A PIP5 kinase essential for efficient chemotactic signaling.
In neutrophils and Dictyostelium, chemoattractant gradients generate directed cell migration by eliciting signaling events that bias intrinsic motility and favor the production and retention of upgradient pseudopods. Phosphoinositides are actively regulated during chemotaxis in these cells, most iconically in the production of PI(3,4,5)P3 gradients within the plasma membrane. Although it is now known that PI(3,4,5)P3 signaling is nonessential for gradient sensing, the role of the related phosphoinositide PI(4,5)P2 is little understood, despite its clear importance in many cell biological processes. We describe here a PIP5 kinase, PikI, which produces PI(4,5)P2 and is essential for efficient chemotaxis of Dictyostelium cells. Without PikI, PI(4,5)P2 levels are reduced by 90%, and while pikI(-) cells move at normal speeds, they are highly disorientated in cAMP gradients. Following chemotactic stimulation, Ras is efficiently activated in pikI(-) cells, yet Ras-dependent responses (including activation of PKB) are severely impaired. PikI is phosphorylated by PKB, and in vitro studies of a phosphomimic mutant suggest that this phosphorylation increases PikI activity. We propose that adequate PI(4,5)P2 levels are required to couple activated Ras to its downstream effectors and that these levels are regulated by PikI, making it a crucial player in gradient sensing.
Cell Biology Division, MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Francis Crick Avenue, Cambridge CB2 0QH, UK. Electronic address: lfets@nimr.mrc.ac.uk.
Louise
L
Fets
Cell Biology Division, MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Francis Crick Avenue, Cambridge CB2 0QH, UK.
John M E
JM
Nichols
Cell Biology Division, MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Francis Crick Avenue, Cambridge CB2 0QH, UK.
Robert R
RR
Kay
D002633:Chemotaxis; D000242:Cyclic AMP / Q000378:metabolism; D004023:Dictyostelium / Q000166:cytology / Q000201:enzymology*; D004789:Enzyme Activation; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction
D000242:Cyclic AMP; D017853:Phosphotransferases (Alcohol Group Acceptor); C020077:1-phosphatidylinositol-4-phosphate 5-kinase; D051057:Proto-Oncogene Proteins c-akt