Pellino-1 promotes intrinsic activation of skin-resident IL-17A-producing T cells in psoriasis.

BACKGROUND: Psoriasis is a chronically relapsing inflammatory skin disease primarily perpetuated by skin-resident IL-17-producing T (T17) cells. Pellino-1 (Peli1) belongs to a member of E3 ubiquitin ligase mediating immune receptor signaling cascades, including nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB) pathway. OBJECTIVE: We explored the potential role of Peli1 in psoriatic inflammation in the context of skin-resident T17 cells. METHODS: We performed single-cell RNA sequencing of relapsing and resolved psoriatic lesions with analysis for validation data set of psoriasis. Mice with systemic and conditional depletion of Peli1 were generated to evaluate the role of Peli1 in imiquimod-induced psoriasiform dermatitis. Pharmacologic inhibition of Peli1 in human CD4+ T cells and ex vivo human skin cultures was also examined to evaluate its potential therapeutic implications. RESULTS: Single-cell RNA sequencing analysis revealed distinct T-cell subsets in relapsing psoriasis exhibiting highly enriched gene signatures for (1) tissue-resident T cells, (2) T17 cells, and (3) NF-κB signaling pathway including PELI1. Peli1-deficient mice were profoundly protected from psoriasiform dermatitis, with reduced IL-17A production and NF-κB activation in γδ T17 cells. Mice with conditional depletion of Peli1 treated with FTY720 revealed that Peli1 was intrinsically required for the skin-resident T17 cell immune responses. Notably, pharmacologic inhibition of Peli1 significantly ameliorated murine psoriasiform dermatitis and IL-17A production from the stimulated human CD4+ T cells and ex vivo skin explants modeling psoriasis. CONCLUSION: Targeting Peli1 would be a promising therapeutic strategy for psoriasis by limiting skin-resident T17 cell immune responses.

A Reciprocal Role of the Smad4-Taz Axis in Osteogenesis and Adipogenesis of Mesenchymal Stem Cells.

Mesenchymal stem cells (MSCs) are multipotent cells that can differentiate into mature cells of various cell types. Although the differentiation process of MSCs requires lineage-specific transcription factors, the exact molecular mechanism that determines MSCs differentiation is not clearly addressed. Here, we demonstrate a Smad4-Taz axis as a new intrinsic regulator for adipo-osteogenic differentiation of MSCs and show that this function of Smad4 is independent of the transforming growth factor-ß signal. Smad4 directly bound to the Taz protein and facilitated nuclear localization of Taz through its nuclear localization signal. Nuclear retention of Taz by direct binding to Smad4 increased expression of osteogenic genes through enhancing Taz-runt-related transcription factor 2 (Runx2) interactions in the C3H10T1/2 MSC cell line and preosteoblastic MC3T3-E1 cells, whereas it suppressed expression of adipogenic genes through promoting Taz-peroxisome proliferator-activated receptor-γ (PPARγ) interaction in C3H10T1/2 and preadipogenic 3T3-L1 cells. A reciprocal role of the Smad4 in osteogenic and adipogenic differentiation was also observed in human adipose tissue-derived stem cells (hASCs). Consequently, Smad4 depletion in C3H10T1/2 and hASCs reduced nuclear retention of Taz and thus caused the decreased interaction with Runx2 or PPARγ, resulting in delayed osteogenesis or enhanced adipogenesis of the MSC. Therefore, these findings provide insight into a novel function of Smad4 to regulate the balance of MSC lineage commitment through reciprocal targeting of the Taz protein in osteogenic and adipogenic differentiation pathways. Stem Cells 2019;37:368-381.

The deubiquitinating enzyme USP20 stabilizes ULK1 and promotes autophagy initiation.

Autophagy begins with the formation of autophagosomes, a process that depends on the activity of the serine/threonine kinase ULK1 (hATG1). Although earlier studies indicated that ULK1 activity is regulated by dynamic polyubiquitination, the deubiquitinase involved in the regulation of ULK1 remained unknown. In this study, we demonstrate that ubiquitin-specific protease 20 (USP20) acts as a positive regulator of autophagy initiation through stabilizing ULK1. At basal state, USP20 binds to and stabilizes ULK1 by removing the ubiquitin moiety, thereby interfering with the lysosomal degradation of ULK1. The stabilization of basal ULK1 protein levels is required for the initiation of starvation-induced autophagy, since the depletion of USP20 by RNA interference inhibits LC3 puncta formation, a marker of autophagic flux. At later stages of autophagy, USP20 dissociates from ULK1, resulting in enhanced ULK1 degradation and apoptosis. Taken together, our findings provide the first evidence that USP20 plays a crucial role in autophagy initiation by maintaining the basal expression level of ULK1.

