Cross-talk between SIM2s and NFkB regulates cyclooxygenase 2 expression in breast cancer

Abstract

BackgroundBreast cancer is a leading cause of cancer-related death for women in the United States. Thus, there a need to investigate novel prognostic markers and therapeutic strategies. Inflammation raises challenges to both treating and preventing the spread of breast cancer. Specifically, the nuclear factor kappa b (NFkB) pathway contributes to cancer progression by stimulating proliferation and preventing apoptosis. One target gene of this pathway is PTGS2, the gene that encodes for cyclooxygenase 2 (COX-2), which is upregulated in 40% of human breast carcinomas. COX-2 is an enzyme involved in inflammation. Here we investigate the effect of Singleminded 2s, a transcriptional tumor suppressor that is implicated in inhibition of tumor growth and metastasis, in regulating NFkB and COX-2.\n\nMethodsWe utilized in vitro reporter assays, immunoblot analyses, qPCR and immunohistochemical analysis to dissect the relationship between NF{kappa}B, SIM2s, and COX-2. Furthermore, we utilized COX-2 targeting strategies to determine tumor suppressive activities.\n\nResultsOur results reveal that SIM2s attenuates the activation of a NF{kappa}B via luciferase reporter assays. Furthermore, immunostaining of lysates from breast cancer cells over expressing SIM2s showed reduction in various NF{kappa}B signaling proteins, whereas knockdown of SIM2 revealed increases in the same NF{kappa}B signaling proteins. Additionally, by increasing NF{kappa}B translocation to the nucleus in DCIS.COM cells, we show that NF{kappa}B signaling can act in a reciprocal manner to decrease expression of SIM2s. Likewise, suppressing NF{kappa}B translocation in DCIS.COM cells increases SIM2s expression. We also found that NF{kappa}B/p65 represses SIM2 in via dose-dependent manner and when NF{kappa}B is suppressed the effect on the SIM2 is negated. Additionally, our CHIP analysis confirms that NF{kappa}B/p65 binds directly to SIM2 promoter site and that the NF{kappa}B sites in the SIM2 promoter are required for NFkB-mediated suppression of SIM2s. Finally, over expression of SIM2s decreases PTGS2 in vitro and COX-2 staining in vivo while decreasing PTGS2 and/or Cox-2 activity results in re-expression of SIM2. Our findings identify a novel role for SIM2s in NF{kappa}B signaling and COX-2 expression.\n\nConclusionsThese findings provide evidence for a mechanism where SIM2s may represses COX-2 expression to provide an overall better prognosis for breast cancer patients.