Abstract 3871: Analysis of gene expression patterns downstream of multiple metastatic suppressor genes.
Authors: Marino Natascia , Collins Joshua W. , Shen Changyu , Sledge George W. , Steeg Patricia S. 
Published: August 2014

In recent decades, a distinction has been made between the tumorigenesis and metastasis processes. Metastasis Suppressor Genes (MSGs) are down-regulated in the metastasis compared with the primary tumor. When re-expressed in experimental models, MSGs are able to block spread to distant sites without effecting primary tumor formation. After the discovery of the first MSG, NME1, many others have been identified. To date more than 20 genes have been described to have MSG functions. They include factors involved in cellular proliferation, motility, adhesion, invasion, resistance to apoptosis, and angiogenesis. We hypothesized that common signaling pathways mediate the effects of many MSGs. Using microarray databases of breast cancer cell lines, and siRNA down regulation of 18 MSGs in human MCF-7 breast carcinoma cells (NME1, BRMS1, CD82, CDH1, CDH2, CASP8, MKK4, MKK6, MKK7, MAPK14, GSN, ARHGDIB, AKAP12, DRG1, CD44, PEPB1, RRM1, KISS), we conducted a bioinformatic search for common pathways.

Several candidate genes were identified whose expression was inversely related to at least five MSGs. These candidates include UGT1A, PDE5A, SRMS, IL11Ralpha, DNM3, OAS1, BCAR4, and CA9, many of which are previously unknown in the metastasis literature. After stable down-regulation of each candidate gene in the highly aggressive breast cancer cell line MDA-MB-231, in vitro experiments evaluating cell proliferation and motility were performed to validate their link to the metastatic property of tumor cells. Promising data have been obtained with PDE5A. PDE5 (phosphodiesterase type 5A) is a key enzyme involved in the regulation of cGMP-specific signaling pathways in processes such as smooth muscle contraction and relaxation. PDE5A mRNA expression was upregulated by siRNA to 13 MSGs: ARHGDIB, CASP8, CD44, CDH1, CDH2, CDH11, GSN, MKK4, MKK6, MKK7, NME1, PEBP1, RRM1. Stable clones down-regulating PDE5A (MDA-MB-231 shPDE5A) were tested as described above and no difference in cell proliferation was observed, while a 58% reduction in cell motility compared to the empty vector-expressing cells was measured (p=0.0001). An experimental metastasis assay was conducted to determine if altered PDE5A expression functionally contributed to breast cancer metastasis. Tail vein injection of MDA-MB-231 shPDE5A in athymic/nude mice resulted in a 62% reduction in lung metastasis formation compared to the injection of empty-vector expressing cells (p= 0.0004). This result suggests that PDE5A is a new potential therapeutic target in breast cancer metastasis.

Citation Format: Natascia Marino, Joshua W. Collins, Changyu Shen, George W. Sledge, Patricia S. Steeg. Analysis of gene expression patterns downstream of multiple metastatic suppressor genes. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3871. doi:10.1158/1538-7445.AM2013-3871