Role of Ubiquitin in Cellular Quality Control

Dear Colleagues,

Under cellular stress conditions, proteins can be damaged or misfolded; they then must be degraded by the proteasome in a timely manner, otherwise they may accumulate inside cells as toxic protein aggregates. Ubiquitin is a highly conserved eukaryotic protein with various roles inside the cell. Among these roles, targeting misfolded proteins to the proteasome prior to aggregation is essential for cellular survival. When protein aggregates are generated, they can be degraded by autophagy, which is another cellular quality control system. Ubiquitin also plays an essential role in the recognition of protein aggregates by autophagic machinery. Therefore, ubiquitin is required throughout these cellular quality control processes under proteotoxic stress conditions.

Cellular ubiquitin pools are composed of free ubiquitin and ubiquitin conjugates that are in dynamic equilibrium. Cells must maintain free ubiquitin above certain threshold levels, which can fluctuate depending on the cellular environment. As one can imagine, cells need sufficient free ubiquitin to be readily available under stress conditions. In this Special Issue, we would like to focus on the role of ubiquitin in cellular quality control under stress conditions. Cellular effects of ubiquitin can be investigated through alterations in free ubiquitin levels, equilibrium shifts to different forms of ubiquitin, expression of mutant ubiquitin, or regulation of ubiquitin gene expression. Cellular quality control can be monitored by observing the status of protein degradation and protein aggregation, or the activity of the cellular quality control system, such as the ubiquitin–proteasome system or the autophagic pathway. Identifying new roles for ubiquitin or re-examining its role in cellular quality control will provide strong evidence that ubiquitin is a key molecule for cellular survival.

Dr. Kwon-Yul Ryu
Guest Editor

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