Regulation of Protein Phosphatase 4 by a MAP Kinase Cascade Controls Chemotaxis

Classical genetics in model organisms has defined many signaling pathways that control cell movement and multicellular morphogenesis. However,these approaches have not succeeded in placing some established chemotaxis regulators, such as the MAP kinase kinase MEK1, in activator/effector pathways. Here, we combined morphological measurements with epistasis analysis of transcriptional phenotypes and found that the protein phosphatase 4 (PP4) signaling pathway controls Dictyostelium chemotaxis and development. PP4 is a phosphatase that regulates recovery from DNA damage. We show that Dictyostelium SMEK functions as the PP4R3 regulatory subunit and may regulate the subcellular localization of PP4 catalytic subunit PP4C. SMEK binds PP4C and the complex functions downstream of MEK1 to regulate chemotaxis and morphogenesis. Microarray analysis of gene expression in mutant strains indicated that PP4 controls leading edge formation and cellular responses to stress. Thus, the MEKPP4C/SMEK pathway has a direct role in regulating chemotaxis, in addition to regulating the DNA repair checkpoint. Keywords: Developmental time course series from 1 Dictyostelium wildtype and 5 chemotaxis mutants to determine epistatic relationship 6 Dictyostelium strains were analyzed. For each strain, there were 4 developmental time points (0,6,12,18). Each developmental series experiment per strain consisted of 3 biological replicas and 2 technical replications. [6 strain x 4 time point x 3 biologial replica x 2 technical replica] Each test sample(labeled with Cy5) was co-hybridized with a reference sample (labeled with Cy3) consisting of a pool from vegetative wild type cells and 6 developmental time points (0,3,6,12,17,24 hours) 6 strain x 4 time point x 3 biologial replica x 2 technical replica