Identification of New Tumor Suppressor Genes in Triple-Negative Breast Cancer.

Although genomic sequencing has provided a better understating of the genetic landmarks in triple-negative breast cancer (TNBC), functional validation of candidate cancer genes (CCG) remains unsolved. In this study, we used a transposon mutagenesis strategy based on a two-step sleeping beauty (SB) forward genetic screen to identify and validate new tumor suppressors (TS) in this disease. We generated 120 siRNAs targeting 40 SB-identified candidate breast cancer TS genes and used them to downregulate expression of these genes in four human TNBC cell lines. Among CCG, whose SB-mediated genetic mutation resulted in increased cellular proliferation in all cell lines tested, the genes , and showed TS activity in tumor xenograft studies. Subsequent studies showed that ZNF326 regulated expression of multiple epithelial-mesenchymal transition and cancer stem cell (CSC) pathway genes. It also modulated expression of TS genes involved in the regulation of migration and cellular invasion and was a direct transcriptional activator of genes that regulate CSC self-renewal. ZNF326 expression associated with TNBC patient survival, with ZNF326 protein levels showing a marked reduction in TNBC. Our validation of several new TS genes in TNBC demonstrate the utility of two-step forward genetic screens in mice and offer an invaluable tool to identify novel candidate therapeutic pathways and targets. .