Myristoylation of Novel Protein Kinase C Beta II Peptide Inhibitor is Required for the Attenuation of Phorbol 12‐myristate 13‐acetate‐induced Superoxide Release in Isolated Rat Polymorphonuclear Leukocytes

Abstract

Polymorphonuclear leukocyte (PMN) superoxide (SO) production by NADPH oxidase (NOX‐2) activation contributes to myocardial ischemia‐reperfusion (I/R) injury. Protein kinase C beta‐II (PKC βII) is a principal mediator of NOX‐2 activation via phosphorylation of NOX‐2 cytosolic protein p47phox. Phorbol 12‐myristate 13‐acetate (PMA) is a known broad‐spectrum PKC agonist that induces PMN SO release. In prior studies, selective PKCβII inhibition with myristoylated PKCβII peptide inhibitor (N‐myr‐SLNPEWNET; myr‐PKCβII‐) attenuated PMA‐induced PMN SO release and myocardial I/R injury in a dose‐dependent manner. However, the role of myristoylation mediating the inhibitory effects of myr‐PKCβII‐ on PMN SO release needs to be determined. Therefore, we aim to confirm the role of PKCβII by using myristoylated PKCβII peptide activator (N‐myr‐SVEIWD; myr‐PKCβII+) and myr‐PKCβII‐ that influence PKCβII translocation. Whereas, myr‐scrambled PKCβII‐ (N‐myr‐WNPESLNTE; myr‐PKCβII‐scram) is a control for myristoylation. We hypothesize that myr‐PKCβII+ should augment, myr‐PKCβII‐should attenuate, and myr‐PKCβII‐scram should have no effect on PMA‐induced PMN SO release compared to non‐treated and unconjugated peptide controls. PMNs (5×106) isolated from male Sprague‐Dawley rats (~400g) were incubated for 15 min at 37°C in the presence/absence of SO dismutase (SOD; 10μg/mL, positive control), unconjugated PKCβII+/− (20 μM), myr‐PKCβII+/− (20 μM), or myr‐PKCβII‐scram (20 μM). SO release was evaluated by the absorbance change (at 550 nm) via ferricytochrome c reduction after PMA stimulation (100 nM) for 390 sec. Data were analyzed by ANOVA using Bonferroni‐Dunn post‐hoc analysis. Myr‐PKCβII‐ significantly attenuated PMA‐induced PMN SO release (0.29±0.02; n=36; p<0.05) when compared to myr‐PKCβII+ (0.42±0.03; n=29), myr‐PKCβII‐scram (0.53±0.05; n=10), and non‐treated controls (0.41±0.02; n=55). Unconjugated PKCβII+ (0.41±0.04; n=16) and PKCβII‐(0.40±0.04; n=28) were similar to non‐treated controls. SOD (n=8) significantly reduced SO release by 94±7% compared to all groups (p<0.01). Cell viability determined by 0.2% trypan blue exclusion was similar in all groups, 94±2%. Unexpectedly, myr‐PKCβII‐scram rather than myr‐PKCβII+ PMNs exhibited the highest PMA‐induced PMN SO release but was not significantly different from untreated controls. Additional experiments will determine whether myr‐PKCβII‐scram significantly enhances SO release. Results suggest myr‐ conjugation improved myr‐PKCβII‐ delivery compared to unconjugated PKCβII‐ but does not contribute to the inhibitory effects of PMA‐induced PMN SO release. Therefore, myr‐PKCβII‐ may be an effective therapeutic intervention to limit inflammation‐induced I/R injury.Support or Funding InformationThis research was supported by the Division of Research, Department of Biomedical Sciences, and the Center for Chronic Disorders of Aging at Philadelphia College of Osteopathic Medicine. Current license is supported by Young Therapeutics, LLC.