title: CCR4-NOT deadenylates mRNA associated with RNA-induced silencing complexes in human cells.
abstract: MicroRNAs (miRNAs) repress gene expression posttranscriptionally by inhibiting translation and by expediting deadenylation so as to trigger rapid mRNA decay. Their regulatory influence is mediated by the protein components of the RNA-induced silencing complex (RISC), which deliver miRNAs and siRNAs to their mRNA targets. Here, we present evidence that CCR4-NOT is the deadenylase that removes poly(A) from messages destabilized by miRNAs in human cells. Overproducing a mutationally inactivated form of either of the catalytic subunits of this deadenylase (CCR4 or CAF1/POP2) significantly impedes the deadenylation and decay of mRNA targeted by a partially complementary miRNA. The same deadenylase initiates the degradation of "off-target" mRNAs that are bound by an imperfectly complementary siRNA introduced by transfection. The greater inhibitory effect of inactive CAF1 or POP2 (versus inactive CCR4) suggests a predominant role for this catalytic subunit of CCR4-NOT in miRNA- or small interfering RNA (siRNA)-mediated deadenylation. These effects of mi/siRNAs and CCR4-NOT can be fully reproduced by directly tethering RISC to mRNA without the guidance of a small RNA, indicating that the ability of RISC to accelerate deadenylation is independent of RNA base pairing. Despite its importance for mi/siRNA-mediated deadenylation, CCR4-NOT appears not to associate significantly with RISC, as judged by the failure of CAF1 and POP2 to coimmunoprecipitate detectably with either the Ago or TNRC6 subunit of RISC, a finding at odds with deadenylase recruitment as the mechanism by which RISC accelerates poly(A) removal.
authors.affiliation: State Key Laboratory of Molecular Biology and Shanghai Key Laboratory of Molecular Andrology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Xianghua
authors.initials: X
authors.lastname: Piao
authors.forename: Xue
authors.initials: X
authors.lastname: Zhang
authors.forename: Ligang
authors.initials: L
authors.lastname: Wu
authors.forename: Joel G
authors.initials: JG
authors.lastname: Belasco
mesh_terms: D055162:Biocatalysis; D005799:Genes, Dominant; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D035683:MicroRNAs / Q000378:metabolism; D011061:Poly A / Q000378:metabolism; D021122:Protein Subunits / Q000378:metabolism; D034622:RNA Interference; D020871:RNA Stability; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D034743:RNA-Induced Silencing Complex / Q000378:metabolism*; D012260:Ribonucleases / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: C489780:CNOT8 protein, human; D035683:MicroRNAs; D021122:Protein Subunits; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D034743:RNA-Induced Silencing Complex; D014157:Transcription Factors; D011061:Poly A; D012260:Ribonucleases; C445084:mRNA deadenylase