title: In vivo, Argonaute-bound microRNAs exist predominantly in a reservoir of low molecular weight complexes not associated with mRNA.
abstract: MicroRNAs repress mRNA translation by guiding Argonaute proteins to partially complementary binding sites, primarily within the 3' untranslated region (UTR) of target mRNAs. In cell lines, Argonaute-bound microRNAs exist mainly in high molecular weight RNA-induced silencing complexes (HMW-RISC) associated with target mRNA. Here we demonstrate that most adult tissues contain reservoirs of microRNAs in low molecular weight RISC (LMW-RISC) not bound to mRNA, suggesting that these microRNAs are not actively engaged in target repression. Consistent with this observation, the majority of individual microRNAs in primary T cells were enriched in LMW-RISC. During T-cell activation, signal transduction through the phosphoinositide-3 kinase-RAC-alpha serine/threonine-protein kinase-mechanistic target of rapamycin pathway increased the assembly of microRNAs into HMW-RISC, enhanced expression of the glycine-tryptophan protein of 182 kDa, an essential component of HMW-RISC, and improved the ability of microRNAs to repress partially complementary reporters, even when expression of targeting microRNAs did not increase. Overall, data presented here demonstrate that microRNA-mediated target repression in nontransformed cells depends not only on abundance of specific microRNAs, but also on regulation of RISC assembly by intracellular signaling.
authors.affiliation: Cancer Biology and Genetics Program.
authors.forename: Gaspare
authors.initials: G
authors.lastname: La Rocca
authors.affiliation: Cancer Biology and Genetics Program.
authors.forename: Scott H
authors.initials: SH
authors.lastname: Olejniczak
authors.affiliation: Computational Biology Program, and.
authors.forename: Alvaro J
authors.initials: AJ
authors.lastname: González
authors.affiliation: Howard Hughes Medical Institute, Laboratory of RNA Molecular Biology, The Rockefeller University, New York, NY 10065.
authors.forename: Daniel
authors.initials: D
authors.lastname: Briskin
authors.affiliation: Cancer Biology and Genetics Program.
authors.forename: Joana A
authors.initials: JA
authors.lastname: Vidigal
authors.affiliation: Cancer Biology and Genetics Program.
authors.forename: Lee
authors.initials: L
authors.lastname: Spraggon
authors.affiliation: Cancer Biology and Genetics Program.
authors.forename: Raymond G
authors.initials: RG
authors.lastname: DeMatteo
authors.affiliation: Cancer Biology and Genetics Program.
authors.forename: Megan R
authors.initials: MR
authors.lastname: Radler
authors.affiliation: Immunology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10065; and.
authors.forename: Tullia
authors.initials: T
authors.lastname: Lindsten
authors.affiliation: Cancer Biology and Genetics Program.
authors.forename: Andrea
authors.initials: A
authors.lastname: Ventura
authors.affiliation: Howard Hughes Medical Institute, Laboratory of RNA Molecular Biology, The Rockefeller University, New York, NY 10065.
authors.forename: Thomas
authors.initials: T
authors.lastname: Tuschl
authors.affiliation: Computational Biology Program, and.
authors.forename: Christina S
authors.initials: CS
authors.lastname: Leslie
authors.affiliation: Cancer Biology and Genetics Program, thompsonc@mskcc.org.
authors.forename: Craig B
authors.initials: CB
authors.lastname: Thompson
mesh_terms: D060565:Argonaute Proteins / Q000378:metabolism*; D008213:Lymphocyte Activation; D035683:MicroRNAs / Q000378:metabolism*; D008970:Molecular Weight; D012333:RNA, Messenger / Q000378:metabolism*; D013601:T-Lymphocytes / Q000378:metabolism
chemical_list: D060565:Argonaute Proteins; D035683:MicroRNAs; D012333:RNA, Messenger
keywords: Argonaute; GW182; T cells; mTOR; microRNA