A20 promotes metastasis of aggressive basal-like breast cancers through multi-monoubiquitylation of Snail1.

Although the ubiquitin-editing enzyme A20 is a key player in inflammation and autoimmunity, its role in cancer metastasis remains unknown. Here we show that A20 monoubiquitylates Snail1 at three lysine residues and thereby promotes metastasis of aggressive basal-like breast cancers. A20 is significantly upregulated in human basal-like breast cancers and its expression level is inversely correlated with metastasis-free patient survival. A20 facilitates TGF-ß1-induced epithelial-mesenchymal transition (EMT) of breast cancer cells through multi-monoubiquitylation of Snail1. Monoubiquitylated Snail1 has reduced affinity for glycogen synthase kinase 3ß (GSK3ß), and is thus stabilized in the nucleus through decreased phosphorylation. Knockdown of A20 or overexpression of Snail1 with mutation of the monoubiquitylated lysine residues into arginine abolishes lung metastasis in mouse xenograft and orthotopic breast cancer models, indicating that A20 and monoubiquitylated Snail1 are required for metastasis. Our findings uncover an essential role of the A20-Snail1 axis in TGF-ß1-induced EMT and metastasis of basal-like breast cancers.

The deubiquitinating enzyme, ubiquitin-specific peptidase 50, regulates inflammasome activation by targeting the ASC adaptor protein.

NOD-like receptor family protein 3 (NLRP3)-mediated inflammasome activation promotes caspase-1-dependent production of interleukin-1ß (IL-1ß) and requires the adaptor protein ASC. Compared with the priming and activation mechanisms of the inflammasome signaling pathway, post-translational ubiquitination/deubiquitination mechanisms controlling inflammasome activation have not been clearly addressed. We here demonstrate that the deubiquitinating enzyme USP50 binds to the ASC protein and subsequently regulates the inflammasome signaling pathway by deubiquitinating the lysine 63-linked polyubiquitination of ASC. USP50 knockdown in human THP-1 cells and mouse bone marrow-derived macrophages shows a significant decrease in procaspase-1 cleavage, resulting in a reduced secretion of IL-1ß and interleukin-18 (IL-18) upon treatment with NLRP3 stimuli and a reduction in ASC speck formation and oligomerization. Thus, we elucidate a novel regulatory mechanism of the inflammasome signaling pathway mediated by the USP50 deubiquitinating enzyme.

Therapeutic effects of mouse bone marrow-derived clonal mesenchymal stem cells in a mouse model of inflammatory bowel disease.

Mouse bone marrow-derived clonal mesenchymal stem cells (mcMSCs), which were originated from a single cell by a subfractionation culturing method, are recognized as new paradigm for stem cell therapy featured with its homogenous cell population. Next to proven therapeutic effects against pancreatitis, in the current study we demonstrated that mcMSCs showed significant therapeutic effects in dextran sulfate sodium (DSS)-induced experimental colitis model supported with anti-inflammatory and restorative activities. mcMSCs significantly reduced the disease activity index (DAI) score, including weight loss, stool consistency, and intestinal bleeding and significantly increased survival rates. The pathological scores were also significantly improved with mcMSC. We have demonstrated that especial mucosal regeneration activity accompanied with significantly lowered level of apoptosis as beneficiary actions of mcMSCs in UC models. The levels of inflammatory cytokines including TNF-α, IFN-γ, IL-1ß, IL-6, and IL-17 were all significantly concurrent with significantly repressed NF-κB activation compared to the control group and significantly decreased infiltrations of responsible macrophage and neutrophil. Conclusively, our findings provide the rationale that mcMSCs are applicable as a potential source of cell-based therapy in inflammatory bowel diseases, especially contributing either to prevent relapse or to accelerate healing as solution to unmet medical needs in IBD therapy.

Inhibition of lethal inflammatory responses through the targeting of membrane-associated Toll-like receptor 4 signaling complexes with a Smad6-derived peptide.

