title: Role of protein kinase C in the phosphatidylserine-induced inhibition of DNA synthesis in blood mononuclear cells.
abstract: The mechanism of immunosuppressant activity of phosphatidylserine has been studied in peripheral blood mononuclear cells depleted or not of monocytes. After the addition of phosphatidylserine, mass determinations and uptake of labeled compound demonstrate its transfer into the cells. Phosphatidylserine incorporation causes a 2.5-fold increase of membrane-bound protein kinase C activity. The activation of translocated enzyme is indicated by the inhibition of phosphoinositide hydrolysis, and early feedback effect induced by activated protein kinase C. This action of phosphatidylserine is reproduced by tetradecanoylphorbolacetate and is prevented by the protein kinase C inhibitor, staurosporine. Consistently, phosphatidylserine (8 nmol/10(6) cells) decreases by 46% the production of inositol phosphates in cells responding to phytohemagglutinin. The decrease of phosphoinositide signal pathway as well as the inhibition of mitogen-induced DNA synthesis are produced at the same phosphatidylserine concentration and are equally manifest in total mononuclear cells or in preparations depleted of monocytes. However, only in the presence of monocytes does tetradecanoylphorbolacetate enhance the action of phospholipid, decreasing its IC50 from 13-15 microM to 7 microM. Thus, the data suggest that a reaction driven by protein kinase-C and a factor released by activated monocytes are involved in the phosphatidylserine-induced inhibition of lymphocyte DNA synthesis.
authors.affiliation: Fidia Research Laboratories, Abano Terme, Padua, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Caselli
authors.forename: F
authors.initials: F
authors.lastname: Bellini
authors.forename: D
authors.initials: D
authors.lastname: Ponzin
authors.forename: O R
authors.initials: OR
authors.lastname: Baricordi
authors.forename: A
authors.initials: A
authors.lastname: Bruni
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis*; D004789:Enzyme Activation; D006801:Humans; D007165:Immunosuppression Therapy; D007963:Leukocytes, Mononuclear / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000470:Alkaloids; D010716:Phosphatidylinositols; D010718:Phosphatidylserines; D004247:DNA; D011493:Protein Kinase C; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate