Signal regulatory protein alpha negatively regulates both TLR3 and cytoplasmic pathways in type I interferon induction

Leishmania Infection-Induced Proteolytic Processing of SIRPα in Macrophages

The shedding of cell surface receptors may bring synergistic outcomes through the loss of receptor-mediated cell signaling and competitive binding of the shed soluble receptor to its ligand. Thus, soluble receptors have both biological importance and diagnostic importance as biomarkers in immunological disorders. Signal regulatory protein α (SIRPα), one of the receptors responsible for the 'don't-eat-me' signal, is expressed by myeloid cells where its expression and function are in part regulated by proteolytic cleavage. However, reports on soluble SIRPα as a biomarker are limited. We previously reported that mice with experimental visceral leishmaniasis (VL) manifest anemia and enhanced hemophagocytosis in the spleen accompanied with decreased SIRPα expression. Here, we report increased serum levels of soluble SIRPα in mice infected with Leishmania donovani, a causative agent of VL. Increased soluble SIRPα was also detected in a culture supernatant of macrophages infected with L. donovani in vitro, suggesting the parasite infection promotes ectodomain shedding of SIRPα on macrophages. The release of soluble SIRPα was partially inhibited by an ADAM proteinase inhibitor in both LPS stimulation and L. donovani infection, suggesting a shared mechanism for cleavage of SIRPα in both cases. In addition to the ectodomain shedding of SIRPα, both LPS stimulation and L. donovani infection induced the loss of the cytoplasmic region of SIRPα. Although the effects of these proteolytic processes or changes in SIRPα still remain unclear, these proteolytic regulations on SIRPα during L. donovani infection may explain hemophagocytosis and anemia induced by infection, and serum soluble SIRPα may serve as a biomarker for hemophagocytosis and anemia in VL and the other inflammatory disorders.

Overcoming Immunotherapeutic Resistance in PDAC: SIRPα-CD47 blockade

A daily increase in the number of new cases of pancreatic ductal adenocarcinoma remains an issue of contention in cancer research. The data revealed that a global cumulated case of about 500, 000 have been reported. This has made PDAC the fourteenth most occurring tumor case in cancer research. Furthermore, PDAC is responsible for about 466,003 deaths annually, representing the seventh prevalent type of cancer mortality. PDAC has no salient symptoms in its early stages. This has exasperated several attempts to produce a perfect therapeutic agent against PDAC. Recently, immunotherapeutic research has shifted focus to the blockade of checkpoint proteins in the management and of some cancers. Investigations have centrally focused on developing therapeutic agents that could at least to a significant extent block the SIRPα-CD47 signaling cascade (a cascade which prevent phagocytosis of tumors by dendritic cells, via the deactivation of innate immunity and subsequently resulting in tumor regression) with minimal side effects. The concept on the blockade of this interaction as a possible mechanism for inhibiting the progression of PDAC is currently being debated. This review examined the structure--function activity of SIRPα-CD47 interaction while discussing in detail the mechanism of tumor resistance in PDAC. Further, this review details how the blockade of SIRPα-CD47 interaction serve as a therapeutic option in the management of PDAC.

Modulation of Signal Regulatory Protein α (SIRPα) by Plasmodium Antigenic Extract: A Preliminary In Vitro Study on Peripheral Blood Mononuclear Cells

Signal regulatory protein α (SIRPα) is an immunoreceptor expressed in myeloid innate immune cells that signals for inhibition of both phagocytosis and inflammatory response. Malaria parasites have evolutionarily selected multiple mechanisms that allow them to evade host immune defenses, including the modulation of cells belonging to innate immunity. Notwithstanding, little attention has been given to SIRPα in the context of immunosuppressive states induced by malaria. The present study attempted to investigate if malaria parasites are endowed with the capacity of modulating the expression of SIRPα on cells of innate immune system. Human peripheral blood mononuclear cells (PBMC) from healthy individuals were incubated in the presence of lipopolysaccharide (LPS) or crude extracts of P. falciparum or P. vivax and then, the expression of SIRPα was evaluated by flow cytometry. As expected, LPS showed an inhibitory effect on the expression of SIRPα in the population of monocytes, characterized by cell morphology in flow cytometry analysis, while Plasmodium extracts induced a significant positive modulation. Additional phenotyping of cells revealed that the modulatory potential of Plasmodium antigens on SIRPα expression was restricted to the population of monocytes (CD14⁺CD11c⁺), as no effect on myeloid dendritic cells (CD14⁻CD11c⁺) was observed. We hypothesize that malaria parasites explore inhibitory signaling of SIRPα to suppress antiparasitic immune responses contributing to the establishment of infection. Nevertheless, further studies are still required to better understand the role of SIRPα modulation in malaria immunity and pathogenesis.

Targeting the cluster of differentiation 47/signal-regulatory protein alpha axis in myeloid malignancies

PURPOSE OF REVIEW

The antitumor activity of macrophages is regulated by a balance of prophagocytic and antiphagocytic signals. Cluster of differentiation 47 (CD47), the dominant macrophage immune checkpoint ('do not eat me' signal), interacts with its receptor signal-regulatory protein alpha (SIRPα) to suppress phagocytic activities. This axis plays a pivotal role in immune evasion in myeloid malignancies as well as multiple cancers providing strong rationale for therapeutic exploitation.

RECENT FINDINGS

Preclinical studies have revealed overexpression of CD47 on leukemic stem cells and myeloblasts from patients with myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML), which contributes to immune surveillance evasion and is associated with poor outcomes. Blockade of CD47 with different approaches has demonstrated proof-of-concept antitumor activities mainly through phagocytic clearance. Early phase clinical trials combining the anti-CD47 mAb magrolimab with the hypomethylating agent azacitidine have showed synergistic activities, deep and durable responses, as well as a tolerable safety profile in these patients, including those with TP53 mutations.

SUMMARY

Targeting CD47/SIRPα axis, in combination with other therapeutic agents, represents a promising treatment approach for patients with myeloid malignancies, particularly the challenging TP53-mutated subgroup.

