miR-155 is an oncogenic microRNA which is upregulated in many solid cancers. The targets of miR-155 are well established, with over 100 confirmed mRNA targets. However, the regulation of miR-155 and the basis of its upregulation in cancer is not well understood. We have previously shown that miR-155 is regulated by p63, and here we investigate the role of the major p63 isoforms TAp63 and ΔNp63 in this regulation. When the TAp63 isoform was knocked down, or exogenously overexpressed, miR-155 levels were elevated in response to TAp63 knockdown or reduced in response to TAp63 overexpression. The ΔNp63 isoform is shown to directly bind to the p63 response element on the miR-155 host gene, and this binding is enriched when TAp63 is knocked down. This could indicate that TAp63 prevents ?Np63 from binding to the miR-155 host gene. The knockdown of TAp63, and the subsequent elevation of miR-155, enhances migration and tumour growth similar to that seen when directly overexpressing miR-155. The migratory phenotype is abrogated when miR-155 is inhibited, indicating that miR-155 is responsible for the phenotypic effect of TAp63 knockdown.
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