Yersinia Virulence Factor YopM Induces Sustained RSK Activation by Interfering with Dephosphorylation

Background: Pathogenic yersiniae inject several effector proteins (Yops) into host cells, which subverts immune functions and enables the bacteria to survive within the host organism. YopM, whose deletion in enteropathogenic yersiniae results in a dramatic loss of virulence, has previously been shown to form a complex with and activate the multifunctional kinases PKN2 and RSK1 in transfected cells. Methodology/Principal Findings: In a near physiological approach with double-affinity-tagged YopM being translocated into the macrophage cell line J774A.1 via the natural type three secretion system of Yersinia we verified the interaction of YopM with PKN2 and RSK1 and detected association with additional PKN and RSK isoforms. In transfected and infected cells YopM induced sustained phosphorylation of RSK at its activation sites serine-380 and serine-221 even in the absence of signalling from its upstream kinase ERK1/2, suggesting inhibition of dephosphorylation. ATP-depletion and in vitro assays using purified components directly confirmed that YopM shields RSK isoforms from phosphatase activity towards serines 380 and 221. Conclusions/Significance: Our study suggests that during Yersinia infection YopM induces sustained activation of RSK by blocking dephosphorylation of its activatory phosphorylation sites. This may represent a novel mode of action of a bacterial virulence factor

Serine 25 phosphorylation inhibits RIPK1 kinase-dependent cell death in models of infection and inflammation

RIPK1 regulates cell death and inflammation through kinase-dependent and -independent mechanisms. As a scaffold, RIPK1 inhibits caspase-8-dependent apoptosis and RIPK3/MLKL-dependent necroptosis. As a kinase, RIPK1 paradoxically induces these cell death modalities. The molecular switch between RIPK1 pro-survival and pro-death functions remains poorly understood. We identify phosphorylation of RIPK1 on Ser25 by IKKs as a key mechanism directly inhibiting RIPK1 kinase activity and preventing TNF-mediated RIPK1-dependent cell death. Mimicking Ser25 phosphorylation (S > D mutation) protects cells and mice from the cytotoxic effect of TNF in conditions of IKK inhibition. In line with their roles in IKK activation, TNF-induced Ser25 phosphorylation of RIPK1 is defective in TAK1- or SHARPIN-deficient cells and restoring phosphorylation protects these cells from TNF-induced death. Importantly, mimicking Ser25 phosphorylation compromises the in vivo cell death-dependent immune control of Yersinia infection, a physiological model of TAK1/IKK inhibition, and rescues the cell death-induced multi-organ inflammatory phenotype of the SHARPIN-deficient mice

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018.

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field

Lipopolysaccharide Desensitization of Macrophages Provides Protection against Yersinia enterocolitica-Induced Apoptosis

Pathogenic Yersinia spp. uncouple an array of signal transduction pathways in macrophages to disrupt their response to infection. This compels the macrophage to undergo apoptosis. Our study shows that macrophages that had acquired tolerance to Yersinia infection by preexposure to lipopolysaccharide were considerably protected against Y. enterocolitica-induced apoptosis. The desensitization of macrophages by lipopolysaccharide, which is thought to be a self-protective, adaptive response to sustained bacterial stimulation, may represent an immune mechanism that aids in overcoming Yersinia-mediated apoptosis and infection

To die or not to die: Regulatory feedback phosphorylation circuits determine receptor-interacting protein kinase-1 (RIPK1) function

Complex posttranslational modifications determine the effects of receptor-interacting protein kinase-1 (RIPK1) on cell survival and death. Studies from us and others have revealed a p38MAPK/MK2-dependent checkpoint in RIPK1 signaling. MAPKAP kinase 2 (MK2) phosphorylates RIPK1 to suppress RIPK1-mediated apoptosis and necroptosis in response to diverse stimuli relevant to inflammation, infection, genotoxic stress and chemotherapy