Abstract Intestine-specific homeobox (ISX), a newly identified proto-oncogene, regulated cell proliferation and drives hepatocellular carcinoma (HCC) formation but the underlying mechanisms linking gene expression and tumor formation remain obscure. In this study, we compared the expression of MAPK (ERK1/2), E2F1 and homeobox gene ISX in 190 paired specimens of HCC and adjacent normal tissues, and also in paired specimens from 11 non-HCC patients. In pathological analysis, ERK1/2 and E2F1 , as ISX expression, exhibited a tumor-specific expression pattern and a high correlation to patient survival time, tumor size, tumor number and progression stage. Enforced expression of ERK1/2 translocated cytoplasm ISX into nucleus and increased cell proliferation by which increased downstream E2F1 expression in hepatoma cells through ISX induction. In contrast, dominant negative ERK1/2 and shRNA-mediated attenuation of ERK1/2 in hepatoma cells decreased nucleus translocation, cell proliferation and malignant transformation in vitro and in vivo. A high positive correlation existed in human hepatoma tumors between ISX and ERK1/2 expression. Together, our results highlight ERK1/2 as an important regulator of ISX in hepatoma progression with significant potential as a prognostic and therapeutic target in HCC. Citation Format: Shen-Nien Wang, Shih-Hsien Hsu. ERK1/2 regulates hepatocellular carcinoma through proinflammatory homeobox gene, ISX. [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 4709. doi:10.1158/1538-7445.AM2014-4709