Screening for modulators of spermine tolerance identifies Sky1, the SR protein kinase of Saccharomyces cerevisiae, as a regulator of polyamine transport and ion homeostasis.
Although most cells are capable of transporting polyamines, the mechanism that regulates polyamine transport in eukaryotes is still largely unknown. Using a genetic screen for clones capable of restoring spermine sensitivity to spermine-tolerant mutants of Saccharomyces cerevisiae, we have demonstrated that Sky1p, a recently identified SR protein kinase, is a key regulator of polyamine transport. Yeast cells deleted for SKY1 developed tolerance to toxic levels of spermine, while overexpression of Sky1p in wild-type cells increased their sensitivity to spermine. Expression of the wild-type Sky1p but not of a catalytically inactive mutant restored sensitivity to spermine. SKY1 disruption results in dramatically reduced uptake of spermine, spermidine, and putrescine. In addition to spermine tolerance, sky1Delta cells exhibit increased tolerance to lithium and sodium ions but somewhat increased sensitivity to osmotic shock. The observed halotolerance suggests potential regulatory interaction between the transport of polyamines and inorganic ions, as suggested in the case of the Ptk2p, a recently described regulator of polyamine transport. We demonstrate that these two kinases act in two different signaling pathways. While deletion or overexpression of SKY1 did not significantly affect Pma1p activity, the ability of overexpressed Sky1p, Ptk1p, and Ptk2p to increase sensitivity to LiCl depends on the integrity of PPZ1 but not of ENA1.
Erez
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Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel.
Kahana
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C
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D027682:Cation Transport Proteins; D002455:Cell Division / Q000187:drug effects; D004352:Drug Resistance, Microbial; D051416:Focal Adhesion Protein-Tyrosine Kinases; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D005816:Genetic Complementation Test; D006706:Homeostasis; D007477:Ions / Q000378:metabolism; D007700:Kinetics; D018021:Lithium Chloride / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D009997:Osmotic Pressure; D010641:Phenotype; D011073:Polyamines / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism; D011700:Putrescine / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D015398:Signal Transduction; D012965:Sodium Chloride / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase; D013095:Spermidine / Q000378:metabolism; D013096:Spermine / Q000378:metabolism* / Q000494:pharmacology
D027682:Cation Transport Proteins; C086375:ENA1 protein, S cerevisiae; D005656:Fungal Proteins; D007477:Ions; C434364:PMA2 protein, S cerevisiae; D011073:Polyamines; D029701:Saccharomyces cerevisiae Proteins; D013096:Spermine; D012965:Sodium Chloride; C490216:SKY1 protein, S cerevisiae; D011505:Protein-Tyrosine Kinases; D051416:Focal Adhesion Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D000251:Adenosine Triphosphatases; C092477:PMA1 protein, S cerevisiae; D006180:Proton-Translocating ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D018021:Lithium Chloride; D013095:Spermidine; D011700:Putrescine