title: The ubiquitin ligase human TRIM71 regulates let-7 microRNA biogenesis via modulation of Lin28B protein.
abstract: let-7 microRNA (miRNA) is implicated in various biological processes, and its downregulation essentially linked to human malignancy. Regulation of gene expression of the let-7 family is critically linked to RNA-binding proteins. For instance, Lin28B and its paralog, Lin28A, inhibit the pre-let-7 precursor from being processed to mature miRNA by recruiting terminal uridyltransferase, TUT4, which adds oligomeric U at the 3' end, suggesting that deregulation of Lin28B, together with Lin28A, may alter various biological processes through modulation of let-7 expression. Here, we showed that the Lin28B protein level is regulated via ubiquitin-mediated proteasomal degradation, and identified the ubiquitin ligase as human TRIM-NHL domain-containing TRIM71. In cells, TRIM71 negatively regulates Lin28B protein stability by catalyzing polyubiquitination. Compared with its paralog, Lin28A, a C-terminal unique ~50 amino acid stretch of Lin28B is essential for TRIM71 interactions and subsequent polyubiquitination. Moreover, the N-terminal RING finger motif of TRIM71 is critical for protein-protein interactions and polyubiquitination of Lin28B, and consequent let-7 expression. Consistent with the let-7 stimulatory role of TRIM71 via Lin28B polyubiquitination, specific knockdown of TRIM71 led to downregulation of let-7 expression. Expression of one of the known let-7 targets, HMGA2, was derepressed after knockdown of TRIM71. We additionally showed that enhanced expression of let-7 is part of a feedback loop that targets TRIM71 3'UTR, which contains two conserved let-7 target sites. Our findings collectively reveal critical aspects of regulatory complexity of let-7 biogenesis at the posttranscriptional level.
authors.affiliation: Cancer Cell and Molecular Biology Branch, Research Institute, National Cancer Center, Goyang, Gyeonggi 410-769, Republic of Korea.
authors.forename: Seo Hyun
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Targeted Medicine Research Center, Korea Research Institute of Bioscience and Biotechnology, Ochang 685-1, Republic of Korea.
authors.forename: Sungchan
authors.initials: S
authors.lastname: Cho
authors.affiliation: Cancer Cell and Molecular Biology Branch, Research Institute, National Cancer Center, Goyang, Gyeonggi 410-769, Republic of Korea.
authors.forename: M Sun
authors.initials: MS
authors.lastname: Kim
authors.affiliation: Targeted Medicine Research Center, Korea Research Institute of Bioscience and Biotechnology, Ochang 685-1, Republic of Korea.
authors.forename: Kwangman
authors.initials: K
authors.lastname: Choi
authors.affiliation: Department of Genetic Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea.
authors.forename: Jae Youl
authors.initials: JY
authors.lastname: Cho
authors.affiliation: Specific Organs Cancer Branch, Research Institute, National Cancer Center, Goyang, Gyeonggi 410-769, Republic of Korea.
authors.forename: Ho-Shin
authors.initials: HS
authors.lastname: Gwak
authors.affiliation: Specific Organs Cancer Branch, Research Institute, National Cancer Center, Goyang, Gyeonggi 410-769, Republic of Korea.
authors.forename: Youn-Jae
authors.initials: YJ
authors.lastname: Kim
authors.affiliation: Specific Organs Cancer Branch, Research Institute, National Cancer Center, Goyang, Gyeonggi 410-769, Republic of Korea; Department of System Cancer Science, Graduate School of Cancer Science and Policy, National Cancer Center, Goyang, Gyeonggi 410-769, Republic of Korea.
authors.forename: Heon
authors.initials: H
authors.lastname: Yoo
authors.affiliation: Specific Organs Cancer Branch, Research Institute, National Cancer Center, Goyang, Gyeonggi 410-769, Republic of Korea; Department of System Cancer Science, Graduate School of Cancer Science and Policy, National Cancer Center, Goyang, Gyeonggi 410-769, Republic of Korea.
authors.forename: Seung-Hoon
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Specific Organs Cancer Branch, Research Institute, National Cancer Center, Goyang, Gyeonggi 410-769, Republic of Korea; Department of System Cancer Science, Graduate School of Cancer Science and Policy, National Cancer Center, Goyang, Gyeonggi 410-769, Republic of Korea.
authors.forename: Jong Bae
authors.initials: JB
authors.lastname: Park
authors.affiliation: Cancer Cell and Molecular Biology Branch, Research Institute, National Cancer Center, Goyang, Gyeonggi 410-769, Republic of Korea; Department of System Cancer Science, Graduate School of Cancer Science and Policy, National Cancer Center, Goyang, Gyeonggi 410-769, Republic of Korea. Electronic address: jhkim@ncc.re.kr.
authors.forename: Jong Heon
authors.initials: JH
authors.lastname: Kim
mesh_terms: D020413:3' Untranslated Regions; D002460:Cell Line; D015536:Down-Regulation; D015870:Gene Expression; D057809:HEK293 Cells; D025743:HMGA2 Protein / Q000235:genetics / Q000378:metabolism; D006801:Humans; D035683:MicroRNAs / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D059748:Proteolysis; D054829:RING Finger Domains; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D000070584:Tripartite Motif Proteins; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics* / Q000378:metabolism
chemical_list: D020413:3' Untranslated Regions; D025743:HMGA2 Protein; C516326:LIN28B protein, human; D035683:MicroRNAs; D016601:RNA-Binding Proteins; D000070584:Tripartite Motif Proteins; D025801:Ubiquitin; C487931:mirnlet7 microRNA, human; C584142:TRIM71 protein, human; D044767:Ubiquitin-Protein Ligases
keywords: Lin28B; MicroRNA; TRIM71; Ubiquitination; let-7