Activation
and significance of vacuolar H+-ATPase during yeast adaptation to
stressful concentrations of the herbicide 2,4-D.
Alexandra R. Fernandes, Paulo J. Durão, Pedro M. Santos, Isabel Sá-Correia
Centre Biological Chem Eng, Instituto Superior Técnico, Av. Rovisco Pais,
Lisbon, 1049-001, Portugal (pcxana@popsrv.ist.utl.pt)
A rapid and transient stimulation of Saccharomyces cerevisiae vacuolar H+-ATPase (V-ATPase) activity, in coordination with plasma membrane H+-ATPase (PM-ATPase) activation, takes place during the adaptation period preceding cell division of an yeast population suddenly exposed to 2,4-dichlorophenoxyacetic acid (2,4-D). V-ATPase is a proton pump energized by ATP hydrolysis; it functions to acidify the vacuole, leading to a H+-gradient across the vacuolar membrane which is used to drive the accumulation of ions, aminoacids and metabolites into the vacuole. The V-ATPase is a multi-subunit complex encoded by 17 VMA (Vacuolar Membrane ATPase) genes. Differently from PM-ATPase activation by 2,4-D, which is due to post-transcriptional regulation, V-ATPase activation correlates with the increased expression (by Northern experiments and immunoquantification) of VMA1. The up-regulation of the peripheral subunit Vma1p was first suggested by the ongoing proteomic analysis. Single deletion of VMA1, and of any of the other VMA genes, leads to a more extended period of adaptation to eventual growth under herbicide stress, at low pH. Activation of V- and PM-ATPases correlates with the decrease of cytosolic and vacuolar pH in cells suddenly exposed to 2,4-D, a highly-lipophilic weak acid, consistent with their proposed role in pHc homeostasis. Moreover, V-ATPase activation is essential to the recovery of the physiological H+-gradient across vacuolar membrane during adaptation to 2,4-D.