Trp63 is regulated by STAT5 in mammary tissue and subject to differentiation in cancer

Abstract

Transformation-related protein 63 (Trp63), the predominant member of the Trp53 family, contributes to epithelial differentiation and is expressed in breast neoplasia.Trp63features two distinct promoters yielding specific mRNAs encoding two major TRP63 isoforms, a transactivating transcription factor and a dominant negative isoform. Specific TRP63 isoforms are linked to cell cycle arrest, apoptosis, survival, and epithelial mesenchymal transition (EMT). Although TRP63 overexpression in cultured cells is used to elucidate functions, little is known aboutTrp63regulation in normal and cancerous mammary tissues. This study used ChIP-seq to interrogate transcription factor binding and histone modifications of theTrp63locus in mammary tissue and RNA-seq and immunohistochemistry to gauge gene expression. H3K4me2 and H3K4me3 marks coincided only with the proximal promoter, supporting RNA-seq data showing the predominance of the dominant negative isoform. STAT5 bound specifically to theTrp63proximal promoter andTrp63mRNA levels were elevated upon deletingStat5from mammary tissue, suggesting its role as a negative regulator. The dominant negative TRP63 isoform was localized to nuclei of basal mammary epithelial cells throughout reproductive cycles and retained in a majority of the triple-negative cancers generated from loss of full-lengthBrca1. Increased expression of dominant negative isoforms was correlated with developmental windows of increased progesterone receptor binding to the proximalTrp63promoter and decreased expression during lactation was correlated with STAT5 binding to the same region. TRP63 is present in the majority of triple-negative cancers resulting from loss ofBrca1but diminished in less differentiated cancer subtypes and in cancer cells undergoing EMT.