Ca ²⁺-induced PARP-1 activation and ANF expression are coupled events in cardiomyocytes

The nuclear protein PARP-1 [poly(ADP-ribose) polymerase-1] is activated in cardiomyocytes exposed to hypoxia causing DNA breaks. Unlike this stress-induced PARP-1 activation, our results provide evidence for Ca ²⁺-induced PARP-1 activation in contracting newborn cardiomyocytes treated with growth factors and hormones that increased their contraction rate, induced intracellular Ca ²⁺ mobilization and its rhythmical and transient translocation into the nucleus. Furthermore, activated PARP-1 up-regulated the activity of phosphorylated ERK (extracellular-signal-regulated kinase) in the nucleus, promoting expression of the Elk1 target gene c-fos. Up-regulation of the transcription factor c-Fos/GATA-4 promoted ANF (atrial natriuretic factor) expression. Given that expression of ANF is known to be implicated in morphological changes, growth and development of cardiomyocytes, these results outline a PARP-1-dependent signal transduction mechanism that links contraction rate and Ca ²⁺ mobilization with the expression of genes underlying morphological changes in cardiomyocytes.