Ryusuke Yoshimi

Comment on “Gene Disruption Study Reveals a Nonredundant Role for TRIM21/Ro52 in NF-κB-Dependent Cytokine Expression in Fibroblasts”

The tripartite motif (TRIM) family member, TRIM21, is an E3 ubiquitin ligase for IFN regulatory factor (IRF)3 and IRF8 that functions in both innate and acquired immunity. It is also an autoantigen known as Ro52/SS-A. The function of TRIM21 in vivo, however, has remained elusive. We generated Trim21−/− mice with the Trim21 gene replaced by an enhanced GFP (EGFP) reporter. EGFP expression analyses showed that Trim21 was widely expressed in many tissues, with the highest levels in immune cells. Studies of Trim21−/− embryonic fibroblasts demonstrated that TLR-mediated induction of proinflammatory cytokines, including IL-1β, IL-6, TNF-α, and CXCL10, was consistently up-regulated relative to wild-type cells. Reporter analyses demonstrated that TLR-mediated NF-κB activation was higher in Trim21−/− cells than in wild-type cells, most likely accounting for their enhanced cytokine expression. In contrast, functional analyses of immune cells from Trim21−/− mice revealed no abnormalities in their composition or function, even though ubiquitylation of IRF3 and IRF8 was impaired. These results suggested possible redundancies in activities mediated by TRIM21. In keeping with this concept, we found that a number of TRIM family members were up-regulated in Trim21−/− cells. Taken together, these findings demonstrate that TRIM21 plays a previously unrecognized role in the negative regulation of NF-κB-dependent proinflammatory cytokine responses, and suggest that multiple TRIM proteins contribute to the maintenance of functional equilibrium in inflammatory responses, in part through functional redundancy.

Affixin interacts with α-actinin and mediates integrin signaling for reorganization of F-actin induced by initial cell–substrate interaction

The linking of integrin to cytoskeleton is a critical event for an effective cell migration. Previously, we have reported that a novel integrin-linked kinase (ILK)–binding protein, affixin, is closely involved in the linkage between integrin and cytoskeleton in combination with ILK. In the present work, we demonstrated that the second calponin homology domain of affixin directly interacts with α-actinin in an ILK kinase activity–dependent manner, suggesting that integrin–ILK signaling evoked by substrate adhesion induces affixin–α-actinin interaction. The overexpression of a peptide corresponding to the α-actinin–binding site of affixin as well as the knockdown of endogenous affixin by small interference RNA resulted in the blockade of cell spreading. Time-lapse observation revealed that in both experiments cells were round with small peripheral blebs and failed to develop lamellipodia, suggesting that the ILK–affixin complex serves as an integrin-anchoring site for α-actinin and thereby mediates integrin signaling to α-actinin, which has been shown to play a critical role in actin polymerization at focal adhesions.

Ultrasonography is a potent tool for the prediction of progressive joint destruction during clinical remission of rheumatoid arthritis

ObjectivesAlthough “clinical remission” has been a realistic goal of treatment in rheumatoid arthritis (RA), there is evidence that subclinical synovitis is associated with ongoing structural damage even after clinical remission is achieved. In the study reported here, we assessed whether ultrasonography (US) can predict progressive joint destruction during clinical remission of RA.MethodsThirty-one patients with RA in clinical remission based on the disease activity score in 28 joints were recruited for this study. Bilateral wrists and all of the metacarpophalangeal and proximal interphalangeal (PIP) joints were examined by power Doppler (PD) ultrasonography (US), and the PD signals were scored semiquantitatively in each joint. The total PD score was calculated as the sum of individual scores for each joint.ResultsAmong 22 RA patients who maintained clinical remission during the 2-year follow-up period, seven showed radiographic progression. Radiographic progression was strongly associated with total PD score at entry, with all patients showing radiographic progression having a total PD score of ≥2 at entry and none of the patients with a total PD score of ≤1 showing any radiographic progression. There was no significant association of therapeutic agents with progressing or non-progressing cases.ConclusionsPD-US detects synovitis causing joint destruction even when the patient is in clinical remission. Thus, remission visible on US is essential to reach “true remission” of RA.