Hepatitis E virus-encoded microRNA promotes viral replication by inhibiting type I interferon

MicroRNAs (miRNAs), the non-coding RNAs of ~22 nucleotides (nt) in length, play a vital role in regulating viral replication. Hepatitis E virus (HEV), a single-stranded RNA virus, is a predominant pathogen of acute hepatitis worldwide. Virus-encoded miRNAs regulate the viral life cycle and escape from the host innate immune system. However, it is rarely known about HEV-encoded miRNA (HEV-miR-A6). In the present study, HEV-miR-A6 was screened by microarray, and further identified in vivo and in vitro. HEV-miR-A6 originated from the methylase (MeT) of HEV open reading frame 1 (ORF1) and was highly conserved in eight HEV genotypes. HEV-miR-A6 expression was growing during HEV replication, and significantly increased in acute hepatitis E patients than convalescence patients. Furthermore, HEV-miR-A6 was specifically detected in liver, spleen, kidney and colon by in situ hybridization. To identify the specificity of HEV-miR-A6, its mutants (HEV-miR-A6M1 and HEV-miR-A6M2) were constructed to change the stem-loop structure. Interestingly, over-expression of HEV-miR-A6 or HEV-miR-A6M1 significantly facilitated viral replication, while HEV-miR-A6M2, another mutant completely changed the stem-loop structure was invalid. SIRP-α, a candidate target gene of HEV-miR-A6, was activated when HEV-miR-A6 over-expressed to inhibit the phosphorylation of IRF3, and subsequently suppressed the expression of type I interferon β (IFN-β). The promotion of viral replication by HEV-miR-A6 further identified in vivo. Significant suppression of IFN-β production in the serum of HEV-infected mice pre-treated with HEV-miR-A6 was observed. In summary, HEV-miR-A6 activates SIRP-α to promote viral replication by inhibition of IFN-β expression.

Enhanced expression of immune checkpoint receptors during SARS-CoV-2 viral infection

The immune system is tightly regulated by the activity of stimulatory and inhibitory immune receptors. This immune homeostasis is usually disturbed during chronic viral infection. Using publicly available transcriptomic datasets, we conducted in silico analyses to evaluate the expression pattern of 38 selected immune inhibitory receptors (IRs) associated with different myeloid and lymphoid immune cells during coronavirus disease 2019 (COVID-19) infection. Our analyses revealed a pattern of overall upregulation of IR mRNA during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. A large number of IRs expressed on both lymphoid and myeloid cells were upregulated in nasopharyngeal swabs (NPSs), while lymphoid-associated IRs were specifically upregulated in autopsies, reflecting severe, terminal stage COVID-19 disease. Eight genes (BTLA, LAG3, FCGR2B, PDCD1, CEACAM1, CTLA4, CD72, and SIGLEC7), shared by NPSs and autopsies, were more expressed in autopsies and were directly correlated with viral levels. Single-cell data from blood and bronchoalveolar samples also reflected the observed association between IR upregulation and disease severity. Moreover, compared to SARS-CoV-1, influenza, and respiratory syncytial virus infections, the number and intensities of upregulated IRs were higher in SARS-CoV-2 infections. In conclusion, the immunopathology and severity of COVID-19 could be attributed to dysregulation of different immune inhibitors. Targeting one or more of these immune inhibitors could represent an effective therapeutic approach for the treatment of COVID-19 early and late immune dysregulations.

The CD47-SIRPα Immune Checkpoint

The cytotoxic activity of myeloid cells is regulated by a balance of signals that are transmitted through inhibitory and activating receptors. The Cluster of Differentiation 47 (CD47) protein, expressed on both healthy and cancer cells, plays a pivotal role in this balance by delivering a "don't eat me signal" upon binding to the Signal-regulatory protein alpha (SIRPα) receptor on myeloid cells. Here, we review the current understanding of the role of the CD47-SIRPα axis in physiological tissue homeostasis and as a promising therapeutic target in, among others, oncology, fibrotic diseases, atherosclerosis, and stem cell therapies. We discuss gaps in understanding and highlight where additional insight will be beneficial to allow optimal exploitation of this myeloid cell checkpoint as a target in human disease.

Low-dose 2-deoxy glucose stabilises tolerogenic dendritic cells and generates potent in vivo immunosuppressive effects

Cell therapies for autoimmune diseases using tolerogenic dendritic cells (tolDC) have been promisingly explored. A major stumbling block has been generating stable tolDC, with low risk of converting to mature immunogenic DC (mDC), exacerbating disease. mDC induction involves a metabolic shift to lactate production from oxidative phosphorylation (OXPHOS) and β-oxidation, the homeostatic energy source for resting DC. Inhibition of glycolysis through the administration of 2-deoxy glucose (2-DG) has been shown to prevent autoimmune disease experimentally but is not clinically feasible. We show here that treatment of mouse bone marrow-derived tolDC ex vivo with low-dose 2-DG (2.5 mM) (2-DGtolDC) induces a stable tolerogenic phenotype demonstrated by their failure to engage lactate production when challenged with mycobacterial antigen (Mtb). ~ 15% of 2-DGtolDC express low levels of MHC class II and 30% express CD86, while they are negative for CD40. 2-DGtolDC also express increased immune checkpoint molecules PDL-1 and SIRP-1α. Antigen-specific T cell proliferation is reduced in response to 2-DGtolDC in vitro. Mtb-stimulated 2-DGtolDC do not engage aerobic glycolysis but respond to challenge via increased OXPHOS. They also have decreased levels of p65 phosphorylation, with increased phosphorylation of the non-canonical p100 pathway. A stable tolDC phenotype is associated with sustained SIRP-1α phosphorylation and p85-AKT and PI3K signalling inhibition. Further, 2-DGtolDC preferentially secrete IL-10 rather than IL-12 upon Mtb-stimulation. Importantly, a single subcutaneous administration of 2-DGtolDC prevented experimental autoimmune uveoretinitis (EAU) in vivo. Inhibiting glycolysis of autologous tolDC prior to transfer may be a useful approach to providing stable tolDC therapy for autoimmune/immune-mediated diseases.

