Elsevier

Gene

Volume 594, Issue 1, 5 December 2016, Pages 160-164
Gene

Research paper
PRAME is critical for breast cancer growth and metastasis

https://doi.org/10.1016/j.gene.2016.09.016Get rights and content

Highlights

  • Knockdown of PRAME promotes breast cancer cell proliferation and inhibits apoptosis.

  • Inhibition of PRAME promotes the invasion of breast cancer cells.

  • Suppression of PRAME increases tumor initiation.

Abstract

Breast cancer is the most common cause of cancer death in women and ranks second among cancer deaths. Metastasis is the main cause of death in breast cancer patients. However, the mechanisms underlying the invasion and metastasis of breast cancer cells remain largely elusive. Here we report that the protein PRAME, a tumor-associated antigen isolated from a melanoma, plays a role in preventing the proliferation and metastasis of breast cancer cells. Knocking down of PRAME promotes breast cancer cell proliferation and inhibits apoptosis. In addition, inhibition of PRAME promotes the invasion of breast cancer cells. To further examine the role of PRAME in vivo, we utilized mouse model and found the volume and the weight of tumors was markedly increased after PRAME was knocked down. This study demonstrates that PRAME functions as a tumor suppressor in breast cancer.

Introduction

Breast cancer is the most frequently diagnosed cancer in women worldwide with nearly 1.7 million new cases diagnosed in 2012, accounting for 25% of all new cancer cases in women. An estimated 521,900 breast cancer deaths occurred in women in 2012 (Torre et al., 2015). Although once primarily considered a disease of Western women, more than half of new breast cancer cases and deaths occur in economically developing countries. In developed countries, many breast cancers are caught early and prognosis is often very good. By contrast, in economically developing countries, breast cancers are often diagnosed after the disease has progressed and survival is poorer (Ferlay et al., 2015, Torre et al., 2015).

Metastasis is the spread of tumor cells to tissues and the metastatic cascade is composed of three main processes: invasion, intravasation and extravasation. A large number of molecular and cell-biological events are involved in each of these processes (Valastyan and Weinberg, 2011). Epithelial-mesenchymal transition (EMT) has been the favored explanation of distant metastases for epithelial cancers including breast cancer (Kalluri and Weinberg, 2009). Loss of E-cadherin decreases the strength of cellular adhesion and cellular polarity of epithelial cells and promotes the cell migration (Onder et al., 2008). The expression of E-cadherin is under the control of a variety of signaling molecules including transforming growth factor-β (TGF-β) and epidermal growth factor (EGF). The pathologic evidence of EMT in human cancer tissue samples has not yet been well established. It has been commonly believed that EMT may theoretically contribute to breast tumor metastasis (Armstrong et al., 2011, Yu et al., 2013). Similar studies also detected EMT markers such as Twist and Vimentin in circulating tumor cells from early and metastatic breast cancer patients (Kallergi et al., 2011, Papadaki et al., 2014).

The protein PRAME was initially detected as a tumor-associated antigen in cells isolated from a melanoma, and high PRAME expression has been detected in 88–95% of primary melanomas (Ikeda et al., 1997).

PRAME encodes a putative protein of 509 amino acids, and its function is still unknown. PRAME has found to be an absent or low expression in most normal tissues tested, such as CD34 + sorted bone marrow cells or sorted B and T lymphocytes (Abdelmalak et al., 2014, Mitsuhashi et al., 2014). It was reported that PRAME was expressed not only in solid tumors but also in leukemia cells (Hermes et al., 2016). High levels of PRAME are found in malignant cells, such as primary and metastatic melanomas (Haqq et al., 2005), Hodgkin's lymphoma (Ercolak et al., 2015), and neck squamous cell carcinomas (Atanackovic et al., 2006). However, it was reported that PRAME's expression was associated with reduced proliferation of KG-1 leukemic cells (Tajeddine et al., 2005). PRAME promotes in vitro leukemia cell ls death by regulating S100A4/p53 signaling recently (Xu et al., 2016). Therefore, PRAME functions depending on the different genetic or epigenetic mechanisms. Although some reports have linked PRAME gene expression data to clinical information (Epping et al., 2008), the function and mechanism of PRAME in breast cancer is still elusive.

In this study, we demonstrated that knockdown of PRAME decreased the expression of E-cadherin and promoted the proliferation of breast cancer cells. Subsequently, the migration and invasion of breast cancer cells were enhanced after PRAME inhibition. Knocking down PRAME downregulated E-cadherin, suggesting that it serves as a tumor suppressor of breast cancer.

Section snippets

Cell culture and RNA interference

MCF-7 and MDA-MB-231 cells were purchased from ATCC. They were cultured in DMEM and MEM in a humidified atmosphere of 95% air and 5% CO2 at 37 °C. The MDA-MB-231 stable cell lines were generated by integration of retroviral shRNA vectors specific for PRAME or a control gene.

The transfection reagent TransExcellent-siRNA was purchased from Cenji Biotech. (Shanghai, China) 2 μg of total RNA was transcribed into cDNA with M-MLV reverse transcriptase (Invitrogen) following the manufacturer's

Knockdown of PRAME promotes breast cancer cell proliferation and inhibits apoptosis

To investigate the role of PRAME in breast cancer cells, we tested the effect of PRAME knockdown on breast cancer proliferation. As shown in Fig. 1A, 3 days after the PRAME siRNA transfection with two independent hairpins(1#/2#), the PRAME expression was significantly reduced in MCF-7 cells compared with that in control cells along with an increased level of PCNA which was as a proliferation marker. Next, we chosen one PRAME siRNA(1#) for additional experiment. The proliferation was

Discussion

In the present study, we analyzed the potential role of PRAME in breast cancer using in vitro and in vivo model. We demonstrate that PRAME functions as a tumor suppressor for breast tumorigenesis. Inhibition of the expression of PRAME by siRNA dramatically increased the proliferation of breast cancer cells. In addition, inhibition of PRAME promotes the invasion of breast cancer cells. Furthermore, the data of in vivo mouse model indicated that the volume and weight of tumors were markedly

Conflict of interest

There is no conflict of interest.

Acknowledgment

This study was funded by the grant from National Natural Science Foundation of China (81401837) and the Science and Technology Commission of Shanghai Municipality (16QA1401500) for financial support.

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    1

    These authors contributed equally to this work.

    2

    Authors for correspondence with equal contribution.

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