The first CH domain of affixin activates Cdc42 and Rac1 through αPIX, a Cdc42/Rac1-specific guanine nucleotide exchanging factor

Rho GTPases, Cdc42 and Rac1, play pivotal roles in cell migration by efficiently integrating cell‐substrate adhesion and actin polymerization. Although it has been suggested that integrins stimulate these Rho GTPases via some of integrin binding proteins such as focal adhesion kinase (FAK) and paxillin, the precise molecular mechanism is largely unknown. In this study, we showed that the over‐expression of RP1 corresponding to the first CH domain (CH1) of affixin, an integrin‐linked kinase (ILK)‐binding protein, induced a significant actin reorganization in MDCK cells by activating Cdc42/Rac1. Affixin full length and RP1 co‐immunoprecipitated with αPIX, a Cdc42/Rac1‐specific guanine nucleotide exchanging factor (GEF), and they co‐localized at the tips of lamellipodia in motile cells. The involvement of αPIX in the RP1‐induced Cdc42 activation was demonstrated by the significant dominant negative effect of a point mutant of αPIX, αPIX (L383R, L384S), lacking GEF activity. Our data strongly support that ILK and affixin provide a novel signalling pathway that links integrin signalling to Cdc42/Rac1 activation.

Clinical and Pathological Roles of Ro/SSA Autoantibody System

Anti-Ro/SSA antibodies are among the most frequently detected autoantibodies against extractable nuclear antigens and have been associated with systemic lupus erythematosus (SLE) and Sjögrens syndrome (SS). Although the presence of these autoantibodies is one of the criteria for the diagnosis and classification of SS, they are also sometimes seen in other systemic autoimmune diseases. In the last few decades, the knowledge of the prevalence of anti-Ro/SSA antibodies in various autoimmune diseases and symptoms has been expanded, and the clinical importance of these antibodies is increasing. Nonetheless, the pathological role of the antibodies is still poorly understood. In this paper, we summarize the milestones of the anti-Ro/SSA autoantibody system and provide new insights into the association between the autoantibodies and the pathogenesis of autoimmune diseases.

A Reporter Mouse Reveals Lineage-Specific and Heterogeneous Expression of IRF8 during Lymphoid and Myeloid Cell Differentiation

The IFN regulatory factor family member 8 (IRF8) regulates differentiation of lymphoid and myeloid lineage cells by promoting or suppressing lineage-specific genes. How IRF8 promotes hematopoietic progenitors to commit to one lineage while preventing the development of alternative lineages is not known. In this study, we report an IRF8–EGFP fusion protein reporter mouse that revealed previously unrecognized patterns of IRF8 expression. Differentiation of hematopoietic stem cells into oligopotent progenitors is associated with progressive increases in IRF8-EGFP expression. However, significant induction of IRF8-EGFP is found in granulocyte–myeloid progenitors and the common lymphoid progenitors but not the megakaryocytic–erythroid progenitors. Surprisingly, IRF8-EGFP identifies three subsets of the seemingly homogeneous granulocyte–myeloid progenitors with an intermediate level of expression of EGFP defining bipotent progenitors that differentiation into either EGFPhi monocytic progenitors or EGFPlo granulocytic progenitors. Also surprisingly, IRF8-EGFP revealed a highly heterogeneous pre–pro-B population with a fluorescence intensity ranging from background to 4 orders above background. Interestingly, IRF8–EGFP readily distinguishes true B cell committed (EGFPint) from those that are noncommitted. Moreover, dendritic cell progenitors expressed extremely high levels of IRF8-EGFP. Taken together, the IRF8-EGFP reporter revealed previously unrecognized subsets with distinct developmental potentials in phenotypically well-defined oligopotent progenitors, providing new insights into the dynamic heterogeneity of developing hematopoietic progenitors.

