MiR-150 promotes gastric cancer proliferation by negatively regulating the pro-apoptotic gene EGR2

Abstract

Accumulating evidence suggests small non-coding RNAs (microRNAs) play important roles in human cancer progression. In the present study, we found miR-150 was overexpressed in gastric cancer cell lines and tissues. Ectopic expression of miR-150 promoted tumorigenesis and proliferation of gastric cancer cells. Luciferase reporter assay demonstrated that EGR2 was a direct target of miR-150. Collectively, our study demonstrated that overexpression of miR-150 in gastric cancer could promote proliferation and growth of cancer cells at least partially through directly targeting the tumor-suppressor EGR2, suggesting a potential strategy for the development of miRNA-based treatment of gastric cancer.

Introduction

Gastric cancer is the second most common malignancy of tumor-related deaths worldwide, with particularly high incidences and mortality rates in eastern Asia [1]. Recently, the classical categories of oncogenes and tumor suppressor genes have been expanded to include a new family of RNAs known as microRNAs (miRNAs), which may regulate a vast number of protein-coding genes, including tumor-related genes.

MiRNAs are small non-coding RNA molecules that regulate the translation of target mRNAs. Binding of miRNAs to target mRNAs results in translational arrest and, in some instances, transcript degradation [2]. At least 1000 miRNAs have been identified in the human genome, and most of them have their genes in the non-coding regions [3]. Of all human whole genome mRNAs, approximately one-third are predicted to be miRNA targets by bioinformatics analysis [4].

MiRNAs have key roles in diverse physiological processes, including control of angiogenesis, cell differentiation, apoptosis, proliferation, and self-renewal of stem cells, and they simultaneously controlling the expression levels of hundreds of genes. Many miRNAs are highly conserved, and their deregulation is often associated with human malignancy [5], thus establishing them as a relatively new and important class of oncogenes and tumor suppressors.

High throughput technologies have been used to screen miRNAs differentially expressed between human malignancies and non-malignant samples. To date, several deregulated miRNAs have been found in numerous human cancer types, including liver, colon, breast, esophageal cancers. Among these miRNAs, miR-150, a hematopoietic cell-specific miRNA [6], was identified to affect cell proliferation in functional screening assays by Cheng et al. [7]. Over 90 miRNA inhibitors were synthesized to screen miRNAs involved in cell growth and apoptosis in HeLa and A549 cell lines. MiR-150 inhibitors down regulated cell growth in both cell lines. Interestingly, in our laboratory, we also found anti-growth effects for miR-150 inhibitors in gastric cancer cell line SGC7901 using a library of miRNA inhibitors (data unpublished). Mir-150 gene is on chromosome 19q13, and amplification of this site has been reported in patients with gastric carcinoma. Thus, it is possible that the amplification of this locus is mediated by the increased expression of mir-150 [8]. Katada et al. [8] examined the expression levels of 72 miRNAs in 42 cases of undifferentiated gastric carcinoma using quantitative real-time polymerase chain reaction, finding that the probability of survival was significantly lower in patients with high miR-150 expression levels, demonstrating the oncogenic effect of this miRNA in gastric tumors. However, little has been known about the functions and mechanisms of miR-150 in solid cancers, with the exception of a study by Zhou et al., which found that increased expression of miR-150 in endometrial cancer epithelial cells decreased levels of the pro-apoptotic P2X7 mRNA through activation of miR-150 instability target sites at the 3′-UTR-P2X7 [9].

In this study, we investigated the biological effects and the potential mechanisms of miR-150 in gastric carcinoma by examining the expression of miR-150 in stomach cancer, finding that miR-150 was up-regulated in gastric cancer compared to normal ones. Forced expression of miR-150 promoted the growth of gastric cancer cells in a series of proliferation assays both in vitro and in vivo. By bioinformatics analysis, we identified the tumor-suppressor EGR2 as a putative miR-150 target. Subsequent experiments confirmed that up-regulation of miR-150 repressed the expression of EGR2, which occurred at the translational level.