ABSTRACT
Exogenous lysophosphatidic acid (LPA) has been shown to evoke a chemotactic response in aggregative cells of the social amoeba Dictyostelium discoideum. In this paper, we demonstrate that extracellular LPA is also able to induce activation of mitogen-activated protein (MAP) kinase DdERK2 (extracellular signal regulated kinase 2) in these cells. This activation is independent of cyclic AMP receptors, yet fully dependent on the single Gbeta subunit, hinting to the presence of functional heptahelical LPA receptors in a primitive eukaryote. We did not observe LPA-dependent cyclic GMP accumulation, which suggests that the pathways for LPA-induced and "classical" chemotaxis of D. discoideum cells are substantially different.
Subject(s)
Dictyostelium/physiology , Heterotrimeric GTP-Binding Proteins/metabolism , Lysophospholipids/pharmacology , Mitogen-Activated Protein Kinase 1/metabolism , Receptors, G-Protein-Coupled , Animals , Chemotaxis/drug effects , Cyclic AMP/metabolism , Cyclic GMP/metabolism , Dictyostelium/drug effects , Dictyostelium/genetics , Enzyme Activation/drug effects , Lysophospholipids/metabolism , Receptors, Cell Surface/drug effects , Receptors, Cell Surface/metabolism , Receptors, Lysophosphatidic Acid , Signal TransductionABSTRACT
We describe the identification and characterization of the BMH1 gene from the yeast Saccharomyces cerevisiae. The gene encodes a putative protein of 292 amino acids which is more than 50% identical with the bovine brain 14-3-3 protein and proteins isolated from sheep brain which are strong inhibitors of protein kinase C. Disruption mutants and strains with the BMH1 gene on multicopy plasmids have impaired growth on minimal medium with glucose as carbon source, i.e. a 30-50% increase in generation time. These observations suggest a regulatory function of the bmh1 protein. In contrast to strains with an intact or a disrupted BMH1 gene, strains with the BMH1 gene on multicopy plasmids hardly grew on media with acetate or glycerol as carbon source.
