The HIV-1 restriction factor SAM domain- and HD domain-containing protein 1 (SAMHD1) is proposed to inhibit HIV-1 replication by depleting the intracellular dNTP pool. However, phosphorylation of ...SAMHD1 regulates its ability to restrict HIV-1 without decreasing cellular dNTP levels, which is not consistent with a role for SAMHD1 dNTPase activity in HIV-1 restriction. Here, we show that SAMHD1 possesses RNase activity and that the RNase but not the dNTPase function is essential for HIV-1 restriction. By enzymatically characterizing Aicardi-Goutières syndrome (AGS)-associated SAMHD1 mutations and mutations in the allosteric dGTP-binding site of SAMHD1 for defects in RNase or dNTPase activity, we identify SAMHD1 point mutants that cause loss of one or both functions. The RNase-positive and dNTPase-negative SAMHD1D137N mutant is able to restrict HIV-1 infection, whereas the RNase-negative and dNTPase-positive SAMHD1Q548A mutant is defective for HIV-1 restriction. SAMHD1 associates with HIV-1 RNA and degrades it during the early phases of cell infection. SAMHD1 silencing in macrophages and CD4(+) T cells from healthy donors increases HIV-1 RNA stability, rendering the cells permissive for HIV-1 infection. Furthermore, phosphorylation of SAMHD1 at T592 negatively regulates its RNase activity in cells and impedes HIV-1 restriction. Our results reveal that the RNase activity of SAMHD1 is responsible for preventing HIV-1 infection by directly degrading the HIV-1 RNA.
Abstract
Bone resorption can be caused by excessive differentiation and/or activation of bone‐resorbing osteoclasts. While microbe‐associated molecular patterns can influence the differentiation and ...activation of bone cells, little is known about the role of lipoteichoic acid (LTA), a major cell wall component of Gram‐positive bacteria, in the regulation of bone metabolism. In this study, we investigated the effect of LTA on bone metabolism using wild‐type
Staphylococcus aureus
and the LTA‐deficient mutant strain. LTA‐deficient
S. aureus
induced higher bone loss and osteoclast differentiation than wild‐type
S. aureus
. LTA isolated from
S. aureus
(SaLTA) inhibited osteoclast differentiation from committed osteoclast precursors in the presence of various osteoclastogenic factors by downregulating the expression of NFATc1. Remarkably, SaLTA attenuated the osteoclast differentiation from committed osteoclast precursors of TLR2
−/−
or MyD88
−/−
mice and from the committed osteoclast precursors transfected with paired immunoglobulin‐like receptor B‐targeting siRNA. SaLTA directly interacted with gelsolin, interrupting the gelsolin‐actin dissociation which is a critical process for osteoclastogenesis. Moreover, SaLTA suppressed the mRNA expression of dendritic cell‐specific transmembrane protein, ATPase H
+
transporting V0 subunit D2, and
Integrin
, which encode proteins involved in cell‐cell fusion of osteoclasts. Notably, LTAs purified from probiotics, including
Bacillus subtilis
,
Enterococcus faecalis
, and
Lactobacillus
species, also suppressed Pam2CSK4‐ or RANKL‐induced osteoclast differentiation. Taken together, these results suggest that LTAs have anti‐resorptive activity through the inhibition of osteoclastogenesis by interfering with the gelsolin‐actin dissociation and may be used as effective therapeutic agents for the prevention or treatment of inflammatory bone diseases.
Lipoteichoic acid (LTA), a major cell wall component of Gram-positive bacteria, is associated with various inflammatory diseases ranging from minor skin diseases to severe sepsis. It is known that ...LTA is recognized by Toll-like receptor 2 (TLR2), leading to the initiation of innate immune responses and further development of adaptive immunity. However, excessive immune responses may result in the inflammatory sequelae that are involved in severe diseases such as sepsis. Although numerous studies have tried to identify the molecular basis for the pathophysiology of Gram-positive bacterial infection, the exact role of LTA during the infection has not been clearly elucidated. This review provides an overview of LTA structure and host recognition by TLR2 that leads to the activation of innate immune responses. Emphasis is placed on differential immunostimulating activities of LTAs of various Gram-positive bacteria at the molecular level.
Dental caries is a biofilm-dependent oral disease and Streptococcus mutans is the known primary etiologic agent of dental caries that initiates biofilm formation on tooth surfaces. Although some ...Lactobacillus strains inhibit biofilm formation of oral pathogenic bacteria, the molecular mechanisms by which lactobacilli inhibit bacterial biofilm formation are not clearly understood. In this study, we demonstrated that Lactobacillus plantarum lipoteichoic acid (Lp.LTA) inhibited the biofilm formation of S. mutans on polystyrene plates, hydroxyapatite discs, and dentin slices without affecting the bacterial growth. Lp.LTA interferes with sucrose decomposition of S. mutans required for the production of exopolysaccharide, which is a main component of biofilm. Lp.LTA also attenuated the biding of fluorescein isothiocyanate-conjugated dextran to S. mutans, which is known to have a high affinity to exopolysaccharide on S. mutans. Dealanylated Lp.LTA did not inhibit biofilm formation of S. mutans implying that D-alanine moieties in the Lp.LTA structure were crucial for inhibition. Collectively, these results suggest that Lp.LTA attenuates S. mutans biofilm formation and could be used to develop effective anticaries agents.
