Choline kinase is the most upstream enzyme in the CDP-choline pathway. It catalyzes the phosphorylation of choline to phosphorylcholine in the presence of ATP and Mg2+ during the biosynthesis of phosphatidylcholine, the major phospholipid in eukaryotic cell membranes. In humans, choline kinase (CK) is encoded by two separate genes, ckα and ckβ, which produce three isoforms, CKα1, CKα2, and CKβ. Previous studies have associated ckβ with muscle development; however, the molecular mechanism underlying the transcriptional regulation of ckβ has never been elucidated.
Protein kinase C (PKC) has been implicated in carcinogenesis and displays variable expression profiles during cancer progression. Studies of dietary phytochemicals on cancer signalling pathway regulation have been conducted to search for potent signalling regulatory agents. The present study was designed to evaluate any suppressive effect of maslinic acid on PKC expression in human B-lymphoblastoid cells (Raji cells), and to identify 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 PMA induced 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 values achieved for maslinic acid, staurosporine, H-7, sphingosine, rottlerin, ursolic acid and oleanolic acid were 11.52, 0.011, 0.767, 2.45, 5.46, 27.93 and 39.29 μM, respectively. Four PKC isoforms, PKC βI, βII, δ, and ζ, were identified in Raji cells via western blotting. Maslinic acid suppressed the expression of PKC βI, δ, and ζ in a concentration-dependent manner. These preliminary results suggest promising suppressive effects of maslinic acid on PKC activity in Raji cells. Maslinic acid could be a potent cancer chemopreventive agent that may be involved in regulating many downstream signalling pathways that are activated through PKC receptors.
The aim of this study was to determine the role of intracellular proteins in phagocytosis of opsonized Porphyromonas gingivalis by RAW264.7 cells, a murine macrophage-like cell line. This periodontopathogen was grown anaerobically and opsonized with an IgG2a murine monoclonal anti-P. gingivalis lipopolysaccharide antibody. RAW264.7 cells were preincubated with protein tyrosine kinase inhibitors (staurosporine and genistein), protein kinase C inhibitors (phorbol myristic acetate and bisindolylmaleimide), a serine/threonine phosphatase inhibitor (okadaic acid), a phosphatidylinositol 3-kinase inhibitor (worthmannin), phospholipase A2 inhibitors (bromophenacyl bromide and nordihydroguaiaretic acid), phospholipase C inhibitors (p-chloromercuriphenyl sulfonate and neomycin sulfate), an actin-filament depolymerizer (cytochalasin D), and a microtubule disrupting agent (colchicine). Inhibitor-treated macrophages were then incubated with the opsonized P. gingivalis and the phagocytosed cells determined microscopically. The results showed the percentage of the phagocytosed organisms decreased when the cells were preincubated with protein tyrosine kinase, protein kinase C, protein phosphatase and phosphatidylinositol 3-kinase inhibitors. Of interest, preincubation with phorbol myristic acetate for 30 min increased the ability of RAW264.7 cells to phagocytose the opsonized organisms. Phospholipase A2 and phospholipase C inhibitors only slightly reduced the number of phagocytosed organisms. The results indicated that opsonophagocytosis of P. gingivalis by RAW264.7 cells might be determined by the activation of protein tyrosine kinase, protein kinase C, protein phosphatases, and phosphatidylinositol 3-kinase inhibitor. Both phospholipase A2 and phospholipase C would appear to be involved to a lesser extent. The opsonophagocytosis of this periodontopathogen would also appear to be dependent upon actin and microtubule polymerization.