title: The role of the ribosomal protein S19 C-terminus in Gi protein-dependent alternative activation of p38 MAP kinase via the C5a receptor in HMC-1 cells.
abstract: We have demonstrated that an alternative C5a receptor (C5aR) ligand, the homodimer of ribosomal protein S19 (RP S19), contains a unique C-terminus (I(134)-H(145)) that is distinct from the moieties involved in the C5a-C5aR interaction. To examine the role of I(134)-H(145) in the ligand-C5aR interaction, we connected this peptide to the C-terminus of C5a (C5a/RP S19) and found that it endowed the second binding moiety of RP S19 (L(131)DR) with a relatively higher binding affinity to the C5aR on a human mast cell line, HMC-1. In contrast to the C5aR, the second C5aR C5L2 worked as a decoy receptor. As a result, the mitogen-activated protein kinase (MAPK) downstream of the Gi protein exchanged extracellular-signal regulated kinase for p38MAPK. This alternative p38MAPK activation could be pharmacologically suppressed not only by the downregulation of phosphoinositide 3-kinase (PI3K) by LY294002, but also by the over-activation of protein kinase C by phorbol 12-myristate 13-acetate. The activation was reproduced upon C5a-C5aR interaction by a simultaneous suppression of PI3K and phospholipase C with LY294002 and U73122 at low concentrations. Moreover, p38MAPK phosphorylation upstream of the pertussis toxin-dependent extracellular Ca(2+) entry was also suppressed by high concentrations of MgCl(2), which blocks melastatin-type transient receptor potential Ca(2+) channels (TRPMs). The active conformation of C5aR upon the ligation by C5a, at least on HMC-1 cells, is changed by the additional interaction of the I(134)-H(145) peptide, which seems to guide the alternative activation of p38MAPK. This activation is then amplified by a novel positive feedback loop between p38MAPK and TRPM.
authors.affiliation: Department of Molecular Pathology, Kumamoto University Graduate School, Japan. seino@kumamoto-u.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishiura
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Tokita
authors.forename: Ying
authors.initials: Y
authors.lastname: Li
authors.forename: Koichi
authors.initials: K
authors.lastname: Harada
authors.forename: Trent M
authors.initials: TM
authors.lastname: Woodruff
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Taylor
authors.forename: Tienabe K
authors.initials: TK
authors.lastname: Nsiama
authors.forename: Norikazu
authors.initials: N
authors.lastname: Nishino
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Yamamoto
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008407:Mast Cells / Q000166:cytology / Q000378:metabolism; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D044087:Receptor, Anaphylatoxin C5a / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D010455:Peptides; D044087:Receptor, Anaphylatoxin C5a; D011993:Recombinant Fusion Proteins; D012269:Ribosomal Proteins; C040343:ribosomal protein S19; D019869:Phosphatidylinositol 3-Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D002118:Calcium