Physical Forces and Transient Nuclear Envelope Rupture during Metastasis: The Key for Success?

During metastasis, invading tumor cells and circulating tumor cells (CTC) face multiple mechanical challenges during migration through narrow pores and cell squeezing. However, little is known on the importance and consequences of mechanical stress for tumor progression and success in invading a new organ. Recently, several studies have shown that cell constriction can lead to nuclear envelope rupture (NER) during interphase. This loss of proper nuclear compartmentalization has a profound effect on the genome, being a key driver for the genome evolution needed for tumor progression. More than just being a source of genomic alterations, the transient nuclear envelope collapse can also support metastatic growth by several mechanisms involving the innate immune response cGAS/STING pathway. In this review we will describe the importance of the underestimated role of cellular squeezing in the progression of tumorigenesis. We will describe the complexity and difficulty for tumor cells to reach the metastatic site, detail the genomic aberration diversity due to NER, and highlight the importance of the activation of the innate immune pathway on cell survival. Cellular adaptation and nuclear deformation can be the key to the metastasis success in many unsuspected aspects.

Human Cytomegalovirus UL138 Protein Inhibits the STING Pathway and Reduces Interferon Beta mRNA Accumulation during Lytic and Latent Infections

While a cellular restriction versus viral countermeasure arms race between innate immunity and viral latency is expected, few examples have been documented. Our identification of the first HCMV latency protein that inactivates the cGAS/STING/TBK1 innate immune pathway opens the door to understanding how innate immunity, or its neutralization, impacts long-term persistence by HCMV and other latent viruses.

BnaA03.WRKY28, interacting with BnaA09.VQ12, acts as a brake factor of activated BnWRKY33-mediated resistance outburst against Sclerotinia sclerotiorum in Brassica napus

ABSTRACTSclerotinia sclerotiorum causes substantial damage to the growth of Brassica napus (rapeseed) and makes a significant loss of crop yield. The plant innate immune system may be the primary solution to defense against S. sclerotiorum for rapeseed. Here, we identify that BnWRKY33, a transcription factor in the innate immune pathway, can be rapidly phosphorylated and activated by the MAPK cascade after rapeseed is infected with S. sclerotiorum. In the MAPK cascade, activated BnaA03.MKK4 phosphorylates and activates BnaA06.MPK3 and BnaC03.MPK3. The activated BnMPK3 acts on the substrate BnWRKY33 to enhance its transcriptional activity and trigger a transcriptional burst of BnWRKY33, which helps plants effectively resist the pathogenic fungi by enhancing the expression of phytoalexin synthesis-related genes. With constant infection, BnaA03.WRKY28 and BnaA09.VQ12 are induced, and BnaA03.WRKY28 physically interacts with BnaA09.VQ12 to form a protein complex. BnaA03.WRKY28 preferentially binds to the promoter of BnWRKY33 with the help of BnaA09.VQ12. Compared with activated BnWRKY33, BnaA03.WRKY28 has a lower transcriptional activity on downstream BnWRKY33, which leads to weaker resistance against S. sclerotiorum for rapeseed in the later stage of infection. Furthermore, the induced BnaA03.WRKY28 may promote axillary bud activity and axillary meristem initiation by regulating the expression of branching-related genes (such as BnBRC1), thus promoting the formation of branches in the leaf axils.One-sentence summaryUnder constant infection by Sclerotinia sclerotiorum, BnaA03.WRKY28 interacts with BnaA09.VQ12 and takes precedence over phosphorylated BnWRKY33 to bind to the BnWRKY33 promoter, thereby weakening resistance but promoting branching.

SARS-CoV-2 Nucleocapsid Protein Interacts with RIG-I and Represses RIG-Mediated IFN-β Production

SARS-CoV-2 is highly pathogenic in humans and poses a great threat to public health worldwide. Clinical data shows a disturbed type I interferon (IFN) response during the virus infection. In this study, we discovered that the nucleocapsid (N) protein of SARS-CoV-2 plays an important role in the inhibition of interferon beta (IFN-β) production. N protein repressed IFN-β production induced by poly(I:C) or upon Sendai virus (SeV) infection. We noted that N protein also suppressed IFN-β production, induced by several signaling molecules downstream of the retinoic acid-inducible gene I (RIG-I) pathway, which is the crucial pattern recognition receptor (PRR) responsible for identifying RNA viruses. Moreover, our data demonstrated that N protein interacted with the RIG-I protein through the DExD/H domain, which has ATPase activity and plays an important role in the binding of immunostimulatory RNAs. These results suggested that SARS-CoV-2 N protein suppresses the IFN-β response through targeting the initial step, potentially the cellular PRR–RNA-recognition step in the innate immune pathway. Therefore, we propose that the SARS-CoV-2 N protein represses IFN-β production by interfering with RIG-I.

Targeting macrophage priming by polyphyllin VII triggers anti-tumor immunity via STING-governed cytotoxic T-cell infiltration in lung cancer

Stimulator of interferon genes (STING) controlled innate immune pathway is essential for host defense against pathogenic infection and effective anti-tumor adaptive immunity initiation. Although macrophages transformed across diverse phenotypes play crucial roles in anti-tumor immune response, events determining this transformation and the host-intrinsic role of STING in this process remain controversial. Here we report how STING signaling acts as a key switch to dominate the gene expression patterns of macrophage transformation for promoting priming and releasing immunosuppression. Furthermore, polyphyllin VII, a potential STING agonist, exerts anti-tumor efficacy upon macrophages priming and subsequent cytotoxic T lymphocytes intratumoral infiltration. Meanwhile, the simultaneous PD-L1 amplification on macrophages in response to PP VII is also ruled by STING, thus PP VII may benefit immune-checkpoint blockade therapy for combining. Moreover, PP VII suppresses carcinogenesis upon restraining the immunosuppressed macrophage transformation. This is due to the boosted STING that negatively regulates a STAT3 propagated crosstalk between immune cells and tumor cells. Overall, PP VII-stimulated STING in macrophages provides a paradigm for anti-tumor, and if possible, anti-infection immunotherapy.

