title: MiR-302a/b/c/d cooperatively sensitizes breast cancer cells to adriamycin via suppressing P-glycoprotein(P-gp) by targeting MAP/ERK kinase kinase 1 (MEKK1).
abstract: BACKGROUND
  The importance of individual microRNAs (miRNAs) in tumor has been established in different cancers. However, their association with tumor chemoresistance has not been fully understood. Previously, we found two novel MDR-associated microRNAs (miRNAs). In this report, we investigated the combined effects of miRNA gene cluster in chemoresistance of breast cancer.
  
  
  METHODS
  This study was performed in two different breast cancer cell lines (MCF-7 and MCF-7/ADR). The levels of miRNAs and mRNA expression were determined by using Quantitative Real-Time PCR. Western blotting was used to detect the levels of protein molecules. Cell viability was assessed by MTS assay. Bioinformatics and Luciferase reporter assay was performed to examine miRNA binding to the 3'-UTR of target genes.
  
  
  RESULTS
  The miR-302S family including miR-302a, miR-302b, miR-302c, and miR-302d was significantly down-regulated in P-glycoprotein (P-gp)-overexpressing MCF-7/ADR cells. Overexpression of miR-302 increased intracellular accumulation of ADR and sensitized breast cancer cells to ADR. Most importantly, miR-302S produced stronger effects than each individual member alone. The four miRNAs cooperatively downregulate P-gp expression in regulating drug sensitivity. However, our results showed that the suppression of P-gp expression by miR-302 is not through typical miRNA-mediated mRNA degradation but at the level of protein and transcription. Further studies identified MAP/ERK kinase kinase 1 (MEKK1) as a direct and functional target of miR-302. miR-302 showed combinatorial effects on MKEE1 repression and MEKK1-mediated ERK pathway. The suppression of P-gp by miR-302 was reversed by MEKK1 overexpression.
  
  
  CONCLUSIONS
  Our results indicate that miR-302 cooperatively sensitizes breast cancer cells to adriamycin via suppressing P-glycoprotein by targeting MEKK1 of ERK pathway. miR-302 gene cluster may be a potential target for reversing P-gp-mediated chemoresistance in breast cancer.
authors: Department of Pharmacology, School of Pharmacy, China Medical University, No.77 Puhe Road, Shenyang North New Area, Shenyang City, 110122, Liaoning, China. zl_cmu@163.com.
authors: Lin
authors: L
authors: Zhao
authors: Department of Pharmacology, School of Pharmacy, China Medical University, No.77 Puhe Road, Shenyang North New Area, Shenyang City, 110122, Liaoning, China. cmuwy@126.com.
authors: Yan
authors: Y
authors: Wang
authors: Department of Pharmacology, School of Pharmacy, China Medical University, No.77 Puhe Road, Shenyang North New Area, Shenyang City, 110122, Liaoning, China. jianglongyang1987@126.com.
authors: Longyang
authors: L
authors: Jiang
authors: Department of Pharmacology, School of Pharmacy, China Medical University, No.77 Puhe Road, Shenyang North New Area, Shenyang City, 110122, Liaoning, China. hemiao_cmu@126.com.
authors: Miao
authors: M
authors: He
authors: Department of Pharmacology, School of Pharmacy, China Medical University, No.77 Puhe Road, Shenyang North New Area, Shenyang City, 110122, Liaoning, China. fengfengfriend@163.com.
authors: Xuefeng
authors: X
authors: Bai
authors: Department of Pharmacology, School of Pharmacy, China Medical University, No.77 Puhe Road, Shenyang North New Area, Shenyang City, 110122, Liaoning, China. yumeiren0108@sina.com.
authors: Lifeng
authors: L
authors: Yu
authors: Department of Pharmacology, School of Pharmacy, China Medical University, No.77 Puhe Road, Shenyang North New Area, Shenyang City, 110122, Liaoning, China. weiminjiecmu@163.com.
authors: Minjie
authors: M
authors: Wei
mesh_terms: D020413:3' Untranslated Regions; D018435:ATP Binding Cassette Transporter, Subfamily B / Q000235:genetics; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000235:genetics*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004317:Doxorubicin / Q000494:pharmacology*; D004357:Drug Synergism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D048728:MAP Kinase Kinase Kinase 1 / Q000235:genetics*; D061986:MCF-7 Cells; D035683:MicroRNAs / Q000235:genetics*; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D020413:3' Untranslated Regions; C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D000903:Antibiotics, Antineoplastic; C532169:MIRN302A microRNA, human; D035683:MicroRNAs; D004317:Doxorubicin; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human