Abstract 17164: The Pentameric Form of Phospholamban is Important for the Regulation of Phospholamban Phosphorylation and Function

Phospholamban (PLN) regulates myocyte calcium cycling by inhibiting the Ca2+ATPase SERCA2a. Protein kinase A (PKA) mediated phosphorylation attenuates PLN activity leading to enhanced calcium uptake rates and accelerated cardiac relaxation. In vivo, PLN is present in monomeric and pentameric form. It is believed that PKA primarily targets the PLN monomer. However, we found that a R9C mutant of PLN dominantly inhibits PLN phosphorylation only within the pentamer suggesting a significant role of the pentamer in determining phosphorylation and, thus, PLN activity. To investigate the role of the pentamer in PLN phosphorylation and function, the sensitivity, kinetics and stoichiometry of phosphorylation were analyzed in monomeric and pentameric PLN mutants expressed in a human cell line (HEK293AD). We found an independent increase of phosphorylation for monomer and pentamer upon forskolin stimulation, both in a concentration and time-dependent manner. Intriguingly, phosphorylation signals of PLN pentamers incr...