Cyclic mechanical strain causes cAMP-response element binding protein activation by different pathways in cardiac fibroblasts.

The transcription factor cAMP-response element binding protein (CREB) mediates the mechanical strain-induced gene expression in the heart. This study investigated which signaling pathways are involved in the straininduced CREB activation using cultured ventricular fibroblasts from adult rat hearts. CREB phosphorylation was analyzed by immunocytochemistry and ELISA. Cyclic mechanical strain (1 Hz and 5% elongation) for 15 min induced CREB phosphorylation in all CREB-positive fibroblasts. Several signaling transduction pathways can contribute to strain-induced CREB activation. The inhibition of PKA, PKC, MEK, p38-MAPK or PI3-kinase partially reduced the strain-induced CREB phosphorylation. Activation of PKA by forskolin or PKC by PMA resulted in a level of CREB phosphorylation comparable to the reduced level of the strain-induced CREB phosphorylation in the presence of PKA or PKC inhibitors. Signaling pathways involving PKC, MEK, p38-MAPK or PI3-kinase seem to converge during strain-induced CREB activation. PKA interacted additively with the investigated signaling pathways. The strain-induced c-Fos expression can be reduced by PKC inhibition but not by PKA inhibition. Our results suggest that the complete strain-induced CREB phosphorylation involves several signaling pathways that have a synergistic effect. The influence on gene expression is dependent on the level and the time of CREB stimulation. These wide-ranging possibilities of CREB activation provide a graduated control system.