Hundreds of effector proteins of the human malaria parasite Plasmodium falciparum constitute a “secretome” carrying a host-targeting (HT) signal, which predicts their export from the intracellular ...pathogen into the surrounding erythrocyte. Cleavage of the HT signal by a parasite endoplasmic reticulum (ER) protease, plasmepsin V, is the proposed export mechanism. Here, we show that the HT signal facilitates export by recognition of the lipid phosphatidylinositol-3-phosphate (PI(3)P) in the ER, prior to and independent of protease action. Secretome HT signals, including those of major virulence determinants, bind PI(3)P with nanomolar affinity and amino acid specificities displayed by HT-mediated export. PI(3)P-enriched regions are detected within the parasite's ER and colocalize with endogenous HT signal on ER precursors, which also display high-affinity binding to PI(3)P. A related pathogenic oomycete's HT signal export is dependent on PI(3)P binding, without cleavage by plasmepsin V. Thus, PI(3)P in the ER functions in mechanisms of secretion and pathogenesis.
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► PI(3)P-enriched regions are detected in the malaria endoplasmic reticulum ► HT signals of a P. falciparum “secretome” bind to PI(3)P with nanomolar affinity ► Endogenous, noncleaved HT signal on ER precursors binds PI(3)P in the ER ► PI(3)P binding in the ER and not HT signal cleavage is needed for host cell export
Export of malaria proteins from the parasite into the host erythrocyte relies upon the binding of the virulence factors' targeting sequence to PI(3)P, which is unexpectedly enriched in the parasite's ER.
Cellular senescence is a stable growth arrest that is implicated in tissue ageing and cancer. Senescent cells are characterized by an upregulation of proinflammatory cytokines, which is termed the ...senescence-associated secretory phenotype (SASP). NAD
metabolism influences both tissue ageing and cancer. However, the role of NAD
metabolism in regulating the SASP is poorly understood. Here, we show that nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of the NAD
salvage pathway, governs the proinflammatory SASP independent of senescence-associated growth arrest. NAMPT expression is regulated by high mobility group A (HMGA) proteins during senescence. The HMGA-NAMPT-NAD
signalling axis promotes the proinflammatory SASP by enhancing glycolysis and mitochondrial respiration. HMGA proteins and NAMPT promote the proinflammatory SASP through NAD
-mediated suppression of AMPK kinase, which suppresses the p53-mediated inhibition of p38 MAPK to enhance NF-κB activity. We conclude that NAD
metabolism governs the proinflammatory SASP. Given the tumour-promoting effects of the proinflammatory SASP, our results suggest that anti-ageing dietary NAD
augmentation should be administered with precision.
Tumor-associated macrophages (TAM) contribute to all aspects of tumor progression. Use of CSF1R inhibitors to target TAM is therapeutically appealing, but has had very limited anti-tumor effects. ...Here, we have identified the mechanism that limited the effect of CSF1R targeted therapy. We demonstrated that carcinoma-associated fibroblasts (CAF) are major sources of chemokines that recruit granulocytes to tumors. CSF1 produced by tumor cells caused HDAC2-mediated downregulation of granulocyte-specific chemokine expression in CAF, which limited migration of these cells to tumors. Treatment with CSF1R inhibitors disrupted this crosstalk and triggered a profound increase in granulocyte recruitment to tumors. Combining CSF1R inhibitor with a CXCR2 antagonist blocked granulocyte infiltration of tumors and showed strong anti-tumor effects.
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•PMN-MDSC infiltration of tumors is controlled by carcinoma-associated fibroblasts•CSF-1 silences expression of granulocytic chemokines by CAF mediated by HDAC2•Inhibition of CSF-1R induced tumor infiltration by PMN-MDSC•Combination of CSF-1R with CXCR2 inhibitors demonstrated strong anti-tumor effect
Kumar et al. show that CSF1R inhibition alters chemokine secretion by cancer-associated fibroblasts, which attracts pro-tumor PMN-MDSCs and results in poor efficacy. Combined inhibition of CSF1R and CXCR2 blocks MDSC recruitment and reduces tumor growth, which is further improved by the addition of anti-PD-1.
