The novel oncogenic roles of SET and the therapeutic potential of SET antagonist in cancer

• Main Authors: Man-Hsin Hung, 洪曼馨
• Other Authors: Chung-Wai Shiau
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/95195207361712390736

博士 === 國立陽明大學 === 分子醫學博士學位學程 === 104 === SET protein is known as a potent PP2A inhibitor; however, its role related to tumorigenic potential has not yet been fully discussed. In my PhD dissertation, I explored the roles of SET in promoting carcinogenesis, clinical aggressiveness and the development of treatment resistance in hepatocellular carcinoma (HCC) and non-small cell lung cancer (NSCLC). First, by affecting the expression of SET, I showed that SET was significantly associated with the proliferation, colony formation and the ability of forming tumor sphere of both HCC and NSCLC. Notably, the expression level of SET also determined the sensitivity of cancer cells to chemotherapy and radiotherapy in HCC and NSCLC; silencing SET enhanced the pro-apoptotic effects of paclitaxel, while ectopic expression of SET diminished the effects to both chemotherapy and radiotherapy. Meanwhile, the clinical significance of SET expression in HCC and NSCLC was investigated by immunehistochemical studies. By analyzing tumor samples obtained from 147 HCC and 53 NSCLC patients, we found that SET expression was a recurrent event that specifically occurred in the tumor parts than the normal adjacent tissues. Furthermore, overexpression of SET was significantly associated with worse clinical features and high p-Akt expression in tumors. Moreover, co-overexpression of SET and Akt defined a subgroup of patients with worse clinical outcome. To elucidate the anti-cancer potential on targeting SET, I applied a novel SET antagonist, EMQA, developed in our lab for subsequent experiments. EMQA enhanced PP2A activity via disrupting SET-PP2Ac binding in cancer cells, which restored PP2A-mediated p-Akt downregulation and promoted cell death in HCC and NSCLC. To dissect the critical site for EMQA functioning, I generated several truncated SET proteins. By analyzing the effects of EMQA on the binding affinities of different truncated SET proteins to PP2A-catalytic subunits, we revealed that the 227-277 amino-acid sequence located in the C-terminal of SET protein is critical for EMQA-induced SET inhibition. Since the SET protein was shown to affect therapeutic sensitivity of cancer cells, I tested the effecting of combining EMQA to current standard-of-treatment, namely paclitaxel in NSCLC and sorafenib in HCC. First in NSCLC, both the in vitro and in vivo experiments suggested that EMQA and paclitaxel combination treatment was synergistic. On the other hand, combining sorafenib and EMQA also showed good synergism in inhibiting HCC survival in vitro and in vivo. Importantly, we found that downregulating p-Akt by inhibiting SET-mediated protein phosphatase 2A (PP2A) inactivation determined the pro-apoptotic effects of EMQA in combining with paclitaxel or sorafenib. Our findings suggested the oncogenic role of SET and the adverse prognostic value of SET overexpression in HCC and NSCLC. This alteration defines a subgroup of cancer patients who could benefit from SET antagonists, such as EMQA.