Date of Graduation
Previously, publications from our lab had demonstrated that arsenic can regulate Gadd45Î± through p53-dependent and -independent manner where we explored the regulation of Gadd45Î± by various transcription factors, including Foxo3a, NF-ÎºB and through stress signaling pathways such as JNK. Here we analyzed whether arsenic has any impact on the biosynthesis of Egr-1, since Egr-1 has also been reported to regulate Gadd45Î± in keratinocytes in response to UVB. Our results show arsenic can induce Egr-1 synthesis in a dose- and time-dependent manner. To determine the regulatory sequence responsible for Egr-1 induction, we created deletion constructs in the Egr-1 promoter and found Elk-1 binding site was important in arsenic mediated regulation of Egr-1. Rendering BEAS2B cells deficient in Elk-1 expression abrogated the Egr-1 biosynthesis. Furthermore, Mitogen-activated protein kinase inhibitor U0126 completely blocked the activation of Egr-1. Since Elk-1 is known to be regulated through ERK, our data suggested a signaling event that follows the activation of ERK, Elk-1, Egr-1 and finally to Gadd45Î± in response to arsenic. Further studies suggested arsenic can also regulate Gadd45Î± at the translational level by favoring Gadd45Î± translation through Internal Ribosome Entry Site. In growth arrested cells, arsenic led to the accumulation of Gadd45Î± protein, activation of which did not change in the presence of cap-dependent inhibitor; rapamycin. Further analysis of Gadd45Î± 5â€™-UTR sequence revealed an IRES element which was confirmed by dicistronic reporter gene assay. Immunoprecipitation and proteomic studies suggested arsenic impairs assembly of cap-dependent initiation complex for general protein translation but increases association of eEF2 and hnRNP with this complex. Thus our result suggests arsenic can modulate the expression of Gadd45Î± through post-transcriptional regulation.
Bhatia, Deepak, "Transcriptional and post-transcriptional regulation of Gadd45Î± in response to arsenic." (2007). Graduate Theses, Dissertations, and Problem Reports. 8481.