A PIP5 Kinase Essential for Efficient Chemotactic Signaling

• Published in: Current biology Vol. 24; no. 4; pp. 415 - 421
• Main Authors: Fets, Louise, Nichols, John M.E., Kay, Robert R.
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 17.02.2014; Cell Press
• Subjects: Chemotaxis; Cyclic AMP - metabolism; Dictyostelium; Dictyostelium - cytology; Dictyostelium - enzymology; Enzyme Activation; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor) - genetics; Phosphotransferases (Alcohol Group Acceptor) - metabolism; Proto-Oncogene Proteins c-akt - metabolism; Signal Transduction
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2013.12.052

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 [1, 2]. 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 [3, 4]. Although it is now known that PI(3,4,5)P3 signaling is nonessential for gradient sensing [5, 6], the role of the related phosphoinositide PI(4,5)P2 is little understood, despite its clear importance in many cell biological processes [7]. 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 [8], 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. [Display omitted] •Gradient sensing is severely impaired in pikI− cells, but cell speed is unaffected•PikI is the major PIP5K in Dictyostelium and produces 90% of cellular PI(4,5)P2•PikI is required for active Ras to couple to downstream effectors such as TorC2•Phosphorylation by PKB (downstream of Ras) may increase PikI activity Fets et al. show that PikI, a PIP5 kinase that generates PI(4,5)P2, is vital for chemotaxis in Dictyostelium cells. Without PikI, cells are able to move at normal speeds, but gradient sensing is dramatically attenuated as a result of uncoupling of activated Ras from its downstream effectors.