Human SP-D Acts as an Innate Immune Surveillance Molecule Against Androgen-Responsive and Androgen-Resistant Prostate Cancer Cells

Surfactant Protein D (SP-D), a pattern recognition innate immune molecule, has been implicated in the immune surveillance against cancer. A recent report showed an association of decreased SP-D expression in human prostate adenocarcinoma with an increased Gleason score and severity. In the present study, the SP-D expression was evaluated in primary prostate epithelial cells (PrEC) and prostate cancer cell lines. LNCaP, an androgen dependent prostate cancer cell line, exhibited significantly lower mRNA and protein levels of SP-D than PrEC and the androgen independent cell lines (PC3 and DU145). A recombinant fragment of human SP-D, rfhSP-D, showed a dose and time dependent binding to prostate cancer cells via its carbohydrate recognition domain. This study, for the first time, provides evidence of significant and specific cell death of tumor cells in rfhSP-D treated explants as well as primary tumor cells isolated from tissue biopsies of metatstatic prostate cancer patients. Viability of PrEC was not altered by rfhSP-D. Treated LNCaP (p53+/+) and PC3 (p53 -/-) cells exhibited reduced cell viability in a dose and time dependent manner and were arrested in G2/M and G1/G0 phase of the cell cycle, respectively. rfhSP-D treated LNCaP cells showed a significant upregulation of p53 whereas a significant downregulation of pAkt was observed in both PC3 and LNCaP cell lines. The rfhSP-D-induced apoptosis signaling cascade involved upregulation of Bax:Bcl2 ratio, cytochrome c and cleaved products of caspase 7. The study concludes that rfhSP-D induces apoptosis in prostate tumor explants as well as in androgen dependent and independent prostate cancer cells via p53 and pAkt pathways.

Signal regulatory protein α protects podocytes through promoting autophagic activity

High autophagic activity in podocytes, terminally differentiated cells which serve as main components of the kidney filtration barrier, is essential for podocyte survival under various challenges. How podocytes maintain such a high level of autophagy, however, remains unclear. Here we report that signal regulatory protein α (SIRPα) plays a key role in promoting podocyte autophagy. Unlike other glomerular cells, podocytes strongly express SIRPα, which is, however, downregulated in patients with focal segmental glomerulosclerosis and mice with experimental nephropathy. Podocyte SIRPα levels are inversely correlated with the severity of podocyte injury and proteinuria but positively with autophagy. Compared to wild-type littermates, Sirpa-deficient mice display greater age-related podocyte injury and proteinuria and develop more rapid and severe renal injury in various models of experimental nephropathy. Mechanistically, podocyte SIRPα strongly reduces Akt/GSK-3β/β-catenin signaling, leading to an increase in autophagic activity. Our findings thus demonstrate a critical protective role of SIRPα in podocyte survival via maintaining autophagic activity.

ALX148 blocks CD47 and enhances innate and adaptive antitumor immunity with a favorable safety profile

CD47 is a widely expressed cell surface protein that functions as an immune checkpoint in cancer. When expressed by tumor cells, CD47 can bind SIRPα on myeloid cells, leading to suppression of tumor cell phagocytosis and other innate immune functions. CD47-SIRPα signaling has also been implicated in the suppression of adaptive antitumor responses, but the relevant cellular functions have yet to be elucidated. Therapeutic blockade of the CD47 pathway may stimulate antitumor immunity and improve cancer therapy. To this end, a novel CD47-blocking molecule, ALX148, was generated by fusing a modified SIRPα D1 domain to an inactive human IgG1 Fc. ALX148 binds CD47 from multiple species with high affinity, inhibits wild type SIRPα binding, and enhances phagocytosis of tumor cells by macrophages. ALX148 has no effect on normal human blood cells in vitro or on blood cell parameters in rodent and non-human primate studies. Across several murine tumor xenograft models, ALX148 enhanced the antitumor activity of different targeted antitumor antibodies. Additionally, ALX148 enhanced the antitumor activity of multiple immunotherapeutic antibodies in syngeneic tumor models. These studies revealed that CD47 blockade with ALX148 induces multiple responses that bridge innate and adaptive immunity. ALX148 stimulates antitumor properties of innate immune cells by promoting dendritic cell activation, macrophage phagocytosis, and a shift of tumor-associated macrophages toward an inflammatory phenotype. ALX148 also stimulated the antitumor properties of adaptive immune cells, causing increased T cell effector function, pro-inflammatory cytokine production, and a reduction in the number of suppressive cells within the tumor microenvironment. Taken together, these results show that ALX148 binds and blocks CD47 with high affinity, induces a broad antitumor immune response, and has a favorable safety profile.

Detection of Signal Regulatory Protein α in Saimiri sciureus (Squirrel Monkey) by Anti-Human Monoclonal Antibody

Non-human primates (NHP) are suitable models for studying different aspects of the human system, including pathogenesis and protective immunity to many diseases. However, the lack of specific immunological reagents for neo-tropical monkeys, such as Saimiri sciureus, is still a major factor limiting studies in these models. An alternative strategy to circumvent this obstacle has been the selection of immunological reagents directed to humans, which present cross-reactivity with NHP molecules. In this context and considering the key role of inhibitory immunoreceptors—such as the signal regulatory protein α (SIRPα)—in the regulation of immune responses, in the present study, we attempted to evaluate the ability of anti-human SIRPα monoclonal antibodies to recognize SIRPα in antigen-presenting S. sciureus peripheral blood mononuclear cells (PBMC). As shown by flow cytometry analysis, the profile of anti-SIRPα staining as well as the levels of SIRPα-positive cells in PBMC from S. sciureus were similar to those observed in human PBMC. Furthermore, using anti-SIRPα monoclonal antibody, it was possible to detect a decrease of the SIRPα levels on surface of S. sciureus cells after in vitro stimulation with lipopolysaccharides. Finally, using computed-based analysis, we observed a high degree of conservation of SIRPα across six species of primates and the presence of shared epitopes in the extracellular domain between humans and Saimiri genus that could be targeted by antibodies. In conclusion, we have identified a commercially available anti-human monoclonal antibody that is able to detect SIRPα of S. sciureus monkeys and that, therefore, can facilitate the study of the immunomodulatory role of SIRPα when S. sciureus is used as a model.