Loss of mitochondrial protease CLPP activates type I interferon responses through the mtDNA-cGAS-STING signaling axis

Caseinolytic mitochondrial matrix peptidase proteolytic subunit, CLPP, is a serine protease that degrades damaged or misfolded mitochondrial proteins. CLPP null mice exhibit growth retardation, deafness, and sterility, resembling human Perrault syndrome (PS), but also display immune system alterations. However, the molecular mechanisms and signaling pathways underlying immunological changes in CLPP null mice remain unclear. Here we report the steady state activation of type I interferon (IFN-I) signaling and antiviral gene expression in CLPP deficient cells and tissues. Depletion of the cyclic GMP-AMP (cGAS)-Stimulator of Interferon Genes (STING) DNA sensing pathway ablates heightened IFN-I responses and abrogates the broad viral resistance phenotype of CLPP null cells. Moreover, we report that CLPP deficiency leads to mitochondrial DNA (mtDNA) instability and packaging alterations. Pharmacological and genetic approaches to deplete mtDNA or inhibit cytosolic release markedly reduce antiviral gene expression, implicating mtDNA stress as the driver of IFN-I signaling in CLPP null mice. Our work places the cGAS-STING-IFN-I innate immune pathway downstream of CLPP and may have implications for understanding myriad human diseases involving CLPP dysregulation.

An orally available non-nucleotide STING agonist with antitumor activity

Pharmacological activation of the STING (stimulator of interferon genes)–controlled innate immune pathway is a promising therapeutic strategy for cancer. Here we report the identification of MSA-2, an orally available non-nucleotide human STING agonist. In syngeneic mouse tumor models, subcutaneous and oral MSA-2 regimens were well tolerated and stimulated interferon-β secretion in tumors, induced tumor regression with durable antitumor immunity, and synergized with anti–PD-1 therapy. Experimental and theoretical analyses showed that MSA-2 exists as interconverting monomers and dimers in solution, but only dimers bind and activate STING. This model was validated by using synthetic covalent MSA-2 dimers, which were potent agonists. Cellular potency of MSA-2 increased upon extracellular acidification, which mimics the tumor microenvironment. These properties appear to underpin the favorable activity and tolerability profiles of effective systemic administration of MSA-2.

Porcine Epidemic Diarrhea Virus nsp15 Antagonizes Interferon Signaling by RNA Degradation of TBK1 and IRF3

Porcine epidemic diarrhea virus (PEDV) causes a porcine disease associated with swine epidemic diarrhea. The type I interferon (IFN-I or IFN α/β) is a key mediator of innate antiviral response during virus infection. Different antagonistic strategies have been identified and determined as to how PEDV infection inhibits the host’s IFN responses to escape the host innate immune pathway, but the pathogenic mechanisms of PEDV infection are not fully elucidated. Our preliminary results revealed that endogenous TANK-binding kinase 1 (TBK1) and interferon regulatory factor 3 (IRF3), the key components in the IFN signaling pathway were downregulated in PEDV infected IPEC-J2 cells by iTRAQ analysis. In this study, we screened nsp15 as the most important viral encoded protein involved in TBK1 and IRF3 reduction. Endoribonuclease (EndoU) activity has been well determined for coronavirus nsp15. Three residues (H226, H241, and K282) of PEDV nsp15 were identified as critical amino acids for PEDV EndoU but not D265, which was not well correlated with published results of other coronaviruses, such as severe acute respiratory syndrome virus (SARS-CoV). Moreover, PEDV nsp15 can directly degrade the RNA levels of TBK1 and IRF3 dependent on its EndoU activity to suppress IFN production and constrain the induction of IFN stimulated genes (ISGs), by which PEDV antagonizes the host innate response to facilitate its replication. Collectively, these results have confirmed that PEDV nsp15 was capable of subverting the IFN response by the RNA degradation of TBK1 and IRF3.

Complement C3-dependent glutamatergic synapse elimination in the developing hippocampus is region- and synapse-specific

SummaryThe complement cascade is an innate immune pathway that, in addition to host defense against pathogens, actively maintains tissue homeostasis. Complement is necessary for synaptic pruning during development and drives aberrant synapse loss in a number of neurodegenerative disorders that affect the hippocampus. However, the physiological function of complement in hippocampal synapse development is unknown. To address this, we investigated C3−/− mice at P16-18. We found that VGLUT2+ synapses were increased in the CA1 stratum lacunosum moleculare (SLM) and dentate gyrus molecular layer (DGML) of C3−/− mice compared to wildtype. Conversely, VGLUT1+ synapses, inhibitory synapses and myelin were not affected in the CA1 stratum radiatum (SR), SLM or DGML of C3−/− mice. Finally, we found that there was a decrease in microglial phagocytic activity only in VGLUT2+ regions and this correlated with the amount of VGLUT2+ synapses. Our study elucidates a role of the complement cascade in regulating hippocampus synapse number with exceptional specificity for VGLUT2-containing synapses during development.