Oxidative modulation of cyclic AMP-dependent protein kinase in human fibroblasts: possible role in psoriasis

Abstract

Previous studies have established that cyclic AMP-dependent protein kinase (PKA) activity, as well as 8-azido-[32P]-cAMP binding to the RI and RII regulatory subunits, are decreased in cells from psoriatic patients compared to cells from normal patients. Here we show that the exposure of normal human dermal fibroblasts in culture to hydrogen peroxide and to oxygen free-radical generating systems decreased PKA activity, as well as cyclic AMP binding to the RI and RII regulatory subunits, to levels similar to those observed with psoriatic fibroblasts. Likewise, treatment of normal cytosolic preparations of PKA, as well as purified bovine PKA II, in vitro with free radical generating systems also resulted in decreased PKA activity and 8-azido [32P]-cAMP binding to the RI and RII regulatory subunits. Further, treatment of psoriatic fibroblasts with free radical scavenging agents such as vitamins E and C, and mannitol, and also with superoxide dismutase, restored the ability of RI and RII to bind 8-azido-[32P]-cAMP toward normal levels. Western blot analysis showed that the protein levels of the RI and RII subunits are similar in normal and psoriatic fibroblasts, and that the amounts of RI and RII are not altered by treatment of the cells with free radical-generating systems. These results suggest that oxidative modification may serve as a mechanism to alter PKA activity in human cells, and that an altered oxidative state may be involved in mediating the decrease in PKA activity and cyclic AMP binding noted in cells from psoriatic patients.