the growth, invasion, adhesion and migration in vitro. This EPLIN-α downregulation may have a prognostic value. From these data, we conclude that downregulation of EPLIN-α may be associated with poorer patient prognosis, and that this molecule appears to play a tumour suppressor role by inhibition of EOC growth and migration.

SIRT1 promotes epithelial-mesenchymal transition and metastasis in colorectal cancer by regulating Fra-1 expression

Understanding molecular mechanisms of colorectal cancer (CRC) metastasis is urgently required for targeted therapy and prognosis of metastatic CRC. In this study, we explored potential effects of silent mating type information regulation 2 homolog 1 (SIRT1) on CRC metastasis. Our data showed that ectopic expression of SIRT1 markedly increased the migration and invasion of CRC cells. In contrast, silencing SIRT1 repressed this behavior in aggressive CRC cells. Tumor xenograft experiments revealed that knockdown of SIRT1 impaired CRC metastasis in vivo. Silencing SIRT1 in CRC cells induced mesenchymal-epithelial transition (MET), which is the reverse process of epithelial-mesenchymal transition (EMT) and characterized by a gain of epithelial and loss of mesenchymal markers. We provided a mechanistic insight toward regulation of Fra-1 by SIRT1 and demonstrated a direct link between the SIRT1-Fra-1 axis and EMT. Moreover, SIRT1 expression correlated positively with Fra-1 expression, metastasis and overall survival in patients with CRC. Taken together, our data provide a novel mechanistic role of SIRT1 in CRC metastasis, suggesting that SIRT1 may serve as a potential therapeutic target for metastatic CRC.

Eradication of metastatic melanoma through cooperative expression of RNA-based HDAC1 inhibitor and p73 by oncolytic adenovirus

Malignant melanoma is a highly aggressive cancer that retains functional p53 and p73, and drug unresponsiveness largely depends on defects in death pathways after epigenetic gene silencing in conjunction with an imbalanced p73/DNp73 ratio. We constructed oncolytic viruses armed with an inhibitor of deacetylation and/or p73 to specifically target metastatic cancer. Arming of the viruses is aimed at lifting epigenetic blockage and re-opening apoptotic programs in a staggered manner enabling both, efficient virus replication and balanced destruction of target cells through apoptosis. Our results showed that cooperative expression of shHDAC1 and p73 efficiently enhances apoptosis induction and autophagy of infected cells which reinforces progeny production. In vitro analyses revealed 100% cytotoxicity after infecting cells with OV.shHDAC1.p73 at a lower virus dose compared to control viruses. Intriguingly, OV.shHDAC1.p73 acts as a potent inhibitor of highly metastatic xenograft tumors in vivo. Tumor expansion was significantly reduced after intratumoral injection of 3 × 10⁸ PFU of either OV.shHDAC1 or OV.p73 and, most important, complete regression could be achieved in 100% of tumors treated with OV.shHDAC1.p73. Our results point out that the combination of high replication capacity and simultaneous restoration of cell death routes significantly enhance antitumor activity.

p73 and IGF1R Regulate Emergence of Aggressive Cancer Stem-like Features via miR-885-5p Control

Cancer stem-like cells (CSC) have been proposed to promote cancer progression by initiating tumor growth at distant sites, suggesting that stem-like cell features can support metastatic efficiency. Here, we demonstrate that oncogenic DNp73, a dominant-negative variant of the tumor-suppressor p73, confers cancer cells with enhanced stem-like properties. DNp73 overexpression in noninvasive melanoma and lung cancer cells increased anchorage-independent growth and elevated the expression of the pluripotency factors CD133, Nanog, and Oct4. Conversely, DNp73 depletion in metastatic cells downregulated stemness genes, attenuated sphere formation and reduced the tumor-initiating capability of spheroids in tumor xenograft models. Mechanistic investigations indicated that DNp73 acted by attenuating expression of miR-885-5p, a direct regulator of the IGF1 receptor (IGF1R) responsible for stemness marker expression. Modulating this pathway was sufficient to enhance chemosensitivity, overcoming DNp73-mediated drug resistance. Clinically, we established a correlation between low p73 function and high IGF1R/CD133/Nanog/Oct4 levels in melanoma specimens that associated with reduced patient survival. Our work shows how DNp73 promotes cancer stem-like features and provides a mechanistic rationale to target the DNp73-IGF1R cascade as a therapeutic strategy to eradicate CSC.

