Combination treatment with ionising radiation and gefitinib ('Iressa', ZD1839), an epidermal growth factor receptor (EGFR) inhibitor, significantly inhibits bladder cancer cell growth in vitro and in vivo

Purpose: External beam radiotherapy (EBRT) is the principal bladder-preserving monotherapy for muscle-invasive bladder cancer. Seventy percent of muscle-invasive bladder cancers express epidermal growth factor receptor (EGFR), which is associated with poor prognosis. Ionising radiation (IR) stimulates EGFR causing activation of cytoprotective signalling cascades and thus may be an underlying cause of radioresistance in bladder tumours. Materials and methods: We assessed the ability of IR to activate EGFR in bladder cancer cells and the effect of the anti-EGFR therapy, gefitinib on potential radiation-induced activation. Subsequently we assessed the effect of IR on signalling pathways downstream of EGFR. Finally we assessed the activity of gefitinib as a monotherapy, and in combination with IR, using clonogenic assay in vitro, and a murine model in vivo. Results: IR activated EGFR and gefitinib partially inhibited this activation. Radiation-induced activation of EGFR activated the MAPK and Akt pathways. Gefitinib partially inhibited activation of the MAPK pathway but not the Akt pathway. Treatment with combined gefitinib and IR significantly inhibited bladder cancer cell colony formation more than treatment with gefitinib alone (p = 0.001-0.03). J82 xenograft tumours treated with combined gefitinib and IR showed significantly greater growth inhibition than tumours treated with IR alone (p = 0.04). Conclusions: Combining gefitinib and IR results in significantly greater inhibition of invasive bladder cancer cell colony formation in vitro and significantly greater tumour growth inhibition in vivo. Given the high frequency of EGFR expression by bladder tumours and the low toxicity of gefitinib there is justification to translate this work into a clinical trial.Peer-reviewedPublisher Version1721

SIP1/ZEB2 induces EMT by repressing genes of different epithelial cell–cell junctions

SIP1/ZEB2 is a member of the δEF-1 family of two-handed zinc finger nuclear factors. The expression of these transcription factors is associated with epithelial mesenchymal transitions (EMT) during development. SIP1 is also expressed in some breast cancer cell lines and was detected in intestinal gastric carcinomas, where its expression is inversely correlated with that of E-cadherin. Here, we show that expression of SIP1 in human epithelial cells results in a clear morphological change from an epithelial to a mesenchymal phenotype. Induction of this epithelial dedifferentiation was accompanied by repression of several cell junctional proteins, with concomitant repression of their mRNA levels. Besides E-cadherin, other genes coding for crucial proteins of tight junctions, desmosomes and gap junctions were found to be transcriptionally regulated by the transcriptional repressor SIP1. Moreover, study of the promoter regions of selected genes by luciferase reporter assays and chromatin immunoprecipitation shows that repression is directly mediated by SIP1. These data indicate that, during epithelial dedifferentiation, SIP1 represses in a coordinated manner the transcription of genes coding for junctional proteins contributing to the dedifferentiated state; this repression occurs by a general mechanism mediated by Smad Interacting Protein 1 (SIP1)-binding sites

Widespread FRA1-Dependent Control of Mesenchymal Transdifferentiation Programs in Colorectal Cancer Cells

Tumor invasion and metastasis involves complex remodeling of gene expression programs governing epithelial homeostasis. Mutational activation of the RAS-ERK is a frequent occurrence in many cancers and has been shown to drive overexpression of the AP-1 family transcription factor FRA1, a potent regulator of migration and invasion in a variety of tumor cell types. However, the nature of FRA1 transcriptional targets and the molecular pathways through which they promote tumor progression remain poorly understood. We found that FRA1 was strongly expressed in tumor cells at the invasive front of human colorectal cancers (CRCs), and that its depletion suppressed mesenchymal-like features in CRC cells in vitro. Genome-wide analysis of FRA1 chromatin occupancy and transcriptional regulation identified epithelial-mesenchymal transition (EMT)-related genes as a major class of direct FRA1 targets in CRC cells. Expression of the pro-mesenchymal subset of these genes predicted adverse outcomes in CRC patients, and involved FRA-1-dependent regulation and cooperation with TGFβ signaling pathway. Our findings reveal an unexpectedly widespread and direct role for FRA1 in control of epithelial-mesenchymal plasticity in CRC cells, and suggest that FRA1 plays an important role in mediating cross talk between oncogenic RAS-ERK and TGFβ signaling networks during tumor progression.This work was supported by project grants 1026228 and 1044168 (to A.S.D.) and Senior Research Fellowships (to R.D.H., R.B.P. and J.M.M.) from the National Health and Medical Research Council of Australia

An FBXW7-ZEB2 axis links EMT and tumour microenvironment to promote colorectal cancer stem cells and chemoresistance

