# Transporter-Driven Glycerophosphocholine (GPC) Toxicity Is Conserved from Fission Yeast to Budding Yeast: Roles for Inositol Pyrophosphates and Gde1 Regulation in Fission Yeast

## TL;DR

This study shows that GPC toxicity in yeast is driven by transporters and regulated by inositol pyrophosphates and Gde1, a process conserved across yeast species.

## Contribution

The study reveals a conserved mechanism of GPC toxicity involving transporters, inositol pyrophosphates, and Gde1 regulation in fission and budding yeast.

## Key findings

- Tgp1 in fission yeast specifically transports GPC, causing growth impairment but not reduced viability.
- Gde1 hydrolyzes GPC and its deletion or mutations in key domains suppress GPC toxicity.
- GPC toxicity in overexpressing Tgp1 or Git3 is independent of Gde1 and IP8 in both fission and budding yeast.

## Abstract

Glycerophosphocholine (GPC) and glycerophosphoinositol (GPI) are phospholipid metabolites generated by phospholipase-mediated deacylation. In budding yeast, they enter cells via the Git1 permease; in fission yeast, the homolog is Tgp1. This study investigates why GPC is toxic to asp1-STF mutants, where Tgp1 is upregulated due to loss of Asp1 pyrophosphatase, resulting in elevated inositol pyrophosphate 1,5-IP8. We show that S. pombe Tgp1 specifically transports GPC, explaining why GPC, but not GPI, impairs growth. Increased GPC uptake slows doubling time but does not reduce viability. Toxicity is relieved by deletion of Gde1, a phosphodiesterase that hydrolyzes GPC to choline and glycerol-3-phosphate. Mutations in either the Gde1 active site or SPX domain also suppress toxicity, and radiolabeling confirms both domains are required for enzymatic activity. GPC is toxic in cells vastly overexpressing Tgp1 even without elevated IP8, but Gde1 loss does not suppress this effect. Similarly, in S. cerevisiae overexpressing the Candida albicans Git3 transporter, GPC provision causes toxicity independent of Gde1. Loss of Gpc1, the acyltransferase converting GPC to lysophosphatidylcholine, does not alter toxicity in either yeast. These findings highlight a conserved process by which GPC regulates growth and reveal a role for IP8 in modulating this process.