title: The transformation suppressor Pdcd4 is a novel eukaryotic translation initiation factor 4A binding protein that inhibits translation.
abstract: Pdcd4 is a novel transformation suppressor that inhibits tumor promoter-induced neoplastic transformation and the activation of AP-1-dependent transcription required for transformation. A yeast two-hybrid analysis revealed that Pdcd4 associates with the eukaryotic translation initiation factors eIF4AI and eIF4AII. Immunofluorescent confocal microscopy showed that Pdcd4 colocalizes with eIF4A in the cytoplasm. eIF4A is an ATP-dependent RNA helicase needed to unwind 5' mRNA secondary structure. Recombinant Pdcd4 specifically inhibited the helicase activity of eIF4A and eIF4F. In vivo translation assays showed that Pdcd4 inhibited cap-dependent but not internal ribosome entry site (IRES)-dependent translation. In contrast, Pdcd4(D418A), a mutant inactivated for binding to eIF4A, failed to inhibit cap-dependent or IRES-dependent translation or AP-1 transactivation. Recombinant Pdcd4 prevented eIF4A from binding to the C-terminal region of eIF4G (amino acids 1040 to 1560) but not to the middle region of eIF4G(amino acids 635 to 1039). In addition, both Pdcd4 and Pdcd4(D418A) bound to the middle region of eIF4G. The mechanism by which Pdcd4 inhibits translation thus appears to involve inhibition of eIF4A helicase, interference with eIF4A association-dissociation from eIF4G, and inhibition of eIF4A binding to the C-terminal domain of eIF4G. Pdcd4 binding to eIF4A is linked to its transformation-suppressing activity, as Pdcd4-eIF4A binding and consequent inhibition of translation are required for Pdcd4 transrepression of AP-1.
authors.affiliation: Gene Regulation Section, Center for Cancer Research, National Cancer Institute, Frederick, Maryland 21702, USA. hyang@ncifcrf.gov
authors.forename: Hsin-Sheng
authors.initials: HS
authors.lastname: Yang
authors.forename: Aaron P
authors.initials: AP
authors.lastname: Jansen
authors.forename: Anton A
authors.initials: AA
authors.lastname: Komar
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Zheng
authors.forename: William C
authors.initials: WC
authors.lastname: Merrick
authors.forename: Sylvain
authors.initials: S
authors.lastname: Costes
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Lockett
authors.forename: Nahum
authors.initials: N
authors.lastname: Sonenberg
authors.forename: Nancy H
authors.initials: NH
authors.lastname: Colburn
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins; D001665:Binding Sites; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D002478:Cells, Cultured; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism; D004265:DNA Helicases / Q000378:metabolism; D000078404:Epidermal Cells; D004817:Epidermis / Q000502:physiology; D005057:Eukaryotic Cells / Q000502:physiology; D039601:Eukaryotic Initiation Factor-4A / Q000235:genetics* / Q000378:metabolism*; D039603:Eukaryotic Initiation Factor-4G / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009154:Mutation; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012315:RNA Caps / Q000378:metabolism; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid; D012270:Ribosomes / Q000235:genetics; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D020798:Two-Hybrid System Techniques
chemical_list: D051017:Apoptosis Regulatory Proteins; D039603:Eukaryotic Initiation Factor-4G; C498443:Pdcd4 protein, mouse; D011506:Proteins; D012315:RNA Caps; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D018808:Transcription Factor AP-1; D039601:Eukaryotic Initiation Factor-4A; D004265:DNA Helicases