title: PP2A/B56 and GSK3/Ras suppress PKB activity during Dictyostelium chemotaxis.
abstract: We have previously shown that the Dictyostelium protein phosphatase 2A regulatory subunit B56, encoded by psrA, modulates Dictyostelium cell differentiation through negatively affecting glycogen synthase kinase 3 (GSK3) function. Our follow-up research uncovered that B56 preferentially associated with GDP forms of RasC and RasD, but not with RasG in vitro, and psrA(-) cells displayed inefficient activation of multiple Ras species, decreased random motility, and inefficient chemotaxis toward cAMP and folic acid gradient. Surprisingly, psrA(-) cells displayed aberrantly high basal and poststimulus phosphorylation of Dictyostelium protein kinase B (PKB) kinase family member PKBR1 and PKB substrates. Expression of constitutively active Ras mutants or inhibition of GSK3 in psrA(-) cells increased activities of both PKBR1 and PKBA, but only the PKBR1 activity was increased in wild-type cells under the equivalent conditions, indicating that either B56- or GSK3-mediated suppressive mechanism is sufficient to maintain low PKBA activity, but both mechanisms are necessary for suppressing PKBR1. Finally, cells lacking RasD or RasC displayed normal PKBR1 regulation under GSK3-inhibiting conditions, indicating that RasC or RasD proteins are essential for GSK3-mediated PKBR1 inhibition. In summary, B56 constitutes inhibitory circuits for PKBA and PKBR1 and thus heavily affects Dictyostelium chemotaxis.
authors.affiliation: Department of Biological Sciences, Florida International University, Miami, FL 33199.
authors.forename: Marbelys
authors.initials: M
authors.lastname: Rodriguez Pino
authors.affiliation: Department of Biological Sciences, Florida International University, Miami, FL 33199.
authors.forename: Boris
authors.initials: B
authors.lastname: Castillo
authors.affiliation: Department of Biological Sciences, Florida International University, Miami, FL 33199.
authors.forename: Bohye
authors.initials: B
authors.lastname: Kim
authors.affiliation: Department of Biological Sciences, Florida International University, Miami, FL 33199 Biochemistry PhD Program, Florida International University, Miami, FL 33199 Biomolecular Sciences Institutes, Florida International University, Miami, FL 33199 kiml@fiu.edu.
authors.forename: Lou W
authors.initials: LW
authors.lastname: Kim
mesh_terms: D002465:Cell Movement / Q000187:drug effects; D002633:Chemotaxis / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism; D004023:Dictyostelium / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D010766:Phosphorylation; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015800:Protozoan Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D015800:Protozoan Proteins; D000242:Cyclic AMP; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; D054648:Protein Phosphatase 2; D018631:ras Proteins