Abstract 4472: A subunit of splicing factor 3b, SF3B4, functions as driver of liver cancer via aberrant splicing activity on tumor suppressor KLF4

Alternative splicing is one of the crucial mechanism that contribute to proteome diversity and, as reported, up to 90% of genes are alternatively spliced in human. In the last few years, a large number of mRNA isoforms revealed to contribute many cellular development and disease, including cancer. SF3B4 is one of six subunits of the splicing factor 3b (SF3b) complex which is an important protein complex in U2 snRNP super complex. In this study, we show that SF3B4 expression was overexpressed in a large cohort of human hepatocellular carcinoma (HCC) patients. SF3B4 knockdown caused G1/S cell cycle arrest by recovering p27 expression and simultaneously suppressing cyclins, and CDKs in liver cancer cell. Consistently, Spliceostatin A, a SF3b complex inhibitor, also suppressed liver cancer cell growth with similar effect on cell cycle regulation. In addition, sustained suppression of SF3B4 reduced the in vivo tumor growth rate in mouse xenograft models. Furthermore, SF3B4 knockdown repressed in vitro tumor cell motility and invasion of liver cancer cells. Notably, we observed that SF3B4 knockdown increased alternative transcript splicing event of a large number of genes in liver cancer cells. From this, we found that SF3B4 knockdown caused induction of wildtype KLF4 transcript expression, and thereby exerted anti-tumor growth effect on liver cancer cells. Indeed, ectopic expression of KLF4 mimicked SF3B4 knockdown effect on same cells. Our results suggest that aberrant regulation of SF3B4 contribute to malignant transformation and growth of liver cancer cells by repression of tumor suppressor via unmodulated alternative splicing activity during liver tumorigenesis. Citation Format: Qingyu Shen, Jung Woo Eun, Hyung Seok Kim, Hee Doo Yang, Sang Yean Kim, Suk Woo Nam. A subunit of splicing factor 3b, SF3B4, functions as driver of liver cancer via aberrant splicing activity on tumor suppressor KLF4 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4472. doi:10.1158/1538-7445.AM2017-4472