Suppressing NRIP1 inhibits growth of breast cancer cells in vitro and in vivo.

Earlier age at menarche is a major risk factor for breast cancer. Our previous study identified Nrip1 (also known as Rip140) as a candidate gene for delaying female sexual maturation (FSM) and found that knocking out Nrip1 could significantly delay FSM in mice. To investigate the effects of NRIP1 in breast cancer we used human cell lines and tissue arrays along with an in vivo study of DMBA-induced carcinogenesis in Nrip1 knockout mice. Analysis of tissue arrays found that NRIP1 is elevated in tumors compared to cancer adjacent normal tissue. Interestingly, in benign tumors NRIP1 levels are higher in the cytosol of stromal cells, but NRIP1 levels are higher in the nuclei of epithelial cells in malignancies. We also found overexpression of NRIP1 in breast cancer cell lines, and that suppression of NRIP1 by siRNA in these cells significantly induced apoptosis and inhibited cell growth. Furthermore, in vivo data suggests that NRIP1 is upregulated in DMBA-induced breast cancer. Importantly, we found that DMBA-induced carcinogenesis is suppressed in Nrip1 knockdown mice. These findings suggest that NRIP1 plays a critical role in promoting the progression and development of breast cancer and that it may be a potential therapeutic target for the new breast cancer treatments.