Hypoxia-Induced MALAT1 Promotes the Proliferation and Migration of Breast Cancer Cells by Sponging MiR-3064-5p.

Chung-Hsien Shih,Mong-Hsun Tsai,Li-Han Chen,Liang-Chuan Lai,Eric Y Chuang,Tzu-Pin Lu,Li-Ling Chuang

doi:10.3389/fonc.2021.658151

Abstract

Hypoxia, a common process during tumor growth, can lead to tumor aggressiveness and is tightly associated with poor prognosis. Long noncoding RNAs (lncRNAs) are long ribonucleotides (>200 bases) with limited ability to translate proteins, and are known to affect many aspects of cellular function. One of their regulatory mechanisms is to function as a sponge for microRNA (miRNA) to modulate its biological functions. Previously, MALAT1 was identified as a hypoxia-induced lncRNA. However, the regulatory mechanism and functions of MALAT1 in breast cancer are still unclear. Therefore, we explored whether MALAT1 can regulate the functions of breast cancer cells through miRNAs. Our results showed the expression levels of MALAT1 were significantly up-regulated under hypoxia and regulated by HIF-1α and HIF-2α. Next, in contrast to previous reports, nuclear and cytoplasmic fractionation assays and fluorescence in situ hybridization indicated that MALAT1 was mainly located in the cytoplasm. Therefore, the labeling of MALAT1 as a nuclear marker should be done with the caveat. Furthermore, expression levels of miRNAs and RNA immunoprecipitation using antibody against AGO2 showed that MALAT1 functioned as a sponge of miRNA miR-3064-5p. Lastly, functional assays revealed that MALAT1 could promote cellular migration and proliferation of breast cancer cells. Our findings provide evidence that hypoxia-responsive long non-coding MALAT1 could be transcriptionally activated by HIF-1α and HIF-2α, act as a miRNA sponge of miR-3064-5p, and promote tumor growth and migration in breast cancer cells. These data suggest that MALAT1 may be a candidate for therapeutic targeting of breast cancer progression.

Highlights

Several studies have confirmed that the tumor microenvironment promotes cancer progression in many ways, especially via therapeutic resistance
Since metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) was significantly up-regulated under hypoxia, we hypothesized that this effect was triggered by hypoxiainducible factors (HIFs)
Overexpression of HIF-1A (Figure 2F) or HIF-2A (Figure 2G) both increased the luciferase activity, and the HRE site mutation significantly (P < 0.05) decreased both luciferase activities (Figures 2F, G). These results indicate that both HIF-1a and HIF-2a up-regulate the transcriptional levels of MALAT1 by binding to the HRE in its promoter

Summary

Introduction

Several studies have confirmed that the tumor microenvironment promotes cancer progression in many ways, especially via therapeutic resistance. Hypoxia is a common feature of malignant tumors [1] It has been described as a complicated incident of the tumor microenvironment that promotes tumor aggressiveness and metastasis [2, 3], and is strongly associated with poor prognosis [4, 5]. Most of the HIF-dependent responses rely on changes in the expression of genes associated with angiogenesis, proliferation, epithelial to mesenchymal transition, and metastasis [9]. These changes allow malignant cells to survive the harsh hypoxic environment. The details of how hypoxia leads to tumor progression remain to be identified

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