RIPK1 dephosphorylation and kinase activation by PPP1R3G/PP1γ promote apoptosis and necroptosis.

Receptor-interacting protein kinase 1 (RIPK1) is a key regulator of inflammation and cell death. Many sites on RIPK1, including serine 25, are phosphorylated to inhibit its kinase activity and cell death. How these inhibitory phosphorylation sites are dephosphorylated is poorly understood. Using a sensitized CRISPR whole-genome knockout screen, we discover that protein phosphatase 1 regulatory subunit 3G (PPP1R3G) is required for RIPK1-dependent apoptosis and type I necroptosis. Mechanistically, PPP1R3G recruits its catalytic subunit protein phosphatase 1 gamma (PP1γ) to complex I to remove inhibitory phosphorylations of RIPK1. A PPP1R3G mutant which does not bind PP1γ fails to rescue RIPK1 activation and cell death. Furthermore, chemical prevention of RIPK1 inhibitory phosphorylations or mutation of serine 25 of RIPK1 to alanine largely restores cell death in PPP1R3G-knockout cells. Finally, Ppp1r3g-/- mice are protected from tumor necrosis factor-induced systemic inflammatory response syndrome, confirming the important role of PPP1R3G in regulating apoptosis and necroptosis in vivo.

Heritable, Allele-Specific Chromosomal Looping between Tandem Promoters Specifies Promoter Usage of SHC1.

One-half of the genes in the human genome contain alternative promoters, some of which generate products with opposing functions. Aberrant silencing or activation of such alternative promoters is associated with multiple diseases, including cancer, but little is known regarding the molecular mechanisms that control alternative promoter choice. The SHC1 gene encodes p46Shc/p52Shc and p66Shc, proteins oppositely regulating anchorage-independent growth that are produced by transcription initiated from the upstream and downstream tandem promoters of SHC1, respectively. Here we demonstrate that activation of these promoters is mutually exclusive on separate alleles in single primary endothelial cells in a heritable fashion, ensuring expression of both transcripts by the cell. Peripheral blood lymphocytes that do not transcribe p66Shc transcribed p52Shc biallelically. This distinct monoallelic transcription pattern is established by allele-specific chromosomal looping between tandem promoters, which silences the upstream promoter. Our results reveal a new mechanism to control alternative promoter usage through higher-order chromatin structure.

MLKL forms disulfide bond-dependent amyloid-like polymers to induce necroptosis.

Mixed-lineage kinase domain-like protein (MLKL) is essential for TNF-α-induced necroptosis. How MLKL promotes cell death is still under debate. Here we report that MLKL forms SDS-resistant, disulfide bond-dependent polymers during necroptosis in both human and mouse cells. MLKL polymers are independent of receptor-interacting protein kinase 1 and 3 (RIPK1/RIPK3) fibers. Large MLKL polymers are more than 2 million Da and are resistant to proteinase K digestion. MLKL polymers are fibers 5 nm in diameter under electron microscopy. Furthermore, the recombinant N-terminal domain of MLKL forms amyloid-like fibers and binds Congo red dye. MLKL mutants that cannot form polymers also fail to induce necroptosis efficiently. Finally, the compound necrosulfonamide conjugates cysteine 86 of human MLKL and blocks MLKL polymer formation and subsequent cell death. These results demonstrate that disulfide bond-dependent, amyloid-like MLKL polymers are necessary and sufficient to induce necroptosis.

A new hypersensitive site, HS10, and the enhancers, E3' and Ed, differentially regulate Igκ gene expression.

The mouse Igκ gene locus has three known transcriptional enhancers: an intronic enhancer (Ei), a 3' enhancer (E3'), and a further downstream enhancer (Ed). We previously discovered, using the chromosome conformation-capture technique, that Ei and E3' interact with a novel DNA sequence near the 3' end of the Igκ locus, specifically in B cells. In the present investigation, we examined the function of this far downstream element. The sequence is evolutionarily conserved and exhibits a plasmacytoma cell-specific DNase I-hypersensitive site in chromatin, henceforth termed HS10 in the locus. HS10 acts as a coactivator of E3' in transient transfection assays. Although HS10(-/-) mice exhibited normal patterns of B cell development, they were tested further along with E3'(-/-) and Ed(-/-) mice for their Igκ expression levels in plasma cells, as well as for both allelic and isotype exclusion in splenic B cells. HS10(-/-) and Ed(-/-), but not E3'(-/-), mice exhibited 2.5-fold lower levels of Igκ expression in antigenically challenged plasma cells. E3'(-/-) mice, but not HS10(-/-) mice, exhibited impaired IgL isotype and allelic exclusion in splenic B cells. We have suggestive results that Ed may also weakly participate in these processes. In addition, HS10(-/-) mice no longer exhibited regional chromosome interactions with E3', and they exhibited modestly reduced somatic hypermutation in the Jκ-Cκ intronic region in germinal center B cells from Peyer's patches. We conclude that the HS10, E3', and Ed differentially regulate Igκ gene dynamics.

Delayed liver injury and impaired hepatocyte proliferation after carbon tetrachloride exposure in BPOZ2-deficient mice.

BPOZ2 is a tumor suppressive mediator in PTEN signaling pathway and plays an important role in cell proliferation. In this study, we investigated the physiology functions of BPOZ2 in CCl(4)-induced liver injury and hepatocyte proliferation afterwards. After acute CCl(4) administration, BPOZ2 null mice exhibited delayed liver injury and impaired hepatocyte proliferation, which was accompanied by altered kinetics of CYP2E1 protein expression, compromised cyclin D1 expression and shortened duration of ERK activation. These results for the first time define that BPOZ2 is an important regulator involved in the injury and repair process induced by acute CC1(4) administration in mouse liver.

[Cloning and structural analysis of mouse genomic nucleophosmin gene].

Nucleophosmin (NPM) is an abundant nucleolar phosphoprotein. NPM gene involved chromosomal translocations were found in the patients with anaplastic large cell lymphomas (ALCL), myelodysplastic syndrome (MDS), acute myeloid leukemia (AML) and acute promyelocytic leukemia (APL). To generate NPM gene knockout mice and study its biological function in vivo, we screened the lambda phage genomic library derived from 129S1 mice with mouse NPM cDNA probe. A positive phage clone which contained the full-length NPM genomic DNA was obtained and the insert of 15.3 kb genomic DNA in this clone was sequenced with shotgun method. BLAST analysis showed that the sequence of insert are 99.8% identity to that of NPM gene of C57BL/6 mouse strain. Based on the sequence, bioinformatics analysis on genomic structure of NPM and the transcription factor binding sites in the NPM 5' flanking region were performed.