MiR-3614-5p Downregulation Promotes Cadmium-Induced Breast Cancer Progression By Targeting TXNRD1

Background: Cadmium(Cd)is widely used in industrial production.It’s easy to discharge into natural environment with industrial wastewater and waste gas.Cd exposure in non-occupational population is mainly through diet and smoking.In recent years,with the acceleration of modernization and the rapid development of industrial production,Cd pollution has become increasingly serious.Environmental chronic Cd exposure is one of the most important risk factors for breast cancer(BC).Current studies reported that Cd-induced BC was mainly through DNA damaging,cell cycle dysregulation,abnormal DNA methylation and non-coding RNA dysregulation.Importantly,previous study indicated that some microRNAs might play an important role in Cd-induced BC progression and metastasis.However,the exact mechanisms in Cd-induced BC still remains unclear.Purpose: To investigate the role and expression of miRNAs in cadmium-induced breast cancer progression and metastasis.Methods: MCF-7 and T-47 D cell lines were treated with different concentrations of Cd(0.1,1 and 10μM)for 24 h,48h or 72 h.MMTV-Erbb2 [mouse mammary tumor virus(MMTV)-Erbb2] mice were exposed to 3.6 mg Cd/L drinking water from 6 until 29 weeks of age to evaluate the tumorigenesis and metastasis of Cd in vivo.Cell proliferation was detected by CCK-8 assay,and cell migration and invasion ability were detected by Transwell.Mi R-seq was performed on Cd-exposed BC cells to screen out differentially expressed miRNAs.RNA-seq sequencing was used for finding the potential target gene of miR-3614-5p.RT-PCR and luciferase assay were used to verify the relationship between miR-3614-5p and its target genes.Ki67 density and TXNRD1 protein level were investigated via immunofluorescence and immunoblotting.H&E staining was used to determine the lung and liver metastasis of BC.Result: Cd exposure enhanced BC cell proliferation,migration and invasion in vitro,and miR-3614-5p was the top downregulated miRNA of Cd-treated T-47 D cells(10μM,72 h)were analyzed by miRNA-seq.Moreover,miR-3614-5p mimic transfection significantly decreased the proliferative ability,migration and invasive ability of BC cell lines(T-47 D and MCF-7).Furthermore,we analyzed the overlapping genes from our RNA-seq data and predicted targets from the mir DIP database,and twelve genes(ALDH1A3,FBN1,GRIA3,NOS1,PLD5,PTGER4,RASGRF2,RELN,RNF150,SLC17A4,TG,and TXNRD1)were identified as potential binding targets of miR-3614-5p in the current model.Nonetheless,only miR-3614-5p inhibition caused an increase in TXNRD1 expression upon Cd exposure in T-47 D and MCF-7 cell lines.Luciferase reporter assays further verified that miR-3614-5p suppressed the expression of TXNRD1 by directly binding to the 3’-untranslated region(UTR),and TXNRD1 inhibition significantly repressed the proliferation and metastasis capacity of BC cells upon Cd exposure.Importantly,Cd exposure dramatically shortened the mammary tumor latency,accelerated tumor growth and increased the incidence of lung and liver metastasis in MMTV-Erbb2 mice.Mi R-3614-5p was also downregulated in Cd-exposed BC tissue and was negatively correlated with TXNRD1 expression.Conclusion: Mi R-3614-5p downregulation enhances Cd-induced BC progression by targeting TXNRD1 both in vitro cell study and in vivo animal study.Our results provide a deeper understanding of the underlying molecular mechanisms linking exposure to Cd and carcinogenic activity.