The aim of this project is to better elucidate the role(s) of specific protein kinases in the regulation of cell growth and in malignant transformation. Since subcellular localization is important in determining the functional and regulatory specificity of protein kinases, studies were carried out to characterize the relationship between the domain organization and subcellular localization of protein kinase Ce (PKCe). A series of NIH3T3 cell lines were created, each overexpressing a different truncated version of PKCe. Holo PKCe was found to localize to the Golgi as well as to the plasma membrane, while the zinc-finger domain localized exclusively to the Golgi. Other domains of PKCe (pseudosubstrate and hinge regions) also were found to contain putative subcellular localization signals involved in targeting PKCe to subcellular fractions. In addition, these domains appear to influence the phorbol ester-induced translocation of PKCe from the Golgi to the plasma membrane. Phorbol ester-induced translocation from the Golgi to the plasma membrane was observed to proceed by at least two mechanisms: a rapid, vesicle-independent process noted with holo PKCe, and a slow, vesicle-dependent pathway noted with the zinc-finger fragment. Previous studies have established that cAMP-dependent protein kinase (PKA) activity, as well as cAMP binding to its RI and RII regulatory subunits, are decreased in fibroblasts and erythrocytes isolated from patients with psoriasis. It now has been determined that exposure of normal human dermal fibroblasts in culture to hydrogen peroxide and to other oxygen free radical generating systems decreased PKA activity and also cAMP binding to the RI and RII regulatory subunits. Conversely, treatment of psoriatic fibroblasts with free radical scavenging agents restored the ability of RI and RII to bind cAMP toward normal levels. The protein levels of RI and RII are similar in normal and psoriatic fibroblasts, and were not changed by exposure to oxygen free radicals. These results suggest that oxidative modification may be an important regulatory mechanism for PKA, and that an altered oxidative state may be involved in mediating the decrease in PKA activity and cAMP binding noted in cells from psoriatic patients.
NIH ExPorter
NIH ExPorter