Abstract B53: Differential functions of splicing factors in breast-cancer initiation and metastasis (2013)

Abstract Cancer cells often display aberrant profiles of alternative splicing, leading to the production of isoforms that can stimulate cell proliferation and migration, increase resistance to apoptosis, or alter cell metabolism. Recently, recurrent somatic mutations in components of the splicing machinery have been identified in human tumors, raising a new interest in the field and suggesting that alterations in splicing factors are a new hallmark of cancer. Splicing factors elicit changes in splicing in a concentration-dependent manner. Thus, changes in the expression of these proteins, as reported in different types of cancers, can affect the splicing of multiple genes and are likely involved in splicing deregulation in cancer, even in the absence of mutations. We previously demonstrated that the splicing factor SRSF1'formerly SF2/ASF' is often upregulated in human breast cancers and can transform mammary epithelial cells in vivo and in vitro. SRSF1 is a prototypical member of the SR protein family, composed of 12 members sharing structural similarities. However, little is known about differences and redundancies in their splicing targets and thus in their specific biological functions. We are now investigating wherever additional splicing factors can promote mammary epithelial cell transformation by using models that mimic the correct biological context in which tumors arise. We have mined data from a large collection of human breast tumors and cancer cell lines to identify splicing factors overexpressed at the transcript and protein levels. We then compared the ability of 10 selected splicing factors to transform human mammary epithelial MCF-10A cells grown in organotypic 3-D culture. Under these conditions, the cells undergo a 16-day differentiation program, forming growth-arrested, hollow acinar structures with polarized architecture, similar to the terminal units of mammary ducts. Various oncogenes associated with breast cancer are known to disrupt acinar growth and/or architecture. We assessed how splicing-factor overexpression affects cell proliferation and apoptosis, as well as cell migration and invasion. Interestingly, only certain splicing factors are oncogenic in this context, suggesting functional differences. Furthermore, specific splicing factors increase cell migration and invasion but are unable to promote transformation. We have demonstrated specificity in splicing-factor mediated transformation, and we are now investigating what are the relevant splicing targets for transformation by several of these oncogenic splicing factors. Furthermore, we are investigating which splicing factors are necessary or sufficient to promote cell invasion and metastatic potential in human breast cancer cell lines in vitro and in vivo. Finally, we have identified splicing factors that cooperate specifically with the MYC oncogene and are significantly co-expressed with MYC in human breast tumors. By identifying oncogenic splicing factors that can promote breast cancer, and their downstream effectors, we hope to establish candidate targets for therapeutics development based on the modulation of oncogenic splicing events and their regulators. Citation Format: Olga Anczukow, Kuan-Ting Lin, Martin Akerman, Shipra Das, Senthil K. Muthuswamy, Adrian Krainer. Differential functions of splicing factors in breast-cancer initiation and metastasis. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr B53.