Repression of anti-apoptotic genes via AP-1 as a mechanism of apoptosis induction in ventricular cardiomyocytes

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Abstract
Nitric oxide (NO) is increased under several pathophysiological, mainly inflammatory processes in the heart and has been characterized as an inducer of apoptosis in cardiomyocytes. The transcription factor activating protein-1 (AP-1) has been identified as a mediator of NO-induced apoptosis. Genes that are regulated by AP-1 under apoptotic conditions have not been identified yet. Therefore, we performed a microarray analysis with subsequent real-time polymerase chain reaction (PCR) to identify genes regulated by AP-1 in NO-induced ventricular cardiomyocytes of rats and tested the functional role of these genes in apoptosis. Cardiomyocytes were transformed with AP-1 decoy oligonucleotides for inhibition of AP-1 activity. These, as well as non-transformed control cells, were stimulated with the NO donor (±)-S-nitroso-N-acetylpenicillamine (SNAP, 100 μM) for 2 h. Some of the genes with differential gene expression on microarrays were further analysed by real-time PCR. Genes that are induced by SNAP were not identified. However, four genes, pyridoxal kinase, heat shock protein 10 (Hsp10), antigen identified by monoclonal antibodies 4F2 (4F2) and myosin light chain 2, were downregulated by SNAP in presence of AP-1. Pyridoxal kinase, Hsp10 and 4F2 have anti-apoptotic effects in unstimulated cells because downregulation of their expression by antisense oligos induced apoptosis in cardiomyocytes. An involvement of these genes in NO-induced apoptosis could only be proven for pyridoxal kinase. In conclusion, using microarray technology, we identified three anti-apoptotic genes (Hsp10, 4F2 and pyridoxal kinase) in ventricular cardiomyocytes, which may help the cells to resist some apoptotic stimuli. The downregulation of these genes results in cardiomyocyte apoptosis. Prevention of their downregulation may protect cardiomyocytes against apoptotic stimuli, and this may be of therapeutic benefit.