We have previously shown that trivalent arsenic (arsenite, As3+) is able to induce GADD45α 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 GADD45α protein through a cap-independent, or rather, an internal ribosome entry site (IRES)-dependent mechanism. In growth-arrested cells, As3+ elevated the GADD45α protein level in a dose- and time-dependent manner which did not correlate with the GADD45α 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 GADD45α protein induced by As3+. Sequence analysis revealed a potential IRES element in the 5′-untranslated region of the GADD45α mRNA. This IRES element in the 5′-untranslated region of the GADD45α mRNA is functional in mediating As3+-induced translation of the GADD45α 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 GADD45α expression through an IRES-dependent translational regulation.
|Number of pages||9|
|State||Published - Jul 1 2007|
ASJC Scopus subject areas
- Cancer Research