Protein kinase C alpha regulates human monocyte O-2(center dot-) production and low density lipoprotein lipid oxidation

Our previous studies have shown that human native low density lipoprotein ( LDL) can be oxidized by activated human monocytes, In this process, both ac tivation of protein kinase C (PKC) and induction of superoxide anion (O-2(r adical anion)) production are required. PKC is a family of isoenzymes, and the functional roles of individual PKC isoenzymes are believed to differ ba sed on subcellular location and distinct responses to regulatory signals. W e have shown that the PKC isoenzyme that is required for both monocyte O-2( radical anion) production and oxidation of LDL is a member of the conventio nal PKC group of PKC isoenzymes (Li, Q., and Cathcart, M.K. (1994) J. Biol. Chem, 269, 17508-17515), The conventional PKC group includes PKC alpha, PK C beta I, PKC beta II, and PKC gamma. With the exception of PKC gamma, each of these isoenzymes was detected in human monocytes, in these studies, we investigated the requirement for select PKC isoenzymes in the process of mo nocyte-mediated LDL lipid oxidation, Our data indicate that PKC activity wa s rapidly induced upon monocyte activation with the majority of the activit y residing in the membrane/particulate fraction. This enhanced PRC activity was sustained for up to 24 h after activation. PKC alpha, PKC beta I, and PKC beta II protein levels were induced upon monocyte activation, and PKC a lpha and PKC beta II substantially shifted their location from the cytosol to the particulate/ membrane fraction. To distinguish between these isoenzy mes for regulating monocyte O-2(radical anion) production and LDL oxidation , PKC alpha or PKC beta isoenzyme-specific antisense oligonucleotides were used to selectively suppress isoenzyme expression. We found that suppressio n of PKC alpha expression inhibited both monocyte-mediated O-2(radical anio n) production and LDL lipid oxidation by activated human monocytes, In cont rast, inhibition of PKC beta expression (including both PKC beta I and PKC beta II) did not affect O-2(radical anion) production or LDL lipid oxidatio n, Further studies demonstrated that the respiratory burst oxidase responsi ble for O-2(radical anion) production remained functionally intact in monoc ytes with depressed levels of PKC alpha because O-2(radical anion) producti on could be restored by treating the monocytes with arachidonic acid. Taken together, our data reveal that PKC alpha, and not PKC beta I or PKC beta I I, is the predominant isoenzyme required for O-2(radical anion) production and maximal oxidation of LDL by activated human monocytes.