A new internal-ribosome-entry-site motif potentiates XIAP- mediated cytoprotection

摘要: rogrammed cell death (apoptosis) plays a critical part in regulating turnover during embryogenesis, metamorphosis, tissue homeostasis and viral infection1. Dysregulation of apoptosis occurs such pathologies as cancer, autoimmunity, immunodeficiency neurodegeneration. Proteins the inhibitor-ofapoptosis (IAP) family are intrinsic cellular suppressors represented by highly conserved members found from insect viruses to mammals2‐4. The most potent mammalian IAP is X-linked IAP, or XIAP5, whose mechanism action involves direct inhibition caspases 3 7, key proteases apoptotic cascade6. Cellular control XIAP expression should be fundamental cell’s ability modulate its responses stimuli. However, messenger RNA expressed tissues cells at fairly constant levels5, indicating that translational levels may an important regulatory mechanism. Here we characterize primary genomic structure function XIAP, show controlled level, specifically through internal ribosome-entry site (IRES). Several features mRNA indicate it translationally regulated, including unusually long 5′ untranslated region (UTR) (>5.5 kilobases (kb) for murine >1.6 kb human transcripts) with predicted complex secondary numerous potential translation start sites upstream authentic initiation codon. This UTR would expected present significant obstacle efficient conventional ribosome scanning7. An alternative initiation, mediated IRES, has been identified picornaviruses few mRNAs8. Thus tested whether could involved reporter-based bicistronic transcripts encoding β-galactosidase chloramphenicol aceytyltransferase (CAT) (for example, see ref. 9). (Translation driven methylguanosine cap.) Both mouse UTRs directed second cistron (encoding CAT) 150fold higher than those produced without reverse orientation, suggesting presence IRES (Fig. 1a). No activity was detected when using identical DNA segments cloned into promoterless construct, confirming P