Interruption of inositol sphingolipid synthesis triggers Stt4p-dependent protein kinase C signaling.
The protein kinase C (PKC)-MAPK signaling cascade is activated and is essential for viability when cells are starved for the phospholipid precursor inositol. In this study, we report that inhibiting inositol-containing sphingolipid metabolism, either by inositol starvation or treatment with agents that block sphingolipid synthesis, triggers PKC signaling independent of sphingoid base accumulation. Under these same growth conditions, a fluorescent biosensor that detects the necessary PKC signaling intermediate, phosphatidylinositol (PI)-4-phosphate (PI4P), is enriched on the plasma membrane. The appearance of the PI4P biosensor on the plasma membrane correlates with PKC activation and requires the PI 4-kinase Stt4p. Like other mutations in the PKC-MAPK pathway, mutants defective in Stt4p and the PI4P 5-kinase Mss4p, which generates phosphatidylinositol 4,5-bisphosphate, exhibit inositol auxotrophy, yet fully derepress INO1, encoding inositol-3-phosphate synthase. These observations suggest that inositol-containing sphingolipid metabolism controls PKC signaling by regulating access of the signaling lipids PI4P and phosphatidylinositol 4,5-bisphosphate to effector proteins on the plasma membrane.
Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853, USA.
Stephen A
SA
Jesch
Maria L
ML
Gaspar
Christopher J
CJ
Stefan
Manuel A
MA
Aregullin
Susan A
SA
Henry
D019870:1-Phosphatidylinositol 4-Kinase / Q000378:metabolism*; D015374:Biosensing Techniques; D002462:Cell Membrane / Q000378:metabolism*; D004789:Enzyme Activation; D015966:Gene Expression Regulation, Fungal; D007294:Inositol / Q000737:chemistry*; D020935:MAP Kinase Signaling System; D010641:Phenotype; D011493:Protein Kinase C / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D015398:Signal Transduction; D013107:Sphingolipids / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors
D029701:Saccharomyces cerevisiae Proteins; D013107:Sphingolipids; D007294:Inositol; D019870:1-Phosphatidylinositol 4-Kinase; C112465:STT4 protein, S cerevisiae; D011493:Protein Kinase C