title: The Dictyostelium MAPK ERK1 is phosphorylated in a secondary response to early developmental signaling.
abstract: Previous reports have suggested that the two mitogen-activated protein kinases (MAPKs) in Dictyostelium discoideum, ERK1 and ERK2, can be directly activated in response to external cAMP even though these MAPKs play different roles in the developmental life cycle. To better characterize MAPK regulation, the levels of phosphorylated MAPKs were analyzed in response to external signals. Only ERK2 was rapidly phosphorylated in response to the chemoattractants, cAMP and folate. In contrast, the phosphorylation of ERK1 occurred as a secondary or indirect response to these stimuli and this phosphorylation was enhanced by cell-cell interactions, suggesting that other external signals can activate ERK1. The phosphorylation of ERK1 or ERK2 did not require the function of the other MAPK in these responses. Folate stimulation of a chimeric population of erk1- and gα4- cells revealed that the phosphorylation of ERK1 could be mediated through an intercellular signal other than folate. Loss of ERK1 function suppressed the developmental delay and the deficiency in anterior cell localization associated with gα5- mutants suggesting that ERK1 function can be down regulated through Gα5 subunit-mediated signaling. However, no major changes in the phosphorylation of ERK1 were observed in gα5- cells suggesting that the Gα5 subunit signaling pathway does not regulate the phosphorylation of ERK1. These findings suggest that the activation of ERK1 occurs as a secondary response to chemoattractants and that other cell-cell signaling mechanisms contribute to this activation. Gα5 subunit signaling can down regulate ERK1 function to promote prestalk cell development but not through major changes to the level of phosphorylated ERK1.
authors.affiliation: Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, OK 74078-3020, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Schwebs
authors.affiliation: Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, OK 74078-3020, USA. Electronic address: jeff.hadwiger@okstate.edu.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Hadwiger
mesh_terms: D002450:Cell Communication / Q000187:drug effects; D048430:Cell Shape / Q000187:drug effects; D000242:Cyclic AMP / Q000494:pharmacology; D004023:Dictyostelium / Q000166:cytology / Q000201:enzymology* / Q000254:growth & development*; D005110:Extracellular Space / Q000378:metabolism; D005492:Folic Acid / Q000494:pharmacology; D044385:GTP-Binding Protein alpha Subunits / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D008954:Models, Biological; D010766:Phosphorylation / Q000187:drug effects; D015800:Protozoan Proteins / Q000378:metabolism
chemical_list: D044385:GTP-Binding Protein alpha Subunits; C099256:Galpha5 protein, Dictyostelium; D015800:Protozoan Proteins; D005492:Folic Acid; D000242:Cyclic AMP; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3
keywords: Chemotaxis; Development; Dictyostelium; G protein signaling; MAPK; Phosphorylation