NTE1-encoded phosphatidylcholine phospholipase b regulates transcription of phospholipid biosynthetic genes.
The Saccharomyces cerevisiae NTE1 gene encodes an evolutionarily conserved phospholipase B localized to the endoplasmic reticulum (ER) that degrades phosphatidylcholine (PC) generating glycerophosphocholine and free fatty acids. We show here that the activity of NTE1-encoded phospholipase B (Nte1p) prevents the attenuation of transcription of genes encoding enzymes involved in phospholipid synthesis in response to increased rates of PC synthesis by affecting the nuclear localization of the transcriptional repressor Opi1p. Nte1p activity becomes necessary for cells growing in inositol-free media under conditions of high rates of PC synthesis elicited by the presence of choline at 37 degrees C. The specific choline transporter encoded by the HNM1 gene is necessary for the burst of PC synthesis observed at 37 degrees C as follows: (i) Nte1p is dispensable in an hnm1Delta strain under these conditions, and (ii) there is a 3-fold increase in the rate of choline transport via the Hnm1p choline transporter upon a shift to 37 degrees C. Overexpression of NTE1 alleviated the inositol auxotrophy of a plethora of mutants, including scs2Delta, scs3Delta, ire1Delta, and hac1Delta among others. Overexpression of NTE1 sustained phospholipid synthesis gene transcription under conditions that normally repress transcription. This effect was also observed in a strain defective in the activation of free fatty acids for phosphatidic acid synthesis. No changes in the levels of phosphatidic acid were detected under conditions of altered expression of NTE1. Consistent with a synthetic impairment between challenged ER function and inositol deprivation, increased expression of NTE1 improved the growth of cells exposed to tunicamycin in the absence of inositol. We describe a new role for Nte1p toward membrane homeostasis regulating phospholipid synthesis gene transcription. We propose that Nte1p activity, by controlling PC abundance at the ER, affects lateral membrane packing and that this parameter, in turn, impacts the repressing transcriptional activity of Opi1p, the main regulator of phospholipid synthesis gene transcription.
Department of Pediatrics and Biochemistry and Molecular Biology, Atlantic Research Centre, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada.
J Pedro
JP
Fernández-Murray
Department of Pediatrics and Biochemistry and Molecular Biology, Atlantic Research Centre, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada.
Gerard J
GJ
Gaspard
Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853.
Stephen A
SA
Jesch
Department of Pediatrics and Biochemistry and Molecular Biology, Atlantic Research Centre, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada. Electronic address: christopher.mcmaster@dal.ca.
Christopher R
CR
McMaster
D001692:Biological Transport / Q000502:physiology; D004721:Endoplasmic Reticulum / Q000201:enzymology / Q000235:genetics; D004950:Esterases / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D015966:Gene Expression Regulation, Fungal / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D010740:Phospholipases / Q000235:genetics / Q000378:metabolism*; D010743:Phospholipids / Q000096:biosynthesis* / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology*
D026901:Membrane Transport Proteins; C096105:OPI1 protein, S cerevisiae; D010743:Phospholipids; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; C065637:choline transporter; D004950:Esterases; C519643:Nte1 protein, S cerevisiae; D010740:Phospholipases