title: Phosphorylation of actin-related protein 2 (Arp2) is required for normal development and cAMP chemotaxis in Dictyostelium.
abstract: Phosphorylation of the actin-related protein 2 (Arp2) subunit of the Arp2/3 complex on evolutionarily conserved threonine and tyrosine residues was recently identified and shown to be necessary for nucleating activity of the Arp2/3 complex and membrane protrusion of Drosophila cells. Here we use the Dictyostelium diploid system to replace the essential Arp2 protein with mutants that cannot be phosphorylated at Thr-235/6 and Tyr-200. We found that aggregation of the resulting mutant cells after starvation was substantially slowed with delayed early developmental gene expression and that chemotaxis toward a cAMP gradient was defective with loss of polarity and attenuated F-actin assembly. Chemotaxis toward cAMP was also diminished with reduced cell speed and directionality and shorter pseudopod lifetime when Arp2 phosphorylation mutant cells were allowed to develop longer to a responsive state similar to that of wild-type cells. However, clathrin-mediated endocytosis and chemotaxis under agar to folate in vegetative cells were only subtly affected in Arp2 phosphorylation mutants. Thus, phosphorylation of threonine and tyrosine is important for a subset of the functions of the Arp2/3 complex, in particular an unexpected major role in regulating development.
authors.affiliation: Department of Cell and Tissue Biology, University of California, San Francisco, California 94143, USA.
authors.forename: Chang-Hoon
authors.initials: CH
authors.lastname: Choi
authors.forename: Peter A
authors.initials: PA
authors.lastname: Thomason
authors.forename: Mehreen
authors.initials: M
authors.lastname: Zaki
authors.forename: Robert H
authors.initials: RH
authors.lastname: Insall
authors.forename: Diane L
authors.initials: DL
authors.lastname: Barber
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D051377:Actin-Related Protein 2 / Q000737:chemistry*; D000199:Actins / Q000378:metabolism; D000483:Alleles; D000818:Animals; D002465:Cell Movement; D002633:Chemotaxis; D000242:Cyclic AMP / Q000378:metabolism*; D004023:Dictyostelium / Q000378:metabolism*; D004705:Endocytosis; D008954:Models, Biological; D009154:Mutation; D010766:Phosphorylation; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D014443:Tyrosine / Q000737:chemistry
chemical_list: D051377:Actin-Related Protein 2; D000199:Actins; D014443:Tyrosine; D000242:Cyclic AMP