TRIM21, a New Component of the TRAIL-Induced Endogenous Necrosome Complex.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a well-known apoptosis inducer and a potential anticancer agent. When caspases and inhibitors of apoptosis proteins (IAPs) are inhibited, TRAIL induces necroptosis. Molecular mechanisms of necroptosis rely on kinase activation, and on the formation of a necrosome complex, bringing together the receptor-interacting protein kinases 1 and 3 (RIPK1, RIPK3), and the mixed lineage kinase domain-like protein (MLKL). In this study, mass spectrometry approach allowed to identify the tripartite motif containing 21 (TRIM21), an E3 ubiquitin-protein ligase as a new partner of the endogenous TRAIL-induced necrosome. Alteration of TRIM21 expression level, obtained by transient transfection of HT29 or HaCat cells with TRIM21-targeted siRNAs or cDNA plasmids coding for TRIM21 demonstrated that TRIM21 is a positive regulator of TRAIL-induced necroptosis. Furthermore, the invalidation of TRIM21 expression in HT29 cells by CRISPR-Cas9 technology also decreased cell sensitivity to TRAIL-induced necroptosis, a shortcoming associated with a reduction in MLKL phosphorylation, the necroptosis executioner. Thus, TRIM21 emerged as a new partner of the TRAIL-induced necrosome that positively regulates the necroptosis process.

PAR-4 and anillin regulate myosin to coordinate spindle and furrow position during asymmetric division.

During asymmetric cell division, the mitotic spindle and polarized myosin can both determine the position of the cytokinetic furrow. However, how cells coordinate signals from the spindle and myosin to ensure that cleavage occurs through the spindle midzone is unknown. Here, we identify a novel pathway that is essential to inhibit myosin and coordinate furrow and spindle positions during asymmetric division. In Caenorhabditis elegans one-cell embryos, myosin localizes at the anterior cortex whereas the mitotic spindle localizes toward the posterior. We find that PAR-4/LKB1 impinges on myosin via two pathways, an anillin-dependent pathway that also responds to the cullin CUL-5 and an anillin-independent pathway involving the kinase PIG-1/MELK. In the absence of both PIG-1/MELK and the anillin ANI-1, myosin accumulates at the anterior cortex and induces a strong displacement of the furrow toward the anterior, which can lead to DNA segregation defects. Regulation of asymmetrically localized myosin is thus critical to ensure that furrow and spindle midzone positions coincide throughout cytokinesis.