The gene encoding ARID1A, a chromatin remodeler, shows one of the highest mutation rates across many cancer types. Notably, ARID1A is mutated in over 50% of ovarian clear cell carcinomas, which ...currently have no effective therapy. To date, clinically applicable targeted cancer therapy based on ARID1A mutational status has not been described. Here we show that inhibition of the EZH2 methyltransferase acts in a synthetic lethal manner in ARID1A-mutated ovarian cancer cells and that ARID1A mutational status correlated with response to the EZH2 inhibitor. We identified PIK3IP1 as a direct target of ARID1A and EZH2 that is upregulated by EZH2 inhibition and contributed to the observed synthetic lethality by inhibiting PI3K-AKT signaling. Importantly, EZH2 inhibition caused regression of ARID1A-mutated ovarian tumors in vivo. To our knowledge, this is the first data set to demonstrate a synthetic lethality between ARID1A mutation and EZH2 inhibition. Our data indicate that pharmacological inhibition of EZH2 represents a novel treatment strategy for cancers involving ARID1A mutations.
Both p150 and p110 isoforms of ADAR1 convert adenosine to inosine in double-stranded RNA (dsRNA). ADAR1p150 suppresses the dsRNA-sensing mechanism that activates MDA5-MAVS-IFN signaling in the ...cytoplasm. In contrast, the biological function of the ADAR1p110 isoform, which is usually located in the nucleus, is largely unknown. Here, we show that stress-activated phosphorylation of ADAR1p110 by MKK6-p38-MSK MAP kinases promotes its binding to Exportin-5 and its export from the nucleus. After translocating to the cytoplasm, ADAR1p110 suppresses apoptosis in stressed cells by protecting many antiapoptotic gene transcripts that contain 3'-untranslated-region dsRNA structures primarily comprising inverted Alu repeats. ADAR1p110 competitively inhibits binding of Staufen1 to the 3'-untranslated-region dsRNAs and antagonizes Staufen1-mediated mRNA decay. Our study reveals a new stress-response mechanism in which human ADAR1p110 and Staufen1 regulate surveillance of a set of mRNAs required for survival of stressed cells.
The Merlin/
NF2 tumor suppressor restrains cell growth and tumorigenesis by controlling contact-dependent inhibition of proliferation. We have identified a tight-junction-associated protein complex ...comprising Merlin, Angiomotin, Patj, and Pals1. We demonstrate that Angiomotin functions downstream of Merlin and upstream of Rich1, a small GTPase Activating Protein, as a positive regulator of Rac1. Merlin, through competitive binding to Angiomotin, releases Rich1 from the Angiomotin-inhibitory complex, allowing Rich1 to inactivate Rac1, ultimately leading to attenuation of Rac1 and Ras-MAPK pathways. Patient-derived Merlin mutants show diminished binding capacities to Angiomotin and are unable to dissociate Rich1 from Angiomotin or inhibit MAPK signaling. Depletion of Angiomotin in
Nf2
−/−
Schwann cells attenuates the Ras-MAPK signaling pathway, impedes cellular proliferation in vitro and tumorigenesis in vivo.
► Merlin forms a tight-junction associated complex with Angiomotin, Patj, and Pals1 ► Merlin negatively regulates Rac1 by interfering with Rich1/Angiomotin interaction ► Merlin modulates MAPK signaling through the Rac1-Pak axis ► Angiomotin is required for tumorigenesis subsequent to loss of NF2
Mitochondria must buffer the risk of proteotoxic stress to preserve bioenergetics, but the role of these mechanisms in disease is poorly understood. Using a proteomics screen, we now show that the ...mitochondrial unfoldase-peptidase complex ClpXP associates with the oncoprotein survivin and the respiratory chain Complex II subunit succinate dehydrogenase B (SDHB) in mitochondria of tumor cells. Knockdown of ClpXP subunits ClpP or ClpX induces the accumulation of misfolded SDHB, impairing oxidative phosphorylation and ATP production while activating "stress" signals of 5' adenosine monophosphate-activated protein kinase (AMPK) phosphorylation and autophagy. Deregulated mitochondrial respiration induced by ClpXP targeting causes oxidative stress, which in turn reduces tumor cell proliferation, suppresses cell motility, and abolishes metastatic dissemination in vivo. ClpP is universally overexpressed in primary and metastatic human cancer, correlating with shortened patient survival. Therefore, tumors exploit ClpXP-directed proteostasis to maintain mitochondrial bioenergetics, buffer oxidative stress, and enable metastatic competence. This pathway may provide a "drugable" therapeutic target in cancer.
