LncRNA MEG3 enhances ¹³¹I sensitivity in thyroid carcinoma via sponging miR-182

Highlights

• MEG3 expression was down-regulated in ¹³¹I-resistant TC cells.

• MEG3 overexpression inhibited proliferation and induced apoptosis in ¹³¹I-resistant TC cells.

• MEG3 suppressed miR-182 expression as a molecular sponge.

• MEG3 exerted functions in ¹³¹I-resistant TC cells by regulating miR-182.

Abstract

Background

Long non-coding RNA (LncRNA) MEG3 has been demonstrated as a tumor suppressor in various cancers, including thyroid carcinoma (TC). However, the detail functions and possible mechanisms of MEG3 in ¹³¹I resistance of TC remain to be uncovered.

Methods

qRT-PCR was performed for the detection of MEG3 and miR-182 levels. ¹³¹I-resistant TC cells were constructed by continuous exposure to stepwise increased concentrations of ¹³¹I. Western blot assay was used to measure the protein expressions of γ-H2 AX and H2 AX. CCK-8 and flow cytometry assays were carried out for the evaluation of cell viability and apoptosis, respectively. Bioinformatics and dual-luciferse assays were conducted to prove the interaction of MEG3 and miR-182.

Results

MEG3 expression was down-regulated in TC tumor tissues, and the cumulative survival rate was decreased in low MEG3 expression group in TC patients under ¹³¹I treatment. MEG3 expression appeared a decline and miR-182 expression displayed an increase in ¹³¹I-resistant FTC-133 (res-FTC-133) and TPC-1 (res-TPC-1) cells. Moreover, MEG3 overexpression suppressed ¹³¹I-resistant cell viability, promoted apoptosis and induced DNA damage. MEG3 was verified as a molecular sponge for miR-182, and inhibition of miR-182 exerted similar functions as MEG3 overexpression. Furthermore, MEG3 knockdown substantially abrogated the anti-cancer functions of anti-miR-182.

Conclusions

MEG3 enhanced the radiosensitivity of ¹³¹I in TC cells via sponging miR-182, indicating that MEG3 may act as a potential biomarker and therapeutic target for TC patients with ¹³¹I resistance.

Introduction

Thyroid cancer (TC) is a prevalent malignant tumor in endocrine system with a steadily increasing morbidity and mortality worldwide in the past decades [1,2]. TC has increased by 3% annually from 1974 to 2013 in United States [3], and a similar trend is also observed in China, especially in East China [4]. Specific genetic abnormalities and environmental exposures associated with immunologic functions represent a series of possible risk factors for the occurrence of TC [5]. Radioiodine (¹³¹I) has been considered as a common strategy for the treatment of TC, with the potential of destroying the occult lesions in remnant tissues after total or near total thyroidectomy [6]. However, several patients fail to respond to radioiodine ablation therapy due to the deficiency of radioiodine aggregate ability of thyroid follicular cells. Thus, it is urgent to develop novel methods for improving the ¹³¹I therapeutic effect.

Long non-coding RNAs (LncRNAs), a novel subgroup of non-protein transcripts with larger than 200 nucleotides in length, are closely involved in the modulation of cell apoptosis, proliferation and invasion through different biological and pathological pathways [7,8]. Mounting evidence has revealed the central participation of lncRNAs in various cancers, including TC [9,10]. Maternally expression gene 3 (MEG3), a lncRNA located on chromosome 14q32, is generally expressed in human normal tissues, while it is lost or decreased in many malignancies [11]. MEG3 have been demonstrated as a tumor-suppressor to be implicated in the etiology and progression of multiple cancers [12]. For instance, MEG3 expression was down-regulated in hepatocellular carcinoma, and MEG3 overexpression blocked cell proliferation at least partly through affecting miR-664-mediated regulation of ADH4 [13]. In TC, MEG3 appeared a decreased expression, and up-regulation of MEG3 strongly weakened cell migration and invasion through negatively regulating Rac1 [14]. However, there is still short of reliable researches on the effects and mechanisms of MEG3 in ¹³¹I-resistant TC.

MicroRNAs (miRNA), a type of endogenous and conserved non-coding RNAs, have been widely reported to be associated with the occurance and development of cancers via regulation of special target genes. MiR-182, located in the region of chromosome 7q32.2 of human genome, is revealed as an oncogene in a variety of tumors, such as non-small cell lung cancer [15], prostate cancer [16], breast cancer [17], sarcomas [18], and ovarian cancer [19]. In papillary thyroid cancer (PTC), increased expression of miR-182 was observed in tumor tissues, and knockdown of miR-182 repressed cell proliferation and invasion by targeting close homolog of LI (CHL1) [20]. However, the exact roles of miR-182 in ¹³¹I-resistant TC have not been elucidated.

It has been shown that lncRNAs could act as competing endogenous RNAs or molecular sponges of miRNAs to modulate the survival and development of multiple cancer cells [21]. In the present study, we observed that MEG3 expression was significantly reduced TC tumor tissues, and low MEG3 expression was associated with an unfavorable prognosis in TC patients. Then, ¹³¹I-resistant TC cells were established successfully, and further functional researches and mechanical assays suggested that MEG3 up-regulation promoted the sensitivity of ¹³¹I treatment in TC cells through acting as a sponge for miR-182, as reflected by the depressed viability, increased apoptotic rate, and enhanced DNA damage. In all, our study contributes to a better understanding of the involvement of MEG3 in TC progression, providing a potential target for TC patients with ¹³¹I resistance.