Abstract
Beta-1,3-glucanosyltransferase (Gas1p) plays important roles in cell wall biosynthesis and morphogenesis and has been implicated in DNA damage responses and cell cycle regulation in fungi. Yeast Gas1p has also been reported to participate in endoplasmic reticulum (ER) stress responses. However, the precise roles and molecular mechanisms through which Gas1p affects these responses have yet to be elucidated. In this study, we constructed GAS1-deficient (gas1Δ) and GAS1-overexpressing (GAS1 OE) yeast strains and observed that the gas1Δ strain exhibited a decreased proliferation ability and a shorter replicative lifespan (RLS), as well as enhanced activity of the unfolded protein response (UPR) in the absence of stress. However, under the high-tunicamycin-concentration (an ER stress-inducing agent; 1.0 μg/mL) stress, the gas1Δ yeast cells exhibited an increased proliferation ability compared with the wild-type yeast strain. In addition, our findings demonstrated that IRE1 and HAC1 (two upstream modulators of the UPR) are required for the survival of gas1Δ yeast cells under the tunicamycin stress. On the other hand, we provided evidence that the GAS1 overexpression caused an obvious sensitivity to the low-tunicamycin-concentration (0.25 μg/mL). Collectively, our results indicate that Gas1p plays an important role in the ageing and ER stress responses in yeast.
Highlights
Synthesized secretory and transmembrane proteins fold and assemble in the endoplasmic reticulum (ER) with the assistance of chaperones, oxidative folding components, and other systems that support protein posttranslational regulation
The division of S. cerevisiae cells is asymmetric, because a mother cell always produces a smaller daughter cell during each division, with the total number of daughter cells produced before a mother cell dies being greater when the replicative lifespan (RLS) of the mother cell is longer
To assess the budding ability of the yeast cells under the physiological conditions, we assessed the growth rates of strains using the Bioscreen C MB system and determined the RLSs of the gas Δ and GAS -overexpressing (GAS OE) strains under an optical microscope
Summary
Synthesized secretory and transmembrane proteins fold and assemble in the endoplasmic reticulum (ER) with the assistance of chaperones, oxidative folding components, and other systems that support protein posttranslational regulation. Impairments in this complex process cause the accumulation of unfolded/misfolded proteins, provoking a cytoprotective signalling cascade termed the unfolded protein response (UPR) [1]. The UPR signalling pathway and ER protein homeostasis are regulated by three known transmembrane ER stress sensors or transducers: inositol-requiring protein 1 (IRE1), double-stranded RNA-activated protein kinase-like ER kinase (PERK), and activating transcription factor 6 (ATF6). The formation and maintenance of beta-1,3-glucan chains is primarily catalysed by beta-1,3-glucanosyltransferase (Gas1p), which is initially characterized at the cell wall via a glycosylphosphatidylinositol (GPI) anchor and localizes to Strain BY4741 BY4742 gas Δ GAS OE ire Δ hac Δ gas Δire Δ gas Δhac û
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