Authors: Senetibeb Gebre, Richard Connor, Yufeng Xia, Sanaa Jawed, John M. Bush, Martin Bard, Hassan Elsalloukh and Fusheng Tang

Senetibeb Gebre

Department of Biology; University of Arkansas; Little Rock, AR USA
These authors contributed equally.

Richard Connor

Department of Biology; University of Arkansas; Little Rock, AR USA
These authors contributed equally.

Yufeng Xia

Department of Biology; University of Arkansas; Little Rock, AR USA

Sanaa Jawed

Department of Biology; University of Arkansas; Little Rock, AR USA

John M. Bush

Department of Biology; University of Arkansas; Little Rock, AR USA

Martin Bard

Department of Biology; Indiana University-Purdue University, Indianapolis; Indianapolis, IN USA

Hassan Elsalloukh

Department of Mathematics and Statistics; University of Arkansas; Little Rock, AR USA

Fusheng Tang

Corresponding author: fxtang@ualr.edu
Department of Biology; University of Arkansas; Little Rock, AR USA

Abstract:
In yeast cells, the vacuole divides and fuses in each round of cell cycle. While mutants defective in vacuole fusion are “wild type” for vegetative growth, most have shortened replicative lifespans under caloric restriction (CR) condition, a manipulation that extends lifespan in wild type cells. To explore whether vacuole fusion extends lifespan, we screened for genes that can complement the fusion defect of selected mutants (erg6Δ, a sterol mutant; nyv1Δ,  a mutant involved in the vacuolar SNARE complex and vac8Δ, a vacuolar membrane protein mutant). This screen revealed that Osh6, a member of the oxysterol-binding protein family, can complement the vacuole fusion defect of nyv1Δ, but not erg6Δ or vac8Δ, suggesting that Osh6’s function in vacuole fusion is partly dependent on membrane ergosterol and Vac8. To measure the effect of OSH6 on lifespan, we replaced the endogenous promoter of OSH6 with a shorter version of the ERG6 promoter to obtain P_ERG6-OSH6. This mutant construct significantly extended the replicative lifespan in a wild type background and in a nyv1Δ mutant. Interestingly, P_ERG6-OSH6 cells were more sensitive to drugs that inhibit the activity of the TOR complex 1 (TORC1) than wild type cells. Moreover, a P_ERG6-OSH6 tor1Δ double mutant demonstrated a greatly shortened lifespan, suggesting a genetic interaction between Osh6 and Tor1. Since active TORC1 stimulates vacuole scission and CR downregulates TORC1, Osh6 may link these two pathways by adjusting vacuolar membrane organization to extend lifespan.

Received: May 6, 2012; Accepted: May 8, 2012

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