The RNA-binding protein PCBP2 facilitates gastric carcinoma growth by targeting miR-34a

https://doi.org/10.1016/j.bbrc.2014.04.124Get rights and content

Highlights

  • PCBP2 is overexpressed in human gastric cancer.

  • PCBP2 high expression predicts poor survival.

  • PCBP2 regulates gastric cancer growth in vitro and in vivo.

  • PCBP2 regulates gastric cancer apoptosis by targeting miR-34a.

Abstract

Gastric carcinoma is the fourth most common cancer worldwide, with a high rate of death and low 5-year survival rate. However, the mechanism underling gastric cancer is still not fully understood. Here in the present study, we identify the RNA-binding protein PCBP2 as an oncogenic protein in human gastric carcinoma. Our results show that PCBP2 is up-regulated in human gastric cancer tissues compared to adjacent normal tissues, and that high level of PCBP2 predicts poor overall and disease-free survival. Knockdown of PCBP2 in gastric cancer cells inhibits cell proliferation and colony formation in vitro, whereas opposing results are obtained when PCBP2 is overexpressed. Our in vivo subcutaneous xenograft results also show that PCBP2 can critically regulate gastric cancer cell growth. In addition, we find that PCBP2-depletion induces apoptosis in gastric cancer cells via up-regulating expression of pro-apoptotic proteins and down-regulating anti-apoptotic proteins. Mechanically, we identify that miR-34a as a target of PCBP2, and that miR-34a is critically essential for the function of PCBP2. In summary, PCBP2 promotes gastric carcinoma development by regulating the level of miR-34a.

Introduction

Gastric cancer is the fourth most common cancer worldwide, with a high rate of death and low 5-year survival rate [1]. Despite extensive research to identify novel diagnostic and therapeutic agents, patients with advanced gastric cancer suffer from a poor quality of life and poor prognosis, and treatment is dependent mainly on conventional cytotoxic chemotherapy [2]. To improve the quality of life and survival of gastric cancer patients, a better understanding of the underlying molecular mechanisms, and their application towards the development of novel targeted therapies, is urgently needed.

Poly(C)-binding proteins (PCBPs) are generally known as RNA-binding proteins that interact in a sequence-specific fashion with single-stranded poly(C). This family can be divided into two groups: hnRNP K and PCBP1-4. PCBPs are expressed broadly in human and mouse tissues and all members of the PCBP family are related evolutionarily. These proteins are involved mainly in various posttranscriptional regulations (e.g., mRNA stabilization or translational activation/silencing) [3]. It has been suggested that PCBPs play a critical role in carcinogenesis. hnRNP K induces transcriptional activation of the oncogenes c-SRC and c-Myc [4], [5], suggesting that hnRNPK may cooperate with additional oncoproteins to overexpress genes that promote tumor growth. PCBP1 is downregulated in metastatic cervical cancer cells [6] and metastatic breast cancer cells [7]. Knockdown of PCBP1 in the prostate cancer cell line LNCaP promotes androgen receptor (AR) protein targeting to the 3′ untranslated region of AR transcripts [8]. The recent finding that transforming growth factor-β-mediated phosphorylation of PCBP1 induced epithelial–mesenchymal transdifferentiation (EMT) [9], and the evidence that PCBP1 can down-regulate metastasis-associated PRL-3 phosphatase translation [10], indicate that PCBP1 could be a tumor suppressor. It has been suggested that PCBP2 also plays an important role in cancers such as leukemogenesis [11] and oral cancer [12]. Recently, two related reports demonstrated that PCBP2 is overexpressed in human glioma and facilitates glioma growth by targeting four-and-a-half LIM domain 3 (FHL3), which was recently shown to act as tumor suppressor [13], [14]. PCBP2 overexpression is due to the down-regulation of SIRT6, which targets to the promoter of PCBP2 and deacetylates H3K9ac [14].

However, the role of PCBPs in other cancer types, gastric carcinoma for example, remains unknown. Recently, Ghanem et al. [15] showed a specific enrichment of the RNA-binding proteins PCBP1 and PCBP2 in chief cells of the murine gastric mucosa. PCBP1/2 expression correlates with gastric gland elongation in the post-natal period. This finding indicates that PCBPs may act in gastric development and diseases. Here in this study, we show that PCBP2 is overexpressed in human gastric carcinoma and predicts poor survival. We provide evidence that PCBP2 facilitates gastric cancer growth and inhibits apoptosis by targeting miR-34a.

Section snippets

Patients

One hundred and fifty-four cases of gastric cancer with full case history and paraffin-embedded tissue between January 1997 and December 2006 were collected at Huashan Hospital, Fudan University (Shanghai). The patients included 87 (56.5%) males and 67 (43.5%) females with a mean age of 59 years. Tumors were histologically classified into 73 (47.7%) intestinal gastric cancer and 81 (52.3%) diffuse gastric cancer. The diagnosis of gastric cancer was established using World Health Organization

PCBP2 overexpresses in human gastric cancer

To study the potential participation of the PCBP family in human gastric cancer, we firstly evaluated the mRNA levels of the members of PCBP family in human normal gastric mucosa (NGM) and gastric carcinoma tissues. The results showed that the PCBP2 was significantly increased in gastric carcinoma tissues compared to NGM, whereas the mRNA levels of other members did not change (Fig. 1A). To investigate whether this significance change in PCBP2 expression also exists in a larger cohort, we

Discussion

In the present study, we evaluated the changes in expression of PBCPs in human gastric carcinoma compared to normal gastric mucosa, and found that PCBP2 was overexpressed in human gastric carcinoma. The high expression of PCBP2 predicted poor overall and disease-free survival. We further demonstrated that PCBP2 facilitated gastric cancer cell growth and transformation using in vitro and in vivo evidence. Mechanically, we showed that PCBP2 maintained the survival of gastric cancer cells and

Conflict of interest

None.

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