title: Direct biochemical measurements of signal relay during Dictyostelium development.
abstract: Upon starvation, individual Dictyostelium discoideum cells enter a developmental program that leads to collective migration and the formation of a multicellular organism. The process is mediated by extracellular cAMP binding to the G protein-coupled cAMP receptor 1, which initiates a signaling cascade leading to the activation of adenylyl cyclase A (ACA), the synthesis and secretion of additional cAMP, and an autocrine and paracrine activation loop. The release of cAMP allows neighboring cells to polarize and migrate directionally and form characteristic chains of cells called streams. We now report that cAMP relay can be measured biochemically by assessing ACA, ERK2, and TORC2 activities at successive time points in development after stimulating cells with subsaturating concentrations of cAMP. We also find that the activation profiles of ACA, ERK2, and TORC2 change in the course of development, with later developed cells showing a loss of sensitivity to the relayed signal. We examined mutants in PKA activity that have been associated with precocious development and find that this loss in responsiveness occurs earlier in these mutants. Remarkably, we show that this loss in sensitivity correlates with a switch in migration patterns as cells transition from streams to aggregates. We propose that as cells proceed through development, the cAMP-induced desensitization and down-regulation of cAMP receptor 1 impacts the sensitivities of chemotactic signaling cascades leading to changes in migration patterns.
authors.affiliation: Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Satarupa
authors.initials: S
authors.lastname: Das
authors.affiliation: Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742.
authors.forename: Erin C
authors.initials: EC
authors.lastname: Rericha
authors.affiliation: Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Anna
authors.initials: A
authors.lastname: Bagorda
authors.affiliation: Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892. Electronic address: parentc@mail.nih.gov.
authors.forename: Carole A
authors.initials: CA
authors.lastname: Parent
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D001671:Biochemistry / Q000379:methods; D002633:Chemotaxis / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004023:Dictyostelium / Q000254:growth & development*; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods; D020935:MAP Kinase Signaling System; D008954:Models, Biological; D009154:Mutation; D010766:Phosphorylation; D011953:Receptors, Cyclic AMP / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D011953:Receptors, Cyclic AMP; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases