Isoform-specific modulation of coronary artery PKC by glucocorticoids

Glucocorticoids (GC) exert diverse cellular effects in response to both acute and chronic stress, the functional consequences of which have been implicated in the development of cardiovascular pathology such as hypertension and atherosclerosis. However, the mechanisms by which GCs activate divergent signaling pathways are poorly understood. The present study examined the direct effects of natural (cortisol) and synthetic (dexamethasone) GCs on protein kinase C (PKC) isoform expression in coronary arteries. Porcine right coronary arteries were treated in vitro for 18 h in the presence and absence of either dexamethasone (10, 100, or 500 nM) or cortisol (50, 125, 250, or 500 nM). PKC isoform levels and subcellular distribution were determined by immmunoblotting of whole cell homogenates and immunocytofluorescence using PKC-α, -β_II, -ε, -δ, and -ζ specific antibodies. Dexamethasone caused a ∼4-fold increase in PKC-α, a ∼2.5-fold increase in PKC-β_II, and a 2-fold increase in PKC-ε (p < 0.05). In contrast, dexamethasone had no effect on PKC-δ or PKC- ζ levels. Dexamethasone also caused an increase in the activity of PKC-α (285%), -β_II (170%), and -ε (210%). Cortisol produced similar effects on PKC isoform expression. Confocal microscopy revealed that while dexamethasone altered localization patterns for PKC-α, -β_II, and -ε, no such effect was observed for PKC-δ or PKC-ζ. The stimulatory effects of dexamethasone and cortisol on coronary PKC levels and translocation were prevented by the GC receptor (GR) blocker, RU486. These results demonstrate, for the first time, that GCs modulate coronary PKC expression and subcellular distribution in an isoform-specific manner through a GR-dependent mechanism.