p53 Activity Dominates That of p73 upon Mdm4 Loss in Development and Tumorigenesis

Mdm4 negatively regulates the p53 tumor suppressor. Mdm4 loss in mice leads to an embryonic lethal phenotype that is p53-dependent. Biochemical studies indicate that Mdm4 also binds p73, a member of the p53 family, with higher affinity than p53. In this study, the significance of the Mdm4 and p73 interaction in vivo during embryogenesis and tumorigenesis was examined. The data revealed that p73 loss did not rescue either the early Mdm4-deficient embryonic lethality or the runted phenotype of Mdm4(Δ2/Δ2) p53(+/-) embryos. Furthermore, studies in the developing central nervous system wherein both genes have prominent roles indicated that loss of p73 also did not rescue the Mdm4-null brain phenotype as did p53 loss. This p53 dependency occurred despite evidence for p73-specific transcriptional activity. In tumor studies, the combination of Mdm4 overexpression and p73 loss did not alter survival of mice or the tumor spectrum as compared with Mdm4 overexpression alone. In summary, these data demonstrate that the Mdm4-p73 axis cannot override the dominant role of p53 in development and tumorigenesis.

IMPLICATIONS

Genetic characterization of the Mdm4 and p73 interaction during development and tumorigenesis suggests new insight into the role of p53 family members, which may influence treatment options for patients.

Down-regulation of STAT3 expression using vector-based RNA interference promotes apoptosis in Hepatocarcinoma cells

In this study, we followed a DNA vector-based RNAi approach to silence the signal transducer and activator of transcription 3 (STAT3) expression in Bel-7402 cells, to explore how the Janus kinase (JAK)/STAT3 signaling pathway influences the apoptosis of hepatocarcinoma cells. According to GenBank's STAT3 cDNA, the plasmid pGCsi.U6/neoRFP STAT3, which was designed for expression of STAT3 small interfering RNA (siRNA), was constructed and synthesized, and then transfected into Bel-7402 cells using Lipofectamine 2000. Cells with or without siRNA transfection were treated in wells. The apoptotic rate was detected by flow cytometry (FCM) and by staining with the Annexin V/propidium iodide (PI) apoptosis detection kit. Simultaneously, the mitochondrial membrane potential (ΔΨm) was visualized by JC-1 fluorescence staining and observed using the inverted fluorescence microscope. Furthermore, the expression of caspase-3 protein was analyzed by Western blotting. The results showed that treatment with STAT3 siRNA displayed effects in the Bel-7402 cells, causing a significantly increased apoptotic ratio (P < 0.05). The mitochondrial membrane potential of the STAT3 siRNA group, observed by the JC-1 fluorescence staining, decreased significantly. The protein expression of active caspase-3 increased with STAT3 siRNA treatment, and was significantly higher than that of the control group (P < 0.05). STAT3 gene-silencing significantly improves the apoptotic effect against Bel-7402 cells.

The p53 family and the hypoxia-inducible factors (HIFs): determinants of cancer progression

HIFs have long been associated with resistance to therapy, metastasis, and poor survival rates in cancer patients. In parallel, although the tumor-suppressor p53 acts as the first barrier against tumor transformation, its inactivation also appears to be crucial for enabling cancer progression at advanced stages. p53 has been proposed to antagonize HIF, and emerging evidence suggests that the p53 siblings p63 and p73 also participate in this interplay. Crosstalk between HIFs and the p53 family acts as a determinant of cancer progression through regulating angiogenesis, the tumor microenvironment, dormancy, metastasis, and recurrence. We discuss the possible mechanisms underlying this regulation and the controversies in this field in an attempt to provide a unified view of current knowledge.

