Vma3p protects cells from programmed cell death through the regulation of Hxk2p expression

In yeast, the vacuolar proton-pumping ATPase (V-ATPase) acidifies vacuoles to maintain pH of cytoplasm. Yeast cells lacking V-ATPase activity, due to a disruption of any VMA (vacuolar membrane ATPase) gene, remain viable but demonstrate growth defects. Although it has been suggested that VMA genes are critical for phospholipid biosynthesis, the link between VMA genes and phospholipid biosynthesis is still uncertain. Here, we found that cells lacking Vma3p, one of the major V-ATPase assembly genes, had a growth defect in the absence of inositol, suggesting that Vma3p is important in phospholipid biosynthesis. Through real-time PCR, we found that cells lacking Vma3p down-regulated HXK2 expression. Furthermore, acetic acid sensitivity assay showed that cells lacking Vma3p were more sensitive to acetic acid than WT cells. HXK2 encodes hexokinase 2 which can phosphorylate glucose during phospholipid biosynthesis. Since cells lacking HXK2 are sensitive to acetic acid and this is an indicator of programmed cell death, our observations suggest that Vma3p plays an important role in programmed cell death. Taken together, we have proposed a working model to describe how Vma3p protects cells against apoptosis through the regulation of HXK2 expression.