Bone‐resorbing osteoclasts are differentiated from macrophages (MΦ) by M‐CSF and RANKL. MΦ can be mainly classified into M1 and M2 MΦ, which are proinflammatory and anti‐inflammatory, respectively, ...but little is known about their osteoclastogenic potential. Here, we investigated the osteoclastogenic potential of MΦ subtypes. When the two MΦ subtypes were differentiated into osteoclasts using M‐CSF and RANKL, M2 MΦ more potently differentiated into osteoclasts than M1 MΦ. M2 MΦ generated with IL‐4 or IL‐10 also showed enhanced osteoclast differentiation compared with M1 MΦ induced by IFN‐γ and lipopolysaccharide. In addition, robust bone‐resorptive capacity and giant actin rings, which are features of mature osteoclasts, were observed in M2, but not M1 MΦ, under the osteoclast differentiation condition. Osteoclast differentiation was significantly increased in CD206+ M2 MΦ but not in CD86+ M1 MΦ. Compared with M1 MΦ, c‐Fms and RANK were highly expressed in M2 MΦ. Enhanced osteoclastogenesis of M2 MΦ was mediated through sustained ERK activation, followed by efficient c‐Fos and NFATc1 induction. Notably, the osteoclastogenic potential of M1 MΦ converted into M2 MΦ by exposure to M‐CSF was higher than that of M2 MΦ converted into M1 MΦ by exposure to GM‐CSF. Silencing IRF5, which is responsible for M1 MΦ polarization, increased osteoclast differentiation by enhancing c‐Fms expression and activation of ERK, c‐Fos, CREB, and NFATc1, which was inhibited by overexpression of IRF5. Collectively, M2 MΦ are suggested to be more efficient osteoclast precursors than M1 MΦ because of the attenuated expression of IRF5.
M2 MΦ were more potent osteoclast precursors than M1 MΦ. Unlike M1 MΦ, M2 MΦ exhibited a high level of c‐Fms and prolonged ERK activation upon stimulation with M‐CSF. Furthermore, M2 MΦ‐derived osteoclasts showed high bone‐resorptive capacity and giant actin ring formation. Interestingly, decreased IRF5 expression in M2 MΦ contributed to enhanced osteoclastogenic potential through induction of c‐Fms, c‐Fos, NFATc1, and CREB.
The strength of the T cell receptor interaction with self-ligands affects antigen-specific immune responses. However, the precise function and underlying mechanisms are unclear. Here, we demonstrate ...that naive CD8
T cells with relatively high self-reactivity are phenotypically heterogeneous owing to varied responses to type I interferon, resulting in three distinct subsets, CD5
Ly6C
, CD5
Ly6C
, and CD5
Ly6C
cells. CD5
Ly6C
cells differ from CD5
Ly6C
and CD5
Ly6C
cells in terms of gene expression profiles and functional properties. Moreover, CD5
Ly6C
cells demonstrate more extensive antigen-specific expansion upon viral infection, with enhanced differentiation into terminal effector cells and reduced memory cell generation. Such features of CD5
Ly6C
cells are imprinted in a steady-state and type I interferon dependence is observed even for monoclonal CD8
T cell populations. These findings demonstrate that self-reactivity controls the functional diversity of naive CD8
T cells by co-opting tonic type I interferon signaling.
Explosive growth in nanotechnology has merged with vaccine development in the battle against diseases caused by bacterial or viral infections and malignant tumors. Due to physicochemical ...characteristics including size, viscosity, density and electrostatic properties, nanomaterials have been applied to various vaccination strategies. Nanovaccines, as they are called, have been the subject of many studies, including review papers from a material science point of view, although a mode of action based on a biological and immunological understanding has yet to emerge. In this review, we discuss nanovaccines in terms of CD8
T cell responses, which are essential for antiviral and anticancer therapies. We focus mainly on the role and mechanism, with particular attention to the functional aspects, of nanovaccines in inducing cross-presentation, an unconventional type of antigen-presentation that activates CD8
T cells upon administration of exogenous antigens, in dendritic cells followed by activation of antigen-specific CD8
T cell responses. Two major intracellular mechanisms that nanovaccines harness for cross-presentation are described; one is endosomal swelling and rupture, and the other is membrane fusion. Both processes eventually allow exogenous vaccine antigens to be exported from phagosomes to the cytosol followed by loading on major histocompatibility complex class I, triggering clonal expansion of CD8
T cells. Advancement of nanotechnology with an enhanced understanding of how nanovaccines work will contribute to the design of more effective and safer nanovaccines.
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