Cleavage of Signal Regulatory Protein α (SIRPα) Enhances Inflammatory Signaling

Signal regulatory protein α (SIRPα) is a membrane glycoprotein immunoreceptor abundant in cells of monocyte lineage. SIRPα ligation by a broadly expressed transmembrane protein, CD47, results in phosphorylation of the cytoplasmic immunoreceptor tyrosine-based inhibitory motifs, resulting in the inhibition of NF-κB signaling in macrophages. Here we observed that proteolysis of SIRPα during inflammation is regulated by a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10), resulting in the generation of a membrane-associated cleavage fragment in both THP-1 monocytes and human lung epithelia. We mapped a charge-dependent putative cleavage site near the membrane-proximal domain necessary for ADAM10-mediated cleavage. In addition, a secondary proteolytic cleavage within the membrane-associated SIRPα fragment by γ-secretase was identified. Ectopic expression of a SIRPα mutant plasmid encoding a proteolytically resistant form in HeLa cells inhibited activation of the NF-κB pathway and suppressed STAT1 phosphorylation in response to TNFα to a greater extent than expression of wild-type SIRPα. Conversely, overexpression of plasmids encoding the proteolytically cleaved SIRPα fragments in cells resulted in enhanced STAT-1 and NF-κB pathway activation. Thus, the data suggest that combinatorial actions of ADAM10 and γ-secretase on SIRPα cleavage promote inflammatory signaling.

Transcriptome comparative analysis revealed poly(I:C) activated RIG-I/MDA5-mediated signaling pathway in miiuy croaker

Miiuy croker (Miichthys miiuy) as an important economical aquaculture species has challenged many more diseases caused by various pathogens recently. To better explore the immune response to virus, we have analyzed the transcriptome profiling of miiuy croaker challenged with poly(I:C) synthetic analog of virus dsRNA. We have obtained differentially expressed genes (DEGs) with up/down-relevant from comparison of the Ctrl and Poly transcriptome libraries. Through GO and KEGG enrichment analysis, immune-relevant DEGs whose expression are significantly rise or fall after challenged have been identified and classified. In order to detailedly analysis host immune response patterns for dsRNA virus, we have performed a map based on RIG-I/MDA5-mediated and TLR3-mediated signaling pathway which both induced type I IFNs response. In this pathway, both MDA5 and LGP2 are important RLRs in host surveillance against infection of dsRNA viruses and induce type I IFNs response which subsequently form a transcription factor complex ISGF3 that promote downstream genes referred to as ISGs to inhibits virus replication.

PI3K pathway inhibitors: potential prospects as adjuncts to vaccine immunotherapy for glioblastoma

Constitutive activation of the PI3K pathway has been implicated in glioblastoma (GBM) pathogenesis. Pharmacologic inhibition can both inhibit tumor survival and downregulate expression of programmed death ligand-1, a protein highly expressed on glioma cells that strongly contributes to cancer immunosuppression. In that manner, PI3K pathway inhibitors can help optimize GBM vaccine immunotherapy. In this review, we describe and assess the potential integration of various classes of PI3K pathway inhibitors into GBM immunotherapy. While early-generation inhibitors have a wide range of immunosuppressive effects that could negate their antitumor potency, further work should better characterize how contemporary inhibitors affect the immune response. This will help determine if these inhibitors are truly a therapeutic avenue with a strong future in GBM immunotherapy.

Signal regulatory protein α is associated with tumor-polarized macrophages phenotype switch and plays a pivotal role in tumor progression

Macrophages (Mψ) are the major component of infiltrating leukocytes in tumors and exhibit distinct phenotypes according to the microenvironment. We have recently found that signal regulatory protein α (SIRPα), the inhibitory molecule expressed on myeloid cells, plays a critical role in controlling innate immune activation. Here, we identify that SIRPα is down-regulated on monocytes/Mψ isolated from peritumoral areas of hepatocellular carcinoma (HCC) samples, while its level is moderately recovered in intratumor Mψ. In vitro assays demonstrate that SIRPα expression is significantly reduced on Mψ when cocultured with hepatoma cells. This reduction is partly due to the soluble factors in the tumor microenvironment. Knockdown (KD) of SIRPα prolongs activation of nuclear factor kappa B (NF-κB) and PI3K-Akt pathways as Mψ encounter tumor cells, leading to an increased capacity of Mψ for migration, survival, and proinflammatory cytokine production. Enhanced Stat3 and impaired Stat1 phosphorylation are also observed in tumor-exposed SIRPα-KD Mψ. Adoptive transfer with SIRPα-KD Mψ accelerates mouse hepatoma cells growth in vivo by remolding the inflammatory microenvironment and promoting angiogenesis. SIRPα accomplishes this partly through its sequestration of the signal transducer Src homology 2-containing phosphotyrosine phosphatase (SHP2) from IκB kinase β (IKKβ) and PI3K regulatory subunit p85 (PI3Kp85).

CONCLUSION

These findings suggest that SIRPα functions as an important modulator of tumor-polarized Mψ in hepatoma, and the reduction of SIRPα is a novel strategy used by tumor cells to benefit their behavior. Therefore, SIRPα could be utilized as a potential target for HCC therapy.

Sterile-α- and armadillo motif-containing protein inhibits the TRIF-dependent downregulation of signal regulatory protein α to interfere with intracellular bacterial elimination in Burkholderia pseudomallei-infected mouse macrophages

Burkholderia pseudomallei, the causative agent of melioidosis, evades macrophage killing by suppressing the TRIF-dependent pathway, leading to inhibition of inducible nitric oxide synthase (iNOS) expression. We previously demonstrated that virulent wild-type B. pseudomallei inhibits the TRIF-dependent pathway by upregulating sterile-α- and armadillo motif-containing protein (SARM) and by inhibiting downregulation of signal regulatory protein α (SIRPα); both molecules are negative regulators of Toll-like receptor signaling. In contrast, the less virulent lipopolysaccharide (LPS) mutant of B. pseudomallei is unable to exhibit these features and is susceptible to macrophage killing. However, the functional relationship of these two negative regulators in the evasion of macrophage defense has not been elucidated. We demonstrated here that SIRPα downregulation was observed after inhibition of SARM expression by small interfering RNA in wild-type-infected macrophages, indicating that SIRPα downregulation is regulated by SARM. Furthermore, this downregulation requires activation of the TRIF signaling pathway, as we observed abrogation of SIRPα downregulation as well as restricted bacterial growth in LPS mutant-infected TRIF-depleted macrophages. Although inhibition of SARM expression is correlated to SIRPα downregulation and iNOS upregulation in gamma interferon-activated wild-type-infected macrophages, these phenomena appear to bypass the TRIF-dependent pathway. Similar to live bacteria, the wild-type LPS is able to upregulate SARM and to prevent SIRPα downregulation, implying that the LPS of B. pseudomallei may play a crucial role in regulating the expression of these two negative regulators. Altogether, our findings show a previously unrecognized role of B. pseudomallei-induced SARM in inhibiting SIRPα downregulation-mediated iNOS upregulation, facilitating the ability of the bacterium to multiply in macrophages.

