Role of linear ubiquitination in inflammatory responses and tissue homeostasis

The role and advance of ubiquitination and deubiquitination in depression pathogenesis and treatment

Depression is a common neuropsychiatric disease that is characterized by long-term, repeated low mood, pain and despair, pessimism, and even suicidal tendencies. Increasing evidence has shown that ubiquitination and deubiquitination are closely related to the occurrence of depression, including pathological morphogenesis, neuroplasticity, synaptic transmission, neuroinflammation, and so forth. The development of depression is regulated by intracellular proteins that undergo various posttranslational modifications, including ubiquitination, which falls under the epigenetics category. Although there have been studies and reviews of literature on epigenetics and depression, a systematic review of ubiquitination modification and depression has not been reported. In addition, with the deepening of research on depression and ubiquitination, the development of drugs targeting the ubiquitin system has gradually increased, but it is still not mature, so there is an urgent need to find new antidepressant drug targets. E3 ubiquitin ligases and deubiquitinating enzymes can regulate the occurrence and development of depression in a variety of ways, which may be a direction for the treatment of depression in the future. Therefore, this review describes the latest progress of ubiquitination and deubiquitination in the regulation of depression, summarizes the published signal pathways of ubiquitination and deubiquitination involved in depression, emphasizes the targets and mechanisms of E3 ubiquitin ligases and deubiquitinase in the regulation of depression, and further discusses the therapeutic targets of targeting ubiquitination modification systems to regulate depression.

P21 resists ferroptosis in osteoarthritic chondrocytes by regulating GPX4 protein stability

Ferroptosis is involved in the pathogenesis of osteoarthritis (OA) while suppression of chondrocyte ferroptosis has a beneficial effect on OA. However, the molecular mechanism of ferroptosis in OA remains to be elucidated. P21, an indicator of aging, has been reported to inhibit ferroptosis, but the relationship between P21 and ferroptosis in OA remains unclear. Here, we aimed to investigate the expression and function of P21 in OA chondrocytes, and the involvement of P21 in the regulation of ferroptosis in chondrocytes. First, we demonstrated that high P21 expression was observed in the cartilage from OA patients and destabilized medial meniscus (DMM) mice, and in osteoarthritic chondrocytes induced by IL-1β, FAC and erastin. P21 knockdown exacerbated the reduction of Col2a1 and promoted the upregulation of MMP13 in osteoarthritic chondrocytes. Meanwhile, P21 knockdown exacerbated cartilage degradation in DMM-induced OA mouse models and decreased GPX4 expression in vivo. Furthermore, P21 knockdown sensitized chondrocytes to ferroptosis induced by erastin, which was closely associated with the accumulation of lipid peroxides. In mechanism, we demonstrated that P21 regulated the stability of GPX4 protein, and the regulation was independent of NRF2. Meanwhile, we found that P21 significantly affected the recruitment of GPX4 to linear ubiquitin chain assembly complex (LUBAC) and regulated the level of M1-linked ubiquitination of GPX4. Overall, our results suggest that P21 plays an essential anti-ferroptosis role in OA by regulating the stability of GPX4.

Ubiquiton-An inducible, linkage-specific polyubiquitylation tool

The posttranslational modifier ubiquitin regulates most cellular processes. Its ability to form polymeric chains of distinct linkages is key to its diverse functionality. Yet, we still lack the experimental tools to induce linkage-specific polyubiquitylation of a protein of interest in cells. Here, we introduce a set of engineered ubiquitin protein ligases and matching ubiquitin acceptor tags for the rapid, inducible linear (M1-), K48-, or K63-linked polyubiquitylation of proteins in yeast and mammalian cells. By applying the so-called "Ubiquiton" system to proteasomal targeting and the endocytic pathway, we validate this tool for soluble cytoplasmic and nuclear as well as chromatin-associated and integral membrane proteins and demonstrate how it can be used to control the localization and stability of its targets. We expect that the Ubiquiton system will serve as a versatile, broadly applicable research tool to explore the signaling functions of polyubiquitin chains in many biological contexts.