title: Nucleotide composition of cellular internal ribosome entry sites defines dependence on NF45 and predicts a posttranscriptional mitotic regulon.
abstract: The vast majority of cellular mRNAs initiate their translations through a well-defined mechanism of ribosome recruitment that occurs at the 5'-terminal 7-methylguanosine cap with the help of several canonical protein factors. A subset of cellular and viral mRNAs contain regulatory motifs in their 5' untranslated regions (UTRs), termed internal ribosome entry sites (IRES), that sidestep this canonical mode of initiation. On cellular mRNAs, this mechanism requires IRES trans-acting protein factors (ITAFs) that facilitate ribosome recruitment downstream of the cap. While several ITAFs and their target mRNAs have been empirically identified, the in silico prediction of targets has proved difficult. Here, we report that a high AU content (>60%) of the IRES-containing 5' UTRs serves as an excellent predictor of dependence on NF45, a recently identified ITAF. Moreover, we provide evidence that cells deficient in NF45 ITAF activity exhibit reduced IRES-mediated translation of X-linked inhibitor of apoptosis protein (XIAP) and cellular inhibitor of apoptosis protein 1 (cIAP1) mRNAs that, in turn, leads to dysregulated expression of their respective targets, survivin and cyclin E. This specific defect in IRES translation explains in part the cytokinesis impairment and senescence-like phenotype observed in HeLa cells expressing NF45 RNA interference (RNAi). This study uncovers a novel role for NF45 in regulating ploidy and highlights the importance of IRES-mediated translation in cellular homeostasis.
authors.affiliation: Apoptosis Research Centre, Children's Hospital of Eastern Ontario, and University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Mame Daro
authors.initials: MD
authors.lastname: Faye
authors.forename: Tyson E
authors.initials: TE
authors.lastname: Graber
authors.forename: Peng
authors.initials: P
authors.lastname: Liu
authors.forename: Nehal
authors.initials: N
authors.lastname: Thakor
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Baird
authors.forename: Danielle
authors.initials: D
authors.lastname: Durie
authors.forename: Martin
authors.initials: M
authors.lastname: Holcik
mesh_terms: D020121:5' Untranslated Regions; D049109:Cell Proliferation; D016922:Cellular Senescence; D003001:Cloning, Molecular; D019927:Cyclin E / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D051034:Inhibitor of Apoptosis Proteins / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008938:Mitosis; D051903:Nuclear Factor 45 Protein / Q000235:genetics / Q000378:metabolism*; D009711:Nucleotides / Q000737:chemistry*; D010641:Phenotype; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018085:Regulon; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012270:Ribosomes / Q000737:chemistry* / Q000235:genetics; D000077022:Survivin; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D020121:5' Untranslated Regions; C107489:BIRC5 protein, human; D019927:Cyclin E; C494013:ILF2 protein, human; D051034:Inhibitor of Apoptosis Proteins; D051903:Nuclear Factor 45 Protein; D009711:Nucleotides; D012333:RNA, Messenger; D000077022:Survivin; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human