Human blood mDC subsets exhibit distinct TLR repertoire and responsiveness

Human blood DCs encompass pDCs and two subsets of mDCs: CD1c(+) mDCs and CD141(+) mDCs. The rare CD141(+) DC population is thought to be the equivalent of mouse CD8α(+) cDCs that play a significant role in antigen cross-presentation. Here, we analyzed by Q-PCR TLR1-10 expression in blood DC subsets. Whereas CD1c(+) DCs express all TLR except TLR9, CD141(+) DCs present a more restricted pattern with high expression of TLR3 and -10, expression of TLR1,-2, -6, and -8, and lack of TLR4, -5, -7, and -9. The in vitro analysis of isolated mDC subset reponsiveness to an extensive panel of TLR ligands confirmed these results, with CD141(+) DCs responding only to TLR1/2, -3, and -7/8. The cytokine/chemokine production profile of isolated CD141(+) DCs was also more restricted, as they produced mainly proinflammatory cytokines but no IL-12 and to a lower level, in comparison with CD1c(+) DCs, except for CXCL10, CCL5, and IFN-β. In contrast, with the use of a whole blood assay, we found that CD141(+) DCs produce IL-12 in response to TLR1/2, -3, and more surprisingly, -9. Finally, both mDC subsets are potent inducers of Th1 response, particularly after TLR3 triggering. Taken together, these data confirmed functional differences between blood mDC subsets. The major response of CD141(+) mDCs to TLR3 ligand and their cytokine production pattern suggest a role for these cells in antiviral immunity.

Involvement of signal regulatory protein α, a negative regulator of Toll-like receptor signaling, in impairing the MyD88-independent pathway and intracellular killing of Burkholderia pseudomallei-infected mouse macrophages

The facultative intracellular gram-negative bacterium Burkholderia pseudomallei is the causative agent of melioidosis and is known for its ability to evade the Toll-like receptor (TLR)-mediated innate immune response. Previously it has been demonstrated that this bacterium was able to suppress the MyD88-independent pathway and can survive macrophage intracellular killing. However, the underlying mechanisms responsible for the suppression of this pathway are not fully understood. In the present study, we showed that both living and heat-killed B. pseudomallei bacteria restrict the TLR signaling response, particularly macrophage inducible nitric oxide synthase (iNOS) expression, by preventing downregulation of constitutively expressed signal regulatory protein α (SIRPα) molecule, a known negative regulator of TLR signaling. In contrast, a lipopolysaccharide (LPS) mutant of B. pseudomallei, a less virulent strain, was able to downregulate SIRPα expression in mouse macrophages. However, depletion of constitutively expressed SIRPα was able to induce the gene expression downstream of TLR signaling pathways (particularly the MyD88-independent pathway), such as that of the iNOS gene, leading to enhanced macrophage intracellular killing of B. pseudomallei. Induction of gene expression was consistent with the enhanced degradation pattern of IκBα with SIRPα depletion. Additionally, the downregulation of SIRPα expression with upregulation of iNOS was observed when the macrophages were pretreated with gamma interferon (IFN-γ) prior to the infection, suggesting that the enhanced intracellular killing of bacteria by IFN-γ is associated with the decreased SIRPα expression. Altogether our findings demonstrate that B. pseudomallei evades macrophage intracellular killing by preventing the downregulation of SIRPα that results in the inhibition of gene expression downstream of the MyD88-independent pathway.

Phosphatidylinositol-3-kinase (PI3K) is activated by influenza virus vRNA via the pathogen pattern receptor Rig-I to promote efficient type I interferon production

The phosphatidylinositol-3-kinase (PI3K) was identified to be activated upon influenza A virus (IAV) infection. An early and transient induction of PI3K signalling is caused by viral attachment to cells and promotes virus entry. In later phases of infection the kinase is activated by the viral NS1 protein to prevent premature apoptosis. Besides these virus supporting functions, it was suggested that PI3K signalling is involved in dsRNA and IAV induced antiviral responses by enhancing the activity of interferon regulatory factor-3 (IRF-3). However, molecular mechanisms of activation remained obscure. Here we show that accumulation of vRNA in cells infected with influenza A or B viruses results in PI3K activation. Furthermore, expression of the RNA receptors Rig-I and MDA5 was increased upon stimulation with virion extracted vRNA or IAV infection. Using siRNA approaches, Rig-I was identified as pathogen receptor necessary for influenza virus vRNA sensing and subsequent PI3K activation in a TRIM25 and MAVS signalling dependent manner. Rig-I induced PI3K signalling was further shown to be essential for complete IRF-3 activation and consequently induction of the type I interferon response. These data identify PI3K as factor that is activated as part of the Rig-I mediated anti-pathogen response to enhance expression of type I interferons.

Pseudomonas aeruginosa suppresses interferon response to rhinovirus infection in cystic fibrosis but not in normal bronchial epithelial cells

Despite increased morbidity associated with secondary respiratory viral infections in cystic fibrosis (CF) patients with chronic Pseudomonas aeruginosa infection, the underlying mechanisms are not well understood. Here, we investigated the effect of P. aeruginosa infection on the innate immune responses of bronchial epithelial cells to rhinovirus (RV) infection. CF cells sequentially infected with mucoid P. aeruginosa (MPA) and RV showed lower levels of interferons (IFNs) and higher viral loads than those of RV-infected cells. Unlike results for CF cells, normal bronchial epithelial cells coinfected with MPA/RV showed higher IFN expression than RV-infected cells. In both CF and normal cells, the RV-stimulated IFN response requires phosphorylation of Akt and interferon response factor 3 (IRF3). Preinfection with MPA inhibited RV-stimulated Akt phosphorylation and decreased IRF3 phosphorylation in CF cells but not in normal cells. Compared to normal, unstimulated CF cells or normal cells treated with CFTR inhibitor showed increased reactive oxygen species (ROS) production. Treatment of CF cells with antioxidants prior to MPA infection partially reversed the suppressive effect of MPA on the RV-stimulated IFN response. Together, these results suggest that MPA preinfection inhibits viral clearance by suppressing the antiviral response particularly in CF cells but not in normal cells. Further, increased oxidative stress in CF cells appears to modulate the innate immune responses to coinfection.

