Abstract 3750: STEAP2 is upregulated and necessary for hepatocellular carcinoma progression via increased copper levels and stress-activated MAP kinase activity

Abstract

Abstract To understand potential molecular mechanisms that drive hepatocellular carcinoma (HCC) progression, we performed RNA sequencing from paired adjacent non-tumor liver and HCC tumor tissues of nine local HCC patients which revealed significant involvement of a gene coding for Six Transmembrane Epithelial Antigen of Prostate 2 (STEAP2) protein. STEAP2 is a metalloreductase involved in the reduction and indirectly, uptake, of iron and copper ions. We found significantly higher levels of total copper in HCC tissues than those in paired adjacent non-tumor tissues. The upregulation of STEAP2 expression in HCC was confirmed at its protein level and in TCGA and other published HCC gene expression datasets. Hepatic copper overload is associated with Wilson's disease and a known risk factor for HCC, therefore, we hypothesize that STEAP2 upregulation and copper accumulation contribute to HCC progression. Paired HCC and adjacent non-tumor tissues were collected for RNA sequencing, metal ion measurement, and measurements of STEAP2 levels with RT-qPCR and Western blot. Public HCC datasets were queried for STEAP2 expression in HCC and non-tumor tissues. HCC cell lines with knockdown (KD) and overexpression (OE) of STEAP2 were created to perform mechanistic studies including measurements of copper levels and MAP kinase activities, cell proliferation, migration, and anchorage independent growth in vitro and tumor growth in vivo. STEAP2 is significantly upregulated in various HCC gene expression datasets; its expression is positively associated with tumor grade. STEAP2 KD in HCC cell lines decreased cell growth, migration, invasion, and xenograft tumor growth, while STEAP2 OE showed opposite effects. STEAP2 KD in HCC cells also reduced intracellular copper levels and activation of stress-activated MAP kinases including p38 and JNK. Treatment with copper rescued the reduced HCC cell migration due to STEATP2 KD and activated p38 and JNK. Furthermore, treatment with p38 or JNK inhibitors significantly inhibited cell migration. Thus, STEAP2 appears to play a malignant-promoting role in HCC cells by driving migration/invasion via increased copper levels and MAP kinase activities. Our study uncovered a novel molecular mechanism contributing to HCC malignancy and a potential therapeutic target for HCC treatment. Citation Format: Carla R. Zeballos, Acarizia Easley, Hakim Bouamar, Guixi Zheng, Xiang Gu, Yang Junhua, Yidong Chen, Francisco Cigarroa, LuZhe Sun. STEAP2 is upregulated and necessary for hepatocellular carcinoma progression via increased copper levels and stress-activated MAP kinase activity [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3750.