title: MiR-17/106b seed family regulates p21 in Hodgkin's lymphoma.
abstract: Hodgkin's lymphoma (HL) is a B cell-derived lymphoma characterized by a minority of malignant Hodgkin Reed-Sternberg (HRS) cells that have lost their normal B cell phenotype. Alterations in the cell cycle and apoptosis pathways might contribute to their resistance to apoptosis and sustained cell cycle progression. A key player in both cell cycle arrest and apoptosis is CDKN1A, encoding p21$^{{\rm{waf/cip1}}}$ (p21). P21 is regulated by p53 and can function as a cell cycle inhibitor when in the nucleus or as an apoptosis inhibitor when localized in the cytoplasm. We observed expression of p53, p21 and p-p21 in a variable number of HRS cells in 24 of 40 cases. Expression of miR-17 and miR-106a was detected in HRS cells of 10 HL cases. MiR-17/106b seed family members, CDKN1A RNA and p21 protein levels were variable in HL cell lines. We showed effective targeting of the CDKN1A 3' UTR by miR-17/106b in HL cell lines in a luciferase reporter assay and up-regulation of p21 protein levels upon anti-miR-17 treatment of KM-H2 cells. Functional studies indicated a p21-mediated G(1) arrest after miR-17/106b down-regulation in KM-H2, whereas no G(1) arrest was observed for U-HO1 and L428. This difference could not be explained by differences in the 3' UTR, the cellular location of p21 or expression variation during cell cycle progression. A strong correlation was observed for the miR-17/106b:CDKN1A ratio and the responsiveness to miR-17 inhibition, ie a low ratio in KM-H2 and an extremely high ratio in the two unresponsive HL cell lines. In conclusion, we show that miR-17/106b regulates p21 protein levels in HL and that the effect of miR-17/106b-mediated inhibition depends on the miRNA : target gene ratio. Thus, in HL high miR-17/106b expression contributes to a dysfunctional p53 pathway and thereby also to the malignant phenotype.
authors.affiliation: Department of Pathology, Division of Pathology, University Medical Centre Groningen, University of Groningen, The Netherlands.
authors.forename: Johan H
authors.initials: JH
authors.lastname: Gibcus
authors.forename: Bart-Jan
authors.initials: BJ
authors.lastname: Kroesen
authors.forename: Roelof
authors.initials: R
authors.lastname: Koster
authors.forename: Nancy
authors.initials: N
authors.lastname: Halsema
authors.forename: Debora
authors.initials: D
authors.lastname: de Jong
authors.forename: Steven
authors.initials: S
authors.lastname: de Jong
authors.forename: Sibrand
authors.initials: S
authors.lastname: Poppema
authors.forename: Joost
authors.initials: J
authors.lastname: Kluiver
authors.forename: Arjan
authors.initials: A
authors.lastname: Diepstra
authors.forename: Anke
authors.initials: A
authors.lastname: van den Berg
mesh_terms: D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics* / Q000378:metabolism; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic; D018390:Gene Targeting; D006689:Hodgkin Disease / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D017403:In Situ Hybridization / Q000379:methods; D035683:MicroRNAs / Q000235:genetics* / Q000378:metabolism; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; C542541:MIRN106 microRNA, human; C524941:MIRN17 microRNA, human; D035683:MicroRNAs; D009363:Neoplasm Proteins; D016159:Tumor Suppressor Protein p53