Abstract 1794: TXNL2 is a key regulator of reactive oxygen species levels and NF-κB activity in cancer cells

Abstract

Abstract Cancer cells usually generate and maintain higher levels of reactive oxygen species (ROS) compared to normal cells, in part because of their higher metabolic rate and defects in the electron transport chain. Because most tumor cells possess stronger antioxidative defense mechanisms to counterbalance excessive ROS, redox proteins such as thioredoxins (TRXs) and glutaredoxins (GRXs) are potential targets of anticancer therapy. We recently found that a novel redox protein called thioredoxin-like 2 (TXNL2) is required for embryonic stem cell functions and is consistently overexpressed in many different cancers. It has a TRX-homology domain and two GRX-homology domains, suggesting that it may have redox function. Using immunohistochemical and cDNA microarray analyses, we found that levels of TXNL2 were significantly higher (P = 0.00036) in human breast cancers than in normal breast tissues; levels also were higher in human breast cancer cell lines than in normal mammary epithelial cell lines. Knockdown of TXNL2 by shRNA in breast cancer cell lines induced a 5-fold increase of ROS levels and inhibited cell proliferation, survival, invasion, and the expression of genes critically involved in these cellular processes. Breast cancer stem-like cell populations and stem-like properties such as mammosphere formation were reduced by TXNL2 silencing and induced by TXNL2 overexpression. Surprisingly, TXNL2 depletion in normal mammary epithelial cells did not significantly affect ROS levels and cell survival. Xenograft models of orthotopic injection indicated that TXNL2 knockdown inhibited mammary tumor growth and metastasis to the lung. Cell signaling studies showed that TXNL2 knockdown inhibited GSH synthase (GSS) expression, and thereby decreased GSH levels and increased ROS levels; N-acetylcysteine (NAC), a GSH precursor, partially reversed these effects. In addition, TXNL2 knockdown suppressed NF-κB activity by inactivating IKK and p65 via glutathionylation, whereas TXNL2 overexpression markedly increased NF-κB activity. Blockade of NF-κB using its small-molecule inhibitors and IκB overexpression mimicked the effect of TXNL2 depletion. Our results suggest that TXNL2 is a potentially promising target for ROS-based anticancer therapies and is a key regulator of the NF-κB pathway. Because high cellular antioxidant capacity is well-known to impair cellular responses to chemotherapy and radiation therapy, our study may also open up a new avenue of maximize the efficacy of conventional anticancer therapies by targeting TXNL2. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1794.