Several reports have shown the dysregulation of microRNAs in the early stages and development of human cancers. Considering the dysregulated expression of microRNAs in cancers, the regulation of cellular microRNA levels may be developed as a potential therapeutic approach.
Our analysis of two previous RNAseq studies (GSE117452, GSE68085) revealed that various microRNAs were significantly up-regulated in tissues from breast cancer patients compared to tissues from healthy individuals. Mainly, we concentrated on the PI3K/AKT path as one of the most vital signaling pathways included in breast cancer. Thus, miR-183 was selected from the list including microRNAs with dysregulated expression. The reason is that miR-183 can target PTEN, a key gene in the PI3K/AKT pathway, based on the bioinformatics analysis. Furthermore, according to a former work, PTEN can potentially target miR-183 in lung cancer20. In this regard, our study further proved that miR-183 can directly target PTEN via the miR-183 binding site at the 3′-UTR in breast cancer.
PTEN has a key role in tumor growth, metastasis, and invasion. PTEN can restrict survival and growth signals through the limitation of the PI3K/AKT pathway activity. By a reduction in functional PTEN, constitutive activation of downstream components of the PI3K/AKT pathway including Akt is caused, thus resulting in metastasis and tumor progression21. Therefore, down-regulation of PTEN by miR-183 may have a role in the transformation and enhanced tumor cell survival.
It is suggested that miR-183 is included in the BC pathogenesis. Moreover, it may be a biomarker for diagnosing and treating BC. Therefore, in this study the biological impact of miR-183 and the molecular mechanisms by which miR-183 modulates the behavior of breast cancer cells was investigated.
Considering the previous results, it was indicated that miR-183 might stimulate BC progression, thus revealing miR-183 as a cancer promoter. It was revealed that miR-183 overexpression led to the down-regulation of PTEN in the breast cancer cells. Our investigation was also performed on PTEN expression at the protein and mRNA levels in the MDA-MB-231 and MCF7 cells after transfection with miR-183. The findings revealed that by miR-183 overexpression in MCF7 and MDA-MB-231 cells, the expression of PTEN in mRNA and protein levels was down-regulated compared to the control group.
Moreover, MDA-MB-231 and MCF7 were utilized as an in vitro model for examining the miR-183 overexpression functional impact on cell features. The Trans-well and wound-healing assays were used to assess the migration of the breast cancer cells after miR-183 overexpression. According to the results, more MDA-MB-231 and MCF7 cells migrated in the miR-183 transfection group compared to the control group. Based on the cell cycle analysis, the number of cells in the G2 and S stages increased by transfection of the cells with miR-183. Thus, miR-183 enhanced the migration and proliferation of breast cancer cells. Moreover, the results of a luciferase reporter assay indicated that PTEN was a target gene of miR-183. The protein expression analyses of PTEN in the miR-183-treated BC cell lines further supported these results.
Similar reports were provided in various cancers. For instance, it has been shown that in several types of cancer, including gastric and colon cancer, miR-183 is overexpressed and acts as an oncogene22–24. It was also indicated that miR-183 promotes tumor development in pancreatic, prostate, and non-small cell lung cancers20,25,26. Macedo et al. found that miR-183 may play the role of an oncogene by targeting RB1 protein in MDA-MB-231 cells27. Also, miR-183 exerts oncogenic effects in breast cancer and can play an important role in the field of using anti-miRs as a cancer treatment28. Previously, it was revealed that cell proliferation, angiogenesis, and metastasis were promoted by miR-183 through negative regulation of FHL1 in BC29. Nevertheless, it might also act as a tumor suppressor in some cancer types including cervical cancer30. Tumor differentiation, metastasis, and invasion are accelerated by miR-18331,32. It is an important microRNA involved in cellular processes in cancers. According to Wang et al., PTEN is restrained by miR-183 resulting in the promotion of lung cancer20.
As we know, this is the first study to prove the regulation of breast cancer by the miR-183/PTEN pathway. It suggests that the miR-183/PTEN pathway can be considered a possible effective target in the treatment of breast cancer. It previously was reported that PTEN may act as a dual specificity phosphatase thus regulating cell growth, invasion, apoptosis, and differentiation by regulating the PI3K/AKT signaling pathway negatively. It has been known that this pathway plays a main role in several cellular functions such as adhesion, proliferation, migration, angiogenesis, metabolism, and invasion33–35.
According to our data, miR-183 can increase cell viability, accelerate cell cycle progression, and induce further migration of BC cell lines by down-regulation of PTEN. Actually, in this study, it was revealed that malignant phenotypes might be promoted by miR-183 in BC. Thus, it can be considered as a potential biomarker for early diagnosis and treatment of BC. Considering that a microRNA can target more than 100 genes36, it is expected that there are additional targets of miR-183 that have not yet been identified in different cellular systems. These genes may also contribute to metastasis and invasion. Therefore, our study shows that miR-183 targeting may be a suitable approach to prevent tumor metastasis.