Abstract 1406: Enhanced Expression of p21-activated Kinases in an Arrhythmogenic Rabbit Model of Heart Failure Contributes to Dephosphorylation of Connexin 43
p21-activated kinases (PAKs) are a family of serine / threonine protein kinases, three isoforms of which (PAK1, 2, 3) exist in heart. There is emerging evidence that PAKs play an important role in cardiac contractility and development of heart failure (HF). We previously showed that PAK1 dephosphorylated cardiac troponin I by enhancing activity of protein phosphatase 2A (PP2A). In an arrhythmogenic rabbit model of nonischemic HF (aortic insufficiency & constriction), we demonstrated a 2.5-fold increase in the amount of PP2A co-localized with connexin 43 (Cx43) (while global expression of PP2A protein was decreased by 35%) contributing to enhanced Cx43 dephosphorylation and reduced intercellular communication in left ventricular (LV) myocytes. Here we assessed PAK (1, 2, 3) protein expression in HF, its interaction with Cx43 (by immunoblot and co-immunoprecipitation) and the role of PAKs in modulating Cx43 dephosphorylation (by over-expression of the active form of PAK1 in isolated LV myocytes from control (Ctl) rabbits). We found that PAK2 protein was increased 95% in HF (n =8,12, p < 0.01 vs Ctl) while PAK1 & PAK3 were unchanged. We further discovered that PAK2 and PAK3 colocalized with Cx43 protein (co-immunoprecipitated PAK2 and PAK3 with Cx43 antibody) and with HF, co-localized PAK2 was increased by 32% (n =3, 3, p < 0.05) while PAK3 was unchanged. PAK1 over-expression (by adenovirus encoding constitutively activated PAK1) in Ctl myocytes resulted in a 138% increase in the level of dephosphorylated Cx43 compared with adeno-LacZ infected myocytes (n =4). Furthermore, the level of dephosphorylated Cx43 in PAK1 over-expressed myocytes was reduced by 32% (n =4) after PP2A inhibition (1 umol/L okadaic acid). Thus PAKs and PP2A are integral components of a macromolecular complex with cardiac Cx43, and increased levels of co-localized PAK2 can contribute to enhanced Cx43 dephosphorylation and altered cellular coupling that underlies development of reentry in HF.