The Nutrient Stress-Induced small GTPase Rab5 Contributes to the Activation of Vesicle Trafficking and Vacuolar Activity [Membrane Biology]

June 12th, 2014 by Nakatsukasa, K., Kanada, A., Matsuzaki, M., Byrne, S. D., Okumura, F., Kamura, T.

Rab family small GTPases regulate membrane trafficking by spatiotemporal recruitment of various effectors. However, it remains largely unclear how the expression and functions of Rab proteins are regulated in response to extracellular or intracellular stimuli. Here we show that Ypt53, one isoform of Rab5 in Saccharomyces cerevisiae, is significantly upregulated under nutrient stress. Under non-stress conditions, Vps21, a constitutively expressed Rab5 isoform, is crucial to Golgi-vacuole trafficking and to vacuolar hydrolase activity. However, when cells are exposed to nutrient stress for an extended period of time, the upregulated Ypt53 and the constitutive Vps21 function redundantly to maintain these activities, which in turn prevent the accumulation of reactive oxygen species and maintain mitochondrial respiration. Together, our results clarify the relative roles of these constitutive and nutrient stress-inducible Rab5 proteins, which ensure adaptable vesicle trafficking and vacuolar hydrolase activity, thereby allowing cells to adapt to environmental changes.