Effect of increased FOXA1 on gene expression in bladder cancer cells

Urothelial cell carcinoma of the bladder (UCC) is a common disease characterized by FGFR3 mutation. Whilst upregulation of this oncogene occurs most frequently in low-grade non-invasive tumors, recent data reveal increased FGFR3 expression characterizes a common sub-type of invasive UCC sharing genetic similarities with lobular breast cancer. These similarities include upregulation of the FOXA1 transcription factor and reduced expression of microRNAs-99a/100. We have previously identified direct regulation of FGFR3 by these two microRNAs and now search for further targets. Using a microarray meta-database we find potential FOXA1 regulation by microRNAs-99a/100. We confirm direct targeting of the FOXA1 3UTR by microRNAs-99a/100 and also potential indirect regulation through microRNA-485-5p/SOX5/JUN-D/FOXL1 and microRNA-486/FOXO1a. In 292 benign and malignant urothelial samples, we find an inverse correlation between the expression of FOXA1 and microRNAs-99a/100 (r=-0.33 to -0.43, p<0.05). As for FGFR3 in UCC, tumors with high FOXA1 expression have lower rates of progression than those with low expression (Log rank p=0.009). Using global gene expression and CpG methylation profiling we find genotypic consequences of FOXA1 upregulation in UCC. These are associated with regional hypomethylation and near FOXA1 binding sites, and mirror patterns previously reported in FGFR3 mutant UCC. These include gene silencing through aberrant hypermethylation (e.g. IGFBP3) and affect genes that characterize lobular breast cancer (e.g. ERBB2, XBP1). In conclusion, we have identified microRNAs-99a/100 mediate a direct relationship between FGFR3 and FOXA1, and potentially facilitate cross talk between these pathways in UCC.

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Drayton RM, Peter S, Myers K, Miah S, Dudziec E, Bryant HE, Catto JW