Expression and Activity of Protein Kinase D/Protein Kinase C μ in Myocardium: Evidence forα1 -Adrenergic Receptor- and Protein Kinase C-Mediated Regulation

Abstract

R. S. Haworth, M. W. Goss, E. Rozengurt and M. Avkiran. Expression and Activity of Protein Kinase D/Protein Kinase C μ in Myocardium: Evidence for α1-Adrenergic Receptor- and Protein Kinase C-Mediated Regulation. Journal of Molecular and Cellular Cardiology (2000) 32, 1013–1023. Protein kinase D (PKD), which is also known as protein kinase C (PKC) μ, is a novel serine/threonine kinase that can be activated in parallel with or downstream of PKC in various cell types, but its expression and regulation in myocardium have not been characterized. In the present study, two proteins of 110 and 115 kDa were detected in rat ventricular myocardium using antibodies directed at the extreme N- or C-terminus of PKD. Both proteins were highly expressed in the fetal heart but showed a developmental decline in abundance. Fractionation studies showed that PKD was distributed between myocyte and non-myocyte fractions in the neonatal heart, but was found predominantly in the non-myocyte fraction in the adult heart. In cultured neonatal rat ventricular myocytes, an in vitro kinase assay revealed increased autophosphorylation of PKD (EC502.8 n m) in response to phorbol-12-myristate-13-acetate (PMA). Exposure to norepinephrine also induced a dose-dependent increase in PKD autophosphorylation (EC500.6 μm). Pretreatment with the α1-adrenergic receptor (AR) antagonist prazosin blocked norepinephrine-induced PKD autophosphorylation, while the β1-AR antagonist atenolol had no effect, indicating that activation of PKD by norepinephrine occurred via theα1 -AR. Involvement of the α1-AR was confirmed by exposure of myocytes to theα1 -AR agonist phenylephrine, which induced a similar profile of PKD autophosphorylation to norepinephrine (EC500.6 μm). The effects of both α1-AR stimulation and PMA on PKD autophosphorylation were mediated by PKC, since these effects could be attenuated by pretreatment of myocytes with the PKC inhibitor bisindolylmaleimide. These data show that PKD is expressed in rat ventricular myocardium, where its expression is subject to developmental control, and that PKD activity in ventricular myocytes is regulated through α1-AR- and PKC-mediated pathways.