Exosomal PD-L1 harbors active defense function to suppress T cell killing of breast cancer cells and promote tumor growth

Abstract MicroRNAs (miRNAs) are 21–23-nucleotide, short, non-coding RNAs that play important roles in virtually all biological pathways in mammals and other multicellular organisms. The association of miR-221 and miR-222 (miR-221/222) for breast cancer is critical, but their detailed roles in its development and progression remain unclear. In the present study, we found that miR-221/222 were consistently up-regulated in breast cancer tissues. We then investigated the molecular mechanisms by which miR-221/222 contributed to breast cancer and identified growth arrest–specific transcript 5 (GAS5) as a direct target gene of miR-221/222. In contrast with the up-regulated expression levels of miR-221/222, GAS5 levels were significantly down-regulated and negatively correlated with miR-221/222 in breast cancer tissues. In addition, we showed that miR-221/222 inhibitors increased cellular apoptosis, miR-221/222 mimics decreased the cell apoptosis in breast cancer cells, and restoration of GAS5 expression attenuated the anti-apoptotic effects of miR-221/222 in breast cancer cells, indicating that GAS5 was a direct mediator of miR-221/222 function. Finally, we showed that miR-221/222 suppressed GAS5 expression significantly and enhanced tumor growth in a mouse model of breast cancer xenografts. The present study highlighted the important role of miR-221/222 as oncomiRs in breast cancer, which inhibited GAS5 translation. These findings may provide a new perspective for the molecular mechanism of breast carcinogenesis and provide a novel approach to the treatment of breast cancer.

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

Frontiers in Oncology ◽

10.3389/fonc.2021.658151 ◽

2021 ◽

Vol 11 ◽

Author(s):

Chung-Hsien Shih ◽

Li-Ling Chuang ◽

Mong-Hsun Tsai ◽

Li-Han Chen ◽

Eric Y. Chuang ◽

...

Keyword(s):

Breast Cancer ◽

Tumor Growth ◽

Cancer Cells ◽

Cancer Progression ◽

Breast Cancer Cells ◽

Cellular Migration ◽

Expression Levels ◽

Promote Tumor Growth ◽

Rna Immunoprecipitation ◽

And Migration

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.

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