PIAS3 interacts with ATF1 and regulates the human ferritin H gene through an antioxidant-responsive element

Gene transcription is coordinately regulated by the balance between activation and repression mechanisms in response to various external stimuli. Ferritin, composed of Hand L subunits, is the major intracellular iron storage protein involved in iron homeostasis. We previously identified an enhancer, termed antioxidant-responsive element (ARE), in the human ferritin H gene and its respective transcriptional activators including Nrf2 and JunD. Here we found that ATF1 (activating transcription factor 1) is a transcriptional repressor of the ferritin H ARE. Subsequent yeast two-hybrid screening identified PIAS3 (protein inhibitor of activated STAT3) as an ATF1-binding protein. Further investigation of the human ferritin H ARE regulation showed that 1) PIAS3 reversed ATF1-mediated repression of the ferritin H ARE; 2) ATF1 was sumoylated, but PIAS3, a SUMO E3 ligase, did not appear to play a major role in SUMO1-mediated ATF1 sumoylation or ATF1 transcription activating function; 3) PIAS3 decreased ATF1 binding to the ARE; and 4) ATF1 knockdown with siRNA increased ferritin H expression, whereas PIAS3 knockdown decreased basal expression and oxidative stress-mediated induction of ferritin H. These results suggest that PIAS3 antagonizes the repressor function of ATF1, at least in part by blocking its DNA binding, and ultimately activates the ARE. Collectively our results suggest that PIAS3 is a new regulator of ATF1 that regulates the ARE-mediated transcription of the ferritin H gene.