Tyr99 phosphorylation determines the regulatory milieu of tumor suppressor p73

p73 is a member of the p53 tumor suppressor family, which mediates genotoxic stress response by triggering cell cycle arrest and apoptosis. Similar to p53, p73 is maintained at very low levels, but it gets rapidly induced upon genotoxic stress. Mounting evidences demonstrate that p73 is primarily regulated posttranslationally. However, the molecular mechanisms which determine its stability and activity discerningly under normal and stress conditions are still not well understood. Here, we employed a proteomics approach to identify differential interactors of p73 under normal and genotoxic stress conditions. We report here that TRIM28, an E3 ligase, interacts with p73 and targets it for proteasomal degradation under normal conditions. Genotoxic stress-induced phosphorylation of p73 at tyrosine 99 residue by c-abl kinase leads to abrogation of this interaction thereby promoting p73 stabilization. Furthermore, the phosphorylated form of p73 specifically interacts with MED15, which serves as a transcriptional coactivator and leads to activation of proarrest, proapoptotic and anti-metastatic genes. RNAi-mediated abrogation of TRIM28 expression facilitates p73-mediated tumor suppression in mouse tumor models, whereas disruption of MED15 expression abrogates p73 tumor suppressor and anti-metastatic functions. These findings provide new insights into the pivotal role of Tyr99 phosphorylation in determining p73 levels and functions.

p73 is required for endothelial cell differentiation, migration and the formation of vascular networks regulating VEGF and TGFβ signaling

Vasculogenesis, the establishment of the vascular plexus and angiogenesis, branching of new vessels from the preexisting vasculature, involves coordinated endothelial differentiation, proliferation and migration. Disturbances in these coordinated processes may accompany diseases such as cancer. We hypothesized that the p53 family member p73, which regulates cell differentiation in several contexts, may be important in vascular development. We demonstrate that p73 deficiency perturbed vascular development in the mouse retina, decreasing vascular branching, density and stability. Furthermore, p73 deficiency could affect non endothelial cells (ECs) resulting in reduced in vivo proangiogenic milieu. Moreover, p73 functional inhibition, as well as p73 deficiency, hindered vessel sprouting, tubulogenesis and the assembly of vascular structures in mouse embryonic stem cell and induced pluripotent stem cell cultures. Therefore, p73 is necessary for EC biology and vasculogenesis and, in particular, that DNp73 regulates EC migration and tube formation capacity by regulation of expression of pro-angiogenic factors such as transforming growth factor-β and vascular endothelial growth factors. DNp73 expression is upregulated in the tumor environment, resulting in enhanced angiogenic potential of B16-F10 melanoma cells. Our results demonstrate, by the first time, that differential p73-isoform regulation is necessary for physiological vasculogenesis and angiogenesis and DNp73 overexpression becomes a positive advantage for tumor progression due to its pro-angiogenic capacity.

TAp73 suppresses tumor angiogenesis through repression of proangiogenic cytokines and HIF-1α activity

The p53-family member TAp73 is known to function as a tumor suppressor and regulates genomic integrity, cellular proliferation, and apoptosis; however, its role in tumor angiogenesis is poorly understood. Here we demonstrate that TAp73 regulates tumor angiogenesis through repression of proangiogenic and proinflammatory cytokines. Importantly, loss of TAp73 results in highly vascularized tumors, as well as an increase in vessel permeability resulting from disruption of vascular endothelial-cadherin junctions between endothelial cells. In contrast, loss of the oncogenic p73 isoform ΔNp73 leads to reduced blood vessel formation in tumors. Furthermore, we show that up-regulated ΔNp73 levels are associated with increased angiogenesis in human breast cancer and that inhibition of TAp73 results in an accumulation of HIF-1α and up-regulation of HIF-1α target genes. Taken together, our data demonstrate that loss of TAp73 or ΔNp73 up-regulation activates the angiogenic switch that stimulates tumor growth and progression.

