The auto-ubiquitylation of E3 ubiquitin-protein ligase Chfr at G2 phase is required for accumulation of polo-like kinase 1 and mitotic entry in mammalian cells.

The E3 ubiquitin-protein ligase Chfr is a mitotic stress checkpoint protein that delays mitotic entry in response to microtubule damage; however, the molecular mechanism by which Chfr accomplishes this remains elusive. Here, we show that Chfr levels are elevated in response to microtubule-damaging stress. Moreover, G(2)/M transition is associated with cell cycle-dependent turnover of Chfr accompanied by high autoubiquitylation activity, suggesting that regulation of Chfr levels and auto-ubiquitylation activity are functionally significant. To test this, we generated Chfr mutants Chfr-K2A and Chfr-K5A in which putative lysine target sites of auto-ubiquitylation were replaced with alanine. Chfr-K2A did not undergo cell cycle-dependent degradation, and its levels remained high during G(2)/M phase. The elevated levels of Chfr-K2A caused a significant reduction in phosphohistone H3 levels and cyclinB1/Cdk1 kinase activities, leading to mitotic entry delay. Notably, polo-like kinase 1 levels at G(2) phase, but not at S phase, were ∼2-3-fold lower in cells expressing Chfr-K2A than in wild-type Chfr-expressing cells. Consistent with this, ubiquitylation of Plk1 at G(2) phase was accelerated in Chfr-K2A-expressing cells. In contrast, Aurora A levels remained constant, indicating that Plk1 is a major target of Chfr in controlling the timing of mitotic entry. Indeed, overexpression of Plk1 in Chfr-K2A-expressing cells restored cyclin B1/Cdk1 kinase activity and promoted mitotic entry. Collectively, these data indicate that Chfr auto-ubiquitylation is required to allow Plk1 to accumulate to levels necessary for activation of cyclin B1/Cdk1 kinase and mitotic entry. Our results provide the first evidence that Chfr auto-ubiquitylation and degradation are important for the G(2)/M transition.

Caenorhabditis elegans deep lipidome profiling by using integrative mass spectrometry acquisitions reveals significantly altered lipid networks / 药物分析学报

Lipidomics coverage improvement is essential for functional lipid and pathway construction.A powerful approach to discovering organism lipidome is to combine various data acquisitions,such as full scan mass spectrometry(full MS),data-dependent acquisition(DDA),and data-independent acquisition(DIA).Caenorhabditis elegans(C.elegans)is a useful model for discovering toxic-induced metabolism,high-throughput drug screening,and a variety of human disease pathways.To determine the lipidome of C.elegans and investigate lipid disruption from the molecular level to the system biology level,we used integrative data acquisition.The methyl-tert-butyl ether method was used to extract L4 stage C.elegans after exposure to triclosan(TCS),perfluorooctanoic acid,and nanopolystyrene(nPS).Full MS,DDA,and DIA integrations were performed to comprehensively profile the C.elegans lipidome by Q-Exactive Plus MS.All annotated lipids were then analyzed using lipid ontology and pathway analysis.We annotated up to 940 lipids from 20 lipid classes involved in various functions and pathways.The biological in-vestigations revealed that when C.elegans were exposed to nPS,lipid droplets were disrupted,whereas plasma membrane-functionalized lipids were likely to be changed in the TCS treatment group.The nPS treatment caused a significant disruption in lipid storage.Triacylglycerol,glycerophospholipid,and ether class lipids were those primarily hindered by toxicants.Finally,toxicant exposure frequently involved numerous lipid-related pathways,including the phosphoinositide 3-kinase/protein kinase B pathway.In conclusion,an integrative data acquisition strategy was used to characterize the C elegans lipidome,providing valuable biological insights into hypothesis generation and validation.