VGLL1 expression is associated with a triple-negative basal-like phenotype in breast cancer

Abstract

Vestigial-like 1 (VGLL1) is a poorly characterized gene encoding a transcriptional co-activator structurally homologous toTAZandYAPthat modulates the Hippo pathway inDrosophila. In this study, we examined the expression ofVGLL1and its intronic miRNA, miR-934, in breast cancer.VGLL1and miR-934 expression miRNA profiling was carried out on frozen samples of grade 3 invasive ductal carcinomas. VGLL1 protein was also examined in 433 sporadic andBRCA1-associated breast carcinomas on tissue microarrays. RNA-seq data from The Cancer Genome Atlas (TCGA) was used to confirm differences inVGLL1and miR-934 expression in different breast cancer subtypes, and to correlate their expression with that of other genes and miRNAs. Of 28 miRNAs differentially expressed in estrogen receptor (ER)-positive and ER-negative grade 3 breast carcinomas, miR-934 was most strongly upregulated in ER-negative carcinomas, and its expression was correlated with that ofVGLL1. NuclearVGLL1expression was observed in 13% of sporadic breast carcinomas, and whileVGLL1was only occasionally found in luminal A (0.70%) and B (5.60%) carcinomas, it was often expressed in HER2-positive (17%), triple-negative (TN) breast carcinomas (>40%) andBRCA1-associated TN carcinomas (>50%). These findings were confirmed in the TCGA dataset, which revealed positive associations with luminal progenitor genes (GABRP,SLC6A14,FOXC1,PROM1, andBBOX1) and strong negative correlations with ER-associated genes (ESR1,C6ORF211,GATA3, andFOXA1). Moreover,VGLL1expression was associated with reduced overall survival. In conclusion,VGLL1and miR-934 are mainly expressed in sporadic andBRCA1-associated TN basal-like breast carcinomas, and their coordinated expression, at least partially mediated by the direct modulation ofESR1, might be involved in the maintenance of a luminal progenitor phenotype.