Suppressive Effect of Maslinic Acid on PMA-induced Protein Kinase C in Human B-Lymphoblastoid Cells

Protein kinase C (PKC) has been implicated in carcinogenesis and displays variable expression profilesduring cancer progression. Studies of dietary phytochemicals on cancer signalling pathway regulation havebeen conducted to search for potent signalling regulatory agents. The present study was designed to evaluateany suppressive effect of maslinic acid on PKC expression in human B-lymphoblastoid cells (Raji cells), and toidentify the PKC isoforms expressed. Effects of maslinic acid on PKC activity were determined using a PepTag®assay for non-radioactive detection of PKC. The highest expression in Raji cells was obtained at 20 nM PMAinduced for 6 hours. Suppressive effects of maslinic acid were compared with those of four PKC inhibitors (H-7, rottlerin, sphingosine, staurosporine) and two triterpenes (oleanolic acid and ursolic acid). The IC50 valuesachieved for maslinic acid, staurosporine, H-7, sphingosine, rottlerin, ursolic acid and oleanolic acid were11.52, 0.011, 0.767, 2.45, 5.46, 27.93 and 39.29 μM, respectively. Four PKC isoforms, PKC βI, βII, δ, and ζ, wereidentified in Raji cells via western blotting. Maslinic acid suppressed the expression of PKC βI, δ, and ζ in aconcentration-dependent manner. These preliminary results suggest promising suppressive effects of maslinicacid on PKC activity in Raji cells. Maslinic acid could be a potent cancer chemopreventive agent that may beinvolved in regulating many downstream signalling pathways that are activated through PKC receptors.