MicroRNA-143 functions as a tumor suppressor in human esophageal squamous cell carcinoma

Abstract

Esophageal cancer is one of the most common cancers worldwide with a poor prognosis. MicroRNAs(miRNAs) are a class of naturally occurring small noncoding RNAs and play an important role in cancer initiation and development. In this study, we demonstrate that the expression levels of miR-143 and miR-145 were significantly decreased in ESCC tissues in comparison with adjacent normal esophageal squamous tissues(NESTs). Furthermore, an inverse correlation between miR-143 and tumor invasion depth and lymph node metastasis was observed. The enforced expression of miR-143 induced growth suppression and apoptosis of ESCC cells. Rescue of miR-143 significantly suppressed the ESCC cells migration and invasion capabilities. Moreover, we show that functions of miR-143 in ESCC are mediated at least in part by the inhibition of extracellular signal regulated kinase-5(ERK-5) activity. These results prove that miR-143 may act as a tumor suppressor in ESCC.

Introduction

Esophageal cancer is one of the most common cancers worldwide with a variable geographic distribution and ranks eighth in order of occurrence and is the sixth leading cause of cancer mortality, affecting men more than women (Enzinger and Mayer, 2003). It has two main forms, esophageal squamous cell carcinoma (ESCC) and adenocarcinoma, each with distinct etiologic and pathologic characteristics. At present ESCC is the most predominant form worldwide, adenocarcinoma of the esophagus though is increasing at an alarming rate in Western Europe and the United States (Blot and McLaughlin, 1999). Because most cases of ESCC are diagnosed at an advanced stage, the prognosis for patients is poor despite the development of therapeutic options such as surgery, chemotherapy and radiotherapy. Research over the last two decades has identified a variety of oncogenic and tumor-suppressor proteins which are associated with the induction of ESCC (Gratas et al., 1998, Hollstein et al., 1990, Hu et al., 2004, Jiang et al., 1993, Mizushima et al., 2002, Shih et al., 2000). However, to date, efforts to identify accurate molecules that regulate the initiation and progression of ESCC have elucidated only a few molecular mechanisms.

MicroRNAs(miRNAs) are a class of naturally occurring small (21–25 nucleotides) noncoding RNAs which can block the translation of specific messenger RNA by binding through complementary target sequences of the mRNAs (Alvarez-Garcia and Miska, 2005, Bartel, 2004, Croce and Calin, 2005, McManus, 2003, Mendell, 2005). Mature miRNAs play important regulatory roles in processes such as differentiation, proliferation, and apoptosis (Ambros, 2004, Chen et al., 2004). Furthermore, some miRNAs may function either as oncogenes or tumor suppressors. Specifically, miRNA-143 and miRNA-145, which are transcribed as the same primary miR at chromosome 5q33, are often down-regulated in colon, gastric and other cancers (Akao et al., 2006, Akao et al., 2007b, Takagi et al., 2009, Tong et al., 2009, Wang et al., 2008). Previous studies showed that the 5q was one of the most common region of loss in ESCC, which predicts that it may harbor novel tumor suppressor genes (Chang et al., 2010, Hu et al., 2000, Moskaluk et al., 1998, Pack et al., 1999). Furthermore, miRNA-143 was idetified as a putative cancer suppressor in bladder cancer (Lin et al., 2009), colorectal cancer (Zhang et al., 2012) and B-cell malignancies (Akao et al., 2007a). In addition, miRNA-143 has been found to directly target multiple mRNAs of KRAS (Chen et al., 2009, Suzuki et al., 2009), ELK1 (Cordes et al., 2009), MYO6 (Szczyrba et al., 2010), Bcl-2 (Zhang et al., 2010) and ERK5 (Akao et al., 2009), which then are involved in the pathogenesis of cancers.

However, the expression levels and functions of miRNA-143 and miRNA-145 in ESCC tissue and cells are still under debate (Akagi et al., 2011, Kano et al., 2010), indicating that they may play diverse roles in the carcinogenesis of ESCC. Moreover, the impact of miRNA-143 to its most widely reported direct targets-RAS, Bcl-2 and ERK5 in ESCC is still unknown. In the present study, we confirmed the decreased expression levels of miRNA-143 in ESCC patients tissue samples as well as ESCC cell lines. Our results provided evidences that miRNA-143 overexpression could markedly reduce human esophageal cancer cell growth in vitro, causing increased tumor cell apoptosis and decreased proliferation. In addition, miRNA-143 overexpression significantly inhibited ESCC cells invasion and migration with a marked decrease in ERK5 levels but relatively stable RAS and Bcl-2 levels.