Abstract 4967: ESRP1 regulated alternative splicing of CD44mRNA enhances lung colonization of metastatic cancer cell

Cancer metastasis is established by the seeding and successful colonization of stem-like cancer cells which show tumor-initiating ability at distant organs. CD44 is a cell surface marker protein which is highly expressed in stem-like cells of several human cancers including breast cancer. CD44 exists in various isoforms produced through alternative splicing of mRNA. Increased expression of CD44 variant isoform (CD44v) has been shown to correlate with metastatic potential and aggressive clinical behavior of various human cancers. We recently showed that CD44v contributes to reactive oxygen species (ROS)-defense in cancer cells by enhancing cystine uptake by the cystine transporter xCT. However, the functional relevance of CD44v and xCT in the metastatic spread of stem-like cancer cells has remained elusive. In the present study, we show that metastatic breast cancer 4T1 cells consist of CD44v+ and CD44v- cells. The orthotopic transplantation of CD44v+ population but not that of CD44v-, in mice resulted in efficient lung metastasis. We found that CD44v expressing metastatic cancer cells highly express xCT and thereby maintain high reduced glutathione (GSH) level. A specific xCT inhibitor sulfasalazine suppressed lung metastatsis of CD44v+ cells. Alternative splicing of CD44mRNA in such metastatic cancer cells is regulated by Epithelial Splicing Related Protein1 (ESRP1) and short hairpin RNA (shRNA) targeting ESRP1 switched isoform from CD44v to CD44 standard (CD44s), leading to the suppression of lung metastasis. Furthermore, we found that ESRP1 expression is regulated epigenetically through histone modification by performing chromatin immunoprecipitation (ChIP) sequencing analysis of the ESRP1 locus in CD44v+ and CD44v- cells. These findings establish a novel role of ESRP1-regulated alternative splicing program in the regulation of antioxidant status of stem-like cancer cells which is crucial for the metastatic ability. Citation Format: Kenji Tsuchihashi, Osamu Nagano, Toshifumi Yae, Takatsugu Ishimoto, Takeshi Motohara, Momoko Yoshikawa, Go J Yoshida, Takeyuki Wada, Takashi Masuko, Kaoru Mogushi, Hiroshi Tanaka, Tsuyoshi Osawa, Yasuharu Kanki, Takashi Minami, Hiroyuki Aburatani, Mitsuyo Ohmura, Akiko Kubo, Makoto Suematsu, Kazuhisa Takahashi, Eishi Baba, Koichi Akashi, Hideyuki Saya. ESRP1 regulated alternative splicing of CD44mRNA enhances lung colonization of metastatic cancer cell. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4967. doi:10.1158/1538-7445.AM2014-4967