Sorafenib suppresses growth and survival of hepatoma cells by accelerating degradation of enhancer of zeste homolog 2

Abstract

Enhancer of zeste homolog 2 (EZH2) is a mammalian histone methyltransferase that contributes to the epigenetic silencing of target genes that regulate cancer cell growth and survival. It is overexpressed in hepatocellular carcinoma (HCC) with a clinical significance that remains obscure. Sorafenib, a multikinase inhibitor, has been used as a first-line therapeutic drug and shown clinical efficiency for advanced-stage HCC patients. In the present study, we found that sorafenib lowered the protein level of EZH2 through accelerating proteasome-mediated EZH2 degradation in hepatoma cells. Overexpression of EZH2 reversed sorafenibinduced cell growth arrest, cell cycle arrest, and cell apoptosis dependent on histone methyltransferase activity in hepatoma cells. More importantly, shRNA-mediated EZH2 knockdown or EZH2 inhibition with 3-deazaneplanocin A treatment promoted sorafenib-induced hepatoma cell growth arrest and apoptosis. Sorafenib altered the hepatoma epigenome by reducing EZH2 and H3K27 trimethylation. These results revealed a novel therapeutic mechanism underlying sorafenib treatment in suppressing hepatoma growth and survival by accelerating EZH2 degradation. Genetic deletion or pharmacological ablation of EZH2 made hepatoma cells more sensitive to sorafenib, which helps provide a strong framework for exploring innovative combined therapies for advanced-stage HCC patients. (Cancer Sci 2013; 104: 750-759) P rimary liver cancer, predominantly hepatocellular carcinoma (HCC), is a major public health problem worldwide and the third most common cause of cancer-related mortality globally.(1) One of the main reasons for the high mortality rate in patients with HCC is the lack of effective therapeutic options, especially for those with advanced disease.(2) Potentially curative therapies like surgical resection, transplantation, and percutaneous ablation are only available to limited patients with early HCC.(3) Moreover, the majority of patients with HCC present with advanced disease due to the asymptomatic nature of early HCC, lack of awareness, and poorly defined clinical screening strategies.(4) The paucity of effective and well-tolerated treatments for advanced HCC highlights the desperate need for new therapeutic approaches for this deadly disease.The absence of standard systemic therapy for patients with advanced HCC has changed with the recent positive randomized controlled trial testing sorafenib, which represents a breakthrough in the management of this neoplasm.(5) The unprecedented results of a recently published phase III clinical trial show that sorafenib significantly improves survival and time to progression in patients with advanced HCC.(5) Unfortunately, less than half of patients with advanced-stage HCC benefit from these therapies, and the benefits are transient resulting from quickly acquired adaptive resistance to sorafenib treatment.(6) These benefits and challenges highlight the importance of underlying molecular mechanism exploration for sorafenib treatment and novel oncogenic mechanism i...

New knowledge of the mechanisms of sorafenib resistance in liver cancer

“…Studies have demonstrated that the expression of some histone methyltransferases, such as EZH2 [59] , contribute to the epigenetic silencing of target genes that regulate cancer cell growth and survival, which have been associated with sorafenib resistance of HCC cells. EZH2 knockdown or EZH2 inhibition treatment promoted sorafenib-induced hepatoma cell growth arrest and apoptosis.…”

Polycomb-mediated loss of microRNA let-7c determines inflammatory macrophage polarization via PAK1-dependent NF-κB pathway

“…Protein extraction from cultured cells or tissues, immunoblotting, and immunoprecipitation were carried out as previously described. 31,51 Antibodies used here included those against GAPDH, PAK1, EZH2, H3K27me3, p300, HDAC-1, H3K9me3, and H3K4me3 (Santa Cruz Biotechnology, Santa Cruz, CA, USA). Chromatin immunoprecipitation was carried out with the ChIP Assay Kit (Millipore, Billerica, MA, USA) according to instructions.…”

NFAT5 inhibits invasion and promotes apoptosis in hepatocellular carcinoma associated with osmolality

“…Risk factor for HCC are mainly HBV infection, HCV infection, excessive alcohol consumption, and dietary exposure to aflatoxin [3]. Current treating methods, such as surgical resection, radiofrequency ablation (RFA) and transhepatic arterial chemotherapy and embolization (TACE) only control the patient with early HCC [4]. Thus the early diagnosis and early treatment is critical for HCC patients.…”