Loss of the Major Isoform of Phosphoglucomutase Results in Altered Calcium Homeostasis in Saccharomyces cerevisiae

Lianwu Fu,Attila Miseta,Dacia Hunton,Richard B Marchase,David M Bedwell

doi:10.1074/jbc.275.8.5431

Lianwu Fu, Attila Miseta + Show 3 more

Open Access

https://doi.org/10.1074/jbc.275.8.5431

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Abstract

Phosphoglucomutase (PGM) is a key enzyme in glucose metabolism, where it catalyzes the interconversion of glucose 1-phosphate (Glc-1-P) and glucose 6-phosphate (Glc-6-P). In this study, we make the novel observation that PGM is also involved in the regulation of cellular Ca(2+) homeostasis in Saccharomyces cerevisiae. When a strain lacking the major isoform of PGM (pgm2Delta) was grown on media containing galactose as sole carbon source, its rate of Ca(2+) uptake was 5-fold higher than an isogenic wild-type strain. This increased rate of Ca(2+) uptake resulted in a 9-fold increase in the steady-state total cellular Ca(2+) level. The fraction of cellular Ca(2+) located in the exchangeable pool in the pgm2Delta strain was found to be as large as the exchangeable fraction observed in wild-type cells, suggesting that the depletion of Golgi Ca(2+) stores is not responsible for the increased rate of Ca(2+) uptake. We also found that growth of the pgm2Delta strain on galactose media is inhibited by 10 microM cyclosporin A, suggesting that activation of the calmodulin/calcineurin signaling pathway is required to activate the Ca(2+) transporters that sequester the increased cytosolic Ca(2+) load caused by this high rate of Ca(2+) uptake. We propose that these Ca(2+)-related alterations are attributable to a reduced metabolic flux between Glc-1-P and Glc-6-P due to a limitation of PGM enzymatic activity in the pgm2Delta strain. Consistent with this hypothesis, we found that this "metabolic bottleneck" resulted in an 8-fold increase in the Glc-1-P level compared with the wild-type strain, while the Glc-6-P and ATP levels were normal. These results suggest that Glc-1-P (or a related metabolite) may participate in the control of Ca(2+) uptake from the environment.

Highlights

Saccharomyces cerevisiae shares many features of Ca2ϩ homeostasis and signaling pathways with mammals [1]
The pgm1⌬/pgm2⌬ strain could not grow on YPGal media, confirming that PGM activity is essential for growth when galactose is the sole carbon source [31]
When the pmr1⌬ strain was grown in YPGal medium, we found that the total cellular Ca2ϩ level was 7.85 mmol/kg dry mass, a level that was 2.7-fold lower than was observed in cells grown in YPD (Fig. 2A)

Summary

Introduction

Saccharomyces cerevisiae shares many features of Ca2ϩ homeostasis and signaling pathways with mammals [1]. Living organisms that apparently relates to the low solubility of Ca2ϩ complexes of many phosphorylated metabolites [6] This tight control of free cytosolic Ca2ϩ is an essential feature of Ca2ϩ signaling, where Ca2ϩ-sensing proteins like calmodulin utilize a transient increase in the steady-state cytosolic Ca2ϩ concentration to activate various signal transduction pathways [7]. While glucose is frequently considered to be primarily a carbon and energy source in yeast, it can activate several signaling pathways in yeast, including the RAS-cAMP pathway, phosphatidylinositol turnover, Ca2ϩ influx and efflux, and the glucose repression/de-repression pathway [24] It is unclear whether these distinct pathways are regulated by glucose, a glucose derivative, a glycosylated protein, or by some other mechanism. Strains lacking both isoforms of PGM can survive when grown on glucose, apparently because the conversion of Glc-6-P to Glc-1-P can be supported to a small extent by related enzymes such as phosphomannomutase and N-acetylglucosamine-1-phosphate mutase [31, 32]

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