RNA binding protein RBMS3 is a common effector of EMT program that promotes Triple-Negative Breast Cancer Progression by Regulation of PRRX1 mRNA Stability

The epithelial-to-mesenchymal transition (EMT) has been recognized as a driving force for tumor progression in breast cancer. Recently, our group identified the RNA Binding Motif Single Stranded Interacting Protein 3 (RBMS3) to be significantly associated with an EMT transcriptional program in breast cancer. Additional expression profiling demonstrated that RBMS3 was consistently upregulated by multiple EMT transcription factors and correlated with mesenchymal gene expression in breast cancer cell lines. Functionally, RBMS3 was sufficient to induce EMT in two immortalized mammary epithelial cell line. In triple-negative breast cancer (TNBC) models, RBMS3 was necessary for maintaining the mesenchymal phenotype and invasion and migration in vitro. Loss of RBMS3 significantly impaired both tumor progression and spontaneous metastasis in vivo. Using a genome-wide approach to interrogate mRNA stability, we found that ectopic expression of RBMS3 upregulates many genes that are resistant to degradation following transcriptional blockade by actinomycin D. Specifically, RBMS3 was shown to interact with the mRNA of EMT transcription factor PRRX1 and promote PRRX1 mRNA stability. PRRX1 is required for RBMS3-mediated EMT and is partially sufficient to rescue the effect of RBMS3 knockdown in TNBC cell lines. Together, this study identifies RBMS3 as a novel and common effector of EMT, which could be a promising therapeutic target for triple-negative breast cancer treatment. RBMS3 is a protein that binds to RNA and contributes to RNA stability. However, what genes stability are controlled by RBMS3 remains unknown. The treatment of Actinomycin D (ACTD) is expected to result in RNA degradation. We treated the HMLE/LacZ (control/reference) and HMLE/RBMS3 (over-expression) cell models with ACTD at four different time points (0, 90, 180 and 360 minutes), three replicates for each, and tried to identify the genes whose stability is controlled by RBMS3.