The novel mTOR inhibitor Torin-2 induces autophagy and downregulates the expression of UHRF1 to suppress hepatocarcinoma cell growth

Abstract

Mammalian target of rapamycin (mTOR) is frequently upregulated in hepatocellular carcinoma (HCC). Blockage of mTOR was found to induce marked reduction in HCC growth in preclinical models. In the present study, we tested a novel mTOR inhibitor, Torin-2, for its antitumor efficacy in HCC cell lines Hep G2, SNU-182 and Hep 3B2.1-7. The HCC cell lines were cultured in vitro. These cells were treated with Torin-2. Cell apoptosis was evaluated by Annexin V staining. Cell proliferation and cell cycle progression were determined by Ki67 staining and propidium iodide staining, respectively. mTOR signaling, autophagy induction and expression of ubiquitin-like containing PHD and RING finger domains 1 (UHRF1) were assessed by western blot analysis. The UHRF1 mRNA level was determined by real-time PCR. We found that Torin-2 effectively suppressed the growth and survival of HCC cell lines, demonstrated by reduced proliferation and a high rate of apoptosis. Further study elucidated that in addition to blocking mTOR complex 1 (mTORC1)-associated cell cycle progression and induction of autophagy, Torin-2 downregulated transcription of UHRF1, an essential regulator of DNA methylation that is highly expressed in HCC cell lines. Consistently, the level of DNA (cytosine-5)-methyltransferase 1 (DNMT1) was higher after treatment of the HCC cell lines with Torin-2. The downregulation of UHRF1 by Torin-1 was partially due to a decrease in the UHRF1 mRNA level. Torin-2 effectively inhibited HCC cell proliferation through induction of autophagy. Torin‑2-induced downregulation of UHRF1 expression may also contribute to its antitumor effect. Our research provides new clues regarding the antitumor effects of Torin-2 and sheds light on a novel therapeutic approach for HCC.

Evaluation of uttroside B, a saponin from Solanum nigrum Linn, as a promising chemotherapeutic agent against hepatocellular carcinoma

“…Reports indicate that the mammalian target of rapamycin (mTOR) pathway is abnormally activated in a proportion of HCC patients and inhibition of mTOR can suppress liver tumor growth and metastasis212223. Moreover, an up-regulation of mTOR is frequently observed in cholangiocarcinoma, the second most common primary cancer of the liver.…”

Loss of AIM2 expression promotes hepatocarcinoma progression through activation of mTOR-S6K1 pathway

“…mTOR, as a central sensor for cell nutrient and growth, provides a pivotal link between environmental risk factors and the cellular damage that initiates the inflammatory and regenerative responses leading to liver cancer [22–24]. Aberrant activation of mTOR-S6K1 signaling results in several aspects of dysregulation which may lead to liver cancer.…”

Downregulation of UHRF1 increases tumor malignancy by activating the CXCR4/AKT-JNK/IL-6/Snail signaling axis in hepatocellular carcinoma cells

“…However, further studies are warranted to define the differences between upregulation and downregulation of UHRF1 in increasing migratory and invasive properties of cancer cells. UHRF1 upregulation was recently suggested to play a crucial role in the occurrence of primary hepatocellular carcinoma by acting as an oncogene 47, 48 . Furthermore, this upregulation can promote cellular proliferation by reducing either the transcriptional or protein level of tumor suppressors regulating cell growth 41, 49, 50 .…”