Colorectal cancer (CRC) patients develop recurrence after chemotherapy owing to the survival of stem cell-like cells referred to as cancer stem-like cells (CSCs). The origin of CSCs is linked to the epithelial–mesenchymal transition (EMT) process. Currently, it remains poorly understood how EMT programmes enable CSCs residing in the tumour microenvironment to escape the effects of chemotherapy. This study identifies a key molecular pathway that is responsible for the formation of drug-resistant CSC populations. Using a modified yeast-2-hybrid system and 2D gel-based proteomics methods, we show that the E3-ubiquitin ligase FBXW7 directly binds and degrades the EMT-inducing transcription factor ZEB2 in a phosphorylation-dependent manner. Loss of FBXW7 induces an EMT that can be effectively reversed by knockdown of ZEB2. The FBXW7-ZEB2 axis regulates such important cancer cell features, as stemness/dedifferentiation, chemoresistance and cell migration in vitro, ex vivo and in animal models of metastasis. High expression of ZEB2 in cancer tissues defines the reduced ZEB2 expression in the cancer-associated stroma in patients and in murine intestinal organoids, demonstrating a tumour-stromal crosstalk that modulates a niche and EMT activation. Our study thus uncovers a new molecular mechanism, by which the CRC cells display differences in resistance to chemotherapy and metastatic potential

Fos family members: regulation, structure and role in oncogenic transformation

The members of the Fos protein family might be subdivided in two groups, according to their ability to transform rodent fibroblasts, transforming (c-Fos and FosB) and non-transforming (Fra-l and Fra-2) proteins. Members of these groups are differently activated in response to external stimuli and posses different structural features. Importantly, whilst c-Fos and FosB contain multiple transactivation modules in their N- and C-terminal parts, transactivation domains are absent in the non-transforming Fos proteins. As a result, Fra-l and Fra-2 though efficiently form dimers with the Jun proteins, are weak transcriptional activators and inhibit the c-Fos-dependent activation in transient transfection assay. The numerous experiments performed with the different Fos mutant proteins with impaired transforming ability, as well as with chimeric proteins revealed the importance of the transactivation function for transformation. Fra-1 and Fra-2 proteins albeit ineffectively triggering oncogenic transformation, are abundant in ras- and src-transformed murine and chicken fibroblasts, in neoplastic thyroid cells and in highly malignant mouse adenocarcinoma cells, which underwent mesenchymal transition. The abundance of the non-transforming Fos proteins in these systems might be mediated by a positive AP-l-dependent feedback mechanism, as well as by wnt signals. Furthermore, the manipulation of the Fra-l expression level in thyroid and mammary tumor cells modulated the transcription of several tumor progression markers and affected cell morphology and invasiveness. These recent data demonstrate a novel function of non-transforming Fos proteins in the maintenance and progression of the transformed state. Interestingly, this function is independent of the documented invalidity of the Fra-l and Fra-2 proteins as transcriptional activators in rodent fibroblasts

The master-regulators of EMT and E-cadherin constitute a novel pathway in malignant melanoma

The master-regulators of an epithelial-mesenchymal transition (MR-EMT) have a pivotal role in the regulation of carcinoma development, promoting transformation and generating a migratory and invasive phenotype. Within epithelial cells, the ZEB proteins are co-regulated, jointly repressed by the miR-200 family of microRNAs. However, here it is demonstrated that the expression and regulation of the MR-EMT in malignant melanoma cell lines appears to be fundamentally different, with a hierarchical organisation identified. ZEB2 and SNAIL2 were found to be expressed in melanocytes, whilst ZEB1 and TWIST1 expression was acquired by a sub-set of malignant melanoma cell lines. Melanoma-initiating mutations within B-RAF and NRAS were shown to reversibly promote expression of ZEB1 and TWIST1 at the expense of ZEB2 and SNAIL2. Additionally, ZEB2 and SNAIL2 were identified up-stream of ZEB1 and TWIST1 within the MAPK signalling cascade, with ZEB2 functioning as a repressor of ZEB1. Furthermore, ZEB2 and SNAIL2 were found to positively regulate expression of MITF, a marker of melanocyte differentiation. In contrast, ZEB1 repressed expression of MITF and was the primary transcriptional repressor of E-cadherin, an adhesion molecule vital for the interaction between differentiated melanocytes and keratinocytes. Previously, within epithelial cell lines, all the MR-EMT have been identified as transcriptional repressors of E-cadherin. However, ZEB2 and SNAIL2 were co-expressed with E-cadherin within melanocytes and melanoma cell lines and, along with TWIST1, were not able to independently induce E-cadherin re-activation following repression. Surprisingly, ZEB2 became a repressor of E-cadherin in conjunction with ZEB1. Finally, E-cadherin expression was also shown to be controlled in a ZEB1-dependent manner by the transcriptional co-repressor BRG1, the ATPase subunit of the SWI/SNF chromatin remodelling complex, and by the presence of DNA methylation at the E-cadherin promoter. Indeed, DNA methylation was identified as a possible factor controlling the success rate of metastatic colonisation in melanoma cells, allowing for the dynamic re-expression of E-cadherin at the secondary site. These data demonstrate that in malignant melanoma the expression and regulation of the MREMT is fundamentally different to that of epithelial tumours, with the MR-EMT structured hierarchically, with opposing regulatory functions.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Regulation of Fos related antigen-1 (Fra-1) accumulation in human bladder cancer

