Elsevier

Gene

Volume 700, 5 June 2019, Pages 85-95
Gene

Research paper
MiR-155-3p acts as a tumor suppressor and reverses paclitaxel resistance via negative regulation of MYD88 in human breast cancer

https://doi.org/10.1016/j.gene.2019.02.066Get rights and content

Highlights

  • miR-155-3p was a novel tumor-suppressor by targeting MYD88.

  • miR-155-3p showed a negative effect on apoptosis, invasion and metastasis by suppression of the corresponding target gene MYD88 in vitro and vivo.

  • miR-155-3p/MYD88 has important roles in cancer cell resistance to chemotherapy drugs.

Abstract

MiR-155-3p, which is derived from the same pre-miRNA as miR-155-5p, the latter has been reported to be dysregulated in multiple tumor tissues and associated with clinicopathologic markers, tumor subtypes, and poor survival rates. However, the biological effects of miR-155-3p are rarely explored. In this study, we find that miR-155-3p was down-regulated in breast cancer and MYD88 was validated as the target for miR-155-3p. Moreover, miR-155-3p showed a negative effect on apoptosis, invasion and metastasis, reverses paclitaxel resistance by suppression of the corresponding target gene MYD88 in vitro and in vivo experiments. Taking together, our studies suggest that miR-155-3p, which serve as a negative regulatory mechanism for breast cancer development. The mechanism further complicates the regulatory network in human breast cancer.

Introduction

Breast cancer is considered one of the leading causes of cancer deaths worldwide. The high morbidity and mortality of most breast cancers is due to the huge potential for metastatic and uncontrolled growth of in situ tumors (Jemal et al., 2011; Scully et al., 2012). Cancer cells promote tumor rapid proliferation by up-regulating oncogenes and down-regulating of tumor suppressor genes, which is an important mechanism for high risk of malignant tumors (Krifa et al., 2013). MicroRNA (miRNA) is a class of short endogenous single-stranded non-coding RNA that is incompletely or completely complementary to the 3′-noncoding region of the target mRNA, resulting in specifically degradation or translation-inhibiting of the target gene, regulating gene expression, proliferation, polarization, apoptosis and other biological processes. miR-3p and miR-5p are produced by the same precursor RNA structure, however, both are diverse in their direct target genes and expression levels (Masaya et al., 2016; Chiang et al., 2010; Jian and Li, 2016; Kong et al., 2014; Almeida et al., 2014). Because of the Pre-miRNA hairpin structure has a certain double chain nature, resulting in the mature arms have a certain potential combination with different target mRNAs, producing different effects. Some recent studies have reported the abnormal function of miRNAs in various tumors, including several cancer types. Several studies have reported that the different biological activities of two mature miRNA arms from the same pre-miRNA hairpin structure in different tissues or cells (Fornari et al., 2010; Guo et al., 2010; Jiang et al., 2010). Usually, the RNA-induced silencing complex (RISC) happens asymmetrically, with one of the tapes being preferably incorporated while the other would be released into the cytoplasm and degraded, which led to the use of the terms guide chain (miRNA) and transient chain (miRNA*). The most accepted mechanism for determination of the dominant preferentially incorporated into the miRISC and consequently accumulated in larger levels is the thermodynamic model of stability asymmetry in the 5′ region between two ripe tapes. According to this model, the miRNA presenting a lower stability of the 5′ region in the dimer would provide the most favorable for incorporation into the silencing complex, regardless of its location 5p or 3p (Khvorova et al., 2013; Schwarz et al., 2003). However, several studies have begun to bring to light aspects in the biology of miRNAs that question the universality of this selection model. By using PCR analysis or largescale analysis, such as sequencing of small RNAs and use of databases, some authors identified the prevalence in different tissues and stages of embryonic development of mice and two species of insects in the conserved miRNA family miR100/10 (Griffiths-Jones et al., 2011). Studies of comparative genomics have revealed the conservation of miRNA* and complementary sequences in possible target mRNA, indicating the existence of a selective pressure for maintenance (Okamura et al., 2008; Yang et al., 2011). In addition, functional analysis with target validation, gain and loss of function and verification incorporation into miRISC have already proven the physiological importance of miRNA*, which act independently of their sister band, regulating different targets. Those points out that the substitution of the miRNA/miR RNA* nomenclature, based on the opposite functional tape/transient tape, giving preference to the use of the terms miR-5p and miR-3p (Li et al., 2014; Zhou et al., 2010).

