OXIDANT-INDUCED ACTIVATIONS OF NUCLEAR FACTOR-KAPPA-B AND ACTIVATOR PROTEIN-1 IN CARDIAC MYOCYTES

Activator protein-1 (AP-1) and nuclear factor-kappa B (NF-kappa B), tw o transcription factors that respond to a wide range of signals, have been shown to be activated by H2O2 in several cell lines. Since H2O2 a nd related oxidants are implicated in reperfusion injury to the heart, we wished to know if NF-kappa B is present in the myocardium and if c ardiac AP-1 and NF-kappa B also respond to oxidants. Rat neonatal card iac myocytes were exposed to H2O2, and changes in c-fos and c-jun mRNA s, immunoreactive c-Fos and c-Jun proteins (components of AP-1), and i mmunoreactive p50 subunit of NF-kappa B were determined. Changes in nu clear activities of AP-1 and NF-kappa B were also measured by electrop horetic mobility shift assays, When myocytes were exposed to nonlethal concentrations of H2O2, c-fos and c-jun mRNAs were rapidly induced, r eaching peak values at 30-60 min. The levels of c-Fos and c-Jun protei ns increased in nuclei as revealed by immunostaining, and DNA binding activity of nuclear AP-1 increased. The presence of p50 subunit of NF- kappa B and its H2O2-induced shift from cytoplasm to nucleus were show n by immunostaining. H2O2-induced myocyte nuclear proteins capable of binding to a DNA probe containing the NF-kappa B element were also dem onstrated. The findings suggest that altered expressions of cardiac ge nes regulated by AP-1 and NF-kappa B may be components of oxidant-indu ced injury to the heart or a part of the heart's adaptive response to oxidative stress.