Complex genome organizations participate in various nuclear processes including transcription, DNA replication, and repair. However, the mechanisms that generate and regulate these functional genome ...structures remain largely unknown. Here, we describe how the Ku heterodimer complex, which functions in nonhomologous end joining, mediates clustering of long terminal repeat retrotransposons at centromeres in fission yeast. We demonstrate that the CENP-B subunit, Abp1, functions as a recruiter of the Ku complex, which in turn loads the genome-organizing machinery condensin to retrotransposons. Intriguingly, histone H3 lysine 56 (H3K56) acetylation, which functions in DNA replication and repair, interferes with Ku localization at retrotransposons without disrupting Abp1 localization and, as a consequence, dissociates condensin from retrotransposons. This dissociation releases condensin-mediated genomic associations during S phase and upon DNA damage. ATR (ATM- and Rad3-related) kinase mediates the DNA damage response of condensin-mediated genome organization. Our study describes a function of H3K56 acetylation that neutralizes condensin-mediated genome organization.
► Retrotransposon clustering is mediated by Ku, condensin, and CENP-B ► H3K56Ac regulates localization of Ku and condensin at retrotransposons ► Retrotransposon clustering is released during S phase and upon DNA damage ► ATR mediates disassembly of retrotransposon clustering upon DNA damage
Triple-negative breast cancer (BCa) (TNBC) is a deadly form of human BCa with limited treatment options and poor prognosis. In our prior analysis of over 2200 breast cancer samples, the G ...protein-coupled receptor CCR5 was expressed in > 95% of TNBC samples. A humanized monoclonal antibody to CCR5 (leronlimab), used in the treatment of HIV-infected patients, has shown minimal side effects in large patient populations.
A humanized monoclonal antibody to CCR5, leronlimab, was used for the first time in tissue culture and in mice to determine binding characteristics to human breast cancer cells, intracellular signaling, and impact on (i) metastasis prevention and (ii) impact on established metastasis.
Herein, leronlimab was shown to bind CCR5 in multiple breast cancer cell lines. Binding of leronlimab to CCR5 reduced ligand-induced Ca
signaling, invasion of TNBC into Matrigel, and transwell migration. Leronlimab enhanced the BCa cell killing of the BCa chemotherapy reagent, doxorubicin. In xenografts conducted with Nu/Nu mice, leronlimab reduced lung metastasis of the TNBC cell line, MB-MDA-231, by > 98% at 6 weeks. Treatment with leronlimab reduced the metastatic tumor burden of established TNBC lung metastasis.
The safety profile of leronlimab, together with strong preclinical evidence to both prevent and reduce established breast cancer metastasis herein, suggests studies of clinical efficacy may be warranted.
Cyclic cGMP-AMP synthase (cGAS) is a pattern recognition cytosolic DNA sensor that is essential for cellular senescence. cGAS promotes inflammatory senescence-associated secretory phenotype (SASP) ...through recognizing cytoplasmic chromatin during senescence. cGAS-mediated inflammation is essential for the antitumor effects of immune checkpoint blockade. However, the mechanism by which cGAS recognizes cytoplasmic chromatin is unknown. Here we show that topoisomerase 1-DNA covalent cleavage complex (TOP1cc) is both necessary and sufficient for cGAS-mediated cytoplasmic chromatin recognition and SASP during senescence. TOP1cc localizes to cytoplasmic chromatin and TOP1 interacts with cGAS to enhance the binding of cGAS to DNA. Retention of TOP1cc to cytoplasmic chromatin depends on its stabilization by the chromatin architecture protein HMGB2. Functionally, the HMGB2-TOP1cc-cGAS axis determines the response of orthotopically transplanted ex vivo therapy-induced senescent cells to immune checkpoint blockade in vivo. Together, these findings establish a HMGB2-TOP1cc-cGAS axis that enables cytoplasmic chromatin recognition and response to immune checkpoint blockade.
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