Malat1 activates autophagy and promotes cell proliferation by sponging miR-101 and upregulating STMN1, RAB5A and ATG4D expression in glioma

https://doi.org/10.1016/j.bbrc.2017.08.070Get rights and content

Abstract

The long noncoding RNA Malat1 has been reported to be an oncogene that promotes tumor progress and correlates with prognosis in glioma. Growing evidence shows that autophagy plays a very important role in tumorigenesis and tumor cell survival, but whether Malat1 regulates autophagy in glioma is still unclear. In this study, we found that Malat1 expression and autophagy activity were significantly increased in glioma tissues compared with adjacent normal tissues. Additionally, Malat1 level was positively correlated with the expression of LC3-II (autophagy marker) mRNA in vivo. In vitro assays revealed that Malat1 significantly promoted autophagy activation and cell proliferation in glioma cells. More importantly, inhibition of autophagy by 3-MA relieved Malat1-induced cell proliferation. These data demonstrated that Malat1 activates autophagy and increases cell proliferation in glioma. We further investigated the molecular mechanisms whereby Malat1 functioned on glioma cell autophagy and proliferation. We found that Malat1 served as an endogenous sponge to reduce miR-101 expression by directly binding to miR-101. Moreover, Malat1 abolished the suppression effects of miR-101 on glioma cell autophagy and proliferation, which involved in upregulating the expression of miR-101 targets STMN1, RAB5A and ATG4D. Overall, our study elucidated a novel Malat1-miR-101-STMN1/RAB5A/ATG4D regulatory network that Malat1 activates autophagy and promotes cell proliferation by sponging miR-101 and upregulating STMN1, RAB5A and ATG4D expression in glioma cells.

Introduction

Glioma is the most frequent primary brain tumor, and associated with fatal clinical results [1]. Despite the diagnosis and treatment developments of glioma, the prognosis of glioma patients is still poor, and there is no successful treatment for highly malignant glioma [2]. Undoubtedly, a deeper understanding of the molecular mechanisms of glioma initiation and progression will contribute to develop more effective therapy for this disease.

As untranslated RNA molecules, long non-coding RNAs (lncRNAs) with more than 200 nucleotides in length have attracted increasing attention in recent years due to their crucial biological effects in tumor initiation and progression. To date, a large number of lncRNAs have been identified and their roles in cancer have been widely studied. Among these lncRNAs, Malat1, one highly conserved lncRNA amongst mammals, has been widely reported to be upregulated in various tumors, and promote tumor progress by different action mechanisms. For example in glioma, Ma et al. [3] demonstrate that Malat1 is upregulated in glioma tissues, and is associated significantly with WHO grade, tumor size, and overall survival of glioma patients. However, the specific role and molecular mechanism of Malat1 in glioma are still unclear.

Autophagy is a highly conserved catabolic process for the degradation of damaged long-lived proteins and organelles, and helps cells to survive under stressful circumstances. In recent years, increasing evidence suggests that autophagy as a self-protective mechanism can be regulated by miRNA and implicated in various physiologic and pathophysiologic processes, including cancer. For example, miR-375 inhibits autophagy and reduces viability in hepatocellular carcinoma cells under hypoxic conditions; miR-205 impairs the autophagic flux and enhances cisplatin cytotoxicity in castration-resistant prostate cancer cells; and miR-22 regulates 5-FU sensitivity by inhibiting autophagy and promoting apoptosis in colorectal cancer cells [4], [5], [6]. miRNA as small ncRNA with 18–25 nucleotides in length has been widely reported to be sponged by lncRNA and make the derepression of miRNA target, thereby playing the role. Thus, we speculate that lncRNA may participate in autophagy as a miRNA sponge. In fact, many lncRNAs have been reported to be able to regulate autophagy as a miRNA sponge. For example, lncRNA APF regulates autophagy and myocardial infarction by targeting miR-188-3p; and lncRNA HNF1A-AS1 functions as an oncogene and autophagy promoter in hepatocellular carcinoma through sponging miR-30b-5p. Malat1 has also been reported to be able to regulate autophagy in several tumors [7], [8]. However, there are few reports about the role and molecular mechanism of Malat1 on autophagy in glioma.

Here, we determined the expression level of Malat1 in glioma tissues and cell lines by quantitative Real-Time PCR (qRT-PCR), and investigated the association between Malat1 expression and glioma cell autophagy and proliferation. Furthermore, we explored the molecular mechanism whereby Malat1 exerted regulatory effects on glioma cell autophagy and proliferation.

Section snippets

Samples and cell lines

A total 32 glioma tissue and paired adjacent normal tissue specimens were collected from glioma patients receiving no preoperative chemotherapy or radiotherapy in the First Affiliated Hospital of Zhengzhou University. This study was approved by the First Affiliated Hospital ethics committee, and the written informed consent was obtained from all patients. Five human glioma cell lines U87, U118, U251, U373 and D247 were purchased from the Health Science Research Bank (Osaka, Japan). Primary

Upregulated Malat1 is relevant to increased autophagy activation in glioma tissues

Malat1 expression was determined in 32 pairs of glioma tissues and the adjacent normal tissues by using qRT-PCR. The results showed that Malat1 expression was significantly increased in glioma tissues compared with adjacent normal tissues (Fig. 1A). Meanwhile, we also determined autophagy activation in glioma tissues and normal tissues. LC3 is present predominantly in a cytoplasmic form (LC3-I) that, upon autophagy induction, is converted into an active lipidated form (LC3-II) present on

Discussion

The human transcriptome has been found to be not only a collection of protein-coding genes, but also including extensive antisense and non-coding RNA (ncRNA). Although ncRNA is initially considered as the transcriptional noise, it has become increasingly clear that ncRNAs are crucial regulators of cellular activities in various human diseases, including cancer [10], [11].

Malat1 as an oncogenic lncRNA has been reported to promote initiation and progression of many tumors by different action

Disclosure of conflict of interest

None.

References (27)

  • H. Li et al.

    Overexpression of lncRNA H19 enhances carcinogenesis and metastasis of gastric cancer

    Oncotarget

    (2014)
  • Y. Fan et al.

    TGF-β–Induced upregulation of malat1 promotes bladder cancer metastasis by associating with suz12

    Clin. Cancer Res.

    (2014)
  • Q. Ji et al.

    Long non-coding RNA MALAT1 promotes tumour growth and metastasis in colorectal cancer through binding to SFPQ and releasing oncogene PTBP2 from SFPQ/PTBP2 complex

    Brit. J. Cancer

    (2014)
  • Cited by (80)

    • Intermedin induces autophagy and attenuates hypoxia-induced injury in cardiomyocytes by regulation of MALAT1/ULK1

      2023, Peptides
      Citation Excerpt :

      Emerging evidence has illustrated that autophagy is participated in cardiovascular diseases and limits myocardial damage on infarction [32,33]. Importantly, the regulation of autophagy by MALAT1 has been revealed in several researches [34,35]. Our study proved that ULK1 was a critical molecule involved in autophagy initiation [36], and that MALAT1 functioned as a ceRNA to regulate ULK1 by competitively binding with miR-4465.

    View all citing articles on Scopus
    View full text