MiR-142-3p Functions As A Tumor Suppressor By Targeting RAC1/PAK1 Pathway In Breast Cancer

Objective: MicroRNAs(miRNAs)play a critical role in the tumorigenesis and development of malignancy.MiR-142-3p has been demonstrated to be implicated in the development of several tumors,however,the role of miR-142-3p in breast cancer(BC)remains elusive.The present study aimed to investigate the potential molecular mechanisms of miR-142-3p in BC through exploring its expression level and biological characteristics,providing a novel therapeutic target for the treatment of BC.Methods: 1? A total of six pairs of BC tissues and matched adjacent nontumor tissueswere collected.The normal mammary epithelial cell line MCF-10 A andhuman BC cell lines(MCF-7,MDA-MB-231,SK-BR-3)were purchasedfrom the Shanghai Institute of Cell Biology.Real-time quantitative PCR(RT-qPCR)was performed to evaluate the expression of miR-142-3p intissues and cells,respectively.2? The level of miR-142-3p was elevated by transfection with miR-142-3pmimic.Then,Cell Counting Kit-8(CCK-8),colony formation assay,cellapoptosis,wound-healing assay,transwell invasion assay and tubeformation assay were performed to investigate the function ofmiR-142-3p in BC cell lines.3? The online tools(TargetScan,DIANA tools,miRPathDB and PicTardatabases)were used to predict the potential targets of miR-142-3p.Subsequently,these targets were subjected to GO and Pathway analysisand confirmed using Luciferase reporter assay.The protein expression oftarget genes were analysed by western blot and immunohistochemistry.4? To identify RAC1 expression level by Oncomine database and toevaluate the prognostic value of miR-142-3p and RAC1 in BC patientsby Kaplan-Meier plotter database and PROGgene database,respectively.5? Tumor xenograft model in nude mice was established to evaluate thefunction of miR-142-3p in vivo.Results: 1? The levels of miR-142-3p were significantly decreased both in BCtissues and BC cell lines compared with the matched adjacent nontumortissues and the normal mammary epithelial cell,respectively(P < 0.05).2? Ectopic expression of miR-142-3p suppressed BC cell proliferation,migration,invasion and angiogenesis in vitro and inhibited tumor growthin vivo.3? Ras-related C3 botulinum toxin substrate 1(RAC1)was identified as atarget of miR-142-3p.The expression of RAC1 was significantlyupregulated in BC tissues and BC cell lines compared with the normaltissues and the normal mammary epithelial cell,respectively,which wasassociated with poor prognosis(P = 0.013).4? Exogenous expression of miR-142-3p reduced the protein levels ofRAC1 and simultaneously suppressed the epithelial-to-mesenchymal(EMT)related protein levels and the activity of PAK1 phosphorylation,while RAC1 overexpression could reverse tumor-suppressive effect ofmiR-142-3p.Conclusion: Our findings revealed that miR-142-3p could function as a tumor suppressor via targeting RAC1/PAK1 pathway in BC,suggesting a potential therapeutic target for the treatment of BC.