We have previously reported that Smad6, one of the inhibitory Smads of transforming growth factor-ß (TGF-ß)/bone morphogenetic protein (BMP) signaling, inhibits Toll-like receptor (TLR) 4 signaling by disrupting the Pellino-1-mediated TLR4 signaling complex. Here, we developed Smaducin-6, a novel membrane-tethered palmitic acid-conjugated Smad6-derived peptide composed of amino acids 422-441 of Smad6. Smaducin-6 interacted with Pellino-1, located in the inner membrane, thereby disrupting the formation of IRAK1-, RIP1-, IKKε-mediated TLR4 signaling complexes. Systemic administration of Smaducin-6 showed a significant therapeutic effect on mouse TLR4-mediated inflammatory disease models, cecal-ligation-puncture (CLP)-induced sepsis, and lipopolysaccharide-induced endotoxemia, by inhibiting pro-inflammatory cytokine production and apoptosis while enhancing neutrophil migration and bacterial clearance. Our findings provide clues to develop new peptide-based drugs to target Pellino-1 protein in TLR4 signaling pathway for the treatment of sepsis.

Smad6 inhibits non-canonical TGF-ß1 signalling by recruiting the deubiquitinase A20 to TRAF6.

Transforming growth factor (TGF)-ß, a pivotal cytokine involved in a variety of cellular functions, transmits signals through Smad-dependent canonical and Smad-independent noncanonical pathways. In contrast to the canonical TGF-ß pathway, it is unknown how noncanonical TGF-ß pathways are negatively regulated. Here we demonstrate that the inhibitory Smad Smad6, but not Smad7, negatively regulates TGF-ß1-induced activation of the TRAF6-TAK1-p38 MAPK/JNK pathway, a noncanonical TGF-ß pathway. TGF-ß1-induced Smad6 abolishes K63-linked polyubiquitination of TRAF6 by recruiting the A20 deubiquitinating enzyme in AML-12 mouse liver cells and primary hepatocytes. In addition, the knockdown of Smad6 or A20 in an animal model or cell culture system maintains TAK1 and p38 MAPK/JNK phosphorylation and increases apoptosis, emphasizing the crucial role of the Smad6-A20 axis in negative regulation of the TGF-ß1-TRAF6-TAK1-p38 MAPK/JNK pathway. Therefore, our findings provide insight into the molecular mechanisms underlying negative regulation of noncanonical TGF-ß pathways.

Smad6-specific recruitment of Smurf E3 ligases mediates TGF-ß1-induced degradation of MyD88 in TLR4 signalling.

Transforming growth factor-ß (TGF-ß) is a potent anti-inflammatory cytokine that regulates interleukin-1 receptor and Toll-like receptor (TLR) signalling. Here we show a novel mechanism where TGF-ß1-induced K48-linked polyubiquitination and degradation of the adaptor MyD88 protein is dependent on the Smad6 protein, but not Smad7, and mediated by recruitment of the Smad ubiquitin regulator factor proteins, Smurf1 and Smurf2, which have E3-ubiquitin ligase activity. Smurf1 interaction with MyD88 appears to be mediated by Smad6, and Smurf2 interaction by Smurf1. Knockdown of endogenous Smurf1 or Smurf2 by RNA interference significantly suppresses the anti-inflammatory effects of TGF-ß1 by preventing lipopolysaccharide-induced NF-κB nuclear translocation, resulting in de-suppression of pro-inflammatory gene expression. Similar effects are observed on the lipoteichoic-acid-induced TLR2 pathway, which is also MyD88-dependent, but not the MyD88-independent TLR3 pathway. Thus, our results suggest that MyD88 degradation driven by the Smad6-Smurf pathway is a novel mechanism for TGF-ß1-mediated negative regulation of MyD88-dependent pro-inflammatory signalling.

Pellino-1, an adaptor protein of interleukin-1 receptor/toll-like receptor signaling, is sumoylated by Ubc9.

Covalent modifications of the Pellino-1 protein are essential for transmitting innate immune response signals downstream, as the phosphorylation and polyubiquitination of Pellino-1 mediated by the IRAK proteins appear to have roles in regulating Pellino-1 function. In this study, we demonstrate that the Pellino-1 protein is post-translationally modified by small-ubiquitin-related modifier-1 (SUMO-1). Sumoylation assays with Pellino-1 and SUMO-1 expression plasmids reveal that the Pellino-1 protein is sumoylated in vitro and in vivo. Treatment of SUMO-1 specific protease 1 (SENP1) inhibited the sumoylation of the Pellino-1 protein and a GST pull-down assay as well as a yeast two hybrid assay showed that Pellino-1 binds to the SUMO-conjugating enzyme, Ubc9. Furthermore, we identified the five lysine residues of the Pellino-1 protein where SUMO-1 covalently attaches. Some of the sumoylated sites overlap with previously identified ubiquitination sites, suggesting competition between sumoylation and ubiquitination, as well as suggesting that the sumoylated Pellino-1 protein may have a cellular function distinct from previously identified functions.

