PI3K/AKT signaling has a crucial role in breast cancer incidence and finding the miRNAs that regulate this pathway enhances our understanding of breast cancer regulation. Firstly, our bioinformatics analysis suggested miR-1226-3p as a bona fide regulator of HER2, PIK3R2, and AKT1 putative target genes. Secondly, RT-qPCR, ELISA test and western blotting showed that overexpression of miR-1226 was followed by reduced expression of HER2, PIK3R2, and AKT1 putative targets genes in SKBR3 cells. Third, dual luciferase assay verified direct interaction of miR-1226-3p with 3'UTR sequences of these target genes. Then, overexpression of miR-1226 in SKBR3 cells brought about increased population of sub-G1 and decreased populations of G1 cells, measured by flow cytometry. This was consistent to the reduction of p-AKT protein and increased BAX protein levels, detected by western analysis and consistent to decreased CCND1 genes expression, detected by RT-qPCR. The reduced survival and increased apoptosis rate of these cells was also verified through MTT, Annexin V-FITC and Live-Dead cell staining assays. Our results suggest that miR-1226-3p is a tumor suppressor in SKBR3 cells. However, following the overexpression of miR-1226 in MDA-MB-231 cells, Bax/Bcl2 ratio and CCND1 genes expression levels were not significantly changed, sub-G1 and G1 cell cycle population were reduced while, S and G2/M cell populations were increased, consistent to the results acquired from the apoptosis and staining assays. Finally, TCGA data analysis and RT-qPCR against 20 pairs of Normal/Tumor breast tissues indicated that miR-1226-3p has been downregulated in breast cancer. Overall, the present study gathered shreds of evidence that suggest miR-1226-3p as a tumor suppressor that exerts its inhibitory effect on SKBR3 cells through targeting of HER2, PIK3R2, and AKT1 genes and downregulates PI3K/AKT pathway.
Keywords: AKT; Breast cancer; HER2; PIK3R2; miRNA.
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