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A more recent version of this article appeared on March 1, 2005
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Submitted on November 16, 2004
Revised on December 16, 2004
Accepted on December 17, 2004
Departments of *Medicine and Physiology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205
Monitoring Editor: Sandra Schmid
The relationship between endosomal pH and function is well documented in viral entry, endosomal maturation, receptor recycling, and vesicle targeting within the endocytic pathway. However, specific molecular mechanisms that either sense or regulate luminal pH to mediate these processes have not been identified. Herein we describe the use of novel, compartment-specific pH indicators to demonstrate that yeast Nhx1, an endosomal member of the ubiquitous NHE family of Na+/H+ exchangers, regulates luminal and cytoplasmic pH to control vesicle trafficking out of the endosome. Loss of Nhx1 confers growth sensitivity to low pH stress, and concomitant acidification and trafficking defects, which can be alleviated by weak bases. Conversely, weak acids cause wild-type yeast to present nhx1
trafficking phenotypes. Finally, we report that Nhx1 transports K+ in addition to Na+, suggesting that a single mechanism may responsible for both pH and K+-dependent endosomal processes. This presents the newly defined family of eukaryotic endosomal NHE as novel targets for pharmacological inhibition to alleviate pathological states associated with organellar alkalinization.
Present address: Department of Pathology, University of New Mexico School of Medicine, Albuquerque, NM 87131.
Corresponding author.
E-mail: rrao{at}jhmi.edu
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