Smad7 and Smad6 bind to discrete regions of Pellino-1 via their MH2 domains to mediate TGF-beta1-induced negative regulation of IL-1R/TLR signaling.

Transforming growth factor-beta1 (TGF-beta1) performs diverse cellular functions, including anti-inflammatory activity. The inhibitory Smad (I-Smad) Smad6 was previously shown to play an important role in TGF-beta1-induced negative regulation of Interleukin-1/Toll-like receptor (IL-1R/TLR) signaling through binding to Pellino-1, an adaptor protein of interleukin-1 receptor associated kinase 1(IRAK1). However, it is unknown whether Smad7, the other inhibitory Smad, also has a role in regulating IL-1R/TLR signaling. Here, we demonstrate that endogeneous Smad7 and Smad6 simultaneously bind to discrete regions of Pellino-1 upon TGF-beta1 treatment, via distinct regions of the Smad MH2 domains. In addition, the Smad7-Pellino-1 interaction abrogated NF-kappaB activity by blocking formation of the IRAK1-mediated IL-1R/TLR signaling complex, subsequently causing reduced expression of pro-inflammatory genes. Double knock-down of endogenous Smad6 and Smad7 genes by RNA interference further reduced the anti-inflammatory activity of TGF-beta1 than when compared with single knock-down of Smad7. These results provide evidence that the I-Smads, Smad6 and Smad7, act as critical mediators for effective TGF-beta1-mediated suppression of IL-1R/TLR signaling, by simultaneous binding to discrete regions of Pellino-1.

Decreased expression of glutaredoxin 1 is required for transforming growth factor-beta1-mediated epithelial-mesenchymal transition of EpRas mammary epithelial cells.

Transforming growth factor-beta (TGF-beta) is a cytokine important in inducing epithelial-mesenchymal transition (EMT), a crucial morphological event in a wide range of physiological and pathological cellular processes. In this study, we demonstrate that TGF-beta1 induces the EMT phenotype through decreasing the expression of the glutaredoxin 1 (Grx1) gene, an anti-oxidant enzyme, in H-Ras transformed EpH4 mammary epithelial cells (EpRas), but not in the parental EpH4 cells. TGF-beta1-induced reduction of Grx1 expression caused an increase of intracellular reactive oxygen species (ROS) in EpRas cells, and pre-treatment of the ROS scavenger N-acetylcysteine (NAC) inhibited TGF-beta1-induced EMT. Grx1-overexpressing EpRas cells showed a reduction in intracellular ROS generation and suppressed the expression of mesenchymal markers upon treatment of TGF-beta1. In addition, MEK/MAP kinase and phosphatidylinositol-3 kinase (PI3K) signaling were found to mediate the decrease in Grx1 expression upon TGF-beta1 treatment, depending on the presence of Ras protein. Thus our findings strongly suggest that TGF-beta1 promotes EMT by increasing intracellular ROS levels via down-regulation of the Grx1 gene in EpRas cells.

14-3-3epsilon protein increases matrix metalloproteinase-2 gene expression via p38 MAPK signaling in NIH3T3 fibroblast cells.

One of the 14-3-3 protein isoforms, 14-3-3epsilon, was previously shown to be increased during skin aging. We suggest here a possible role for the 14-3-3epsilon protein in skin aging by providing evidence that 14-3-3epsilon increases the expression of the matrix-metalloproteinase (MMP)-2 gene in NIH3T3 fibroblast cells. Expression of the 14-3-3epsilon gene in NIH3T3 cells primarily up-regulated the expression of the MMP-2 gene at the transcriptional level by inducing specific DNA binding proteins bound to an upstream region of the MMP-2 promoter from -1,629 to -1,612. Inhibition of endogenous 14-3-3epsilon gene expression by RNA interference also decreased endogenous MMP-2 gene expression. Furthermore, up-regulation of the MMP-2 gene by 14-3-3epsilon was suppressed by expression of a dominant-negative mutant of p38 MAP kinase. These findings strongly suggest that increased expression of 14-3-3epsilon contributes to remodeling of extracellular matrix in skin through increasing MMP-2 gene expression via p38 MAP kinase signaling.

Etoposide-induced Smad6 expression is required for the G1 to S phase transition of the cell cycle in CMT-93 mouse intestinal epithelial cells.

