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J. Biol. Chem., Vol. 279, Issue 7, 5216-5226, February 13, 2004

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Hypo-osmotic Stress Activates Plc1p-dependent Phosphatidylinositol 4,5-Bisphosphate Hydrolysis and Inositol Hexakisphosphate Accumulation in Yeast^*

Nevin M. Perera, Robert H. Michell, and Stephen K. Dove

From the School of Biosciences, University of Birmingham, Birmingham B15 2TT, United Kingdom

Polyphosphoinositide-specific phospholipases (PICs) of the -subfamily are ubiquitous in eukaryotes, but an inability to control these enzymes physiologically has been a major obstacle to understanding their cellular function(s). Plc1p is similar to metazoan -PICs and is the only PIC in Saccharomyces cerevisiae. Genetic studies have implicated Plc1p in several cell functions, both nuclear and cytoplasmic. Here we show that a brief hypo-osmotic episode provokes rapid Plc1p-catalyzed hydrolysis of PtdIns(4,5)P₂ in intact yeast by a mechanism independent of extracellular Ca²⁺. Much of this PtdIns(4,5)P₂ hydrolysis occurs at the plasma membrane. The hydrolyzed PtdIns(4,5)P₂ is mainly derived from PtdIns4P made by the PtdIns 4-kinase Stt4p. PtdIns(4,5)P₂ hydrolysis occurs normally in mutants lacking Arg82p or Ipk1p, but they accumulate no InsP₆, showing that these enzymes normally convert the liberated Ins(1,4,5)P₃ rapidly and quantitatively to InsP₆. We conclude that hypo-osmotic stress activates Plc1p-catalyzed PtdIns(4,5)P₂ at the yeast plasma membrane and the liberated Ins(1,4,5)P₃ is speedily converted to InsP₆. This ability routinely to activate Plc1p-catalyed PtdIns(4,5)P₂ hydrolysis in vivo opens up new opportunities for molecular and genetic scrutiny of the regulation and functions of phosphoinositidases C of the -subfamily.

Received for publication, May 14, 2003 , and in revised form, November 7, 2003.

^* This work was supported by the Medical Research Council (to N. M. P.) and the Royal Society (to S. K. D. and R. H. M.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK. Tel.: 44-121-414-5413; Fax: 44-870-137-7947; E-mail: r.h.michell{at}bham.ac.uk.

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