Cap43/NDRG1 expression in breast cancer cells promotes osteolytic bone metastasis by inducing MMPs production via NF-kB activation Free

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Cap43 has been identified as a nickel-and calcium-inducible gene, which has also been referred to as Ndrg-1(Shimono 1999), Drg-1(van Belzen 1997), RTP(Kokame 1996) and RIT42(Kurdistani 1998), and has been demonstrated to be an essential factor for the maintenance of myelin sheaths in peripheral nerves in a study using Cap43-deficient mice(Okuda 2004). Cap43 is expressed is normal tissues such as prostate, ovary, colon and kidney, and Cap43 immunoreactivity is mostly found in epithelial cells (Lachat 2002). A relationship between Cap43 and the prognosis of cancer has been reported in several studies. One recent study showed that breast cancer patients with Cap43 expression had a significantly more favorable prognosis than those with reduced expression of the gene (Bandyopadhyay 2004). By contrast, it has been demonstrated that Cap43 expression gradually increase in the course of colorectal carcinogenesis (Wang 2004). Thus, it remains unclear whether Cap43 expression is associated with tumor progression and prognosis in human cancers. Since many patients with advanced breast cancers develop osteolytic bone metastasis, therapeutic strategy to reduce the incidence of bone metastasis is required to improve the quality of life. Therefore, we investigated whether decreased Cap43 expression affects the development of bone metastasis of the human breast cell line MDA-MB-231 using interfering RNA.
 By transfecting breast cancer cells with a small interfering RNA (siRNA) against human Cap43, we established two stable clones that differed in their Cap43 expression. In stable siRNA clones, Cap43 expression was reduced by>40%, and the proliferation rates were similar in all clones. we examined the role of Cap43 in the development of bone metastasis using an animal model in which nude mice received an inoculation of MDA-MB-231 human breast cancer cells into the left cardiac ventricle.
 Although control cells showed extensive metastasis to bone in mice, the number of bone metastases was significantly inhibited by knockdown of Cap43 in comparison with the control, suggesting that Cap43 activity is critical to tumor progression in MDA-MB-231 cells. Knockdown of Cap43 also suppressed the expression of MMP-1, -3 and -13, resulting in decreased invasion in cultured MDA-MB-231 cells. NF-κB has been shown previously to regulate MMPs production in breast cancer, suggesting that Cap43 may affect MMPs production at least in part directly or indirectly through interaction with NF-κB. We therefore examined whether cytoplasmic I-κB degradation was reduced by knockdown of Cap43. There was a notable reduction of I-κB degradation in knockdown of Cap43 cells.
 Cap43 plays a critical role in the development of bone metastasis of breast cancer cells through NF-kB activation and induction of MMPs production, suggesting that Cap43 may be a potent targeting gene for antimetastatic therapy in breast cancer.