The inhibitory Smad6 and Smad7 are responsible for cross-talk between TGF-betabone morphogenic protein (BMP) signaling and other cellular signaling pathways, as well as negative feedback on their own signaling functions. Although inhibitory Smads are induced by various stimuli, little is known about the stimuli that increase Smad6 transcription, in contrast to Smad7. Here we demonstrate that etoposide, which induces double strand breaks during DNA replication, significantly up-regulates the transcription of the Smad6 gene in CMT-93 mouse intestinal cells by increasing specific DNA binding proteins. In addition, endogenous inhibition of the Smad6 gene by RNAi interference led to transient accumulation of G1 phase cells and reduction in incorporation of bromodeoxyuridine (BrdU). These findings strongly suggest that Smad6 plays a distinct role in the signaling of etoposide-induced DNA damage.

Expression of Caveolin-1 reduces cellular responses to TGF-beta1 through down-regulating the expression of TGF-beta type II receptor gene in NIH3T3 fibroblast cells.

Transcriptional repression of Transforming Growth Factor-beta type II receptor (TbetaRII) gene has been proposed to be one of the major mechanisms leading to TGF-beta resistance. In this study, we demonstrate that expression of Caveolin-1 (Cav-1) gene in NIH3T3 fibroblast cells down-regulates the expression of TbetaRII gene in the transcriptional level, eventually resulting in the decreased responses to TGF-beta. The reduced expression of TbetaRII gene by Cav-1 appeared to be due to the changes of the sequence-specific DNA binding proteins to either Positive Regulatory Element 1 (PRE1) or PRE2 of the TbetaRII promoter. In addition, Cav-1 expression inhibited TGF-beta-mediated cellular proliferation and Plasminogen Activator Inhibitor (PAI)-1 gene expression as well as TGF-beta-induced luciferase activity. Furthermore, the inhibition of endogeneous Cav-1 by small interfering RNA increased the expression of TbetaRII gene. These findings strongly suggest that expression of Cav-1 leads to the decreased cellular responsiveness to TGF-beta through down-regulating TbetaRII gene expression.

Smad7 binds to the adaptors TAB2 and TAB3 to block recruitment of the kinase TAK1 to the adaptor TRAF2.

Transforming growth factor-beta1 (TGF-beta1) regulates inflammation and can inhibit activation of the transcription factor NF-kappaB in certain cell types. Here we show that the TGF-beta-induced signaling protein Smad7 bound to TAB2 and TAB3, which are adaptors that link the kinase TAK1 to 'upstream' regulators in the proinflammatory tumor necrosis factor (TNF) signaling pathway. Smad7 thereby promoted TGF-beta-mediated anti-inflammatory effects. The formation of Smad7-TAB2 and Smad7-TAB3 complexes resulted in the suppression of TNF signaling through the adaptors TRAF2, TAB2 and/or TAB3, and TAK1. Furthermore, expression of a transgene encoding Smad7 in mouse skin suppressed inflammation and NF-kappaB nuclear translocation substantially and disrupted the formation of endogenous TRAF2-TAK1-TAB2 and TRAF2-TAK1-TAB3 complexes. Thus, Smad7 is a critical mediator of TGF-beta signals that block proinflammatory TNF signals.

Smad6 negatively regulates interleukin 1-receptor-Toll-like receptor signaling through direct interaction with the adaptor Pellino-1.

Transforming growth factor-beta1 (TGF-beta1) is a potent cytokine with pleiotropic effects, including anti-inflammatory activity. Here we show that the signaling protein Smad6 bound to Pellino-1, an adaptor protein of mammalian interleukin 1 receptor (IL-1R)-associated kinase 1 (IRAK1), and thereby promoted TGF-beta-mediated anti-inflammatory effects. Smad6-Pellino-1 interaction abrogated signaling mediated by a complex of IRAK1, Pellino-1 and adaptor protein TRAF6 that formed after stimulation by IL-1beta treatment. Blockade of IRAK1-Pellino-1-TRAF6 signaling prevented degradation of the inhibitor IkappaBalpha and subsequent nuclear translocation of transcription factor NF-kappaB and thus expression of proinflammatory genes. 'Knockdown' of endogenous Smad6 expression by RNA interference reduced anti-inflammatory activity mediated by TGF-beta1 or the TGF-beta family member BMP-4. Thus Smad6 is a critical mediator of the TGF-beta-BMP pathway that mediates anti-inflammatory activity and negatively regulates IL-1R-Toll-like receptor signals.