NFκB-independent transcriptional induction of the human manganous superoxide dismutase gene

Numerous conditions induce expression of manganese-containing superoxide dismutase (MnSOD) in mammalian cells. The reported inducers of MnSOD are all agents that activate two transcription factors, AP-1 and NFκB, but several reports have suggested that MnSOD induction relies solely on NFκB. We investigated the contribution of the individual transcription factors by using antioxidants and metal chelators to modulate MnSOD transcriptional activation in response to phorbol esters or hydrogen peroxide. The results indicate substantial transcriptional induction of the MnSOD gene independent of NFκB. The metal chelator and antioxidant pyrrolidine dithiocarbamate (PDTC) at 60 or 100 μM induced the MnSOD transcript in HeLa cells while diminishing expression of the NFκB-responsive transcript IκB-α. Induction of the MnSOD mRNA by phorbol-12-myristate-13-acetate (PMA) was only slightly diminished in the presence of PDTC, which in contrast virtually eliminated induction of the NFκB-dependent transcript IκB-α by PMA. MnSOD RNA induction by H₂O₂ was only ~1.5-fold, compared to a ca. 3-fold activation of IκB-α expression. Two other antioxidants, N-acetyl-L-cysteine and butylated hydroxyanisole, failed to block induction of the MnSOD transcript by PMA, which is consistent with a role for AP-1. In vitro DNA binding studies confirmed strong AP-1 activation under conditions where NFκB is blocked but the MnSOD transcript is strongly induced (e.g., PMA treatment in the presence of PDTC).