title: Lipopeptides activate Gi-proteins in dibutyryl cyclic AMP-differentiated HL-60 cells.
abstract: Synthetic lipopeptides activate superoxide-anion (O2-) formation in human neutrophils in a pertussis-toxin (PTX)-sensitive manner, suggesting the involvement of G-proteins of the Gi family in the signal-transduction pathway. We compared G-protein activation by lipopeptides and the chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (fMLP) in dibutyryl-cyclic-AMP-differentiated HL-60 cells. The lipopeptide (2S)-2-palmitoylamino-6-palmitoyloxymethyl-7-palmitoyloxy heptanoyl-SK4 (Pam3AhhSK4) and fMLP activated high-affinity GTPase, i.e. the enzymic activity of G-protein alpha-subunits, in HL-60 membranes in a time- and protein-dependent manner, but they had no effect on Mg(2+)-ATPase and Na+/K(+)-ATPase. Pam3AhhSK4 and fMLP increased Vmax. of GTP hydrolysis. Pam3AhhSK4 activated GTP hydrolysis with half-maximal and maximal effects at about 2 microM and 10 microM respectively. Other lipopeptides activated GTP hydrolysis as well. Lipopeptides were less effective than fMLP to activate GTPase. In membranes from PTX-treated cells, the stimulatory effects of lipopeptides and fMLP on GTPase were abolished. In N-ethylmaleimide-treated membranes, the relative stimulatory effect of Pam3AhhSK4 on GTP hydrolysis was enhanced, whereas that of fMLP was diminished. fMLP and Pam3AhhSK4 activated GTPase in an over-additive manner in N-ethylmaleimide-treated membranes. Unlike fMLP, Pam3AhhSK4 did not enhance incorporation of GTP azidoanilide into, and cholera-toxin-catalysed ADP-ribosylation of Gi-protein alpha-subunits in, HL-60 membranes and did not induce rises in cytosolic Ca2+ concentration. Pam3AhhSK4 and fMLP stimulated phosphatidic acid formation in a PTX-sensitive manner. Pam3AhhSK4 itself did not activate O2- formation, but potentiated the stimulatory effects of fMLP. Our data suggest that (i) lipopeptides activate the GTPase of Gi-proteins, (ii) lipopeptides and fMLP activate Gi-proteins differently, (iii) lipopeptides stimulate phospholipase D via Gi-proteins, and (iv) phosphatidic acid formation is not sufficient for activation of O2- formation.
authors.affiliation: Institut für Pharmakologie, Freie Universität Berlin, Federal Republic of Germany.
authors.forename: J F
authors.initials: JF
authors.lastname: Klinker
authors.forename: A
authors.initials: A
authors.lastname: Höer
authors.forename: I
authors.initials: I
authors.lastname: Schwaner
authors.forename: S
authors.initials: S
authors.lastname: Offermanns
authors.forename: K
authors.initials: K
authors.lastname: Wenzel-Seifert
authors.forename: R
authors.initials: R
authors.lastname: Seifert
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000595:Amino Acid Sequence; D003994:Bucladesine / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects*; D002460:Cell Line; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D015473:Leukemia, Promyelocytic, Acute; D008074:Lipoproteins / Q000494:pharmacology*; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism; D037342:Pertussis Toxin; D013481:Superoxides / Q000378:metabolism; D013997:Time Factors; D014407:Tumor Cells, Cultured; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D008074:Lipoproteins; D008565:Membrane Proteins; D010566:Virulence Factors, Bordetella; D013481:Superoxides; D000246:Adenosine Diphosphate Ribose; D009240:N-Formylmethionine Leucyl-Phenylalanine; D003994:Bucladesine; D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins