title: Internal ribosome entry site-mediated translational regulation of ATF4 splice variant in mammalian unfolded protein response.
abstract: Activating transcription factor 4 (ATF4) is a master regulator of genes involved in unfolded protein response (UPR) and its translation is regulated through reinitiation at upstream open reading frames. Here, we demonstrate internal ribosome entry site (IRES)-mediated translation of an alternatively spliced variant of human ATF4. This variant that contains four upstream open reading frames in the 5' leader region was expressed in leukocytes and other tissues. mRNA and protein expression of this variant was activated in the UPR. Its translation was neither inhibited by steric hindrance nor affected by eIF4G1 inactivation, indicating a cap-independent and IRES-dependent mechanism not mediated by ribosome scanning-reinitiation. The IRES activity mapped to a highly structured region that partially overlaps with the third and fourth open reading frames was unlikely attributed to cryptic promoter or splicing, but was activated by PERK-induced eIF2α phosphorylation. Taken together, our findings reveal a new mechanism for translational regulation of ATF4 in mammalian UPR.
authors.affiliation: Department of Biochemistry, The University of Hong Kong, Pokfulam, Hong Kong.
authors.forename: Ching-Ping
authors.initials: CP
authors.lastname: Chan
authors.forename: Kin-Hang
authors.initials: KH
authors.lastname: Kok
authors.forename: Hei-Man Vincent
authors.initials: HM
authors.lastname: Tang
authors.forename: Chi-Ming
authors.initials: CM
authors.lastname: Wong
authors.forename: Dong-Yan
authors.initials: DY
authors.lastname: Jin
mesh_terms: D051701:Activating Transcription Factor 4 / Q000235:genetics*; D017398:Alternative Splicing / Q000235:genetics*; D015153:Blotting, Western; D015852:Eukaryotic Initiation Factor-2 / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism*; D056811:Unfolded Protein Response / Q000235:genetics*
chemical_list: C497109:ATF4 protein, human; D015852:Eukaryotic Initiation Factor-2; D012333:RNA, Messenger; D051701:Activating Transcription Factor 4; D008156:Luciferases
keywords: ATF4; Internal ribosome entry site (IRES); Translation initiation; Unfolded protein response; Upstream open reading frame; eIF2α