Vacuolar H+-ATPase Works in Parallel with the HOG Pathway To Adapt Saccharomyces cerevisiae Cells to Osmotic Stress

Hyperosmotic stress activates an array of cellular detoxification mechanisms, including the high-osmolarity glycerol (HOG) pathway. We report here that vacuolar H+-ATPase (V-ATPase) activity helps provide osmotic tolerance in Saccharomyces cerevisiae. V-ATPase subunit genes exhibit complex haploinsufficiency interactions with HOG pathway components. vma mutants lacking V-ATPase function are sensitive to high concentrations of salt and exhibit Hog1p activation even at low salt concentrations, as demonstrated by phosphorylation of Hog1p, a shift in Hog1-green fluorescent protein localization, transcriptional activation of a subset of HOG pathway effectors, and transcriptional inhibition of parallel mitogen-activated protein kinase pathway targets. vma2 Delta hog1 Delta and vma3 Delta pbs2 Delta double mutants have a synthetic growth phenotype, poor salt tolerance, and an aberrant, hyper-elongated morphology on solid media, accompanied by activation of a filamentous response element-LacZ construct, indicating cross talk into the filamentous growth pathway. Vacuoles isolated from wild-type cells briefly exposed to salt show higher levels of V-ATPase activity, and Na+/H+ exchange in isolated vacuolar vesicles suggests a biochemical basis for the genetic interactions observed. V-ATPase activity is upregulated during salt stress by increasing assembly of the catalytic V-1 sector with the membrane-bound V-o sector. Together, these data suggest that the V-ATPase acts in parallel with the HOG pathway in order to mediate salt detoxification.