A balancing act: orchestrating amino-truncated and full-length p73 variants as decisive factors in cancer progression

p73 is the older sibling of p53 and mimics most of its tumor-suppressor functions. Through alternative promoter usage and splicing, the TP73 gene generates more than two dozen isoforms of which N-terminal truncated DNp73 variants have a decisive role in cancer pathogenesis as they outweigh the positive effects of full-length TAp73 and p53 in acting as a barrier to tumor development. Beyond the prevailing view that DNp73 predominantly counteract cell cycle arrest and apoptosis, latest progress indicates that these isoforms acquire novel functions in epithelial-to-mesenchymal transition, metastasis and therapy resistance. New insight into the mechanisms underlying this behavior reinforced the expectation that DNp73 variants contribute to aggressive cellular traits through both loss of wild-type tumor-suppressor activity and gain-of-function, suggesting an equally important role in cancer progression as mutant p53. In this review, we describe the novel properties of DNp73 in the invasion metastasis cascade and outline the comprehensive p73 regulatome with an emphasis on molecular processes putting TAp73 out of action in advanced tumors. These intriguing insights provoke a new understanding of the acquisition of aggressive traits by cancer cells and may help to set novel therapies for a broad range of metastatic tumors.

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.

Emerging from the shade of p53 mutants: N-terminally truncated variants of the p53 family in EMT signaling and cancer progression

The prevailing view has been that N-terminally truncated p53 family isoforms (ΔNp53, ΔNp63, and DNp73) predominantly counteract cell cycle arrest and apoptosis. Recent progress in the field extend these well-known functions and place these isoforms in the center of a comprehensive regulatory network controlling major epithelial-to-mesenchymal transition (EMT)-relevant signaling pathways [such as transforming growth factor-β (TGF-β), wingless-int (WNT), insulin-like growth factor (IGF), and signal transducer and activator of transcription (STAT)], microRNAs, and EMT-associated transcription factors that promote invasion, loss of tumor cell polarity, and metastatic behavior in conjunction with a chemoresistant phenotype. These observations add new weight to the concept that currently underappreciated truncated forms of this tumor suppressor family play an equally important role in promoting cancer aggressiveness as do mutant p53 proteins, and illustrate how the consequences of ΔN/DN expression depend on cellular contexts. The tumor microenvironment contributes to the emergence of these variants, thereby linking inflammation to the activation of the mesenchymal program. In addition, molecular connections between ΔN/DN forms and self-renewal have arisen, suggesting their potential function in the generation of cancer stem cells (CSCs) from bulk tumor cells. These intriguing insights provoke a new understanding of the acquisition of aggressive traits by carcinoma cells in the absence of p53 mutations, and may help direct the development of new therapies for a broad range of cancers.

SATB2 enhances migration and invasion in osteosarcoma by regulating genes involved in cytoskeletal organization

Osteosarcoma (OS) is the most common malignant bone tumor and the majority of recurrences are due to metastasis. However, the molecular mechanisms that regulate OS metastatic spread are largely unknown. In this study, we report that special AT-rich-binding protein 2 (SATB2) is highly expressed in OS cells and tumors. Short hairpin RNA-mediated knockdown of SATB2 (sh-SATB2) decreases migration and invasion of OS cells without affecting proliferation or viability. Microarray analysis identified genes that were differentially regulated by SATB2 including the actin-binding protein Epithelial Protein Lost In Neoplasm (EPLIN), which was upregulated in sh-SATB2 cells. Silencing EPLIN rescues the decreased invasion observed in sh-SATB2 cells. Pathway analyses of SATB2-regulated genes revealed enrichment of those involved in cytoskeleton dynamics, and increased stress fiber formation was detected in cells with SATB2 knockdown. Furthermore, sh-SATB2 cells exhibit increased RhoA, decreased Rac1 and increased phosphorylation of focal adhesion kinase (FAK) and paxillin. These findings identify SATB2 as a novel regulator of OS invasion, in part via effects on EPLIN and the cytoskeleton.

