Incorporation of an internal ribosome entry site-dependent mechanism in arsenic-induced GADD45alpha expression.
Chang Q; Bhatia D; Zhang Y; Meighan T; Castranova V; Shi X; Chen F
Cancer Res 2007 Jul; 67(13):6146-6154
We have previously shown that trivalent arsenic (arsenite, As3+) is able to induce GADD45alpha expression in human bronchial epithelial cells through activation of c-Jun NH2-terminal kinase and nucleolin-dependent mRNA stabilization. In the present report, we show that As3+ is capable of inducing translation of the GADD45alpha protein through a cap-independent, or rather, an internal ribosome entry site (IRES)-dependent mechanism. In growth-arrested cells, As3+ elevated the GADD45alpha protein level in a dose- and time-dependent manner which did not correlate with the GADD45 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 GADD45alpha protein induced by As3+. Sequence analysis revealed a potential IRES element in the 5'-untranslated region of the GADD45alpha mRNA. This IRES element in the 5'-untranslated region of the GADD45alpha mRNA is functional in mediating As3+-induced translation of the GADD45alpha protein in a dicistronic reporter gene activity assay. Immunoprecipitation and proteomic studies suggest that As3+ 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, As3+ is still capable of inducing GADD45alpha expression through an IRES-dependent translational regulation.
Chemical-hypersensitivity; Chemical-properties; Chemical-synthesis; Arsenic-compounds; Arsenic-poisoning; Breathing; Respiratory-irritants; Respiratory-system-disorders; Lung-irritants; Lung-cells
Fei Chen, Pathology and Physiology Research Branch, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505