The Ca2+ homeostasis defects in a pgm2Delta strain of Saccharomyces cerevisiae are caused by excessive vacuolar Ca2+ uptake mediated by the Ca2+-ATPase Pmc1p.
Loss of the major isoform of phosphoglucomutase (PGM) causes an accumulation of glucose 1-phosphate when yeast cells are grown with galactose as the carbon and energy source. Remarkably, the pgm2Delta strain also exhibits a severe imbalance in intracellular Ca(2+) homeostasis when grown under these conditions. In the present study, we examined how the pgm2Delta mutation alters yeast Ca(2+) homeostasis in greater detail. We found that a shift from glucose to galactose as the carbon source resulted in a 2-fold increase in the rate of cellular Ca(2+) uptake in wild-type cells, whereas Ca(2+) uptake increased 8-fold in the pgm2Delta mutant. Disruption of the PMC1 gene, which encodes the vacuolar Ca(2+)-ATPase Pmc1p, suppressed the Ca(2+)-related phenotypes observed in the pgm2Delta strain. This suggests that excessive vacuolar Ca(2+) uptake is tightly coupled to these defects in Ca(2+) homeostasis. An in vitro assay designed to measure Ca(2+) sequestration into intracellular compartments confirmed that the pgm2Delta mutant contained a higher level of Pmc1p-dependent Ca(2+) transport activity than the wild-type strain. We found that this increased rate of vacuolar Ca(2+) uptake also coincided with a large induction of the unfolded protein response in the pgm2Delta mutant, suggesting that Ca(2+) uptake into the endoplasmic reticulum compartment was reduced. These results indicate that the excessive Ca(2+) uptake and accumulation previously shown to be associated with the pgm2Delta mutation are due to a severe imbalance in the distribution of cellular Ca(2+) into different intracellular compartments.
Aiello
David P
DP
Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama, USA.
Fu
Lianwu
L
Miseta
Attila
A
Sipos
Katalin
K
Bedwell
David M
DM
D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002244:Carbon / Q000737:chemistry; D002462:Cell Membrane / Q000378:metabolism; D003470:Culture Media / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000378:metabolism; D005958:Glucosephosphates / Q000378:metabolism; D008345:Manganese / Q000737:chemistry; D008954:Models, Biological; D009154:Mutation; D010733:Phosphoglucomutase / Q000235:genetics*; D053499:Plasma Membrane Calcium-Transporting ATPases; D010957:Plasmids / Q000378:metabolism; D020033:Protein Isoforms; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D001616:beta-Galactosidase / Q000378:metabolism
D003470:Culture Media; D005958:Glucosephosphates; C085484:PMC1 protein, S cerevisiae; D020033:Protein Isoforms; D029701:Saccharomyces cerevisiae Proteins; D008345:Manganese; D019298:Glucose-6-Phosphate; D002244:Carbon; C031590:glucose-1-phosphate; D001616:beta-Galactosidase; D053499:Plasma Membrane Calcium-Transporting ATPases; D010733:Phosphoglucomutase; D000252:Calcium-Transporting ATPases; D005947:Glucose; D002118:Calcium; D005690:Galactose