Similarities between UDP-glucose and adenine nucleotide release in yeast: involvement of the secretory pathway.
Extracellular UDP-glucose is a natural purinergic receptor agonist, but its mechanisms of cellular release remain unclear. We studied these mechanisms in Saccharomyces cerevisiae, a simple model organism that releases ATP, another purinergic agonist. Similar to ATP, UDP-glucose was released by S. cerevisiae at a rate that was linear over time. However, unlike ATP release, UDP-glucose release was not dependent on glucose stimulation. This discrepancy was resolved by demonstrating the apparent glucose stimulation of ATP release reflected glucose-dependent changes in the intracellular pattern of adenine nucleotides, with AMP release dominating in the absence of glucose. Indeed, total adenine nucleotide release, like UDP-glucose release, did not vary with glucose concentration over the short term. The genetic basis of UDP-glucose release was explored through analysis of deletion mutants, aided by development of a novel bioassay for UDP-glucose based on signaling through heterologously expressed human P2Y 14 receptors. Using this assay, an elevated rate of UDP-glucose release was demonstrated in mutants lacking the putative Golgi nucleotide sugar transporter YMD8. An increased rate of UDP-glucose release in ymd8Delta was reduced by deletion of the YEA4 UDP- N-acetylglucosamine or the HUT1 UDP-galactose transporters, and overexpression of YEA4 or HUT1 increased the rate of UDP-glucose release. These findings suggest an exocytotic release mechanism similar to that of ATP, a conclusion supported by decreased rates of ATP, AMP, and UDP-glucose release in response to the secretory inhibitor Brefeldin A. These studies demonstrate the involvement of the secretory pathway in nucleotide and nucleotide sugar efflux in yeast and offer a powerful model system for further investigation.
Esther
Charles R
CR
Division of Pediatric Pulmonology, University of North Carolina, Chapel Hill, North Carolina 27599, USA. Charles_Esther@med.unc.edu
Sesma
Juliana I
JI
Dohlman
Henrik G
HG
Ault
Addison D
AD
Clas
Marién L
ML
Lazarowski
Eduardo R
ER
Boucher
Richard C
RC
D000227:Adenine Nucleotides / Q000378:metabolism*; D000249:Adenosine Monophosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D020126:Brefeldin A / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects; D033704:Nucleotide Transport Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D014532:Uridine Diphosphate Glucose / Q000378:metabolism*
D000227:Adenine Nucleotides; D033704:Nucleotide Transport Proteins; D020126:Brefeldin A; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; D014532:Uridine Diphosphate Glucose