Abstract 2188: A high throughput RNAi screen for regulators of thioredoxin in pancreatic cancer cells identifies components of TGFβ-signaling as inducers of thioredoxin expression

Thioredoxin (Txn), thioredoxin reductase (TxnR) and NADPH comprise a thioredoxin system which exists in nearly all living cells functioning in multi-facetted processes in mammalian cells. These include thiol-dependent thiol-disulfide exchange reactions crucial to control the redox homeostasis, cellular growth, defense against oxidative stress and control of apoptosis. Thioredoxin expression has been observed to be elevated in some types of human cancer and has been shown to confer resistance to chemotherapy or radiation-induced apoptosis. It has also been shown that elevated levels of thioredoxin contribute to the carcinogenic process and invasive phenotype of cancer. Identifying key inducers of thioredoxin expression in cancer cells will permit us to specifically target these components with the goal of improving the clinical outcome of treatment of patients with thioredoxin overexpressing cancers. Here, we describe a functional genomic screen designed to identify inducers of thioredoxin expression in which a library of 7040 small interfering RNAs (targeting human kinome and druggable genes) was screened for their ability to block the expression of endogenous thioredoxin in the pancreatic cancer cell line, MiaPaCa2. The primary screen identified numerous potential inducers of thioredoxin expression and, through the use of extensive validation of all these potential hits, yielded 21 high confidence genes that have not previously been associated with the induction of thioredoxin expression. Six of these target genes were associated with TGFβ signaling and selected for this study. Downregulation of these genes strongly inhibited the expression of endogenous thioredoxin in the MiaPaCa pancreatic cancer and other cancer cell lines. Moreover, treating MiaPaCa2 cells with TGF-β1 induced the expression of thioredoxin. TGF-β1-induced expression of thioredoxin is mediated through SMAD2, SNL2, ITGAV, ITGb3 and SP1 thus showing that our study uncovers new aspects of thioredoxin regulation. Collectively, these observations offer several insights on how thioredoxin mediates tumor growth and demonstrates the utility of large-scale RNAi screens in mammalian cells. 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 2188.