ECM1 Overexpression in Bladder Cancer

Analysis of genome-wide mRNA expression data from 45 bladder cancer-derived cell lines revealed a Basal/Squamous subgroup exhibiting upregulation of extracellular matrix protein 1 (ECM1). Assessment of ECM1 at the mRNA and protein levels confirmed an ECM1-high subset of cell lines and primary tumours. Mucin 1 (MUC1) was also significantly upregulated in the ECM1-high subgroup. MUC1 expression was strongly correlation with ECM1 expression. Mining of publicly available microarray data showed significantly reduced overall survival in bladder cancer (BC) patients whose tumours expressed high levels of both ECM1 and MUC1. ECM1 knockdown cell lines were established and in vitro phenotypic assays showed that ECM1 knockdown had an inhibitory effect on wound-healing ability. A previous study in breast cancer reported that ECM1 interacts with and stabilises epidermal growth factor receptor (EGFR) enhancing Ras/Raf/MEK/ERK signalling. A direct interaction between ECM1 and EGFR could not be confirmed in ECM1- high BC-derived cell lines. Treatment of knockdown cell lines with recombinant ECM1 indicated that ECM1 initiates activation of downstream effectors in the EGFR pathway. Comparison of ECM1 knockdown and control cell lines using a phospho- receptor tyrosine kinase array showed that activation of the MET receptor is also ECM1 dependent in ECM1-high cells. Differential gene expression and pathway analysis conducted on ECM1 knockdown and control cell lines revealed that ECM1 modulates the mRNA levels of several extracellular matrix genes and genes linked to a more aggressive Basal/Squamous phenotype including the EGFR ligand amphiregulin, keratins 5 and 6, and the transcription factor ELF5. Drug sensitivity experiments targeting EGFR and mesenchymal epithelial transition factor (MET) revealed partial resistance in the ECM1 high cell lines. Comparison of the inhibitors’ effects on ECM1 KD and control cell lines indicated that high ECM1 expression alone was not influencing this lack of sensitivity and it is likely that there are multiple alternative mechanisms mediating survival in these cells.