Association of RHAMM with E2F1 promotes tumour cell extravasation by transcriptional up-regulation of fibronectin

Dissemination of cancer cells from primary to distant sites is a complex process; little is known about the genesis of metastatic changes during disease development. Here we show that the metastatic potential of E2F1-dependent circulating tumour cells (CTCs) relies on a novel function of the hyaluronan-mediated motility receptor RHAMM. E2F1 directly up-regulates RHAMM, which in turn acts as a co-activator of E2F1 to stimulate expression of the extracellular matrix protein fibronectin. Enhanced fibronectin secretion links E2F1/RHAMM transcriptional activity to integrin-β1-FAK signalling associated with cytoskeletal remodelling and enhanced tumour cell motility. RHAMM depletion abolishes fibronectin expression and cell transmigration across the endothelial layer in E2F1-activated cells. In a xenograft model, knock-down of E2F1 or RHAMM in metastatic cells protects the liver parenchyma of mice against extravasation of CTCs, whereas the number of transmigrated cells increases in response to E2F1 induction. Expression data from clinical tissue samples reveals high E2F1 and RHAMM levels that closely correlate with malignant progression. These findings suggest a requirement for RHAMM in late-stage metastasis by a mechanism involving cooperative stimulation of fibronectin, with a resultant tumourigenic microenvironment important for enhanced extravasation and distant organ colonization. Therefore, stimulation of the E2F1-RHAMM axis in aggressive cancer cells is of high clinical significance. Targeting RHAMM may represent a promising approach to avoid E2F1-mediated metastatic dissemination.

TP63 and TP73 in cancer, an unresolved "family" puzzle of complexity, redundancy and hierarchy

TP53 belongs to a small gene family that includes, in mammals, two additional paralogs, TP63 and TP73. The p63 and p73 proteins are structurally and functionally similar to p53 and their activity as transcription factors is regulated by a wide repertoire of shared and unique post-translational modifications and interactions with regulatory cofactors. p63 and p73 have important functions in embryonic development and differentiation but are also involved in tumor suppression. The biology of p63 and p73 is complex since both TP63 and TP73 genes are transcribed into a variety of different isoforms that give rise to proteins with antagonistic properties, the TA-isoforms that act as tumor-suppressors and DN-isoforms that behave as proto-oncogenes. The p53 family as a whole behaves as a signaling "network" that integrates developmental, metabolic and stress signals to control cell metabolism, differentiation, longevity, proliferation and death. Despite the progress of our knowledge, the unresolved puzzle of complexity, redundancy and hierarchy in the p53 family continues to represent a formidable challenge.

Restoring the tumour suppressive function of p53 as a parallel strategy in melanoma therapy

The tumour suppressor p53 is a master sensor of stress and it controls the expression of hundreds to thousands of genes with diverse biological functions including cell cycle arrest, apoptosis, and senescence. Consequently p53 is the most mutated gene found in human cancer and p53 mutation rate varies from 5% to 95%. Importantly p53 activity is often inactivated in tumours expressing structurally wild type p53. Thus one of the major challenges in cancer research is to restore the tumour suppressive function of p53. Intensive studies in the past decade have demonstrated that in addition to mutation, p53 activities are largely regulated by cellular factors that control the expression level and/or transcriptional activities of p53. MDM2, MDM4, p14(ARF) and the ASPP family of proteins are among the most studied regulators of p53. With increased understanding of the complexity of p53 regulation, various p53 reactivating approaches are being developed. This review will focus on the recent understanding of p53 inactivation in melanoma and the approaches to reactivate p53 in preclinical studies. Recent success in the therapeutic targeting of the BRAFV600E oncogenic protein was accompanied with subsequent relapse caused by acquired drug resistance. Restoration of the tumour suppressive function of p53 presents a parallel cancer therapeutic opportunity alongside BRAFV600E inhibition. Thus targeted therapy and concurrent reactivation of p53 may be a fertile ground to achieve synergistic killing of the 50% of cancer cells that express structurally wild type p53.

Epithelial plasticity: a common theme in embryonic and cancer cells

During embryonic development, many cells are born far from their final destination and must travel long distances. To become motile and invasive, embryonic epithelial cells undergo a process of mesenchymal conversion known as epithelial-to-mesenchymal transition (EMT). Likewise, EMT can be seen in cancer cells as they leave the primary tumor and disseminate to other parts of the body to colonize distant organs and form metastases. In addition, through the reverse process (mesenchymal-to-epithelial transition), both normal and carcinoma cells revert to the epithelial phenotype to, respectively, differentiate into organs or form secondary tumors. The parallels in phenotypic plasticity in normal morphogenesis and cancer highlight the importance of studying the embryo to understand tumor progression and to aid in the design of improved therapeutic strategies.