Inhibition of active autophagy induces apoptosis and increases chemosensitivity in cholangiocarcinoma

Intrahepatic cholangiocellular carcinomas (ICCs) are usually fatal neoplasms originating from bile duct epithelia. However, many cholangiocarcinoma cells are shown to be resistant to chemotherapeutic drugs, which induce cell apoptosis. The role of autophagy and the therapeutic value of autophagy-associated genes are largely unknown in ICC. Here, we showed that autophagy was activated in nutrient starvation and xenograft cholangiocarcinoma cells. Furthermore, expression of autophagic genes and their autophagic activity were higher in clinical ICC specimens than that in normal cholangiocytes separated by laser capture microdissection. Inhibition of autophagy by autophagy inhibitors or siRNA, cholangiocarcinoma cells showed detention of proliferation and increase of apoptosis during nutrient starvation. In addition, autophagy inhibitor treatment or knockdown of beclin 1 suppressed tumor growth and sensitized ICC cells to chemotherapeutic agent-induced cell death. In conclusion, our data showed that autophagy is activated in ICC, and inactivation of autophagy may lead to cell apoptosis and enhance chemotherapy sensitivity.

Classical swine fever virus suppresses maturation and modulates functions of monocyte-derived dendritic cells without activating nuclear factor kappa B

Classical swine fever virus (CSFV) compromises the host immune system, causing the severe disease of pigs. Dendritic cells (DCs) are the most potent inducers of immune responses. In the present study, we investigated the functional properties of porcine monocyte-derived DCs (Mo-DCs) affected by CSFV. Results showed that the expression of surface markers of DCs such as major histocompatibility complex class II (MHC-II), CD80, CD83 and CD86 were unimpaired, but an obviously increased expression of CD172a in DCs was noticed 48 h after CSFV infection. The expression profiles of cytokines were detected in cultured Mo-DCs after various treatments for 48 h by Q-RT-PCR. The findings suggested that CSFV infection significantly increased the mRNA expression of IL-10 and TNF-α, and inhibited IL-12 expression, with little effect on IFN-α and IFN-γ expression. We further demonstrated that CSFV was incapable of activating the nuclear factor kappa B (NF-κB) in infected DCs, which was characterized by an unvaried DNA binding activity of NF-κB, the lack of translocation of p65/RelA from the cytoplasm to the nucleus and the stabilization of p65/RelA expression. Furthermore, Western blot analysis indicated that the inactivation of NF-κB was due to the failure of IκBα degradation. The data demonstrated that CSFV could be replicated in DCs and CSFV infection could modulate the secretion of crucial co-stimulatory molecules and cytokines which down-regulated maturation of DCs, without activating NF-κB in DCs. Thus, the results suggested a possible mechanism for CSFV evasion of innate host defenses, providing the basis for understanding molecular pathways in CSFV pathogenesis.

Zinc finger protein ZBTB20 expression is increased in hepatocellular carcinoma and associated with poor prognosis

Background

Our previous studies showed that ZBTB20, a new BTB/POZ-domain gene, could negatively regulate α feto-protein and other liver-specific genes, concerning such as bio-transformation, glucose metabolism and the regulation of the somatotropic hormonal axis. The aim of this study is to determine the potential clinical implications of ZBTB20 in hepatocellular carcinoma (HCC).

Methods

Quantitative real-time RT-PCR and Western blot analyses were used to detect expression levels of ZBTB20 in 50 paired HCC tumorous and nontumorous tissues and in 20 normal liver tissues. Moreover, expression of ZBTB20 was assessed by immunohistochemistry of paired tumor and peritumoral liver tissue from 102 patients who had undergone hepatectomy for histologically proven HCC. And its relationship with clinicopathological parameters and prognosis was investigated.

Results

Both messenger RNA and protein expression levels of ZBTB20 were elevated significantly in HCC tissues compared with the paired non-tumor tissues and normal liver tissues. Overexpressed ZBTB20 protein in HCC was significantly associated with vein invasion (P = 0.016). Importantly, the recurrence or metastasis rates of HCCs with higher ZBTB20 expression were markedly greater than those of HCCs with lower expression (P = 0.003, P = 0.00015, respectively). Univariate and multivariate analyses revealed that ZBTB20 overexpression was an independent prognostic factor for HCC. The disease-free survival period and over-all survival period in patients with overexpressed ZBTB20 in HCC was significantly reduced.

Conclusions

The expression of ZBTB20 is increased in HCC and associated with poor prognosis in patients with HCC, implicating ZBTB20 as a candidate prognostic marker in HCC.

Double-stranded RNA induces shedding of the 34-kDa soluble TNFR1 from human airway epithelial cells via TLR3-TRIF-RIP1-dependent signaling: roles for dual oxidase 2- and caspase-dependent pathways

TNF, an important mediator of inflammatory and innate immune responses, can be regulated by binding to soluble TNF receptors. The 55-kDa type 1 TNFR (TNFR1), the key receptor for TNF signaling, is released to the extracellular space by two mechanisms, the inducible cleavage and shedding of 34-kDa soluble TNFR1 (sTNFR1) ectodomains and the constitutive release of full-length 55-kDa TNFR1 within exosome-like vesicles. The aim of this study was to identify and characterize TLR signaling pathways that mediate TNFR1 release to the extracellular space. To our knowledge, we demonstrate for the first time that polyinosinic-polycytidylic acid [poly (I:C)], a synthetic dsRNA analogue that signals via TLR3, induces sTNFR1 shedding from human airway epithelial (NCI-H292) cells, whereas ligands for other microbial pattern recognition receptors, including TLR4, TLR7, and nucleotide-binding oligomerization domain containing 2, do not. Furthermore, poly (I:C) selectively induces the cleavage of 34-kDa sTNFR1 ectodomains but does not enhance the release of full-length 55-kDa TNFR1 within exosome-like vesicles. RNA interference experiments demonstrated that poly (I:C)-induced sTNFR1 shedding is mediated via activation of TLR3-TRIF-RIP1 signaling, with subsequent activation of two downstream pathways. One pathway involves the dual oxidase 2-mediated generation of reactive oxygen species, and the other pathway is via the caspase-mediated activation of apoptosis. Thus, the ability of dsRNA to induce the cleavage and shedding of the 34-kDa sTNFR1 from human bronchial epithelial cells represents a novel mechanism by which innate immune responses to viral infections are modulated.

