Tsvetkov Peter, Mendillo Marc L, Zhao Jinghui, Carette Jan E, Merrill Parker H, Cikes Domagoj, Varadarajan Malini, van Diemen Ferdy R, Penninger Josef M, Goldberg Alfred L, Brummelkamp Thijn R, Santagata Sandro, Lindquist Susan
Whitehead Institute for Biomedical Research, Cambridge, United States.
Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, United States.
Elife. 2015 Sep 1;4:e08467. doi: 10.7554/eLife.08467.
Proteasomes are central regulators of protein homeostasis in eukaryotes. Proteasome function is vulnerable to environmental insults, cellular protein imbalance and targeted pharmaceuticals. Yet, mechanisms that cells deploy to counteract inhibition of this central regulator are little understood. To find such mechanisms, we reduced flux through the proteasome to the point of toxicity with specific inhibitors and performed genome-wide screens for mutations that allowed cells to survive. Counter to expectation, reducing expression of individual subunits of the proteasome's 19S regulatory complex increased survival. Strong 19S reduction was cytotoxic but modest reduction protected cells from inhibitors. Protection was accompanied by an increased ratio of 20S to 26S proteasomes, preservation of protein degradation capacity and reduced proteotoxic stress. While compromise of 19S function can have a fitness cost under basal conditions, it provided a powerful survival advantage when proteasome function was impaired. This means of rebalancing proteostasis is conserved from yeast to humans.
蛋白酶体是真核生物中蛋白质稳态的核心调节因子。蛋白酶体功能易受环境损伤、细胞蛋白质失衡和靶向药物的影响。然而，细胞用于对抗这种核心调节因子抑制作用的机制却鲜为人知。为了找到此类机制，我们用特定抑制剂将通过蛋白酶体的通量降低到毒性水平，并对能使细胞存活的突变进行全基因组筛选。与预期相反，降低蛋白酶体19S调节复合体单个亚基的表达可提高细胞存活率。19S亚基的大量减少具有细胞毒性，但适度减少则可保护细胞免受抑制剂的影响。这种保护作用伴随着20S与26S蛋白酶体比例的增加、蛋白质降解能力的保留以及蛋白毒性应激的减轻。虽然在基础条件下19S功能的受损可能会带来适应性代价，但当蛋白酶体功能受损时，它却提供了强大的生存优势。这种重新平衡蛋白质稳态的方式在从酵母到人类的生物中都是保守的。
