Ubiquitin over-expression phenotypes and ubiquitin gene molecular misreading during aging in Drosophila melanogaster

Contrasting Impacts of Ubiquitin Overexpression on Arabidopsis Growth and Development

In plants, the ubiquitin (Ub)-26S proteasome system (UPS) regulates numerous biological functions by selectively targeting proteins for ubiquitylation and degradation. However, the regulation of Ub itself on plant growth and development remains unclear. To demonstrate a possible impact of Ub supply, as seen in animals and flies, we carefully analyzed the growth and developmental phenotypes of two different poly-Ub (UBQ) gene overexpression plants of Arabidopsis thaliana. One is transformed with hexa-6His-UBQ (designated 6HU), driven by the cauliflower mosaic virus 35S promoter, while the other expresses hexa-6His-TEV-UBQ (designated 6HTU), driven by the endogenous promoter of UBQ10. We discovered that 6HU and 6HTU had contrasting seed yields. Compared to wildtype (WT), the former exhibited a reduced seed yield, while the latter showed an increased seed production that was attributed to enhanced growth vigor and an elevated silique number per plant. However, reduced seed sizes were common in both 6HU and 6HTU. Differences in the activity and size of the 26S proteasome assemblies in the two transgenic plants were also notable in comparison with WT, suggestive of a contributory role of UBQ expression in proteasome assembly and function. Collectively, our findings demonstrated that exogenous expression of recombinant Ub may optimize plant growth and development by influencing the UPS activities via structural variance, expression patterns, and abundance of free Ub supply.

Trichinella spiralis inhibits myoblast differentiation by targeting SQSTM1/p62 with a secreted E3 ubiquitin ligase

Trichinella spiralis infection is associated with the formation of cysts within host skeletal muscle cells, thereby enabling immune evasion and subsequent growth and development; however, the pathogenic factors involved in this process and their mechanisms remain elusive. Here, we found that Ts-RNF secreted by T. spiralis is required for its growth and development in host cells. Further study revealed that Ts-RNF functions as an E3 ubiquitin ligase that targets the UBA domain of SQSTM1/p62 by forming K63-type ubiquitin chains. This modification interferes with autophagic flux, leading to impaired mitochondrial clearance and abnormal myotube differentiation and fusion. Our results established that T. spiralis increases its escape by interfering with host autophagy via the secretion of an E3 ubiquitin ligase.

The Good, the Bad, and the Ugly of ROS: New Insights on Aging and Aging-Related Diseases from Eukaryotic and Prokaryotic Model Organisms

Aging is associated with the accumulation of cellular damage over the course of a lifetime. This process is promoted in large part by reactive oxygen species (ROS) generated via cellular metabolic and respiratory pathways. Pharmacological, nonpharmacological, and genetic interventions have been used to target cellular and mitochondrial networks in an effort to decipher aging and age-related disorders. While ROS historically have been viewed as a detrimental byproduct of normal metabolism and associated with several pathologies, recent research has revealed a more complex and beneficial role of ROS in regulating metabolism, development, and lifespan. In this review, we summarize the recent advances in ROS research, focusing on both the beneficial and harmful roles of ROS, many of which are conserved across species from bacteria to humans, in various aspects of cellular physiology. These studies provide a new context for our understanding of the parts ROS play in health and disease. Moreover, we highlight the utility of bacterial models to elucidate the molecular pathways by which ROS mediate aging and aging-related diseases.

Mass spectrometry techniques for studying the ubiquitin system

Post-translational control of proteins through covalent attachment of ubiquitin plays important roles in all eukaryotic cell functions. The ubiquitin system in humans consists of 2 E1, 35 E2 and >600 E3 ubiquitin ligases as well as hundreds of deubiquitylases, which reverse ubiquitin attachment. Moreover, there are hundreds of proteins with ubiquitin-binding domains that bind one of the eight possible polyubiquitin chains. Dysfunction of the ubiquitin system is associated with many diseases such as cancer, autoimmunity and neurodegeneration, demonstrating the importance of ubiquitylation. Therefore, enzymes of the ubiquitin system are considered highly attractive drug targets. In recent years, mass spectrometry (MS)-based techniques have become increasingly important in the deciphering of the ubiquitin system. This short review addresses the state-of-the-art MS techniques for the identification of ubiquitylated proteins and their ubiquitylation sites. We also discuss the identification and quantitation of ubiquitin chain topologies and highlight how the activity of enzymes in the ubiquitin pathway can be measured. Finally, we present current MS tools that can be used for drug discovery in the ubiquitin space.

Ubiquitylation of p62/sequestosome1 activates its autophagy receptor function and controls selective autophagy upon ubiquitin stress

Alterations in cellular ubiquitin (Ub) homeostasis, known as Ub stress, feature and affect cellular responses in multiple conditions, yet the underlying mechanisms are incompletely understood. Here we report that autophagy receptor p62/sequestosome-1 interacts with E2 Ub conjugating enzymes, UBE2D2 and UBE2D3. Endogenous p62 undergoes E2-dependent ubiquitylation during upregulation of Ub homeostasis, a condition termed as Ub+ stress, that is intrinsic to Ub overexpression, heat shock or prolonged proteasomal inhibition by bortezomib, a chemotherapeutic drug. Ubiquitylation of p62 disrupts dimerization of the UBA domain of p62, liberating its ability to recognize polyubiquitylated cargoes for selective autophagy. We further demonstrate that this mechanism might be critical for autophagy activation upon Ub+ stress conditions. Delineation of the mechanism and regulatory roles of p62 in sensing Ub stress and controlling selective autophagy could help to understand and modulate cellular responses to a variety of endogenous and environmental challenges, potentially opening a new avenue for the development of therapeutic strategies against autophagy-related maladies.