Transcriptional activation of the human Galphai2 gene promoter through nuclear factor-kappaB and antioxidant response elements.

Very little is known regarding molecular mechanism(s) underlying transcriptional regulation of any G-protein gene despite the importance of G-protein expression in modulating cellular processes. Here we show that phorbol myristate acetate (PMA) and tert-butylhydroquinone (tBHQ), which induce oxidative stress in cells, up-regulate transcription of Galpha(i2) in K562 cells. Redox-sensing chemicals abrogated this transcriptional effect. A dominant negative I-kappaB double mutant (S32A/S36A) suppressed PMA-induced transcription by 54-62%, suggesting involvement of nuclear factor-kappaB (NF-kappaB). SN50, a cell-permeable peptide that inhibits nuclear import of stress-responsive transcription factors (such as NF-kappaB), inhibited PMA- and tBHQ-induced transcription. Deletion of an NF-kappaB-binding motif that maps at +10/+19 in the promoter resulted in 55-60% suppression of PMA-induced transcription, and 81% suppression of tBHQ-induced transcription. Mutation of an antioxidant response element (ARE) that maps at -84/-76 in the promoter resulted in 51 and 86% decrease in PMA- and tBHQ-induced transcription, respectively. In electrophoretic mobility shift assays, this element formed complexes with the transcription factors NF-E2p45 and Nrf2 that are prototypic for binding to the ARE, as well as with c-Fos, which can also interact with the ARE. Chromatin immunoprecipitation analysis demonstrated recruitment of these transcription factors to the promoter. Exogenously transfected Nrf2 transactivated the Galpha(i2) gene promoter; the cytoskeleton-associated protein, Keap1, abrogated this effect. Taken together, the present studies reveal that transcription factors that bind NF-kappaB and/or antioxidant response elements play an activating role in the transcription of the human Galpha(i2) gene.