MiR-155 can be processed from sequences presented in BIC RNA and accumulated in lymphocytes. It has been reported that miR-155-5p, as a clinically relevant marker of breast cancer, high levels of mir-155-5p predict higher adverse survival rates in several types of tissue subtypes (Kong et al., 2010; Chen et al., 2012). MiR-155-3p, which is cleaved from the same pre-miRNA as miR-155-5p, has never been studied before in breast cancer. In this study, we explored the biological functions of miR-155-3p in vitro and in vivo. Specifically, the expression of miR-155-3p was significantly down-regulated in breast cancer paclitaxel-resistant cell line MCF-7/PR compared to the corresponding cell line MCF-7. Furthermore, we demonstrated that miR-155-3p positively regulated cell apoptosis, inhibited invasion and metastasis by targeting MYD88. Finally, we constructed a xenograft model in vivo, miR-155-3p shows some potential in inhibiting tumor growth. In addition, we demonstrated that miR-155-3p treatment could sensitize paclitaxel-resistant breast cancer cells. Therefore, our data provided evidence that miR-155-3p acts as a tumor suppressor via MYD88 inhibition in breast cancer cells and a novel therapeutic tool for paclitaxel-resistant breast tumor.

Section snippets

TCGA data analysis

TCGA (The Cancer Genome Atlas - Cancer Genome) (https://cancergenome.nih.gov/) was used to identify differential expression of miR-155-3p for 1207 corresponding breast cancer patients (1103 Primary Solid Breast Tumor and 104 Solid Normal Tissue) and of MYD88 for 1109 Breast cancer tissues and 113 normal breast tissues from the TCGA Data portal.

Clinical specimens

Ten freshly frozen breast cancer tissues and ten paired adjacent normal breast tissue were collected from The First Affiliated Hospital of Bengbu Medical

The expression of miR-155-3p was down-regulated in breast cancer

In order to determine the differential expression levels of miR-155-3p in clinical pathology, as shown in Fig. 1A, specifically, miR-155-3p was significantly down-regulated in 1103 primary breast solid tumor compared with 104 solid tissue normal from the TCGA Data portal (P < 0.0001). Similarly, the Real-time PCR analysis showed that miR-155-3p was significantly downregulated in 10 paired fresh breast cancer tissues compared to paired paracancerous tissue as described in Fig. 1B (P < 0.01) and.

Discussion

Carcinogenesis involves a variety of genetic and epigenetic events, but its detailed regulatory mechanisms are poorly understood. In contrast to the abnormal expression of miRNAs in cancerous tissues, microRNA (miRNA) dysregulation has been considered as an important part of the landscape (Martin et al., 2016; Croce, 2012). The hairpin structure of pre-miRNAs derives two arm miR-3p and miR-5p during maturation. However, the functional mechanisms mediated by both arms of miRNA in RNA

Acknowledgments

The work was supported by the Key Program of College Discipline (major) Top-notch Talent Academic Subsidize of Anhui (No. gxbjZD27), the Key Program of college discipline (major) top-notch talent academic subsidize of Anhui (2017H110), the Major Program of Anhui Educational Committee (KJ2015ZD29, KJ2016SD37), and Scientific Research Foundation of Bengbu Medical College (BYKY1810ZD), Bengbu Municipal Scientific Research Key Projects (No. 20150309) as well as the program for graduates research of

Disclosure statement

The authors declare that they have no competing interests.

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