title: Two isoforms of the mRNA binding protein IGF2BP2 are generated by alternative translational initiation.
abstract: IGF2BP2 is a member of a family of mRNA binding proteins that, collectively, have been shown to bind to several different mRNAs in mammalian cells, including one of the mRNAs encoding insulin-like growth factor-2. Polymorphisms in the Igf2bp2 gene are associated with risk of developing type 2 diabetes, but detailed functional characterisation of IGF2BP2 protein is lacking. By immunoblotting with C-terminally reactive antibodies we identified a novel IGF2BP2 isoform with a molecular weight of 58 kDa in both human and rodents, that is expressed at somewhat lower levels than the full-length 65 kDa protein. We demonstrated by mutagenesis that this isoform is generated by alternative translation initiation at the internal Met69. It lacks a conserved N-terminal RNA Recognition Motif (RRM) and would be predicted to differ functionally from the canonical full length isoform. We further investigated IGF2BP2 mRNA transcripts by amplification of cDNA using 5'-RACE. We identified multiple transcription start sites of the human, mouse and rat Igf2bp2 genes in a highly conserved region only 50-90 nts upstream of the major translation start site, ruling out the existence of N-terminally extended isoforms. We conclude that structural heterogeneity of IGF2BP2 protein should be taken into account when considering cellular function.
authors.affiliation: University of Cambridge Metabolic Research Laboratories and Department of Clinical Biochemistry, Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, United Kingdom.
authors.forename: Hang T T
authors.initials: HT
authors.lastname: Le
authors.forename: Alice M
authors.initials: AM
authors.lastname: Sorrell
authors.forename: Kenneth
authors.initials: K
authors.lastname: Siddle
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D018076:DNA, Complementary / Q000235:genetics; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010442:Peptide Chain Initiation, Translational / Q000235:genetics / Q000502:physiology*; D020033:Protein Isoforms / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D051381:Rats; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D024363:Transcription Initiation Site
chemical_list: D018076:DNA, Complementary; C498779:IGF2BP2 protein, human; C559768:IGF2BP2 protein, mouse; D020033:Protein Isoforms; D016601:RNA-Binding Proteins