Abstract 3868: Protein Kinase A Decreases MEF2-Activity by Limited Proteolysis of Histone Deacetylase 4
β-adrenergic receptor (β-AR) signaling plays a critical role in pathological cardiac remodeling, characterized by the activation of fetal genes like ANP. One of the required transcription factors is MEF2, which is repressed by the histone deacetylase 4 (HDAC4). We have shown that CaM Kinase II (CaMKII) de-represses MEF2 via nuclear export of HDAC4. More recently, we found that the canonical downstream kinase of β-ARs, protein kinase A (PKA), induces an N-terminal cleavage product of HDAC4. Now we provide new data about the characteristics and the in vivo role of the cleavage product as well as the interaction between PKA and HDAC4. By mass spectrometry we determined that HDAC4 is cleaved after amino acid Y201, which lies in a unique HDAC4 region that is not conserved in other class IIa HDACs. Luciferase assays confirmed that HDAC4 1–201 is able to repress MEF2 more efficiently than SRF, which was shown to be repressed by a caspase-mediated cleavage product (HDAC4 1–289). Moreover, PKA overcomes CaMKII induced MEF2 activation. The serine protease inhibitor AEBSF was sufficient to prevent PKA mediated cleavage of HDAC4. In H9C2 myocytes, PKA activation by cAMP resulted in repression of MEF2 which was blunted by PKA inhibition and even reversed by AEBSF through PKA-dependent activation of CaMKII. We found that PKA docks to the C-terminal half of HDAC4, which is required for the induction of the cleavage product. The half-life of the cleavage product was shorter (about 2–3 hour) than the half-life of full length HDAC4 1–1084 (about 8 hours). In vivo, β-AR stimulation by isoproteronol (Iso) led to HDAC4 cleavage in hearts of wild type (WT) but not PKA-knockout mice. We generated heart specific HDAC4 conditional knockout mice (CKO) and upon Iso stimulation we observed an exaggerated up-regulation of certain fetal genes such as ANP in the HDAC4 CKO mice compared to WT mice. We speculate that the generation of the HDAC4 cleavage product represents a novel cardioprotective mechanism, preventing pathological cardiac remodeling during short-term β-AR stimulation.