title: MicroRNA-5p and -3p co-expression and cross-targeting in colon cancer cells.
abstract: BACKGROUND
  Two mature miRNA species may be generated from the 5' and 3' arms of a pre-miRNA precursor. In most cases, only one species remains while the complementary species is degraded. However, co-existence of miRNA-5p and -3p species is increasingly being reported. In this work, we aimed to systematically investigate co-expression of miRNA-5p/3p in colon cancer cells in a genome-wide analysis, and to examine cross-targeting of the dysregulated miRNAs and 5p/3p species.
  
  
  RESULTS
  Four colon cancer cell lines were examined relative to two normal colon tissues. Of the 1,190 miRNAs analyzed, 92 and 36 were found to be up- or down-regulated, respectively, in cancer cells. Nineteen co-expressed miRNA-5p/3p pairs were further identified suggesting frequent 5p/3p co-accumulation in colon cancer cells. Of these, 14 pairs were co-up-regulated and 3 pairs were co-down-regulated indicating concerted 5p/3p dysregulation. Nine dysregulated miRNA pairs fell into three miRNA gene families, namely let-7, mir-8/200 and mir-17, which showed frequent cross-targeting in the metastasis process. Focusing on the let-7d-5p/3p pair, the respectively targeted IGF1R and KRAS were shown to be in a reverse relationship with expression of the respective miRNA, which was confirmed in transient transfection assays using let-7d mimic or inhibitor. Targeting of KRAS by let-7d was previous reported; targeting of IGF1R by let-7d-5p was confirmed in luciferase assays in this study. The findings of let-7d-5p/3p and multiple other miRNAs targeting IGF1R, KRAS and other metastasis-related factors suggest that 5p/3p miRNAs contribute to cross-targeting of multiple cancer-associated factors and processes possibly to evade functional abolishment when any one of the crucial factors are inactivated.
  
  
  CONCLUSIONS
  miRNA-5p/3p species are frequently co-expressed and are coordinately regulated in colon cancer cells. In cancer cells, multiple cross-targeting by the miRNAs, including the co-existing 5p/3p species, frequently occurs in an apparent safe-proof scheme of miRNA regulation of important tumorigenesis processes. Further systematic analysis of co-existing miRNA-5p/3p pairs in clinical tissues is important in elucidating 5p/3p contributions to cancer pathogenesis.
authors.forename: Kong Bung
authors.initials: KB
authors.lastname: Choo
authors.forename: Yuen Loon
authors.initials: YL
authors.lastname: Soon
authors.forename: Phan Nguyen Nhi
authors.initials: PN
authors.lastname: Nguyen
authors.forename: Michele Sook Yuin
authors.initials: MS
authors.lastname: Hiew
authors.affiliation: Department of Animal Science, Graduate Institute of Biotechnology, School of Agriculture, Chinese Culture University, 55, Hwa-Kang Road, Yang Ming Shan 111, Taipei, Taiwan. hqr2@faculty.pccu.edu.tw.
authors.forename: Chiu-Jung
authors.initials: CJ
authors.lastname: Huang
mesh_terms: D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D055106:Genome-Wide Association Study; D006801:Humans; D035683:MicroRNAs / Q000096:biosynthesis* / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D012334:RNA, Neoplasm / Q000096:biosynthesis* / Q000235:genetics; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis / Q000235:genetics; D018631:ras Proteins / Q000096:biosynthesis / Q000235:genetics
chemical_list: C117307:KRAS protein, human; D035683:MicroRNAs; D011518:Proto-Oncogene Proteins; D012334:RNA, Neoplasm; D017526:Receptor, IGF Type 1; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins