Constitutive activation of transcription factor AP-2 is associated with decreased MnSOD expression in transformed human lung fibroblasts

Activator protein-2 (AP-2) is a transcription factor with transactivating and transrepressing potential in different promoter contexts. AP-2 contains seven cysteines, and its in vitro DNA binding activity is redox-sensitive. Superoxide dismutase-2 (SOD2), which encodes the antioxidant enzyme manganese superoxide dismutase (MnSOD), is a putative tumor suppressor gene whose loss of expression is associated with the malignant phenotype. SOD2 promoter mutations that generate new AP-2 sites are associated with loss of MnSOD expression in cancer cells. In the current study, we have identified an inverse expression pattern between AP-2 and MnSOD in normal versus transformed human cells. MRC5 cells are a normal human lung fibroblast cell strain that is mortal and senesces after a certain number of passages in vitro. MRC5-VA is a simian virus transformed variant of MRC5. We determined the levels of expression of MnSOD and AP-2 in these two cell types at the levels of mRNA, protein, and activity. Our results indicated that MnSOD expression was significantly decreased in NIRCS-VA cells compared with MRC5 cells at each level of investigation, whereas AP-2 showed an opposing pattern of expression and DNA binding activity. These results suggest that AP-2 may participate in the mechanism(s) underlying decreased expression of SOD2 in transformed cells.