The role of cis dimerization of signal regulatory protein alpha (SIRPalpha) in binding to CD47

Interaction of SIRPα with its ligand, CD47, regulates leukocyte functions, including transmigration, phagocytosis, oxidative burst, and cytokine secretion. Recent progress has provided significant insights into the structural details of the distal IgV domain (D1) of SIRPα. However, the structural roles of proximal IgC domains (D2 and D3) have been largely unstudied. The high degree of conservation of D2 and D3 among members of the SIRP family as well as the propensity of known IgC domains to assemble in cis has led others to hypothesize that SIRPα forms higher order structures on the cell surface. Here we report that SIRPα forms noncovalently linked cis homodimers. Treatment of SIRPα-expressing cells with a membrane-impermeable cross-linker resulted in the formation of SDS-stable SIRPα dimers and oligomers. Biochemical analyses of soluble recombinant extracellular regions of SIRPα, including domain truncation mutants, revealed that each of the three extracellular immunoglobulin loops of SIRPα formed dimers in solution. Co-immunoprecipitation experiments using cells transfected with different affinity-tagged SIRPα molecules revealed that SIRPα forms cis dimers. Interestingly, in cells treated with tunicamycin, SIRPα dimerization but not CD47 binding was inhibited, suggesting that a SIRPα dimer is probably bivalent. Last, we demonstrate robust dimerization of SIRPa in adherent, stimulated human neutrophils. Collectively, these data are consistent with SIRPα being expressed on the cell surface as a functional cis-linked dimer.

Generation of Th1-polarizing dendritic cells using the TLR7/8 agonist CL075

In this paper, we describe a new method for preparation of human dendritic cells (DCs) that secrete bioactive IL-12(p70) using synthetic immunostimulatory compounds as TLR7/8 agonists. Monocyte-derived DCs were generated using a procedure that provided mature cells within 3 d. Several maturation mixtures that contained various cytokines, IFN-gamma, different TLR agonists, and PGE(2) were compared for impact on cell recovery, phenotype, cytokine secretion, migration, and lymphocyte activation. Mixtures that included the TLR7/8 agonists R848 or CL075, combined with the TLR3 agonist polyinosinic:polycytidylic acid, yielded 3-d mature DCs that secreted high levels of IL-12(p70), showed strong chemotaxis to CCR7 ligands, and had a positive costimulatory potential. They also had excellent capacity to activate NK cells, effectively polarized CD4(+) and CD8(+) T cells to secrete IFN-gamma and to induce T cell-mediated cytotoxic function. Thereby, mature DCs prepared within 3 d using such maturation mixtures displayed optimal functions required for vaccine development.

Human CD141+ (BDCA-3)+ dendritic cells (DCs) represent a unique myeloid DC subset that cross-presents necrotic cell antigens

The characterization of human dendritic cell (DC) subsets is essential for the design of new vaccines. We report the first detailed functional analysis of the human CD141⁺ DC subset. CD141⁺ DCs are found in human lymph nodes, bone marrow, tonsil, and blood, and the latter proved to be the best source of highly purified cells for functional analysis. They are characterized by high expression of toll-like receptor 3, production of IL-12p70 and IFN-β, and superior capacity to induce T helper 1 cell responses, when compared with the more commonly studied CD1c⁺ DC subset. Polyinosine-polycytidylic acid (poly I:C)–activated CD141⁺ DCs have a superior capacity to cross-present soluble protein antigen (Ag) to CD8⁺ cytotoxic T lymphocytes than poly I:C–activated CD1c⁺ DCs. Importantly, CD141⁺ DCs, but not CD1c⁺ DCs, were endowed with the capacity to cross-present viral Ag after their uptake of necrotic virus-infected cells. These findings establish the CD141⁺ DC subset as an important functionally distinct human DC subtype with characteristics similar to those of the mouse CD8α⁺ DC subset. The data demonstrate a role for CD141⁺ DCs in the induction of cytotoxic T lymphocyte responses and suggest that they may be the most relevant targets for vaccination against cancers, viruses, and other pathogens.

SIRPalpha1 receptors interfere with the EGFRvIII signalosome to inhibit glioblastoma cell transformation and migration

EGFRvIII, a frequent genetic alteration of the epidermal growth factor receptor (EGFR), has been shown to increase the migratory potential of tumor cells and normal fibroblasts. Previously, we showed that signal regulatory protein alpha1 (SIRPalpha1) receptors interact with SHP-2 to inhibit wild-type (wt) EGFR-mediated tumor migration, survival and cell transformation. However, the effects of SIRPalpha1 inhibitory receptors on EGFRvIII-mediated phenotypes are unclear. The aim of this study was to investigate the effect of SIRPalpha1 receptor on the EGFRvIII signalosome and phenotypes. Overexpression of SIRPalpha1 in U87MG.EGFRvIII cells inhibited transformation and migration in a MAPK-dependent manner, and is independent of the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway. We observed reduced EGFRvIII/SHP-2/Gab1/Grb2/Sos-1 interaction and enhanced SIRP/SHP-2 association in U87MG.EGFRvIII/SIRPalpha1 cells when compared with empty vector control cells. Interestingly, SIRPalpha1 overexpression differentially modulated SHP-2 phosphorylation at tyrosyl 542 and 580 residues, which may regulate Erk1/2 activity and the EGFRvIII phenotype. In addition, SIRPalpha1-expressing cells exhibited reduced focal adhesion kinase (FAK) phosphorylation and its recruitment to the EGFRvIII/Grb2/Sos-1/Gab1/SHP-2 complex. Collectively, our data indicate that SIRPalpha1 specifically affects the SHP-2/FAK/Grb2/Sos-1/MAPK activation loop to downmodulate EGFRvIII-mediated migration and transformation. Further understanding of the molecular interactions between the SIRPalpha1 inhibitory receptor and the EGFRvIII signalosome may facilitate the identification of novel targets to inhibit the EGFRvIII glioblastoma phenotype.

