Abstract 1449: A loss-of-function shRNA library screen for the cell invasion-suppressing genes in LNCaP prostate cancer cells

Abstract

Abstract Metastasis remains the primary cause of cancer-related death. Metastasis reduces the 5-year survival rate dramatically, as observed in prostate cancer, and yet, little is known about the genes that control the metastatic process. shRNA libraries are emerging as powerful tools for the identification of genes with specific functions. Here, we describe the successful application of this functional gene-discovery system by identifying genes suppressing tumor invasion, a process that is essential for metastasis. After infecting human prostate cancer cells, LNCaP, with Decode lentiviruses encoding the entire human genomic shRNA library, highly invasive variants were selected using Matrigel invasion assays. After three cycles of selection, we isolated highly invasive clones from 7 shRNA library pools. Using DNA sequence analysis and a database search, we identified five genes previously not associated with control of tumor cell invasiveness: forkhead box O4 (FOXO4), kinesin family member 3B (KIF 3B), signal transducing adaptor molecule (SH3 domain and ITAM motif) 1 (STAM), SUMO1/sentrin specific peptidase 1 (SENP1), and Homo sapiens solute carrier family 17 (SLC17A4). Silencing of FOXO4, a member of Forkhead transcription factors family, by small interfering RNAs indeed increased invasion of LNCaP cells. Reintroducing FOXO4 decreased invasion in the highly invasive prostate cancer cell lines DU145 and CWR22v1. In order to show that increased invasiveness was not a result of a change in survival ability, apoptosis and proliferation were assessed. The results indicate that FOXO4 did not affect proliferation and apoptosis in LNCaP cells. In mammals, the FOXO family comprises four members (FOXO1, FOXO3, FOXO4 and FOXO6). Though FOXO1, 3 and 4 have previously been described as having redundant functions, it appears that FOXO4 has unique metastasis suppressor function in prostate cancer. Additionally, an analysis of web-based gene expression databanks indicates that FOXO4 typically is downregulated in metastatic lesions of breast, prostate and colon cancers when compared to primary lesions. Further characterization of these candidate genes would clarify the complex mechanisms of invasion and metastasis and might reveal new classes of therapeutic targets distinct from known metastatic genes. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1449. doi:10.1158/1538-7445.AM2011-1449