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Published online 14 May 2001. doi:10.1083/jcb.153.4.795
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© The Rockefeller University Press, 0021-9525/2001/5/795/ $5.00
The Journal of Cell Biology, Volume 153, Number 4, May 14, 2001 795-810


Original Article

Role of Phosphatidylinositol 3' Kinase and a Downstream Pleckstrin Homology Domain–containing Protein in Controlling Chemotaxis in Dictyostelium

Satoru Funamotoa, Kristina Milana, Ruedi Meilia, and Richard A. Firtela
a Section of Cell and Developmental Biology and Center for Molecular Genetics, University of California at San Diego, La Jolla, California 92093

Correspondence to: Richard A. Firtel, Center for Molecular Genetics, Rm. 225, University of California at San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0634. Tel:(858) 534-2788 Fax:(858) 534-7073 E-mail:rafirtel{at}ucsd.edu.

We show that cells lacking two Dictyostelium class I phosphatidylinositol (PI) 3' kinases (PI3K and pi3k1/2-null cells) or wild-type cells treated with the PI3K inhibitor LY294002 are unable to properly polarize, are very defective in the temporal, spatial, and quantitative regulation of chemoattractant-mediated filamentous (F)-actin polymerization, and chemotax very slowly. PI3K is thought to produce membrane lipid-binding sites for localization of PH domain–containing proteins. We demonstrate that in response to chemoattractants three PH domain–containing proteins do not localize to the leading edge in pi3k1/2-null cells, and the translocation is blocked in wild-type cells by LY294002. Cells lacking one of these proteins, phdA-null cells, exhibit defects in the level and kinetics of actin polymerization at the leading edge and have chemotaxis phenotypes that are distinct from those described previously for protein kinase B (PKB) (pkbA)-null cells. Phenotypes of PhdA-dominant interfering mutations suggest that PhdA is an adaptor protein that regulates F-actin localization in response to chemoattractants and links PI3K to the control of F-actin polymerization at the leading edge during pseudopod formation. We suggest that PKB and PhdA lie downstream from PI3K and control different downstream effector pathways that are essential for proper chemotaxis.

Key Words: Dictyostelium, PH domain, actin polymerization, chemotaxis, PI3 kinase


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