title: Incorporation of an internal ribosome entry site-dependent mechanism in arsenic-induced GADD45 alpha expression.
abstract: We have previously shown that trivalent arsenic (arsenite, As(3+)) is able to induce GADD45 alpha expression in human bronchial epithelial cells through activation of c-Jun NH(2)-terminal kinase and nucleolin-dependent mRNA stabilization. In the present report, we show that As(3+) is capable of inducing translation of the GADD45 alpha protein through a cap-independent, or rather, an internal ribosome entry site (IRES)-dependent mechanism. In growth-arrested cells, As(3+) elevated the GADD45 alpha protein level in a dose- and time-dependent manner which did not correlate with the GADD45 alpha mRNA expression. Pretreatment of the cells with rapamycin, an inhibitor for the cap-dependent translation machinery through the suppression of mTOR and p70S6 kinase, failed to affect the induction of the GADD45 alpha protein induced by As(3+). Sequence analysis revealed a potential IRES element in the 5'-untranslated region of the GADD45 alpha mRNA. This IRES element in the 5'-untranslated region of the GADD45 alpha mRNA is functional in mediating As(3+)-induced translation of the GADD45 alpha protein in a dicistronic reporter gene activity assay. Immunoprecipitation and proteomic studies suggest that As(3+) impairs the assembly of the cap-dependent initiating complex for general protein translation but increases the association of human elongation factor 2 and human heterogeneous nuclear ribonucleoprotin with this complex. Thus, these results suggest that in growth-arrested cells, As(3+) is still capable of inducing GADD45 alpha expression through an IRES-dependent translational regulation.
authors.affiliation: Health Effects Laboratory Division, National Institute for Occupational Safety and Health, West Verginia University, Morgantown, WV 26505, USA.
authors.forename: Qingshan
authors.initials: Q
authors.lastname: Chang
authors.forename: Deepak
authors.initials: D
authors.lastname: Bhatia
authors.forename: Yadong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Terry
authors.initials: T
authors.lastname: Meighan
authors.forename: Vince
authors.initials: V
authors.lastname: Castranova
authors.forename: Xianglin
authors.initials: X
authors.lastname: Shi
authors.forename: Fei
authors.initials: F
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D001151:Arsenic / Q000494:pharmacology*; D001483:Base Sequence; D018797:Cell Cycle Proteins / Q000096:biosynthesis* / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000378:metabolism; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000235:genetics; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D012270:Ribosomes / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D000097642:GADD45 Proteins
chemical_list: D001151:Arsenic; D018797:Cell Cycle Proteins; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D048031:JNK Mitogen-Activated Protein Kinases; D009687:Nuclear Proteins; D012333:RNA, Messenger; D038762:Ribosomal Protein S6 Kinases, 70-kDa; C439070:GADD45A protein, human; D000097642:GADD45 Proteins