Cancer Letters

Cancer Letters

Volume 385, 28 January 2017, Pages 234-242
Cancer Letters

Original Article
The oncoprotein HBXIP up-regulates YAP through activation of transcription factor c-Myb to promote growth of liver cancer

https://doi.org/10.1016/j.canlet.2016.10.018Get rights and content

Highlights

  • The expression of HBXIP is positively related to that of YAP in HCC tissues.

  • HBXIP is able to up-regulate the expression of YAP in hepatoma cells.

  • HBXIP stimulates YAP promoter through activating transcription factor c-Myb.

  • HBXIP accelerates the growth of hepatoma cells through YAP.

Abstract

The oncoprotein Yes-associated protein (YAP) in Hippo pathway plays crucial roles in the development of cancer. However, the mechanism of YAP regulation in cancer remains poorly understood. Here, we supposed that the oncoprotein hepatitis B X-interacting protein (HBXIP) might be involved in the modulation of YAP in liver cancer. Interestingly, our data showed that the expression levels of HBXIP were positively associated with those of YAP in clinical hepatocellular carcinoma (HCC) samples by immunohistochemistry (IHC) staining and real-time PCR assays. HBXIP was able to up-regulate YAP in hepatoma cells at the levels of promoter, mRNA and protein. Mechanistically, we identified that HBXIP up-regulated YAP through co-activating the transcription factor c-Myb in hepatoma cells. Functionally, silencing YAP abolished the proliferation of hepatoma cells mediated by HBXIP in vitro. Moreover, knockdown of YAP strongly blocked the HBXIP-enhanced tumor growth in mice. Thus, we conclude that HBXIP up-regulates YAP expression via activating transcription factor c-Myb to facilitate the growth of hepatoma cells. Our finding provides new insights into the mechanism of YAP regulation. Therapeutically, the oncoprotein HBXIP and YAP might serve as targets in liver cancer.

Introduction

The dysregulation of Hippo pathway is wildly involved in the tumorigenesis [1], [2], [3], [4], in which Yes-associated protein (YAP) is able to induce the expression of pro-proliferative and anti-apoptotic genes as a transcription co-activator in the complex of TEAD family [5], [6], [7]. CTGF, CYR61 and SOX2 serve as the downstream target genes of YAP [8], [9]. A host of factors including cell density, extracellular matrix stiffness, G protein–coupled receptors and leukemia inhibitory factor receptor can influence YAP activity through modulating the Hippo pathway. The heightened expression or genomic amplification of YAP is frequently observed in many cancers [10], [11], [12], [13], [14], [15]. The highly expressed YAP is involved in multiple process of liver disease including liver repair, regeneration, hepatocellular carcinoma (HCC) [16], [17], [18]. YAP can serve as an independent prognostic marker in HCC [19]. However, the mechanism of YAP regulation in liver cancer is poorly understood.

Hepatitis B X-interacting protein (HBXIP), originally identified for interacting with hepatitis B virus X proteins, is a conserved ∼18 kDa protein among mammalian species [20]. HBXIP acts as an oncoprotein in controlling cell proliferation, apoptosis and division [21], [22], [23], [24]. HBXIP as a regulator component participates in amino acids-mediated mTORC1 activation [25]. Our group manifested that HBXIP could import into the nucleus of breast cancer cells, acting as a transcription co-activator of transcription factors such as Sp1, cAMP-response element binding protein (CREB), c-Myc and E2F1, to accelerate the progression of liver and breast cancer [26], [27], [28], [29], [30]. However, whether HBXIP is involved in the regulation of YAP in cancers is not well documented.

The transcription factor c-Myb is encoded by the MYB proto-oncogene [31], [32]. Overexpression of c-Myb contributes to malignant transformation by regulating genes participating in multiple processes of tumourigenesis, such as cell growth, angiogenesis and resistance to apoptosis [33], [34], [35], [36]. Myb is able to affect tumor cell self-renewal through the Wnt signaling pathway [37]. Recent studies have shown that c-Myb plays an important role in the development of gastric cancer (GC) [38]. The target genes of c-Myb include SOX2, Bcl-2, Bax, c-Myc, and etc [39]. However, the role of c-Myb in the regulation of YAP remains unclear.

In this study, we investigated the role of oncoprotein HBXIP in modulation of YAP in liver cancer. Interestingly, we found that HBXIP was able to up-regulate YAP through activating YAP promoter, involving co-activating c-Myb, to accelerate the growth of hepatoma cells. Our finding provides new insights into the mechanism by which HBXIP regulates YAP expression in the development of liver cancer.

Section snippets

Patient samples

Twenty-six hepatocellular carcinoma (HCC) tissue samples and their corresponding non-tumorous liver tissues were obtained from Tianjin First Center Hospital and Tianjin Tumor Hospital (Tianjin, China) after surgical resection. Written consents approving the use of tissue samples for research purposes were obtained from HCC patients. The study protocol was approved by the Institute Research Ethics Committee at Nankai University. The information of HCC patients was shown in Supplementary Table S1.

The expression of HBXIP is positively associated with that of YAP in clinical HCC tissues

Our laboratory has reported that the oncoprotein HBXIP contributes to the progression of cancer through acting as a co-activator of transcription factors [26], [27], [28], [29], [30]. Lots of studies have proven that the highly expressed YAP plays a crucial role in the development of cancer [10], [11], [12], [13], [14], [15]. Accordingly, we supposed that HBXIP might be involved in the regulation of Hippo-YAP signaling. Immunohistochemistry (IHC) staining analysis exhibited that the positive

Discussion

Hippo signaling plays pivotal roles in cell proliferation and organ size, and mounting studies have reported that this pathway is involved in the development of numerous cancers [1], [2], [3], [4], [45]. Our laboratory has reported that HBXIP, as an oncoprotein and a transcription co-activator, contributes to the development of breast cancer and liver cancer [26], [27], [28], [29], [30]. However, the effect of HBXIP on YAP in hepatocarcinogenesis is poorly understood. In this study, we

Acknowledgements

This work was supported by the grants of the National Basic Research Program of China (973 Program, No. 2015CB553905, 2015CB553703), the National Natural Scientific Foundation of China (Nos. 81372186, 81272218, 31470756, 31670771, 31670769), and Tianjin Natural Scientific Foundation (No. 14JCZDJC32800).

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