Bladder cancer is one of the commoner malignancies in humans and current treatments for invasive disease typically give a five year survival rate of around fifty percent. Current chemotherapeutic agents increase survival by a small amount; clearly there is the need for improved treatments and for this, novel targets need to be identified. One putative target is the Fos family member Fos-related antigen-1 (Fra-1), which form part of the AP-1 transcription factor complex. Fra-1 is elevated in numerous human malignancies and regulates the transcription of genes involved in many aspects of the malignant process, such as migration and invasion. Regulatory control of Fra-1 has been incompletely studied to date; it is known that MAP Kinase dependent signalling can influence Fra-1 accumulation but other aspects of control are only now being elucidated. This thesis demonstrates that Fra-1 is present in the majority of bladder cancers, that it is regulated by the structure of the C-terminus and MAP Kinase dependent phosphorylation of the amino acids Ser[superscript 252] and Ser[superscript 265], and undergoes proteasomal degradation. This highlights the potential role of Fra-1 as a novel therapeutic target and provides more information on the regulation of Fra-1 which may be targeted with novel agents.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

AXL RECEPTOR IN CANCER METASTASIS AND DRUG RESISTANCE: WHEN NORMAL FUNCTIONS GO ASKEW

The TAM proteins TYRO3, AXL, and MER are receptor tyrosine kinases implicated in the clearance of apoptotic debris and negative regulation of innate immune responses. AXL contributes to immunosuppression by terminating the Toll-like receptor signaling in dendritic cells, and suppressing natural killer cell activity. In recent years, AXL has been intensively studied in the context of cancer. Both molecules, the receptor, and its ligand GAS6, are commonly expressed in cancer cells, as well as stromal and infiltrating immune cells. In cancer cells, the activation of AXL signaling stimulates cell survival and increases migratory and invasive potential. In cells of the tumour microenvironment, AXL pathway potentiates immune evasion. AXL has been broadly implicated in the epithelial-mesenchymal plasticity of cancer cells, a key factor in drug resistance and metastasis. Several antibody-based and small molecule AXL inhibitors have been developed and used in preclinical studies. AXL inhibition in various mouse cancer models reduced metastatic spread and improved the survival of the animals. AXL inhibitors are currently being tested in several clinical trials as monotherapy or in combination with other drugs. Here, we give a brief overview of AXL structure and regulation and discuss the normal physiological functions of TAM receptors, focusing on AXL. We present a theory of how epithelial cancers exploit AXL signaling to resist cytotoxic insults, in order to disseminate and relapse. Keywords: AXL; TAM receptors; epithelial-mesenchymal plasticity; drug resistance; metastasi

Characterization of Sp1, AP-1, CBF and KRC binding sites and minisatellite DNA as functional elements of the metastasis-associated mts1/S100A4 gene intronic enhancer

The mts1/S100A4 gene encodes a small acidic calcium-binding protein that is expressed in a cell-specific manner in development, tumorigenesis and certain tissues of adult mice. A composite enhancer that is active in murine mammary adenocarcinoma cells was previously identified in the first intron of the mts1/S100A4 gene. Here we present a detailed analysis of the structure and function of this enhancer in the Mts1/S100A4-expressing CSML100 and non-expressing CSML0 mouse adenocarcinoma cell lines. In CSML100 cells the enhancer activity is composed of at least six cis-elements interacting with Sp1 and AP-1 family members and CBF/AML/PEBP2 and KRC transcription factors. In addition, a minisatellite-like DNA sequence significantly contributes to the enhancer activity via interaction with abundant proteins, which likely have been described previously under the name minisatellite-binding proteins. Extensive mutational analysis of the mts1/S100A4 enhancer revealed a cooperative function of KRC and the factors binding minisatellite DNA. This is the first example of an enhancer where two nuclear factors earlier implicated in different recombination processes cooperate to activate transcription. In Mts1/S100A4-negative CSML0 cells the strength of the enhancer was 7- to 12.5-fold lower compared to that in CSML100 cells, when referred to the activities of three viral promoters. In CSML0 cells the enhancer could be activated by exogenous AP-1 and CBF transcription factors