Human neuronal cells possess functional cytoplasmic and TLR-mediated innate immune pathways influenced by phosphatidylinositol-3 kinase signaling

Innate immune pathways are early defense responses important for the immediate control and eventual clearance of many pathogens, where signaling is initiated via pattern recognition receptor (PRR)-mediated events that occur in a ligand- and cell-type specific manner. Within CNS neurons, innate immune pathways are likely crucial to control pathogens that target these essential yet virtually irreplaceable cells. However, relatively little is known about the induction and regulation of neuronal PRR signaling. In this report, we used human neuronal cell lines and primary rat neuronal cultures to examine PRR expression and function. We found that several innate immune receptor ligands, including Sendai virus, the dsRNA mimetic polyinosinic-polycytidylic acid, and LPS all activated differentiation-dependent neuronal innate immune pathways. Functional genetic analyses revealed that IFN regulatory factor 3-mediated pathways that resulted in IFN-beta transcriptional upregulation were activated in cultured human neuronal cells by the PRRs TLR3, MDA5, or RIG-I in a ligand-specific manner. Furthermore, genome-wide transcriptional array and targeted genetic and pharmacologic analyses identified PI3K signaling as crucial for the induction of innate immune pathways in neurons. These results indicate that human neuronal cells possess specific and functional PRR pathways essential for the effective induction of innate immune responses, and suggest that neurons can play an active role in defense against neurotropic pathogens.

Activation of host antiviral RNA-sensing factors necessary for herpes simplex virus type 1-activated transcription of host cell fucosyltransferase genes FUT3, FUT5, and FUT6 and subsequent expression of sLe(x) in virus-infected cells

Herpes simplex virus type 1 (HSV-1) induces expression of a selectin receptor, the carbohydrate epitope sialyl Lewis X (sLe(x)), at the surface of infected cells. The molecular background to this phenomenon is that a viral immediate early RNA interacts with as yet unidentified host factors, eventually resulting in transcription of three dormant host fucosyltransferase genes (FUT3, FUT5, and FUT6), whose gene products are rate-limiting for synthesis of sLe(x). The aim of the present study was to define the immediate targets for the viral RNA in this process. We found that the Protein Kinase R (PKR) inhibitors 2-aminopurine (2-AP) and C16 inhibited FUT3, FUT5, and FUT6 expression as well as HSV-1-induced expression of sLe(x), indicating a primary role of PKR as a viral RNA target. The PKR-dependent activation of the FUT genes seemed neither to involve PKR effects on translation nor to involve NF-kappaB- or JNK-dependent activation. IMD-0354, known as an inhibitor of the NF-kappaB-activating factor IKK-2, induced FUT transcription via a novel IKK-2-independent mechanism, irrespective of whether the cells were virus-infected or not. Altogether, the results suggested that PKR is the primary target for HSV-1 early RNA during induction of FUT3, FUT5, and FUT6, and that the subsequent steps in the transcriptional activation of these host genes involve a hitherto unknown IMD-0354, yet IKK-2-independent, pathway.

IL-10-dependent S100A8 gene induction in monocytes/macrophages by double-stranded RNA

The S100 calcium-binding proteins S100A8 and S100A9 are elevated systemically in patients with viral infections. The S100A8-S100A9 complex facilitated viral replication in human CD4(+) T lymphocytes latently infected with HIV-1- and S100A8-induced HIV-1 transcriptional activity. Mechanisms inducing the S100 genes and the potential source of these proteins following viral activation are unknown. In this study, we show that S100A8 was induced in murine macrophages, and S100A8 and S100A9 in human monocytes and macrophages, by polyinosinic:polycytidylic acid, a dsRNA mimetic. Induction was at the transcriptional level and was IL-10 dependent. Similar to LPS-induced S100A8, induction by dsRNA was dependent on p38 and ERK MAPK. Protein kinase R (PKR) mediates antiviral defense and participates in MyD88-dependent/independent signaling triggered by TLR4 or TLR3. Like IL-10, S100 induction by polyinosinic:polycytidylic acid and by LPS was inhibited by the specific PKR inhibitor 2-aminopurine, indicating a novel IL-10, PKR-dependent pathway. Other mediators such as IFN-beta, which synergized with dsRNA, may also be involved. C/EBPbeta bound the defined promoter region in response to dsRNA. S100A8 was expressed in lungs of mice infected with influenza virus and was maximal at day 8 with strong immunoreactivity in epithelial cells lining the airways and in mononuclear cells and declined early in the recovery phase, implying down-regulation by mediator(s) up-regulated during resolution of the infection. IL-10 is implicated in viral persistence. Since S100A8/S100A9 levels are likely to be maintained in conditions where IL-10 is raised, these proteins may contribute to viral persistence in patients infected by some RNA viruses.

Signal regulatory protein alpha (SIRPalpha)/CD47 interaction and function

SIRPalpha is an inhibitory receptor present on myeloid cells that interacts with a widely distributed membrane protein CD47. The activating member SIRPbeta, despite extensive sequence similarity to SIRPalpha in the extracellular region, shows negligible binding to CD47. The SIRPalpha/CD47 interaction is unusual in that it can lead to bidirectional signalling through both SIRPalpha and CD47. This review concentrates on the interactions of SIRPalpha with CD47 where recent data have shed light on the structure of the proteins including determining why the activating SIRPbeta does not bind CD47, evidence of extensive polymorphisms and implication for the evolution and function of this protein and paired receptors in general. The interaction may be modified by endocytosis of the receptors, cleavage by proteolysis and through interactions of surfactant proteins.