AFos dissociates cardiac myocyte hypertrophy and expression of the pathological gene program

Background - Although induction of activator protein-1 (AP-1) transcription factor activity has been observed in cardiac hypertrophy, a direct role for AP-1 in myocardial growth and gene expression remains obscure. Methods and Results - Hypertrophy was induced in cultured neonatal rat cardiomyocytes with phenylephrine or overexpression of a constitutively active MAP3K, MKK6. In both treatment groups, induction of the pathological gene profile was observed, ie, expression of β-myosin heavy chain (βMHC), atrial/brain natriuretic peptides (ANP/BNP), and skeletal α-actin (sACT) was increased, whereas expression for α-myosin heavy chain (αMHC) and the sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) genes was repressed. The role of AP-1 in the hypertrophic phenotype was evaluated with the use of an adenoviral construct expressing a dominant negative mutant of the c-Fos proto-oncogene (AdAFos). Although AFos did not change the myocyte growth response, it abrogated the gene profile to both agonists, including the upregulation of both aMHC and SERCA expression. Conclusions - Although c-Fos/AP-1 is necessary for induction of the pathological/fetal gene program, it does not appear to be critical for cardiomyocyte hypertrophy.