Upregulation of the oncoprotein SET determines poor clinical outcomes in hepatocellular carcinoma and shows therapeutic potential

Abstract

The SET protein is a potent inhibitor of protein phosphatase 2A (PP2A). Here, we report the oncogenic role of SET in hepatocarcinogenesis, clinical aggressiveness and anti-hepatocellular carcinoma (HCC) therapeutics. By analyzing samples obtained from 147 HCC patients, we found that SET overexpression was detected specifically in 30.6% HCC tumor samples, and was significantly associated with worse clinical features and high p-Akt expression in HCC tumors. Co-expression of SET and Akt predicted shorter post-operative recurrence-free survival in this cohort (P=0.045). Furthermore, SET was significantly associated with cell growth and hepatosphere formation. To elucidate the anti-HCC potential of targeting SET, we generated a novel SET antagonist, EMQA (N(4)-(3-ethynylphenyl)-6,7-dimethoxy-N(2)-(4-phenoxyphenyl) quinazoline-2,4-diamine). EMQA enhanced PP2A activity via disrupting SET-PP2Ac (catalytic domain of PP2A) binding in HCC cells, which restored PP2A-mediated p-Akt downregulation and promoted HCC cell death. In HCC cells or recombinant proteins expressing the N- and C- truncated forms of SET, only the C-terminal SET was required for EMQA targeting. Furthermore, combining sorafenib and EMQA showed good synergism in inhibiting HCC survival. Our findings suggested the oncogenic role of SET and the adverse prognostic value of SET overexpression in HCC. This alteration defines a subgroup of HCC patients who could benefit from SET antagonists, such as EMQA.

Antagonizing SET Augments the Effects of Radiation Therapy in Hepatocellular Carcinoma through Reactivation of PP2A-Mediated Akt Downregulation

“…Our group and others have previously characterized the tumor suppressor roles of PP2A in HCC as a negative regulation of many critical oncogenic signals, such as AKT (Chen et al, 2010;Yu et al, 2014;Hung et al, 2016;Ruvolo, 2016). More interestingly, we have shown that aberrant expression of SET, a PP2A inhibitor, promoted the maintenance of HCC cells, and that antagonizing SETmediated PP2A inactivation induced apoptosis of HCC cells (Hung et al, 2016). SET is a multifunctional oncoprotein involved in a number of important cellular functions (Switzer et al, 2011;Hung and Chen, 2017).…”

“…X Phospho (Ser139) Antibody (BioLegend, San Diego, CA) was used. To validate the clinical relevance of targeting SET to enhance the anti-HCC effect of RT, we used a novel compound, EMQA, developed in our laboratory (Hung et al, 2016). For this experiment, EMQA was dissolved in dimethyl sulfoxide and then added to cells in 5% fetal bovine serum (FBS)-containing medium.…”

“…PP2A Phosphatase Activity. The PP2A activities in cancer cells and tumor tissues were determined using the PP2A activity kit obtained from Upstate Biotechnology Inc. (Lake Placed, NY) and carried out as previously described (Hung et al, 2016).…”

“…Protein phosphatase 2A (PP2A) is a major serine/ threonine phosphatase that participates in many important cellular functions, including DNA damage repair, cell survival, and cellular transformation (Mumby, 2007;Perrotti and Neviani, 2013). Our group and others have previously characterized the tumor suppressor roles of PP2A in HCC as a negative regulation of many critical oncogenic signals, such as AKT (Chen et al, 2010;Yu et al, 2014;Hung et al, 2016;Ruvolo, 2016). More interestingly, we have shown that aberrant expression of SET, a PP2A inhibitor, promoted the maintenance of HCC cells, and that antagonizing SETmediated PP2A inactivation induced apoptosis of HCC cells (Hung et al, 2016).…”

Molecular mechanisms of circular RNAs, transforming growth factor‐β, and long noncoding RNAs in hepatocellular carcinoma

“…75,76 Interestingly, SET was highly expressed in HCC and was significantly linked to adverse clinical outcomes. 77 Elsewhere, it was found that hsa_circ_0000673 enhanced HCC severity via by modulating the miR-767-3p/SET pathway. A previous study showed that hsa_circ_0067934 can increase invasion, migration, and proliferation of HCC cells.…”