Autoantigen TRIM21/Ro52 as a Possible Target for Treatment of Systemic Lupus Erythematosus.

Systemic lupus erythematosus (SLE) is a chronic, systemic, and autoimmune disease, whose etiology is still unknown. Although there has been progress in the treatment of SLE through the use of glucocorticoid and immunosuppressive drugs, these drugs have limited efficacy and pose significant risks of toxicity. Moreover, prognosis of patients with SLE has remained difficult to assess. TRIM21/Ro52/SS-A1, a 52-kDa protein, is an autoantigen recognized by antibodies in sera of patients with SLE and Sjögrens syndrome (SS), another systemic autoimmune disease, and anti-TRIM21 antibodies have been used as a diagnostic marker for decades. TRIM21 belongs to the tripartite motif-containing (TRIM) super family, which has been found to play important roles in innate and acquired immunity. Recently, TRIM21 has been shown to be involved in both physiological immune responses and pathological autoimmune processes. For example, TRIM21 ubiquitylates proteins of the interferon-regulatory factor (IRF) family and regulates type I interferon and proinflammatory cytokines. In this paper, we summarize molecular features of TRIM21 revealed so far and discuss its potential as an attractive therapeutic target for SLE.

The γ-Parvin-Integrin-Linked Kinase Complex Is Critically Involved in Leukocyte-Substrate Interaction

Leukocyte extravasation is an important step of inflammation, in which integrins have been demonstrated to play an essential role by mediating the interaction of leukocytes with the vascular endothelium and the subendothelial extracellular matrix. Previously, we identified an integrin-linked kinase (ILK)-binding protein affixin (β-parvin), which links initial integrin signals to rapid actin reorganization, and thus plays critical roles in fibroblast migration. In this study, we demonstrate that γ-parvin, one of three mammalian parvin family members, is specifically expressed in several lymphoid and monocytic cell lines in a complementary manner to affixin. Like affixin, γ-parvin directly associates with ILK through its CH2 domain and colocalizes with ILK at focal adhesions as well as the leading edge of PMA-stimulated U937 cells plated on fibronectin. The overexpression of the C-terminal fragment containing CH2 domain or the depletion of γ-parvin by RNA interference inhibits the substrate adhesion of MCP-1-stimulated U937 cells and the spreading of PMA-stimulated U937 cells on fibronectin. Interestingly, the overexpression of the CH2 fragment or the γ-parvin RNA interference also disrupts the asymmetric distribution of PTEN and F-actin observed at the very early stage of cell spreading, suggesting that the ILK-γ-parvin complex is essential for the establishment of cell polarity required for leukocyte migration. Taken together with the results that γ-parvin could form a complex with some important cytoskeletal proteins, such as αPIX, α-actinin, and paxillin as demonstrated for affixin and actopaxin (α-parvin), the results in this study suggest that the ILK-γ-parvin complex is critically involved in the initial integrin signaling for leukocyte migration.

A novel 8-joint ultrasound score is useful in daily practice for rheumatoid arthritis

Abstract Objectives. To investigate the optimal number and combination of joints to be assessed by power Doppler ultrasonography (PDUS) in daily practice for rheumatoid arthritis (RA). Methods. PDUS were performed in 24 joints, including all proximal interphalangeal, metacarpophalangeal (MCP), and bilateral wrist and knee joints in 234 patients with RA. PD signals were scored semiquantitatively from 0 to 3 in each joint, and total PD score-24 was calculated by summing them up as comprehensive assessment. Results. Positive PD signals were more frequently found in bilateral wrist, knee, and the second and third MCP joints than the other joints. The individual PD scores of these 8 joints also showed higher correlation coefficients with total PD score-24 (rs ≥ 0.4). Among the sum PD scores of various selected joint combinations, the score of the combination of 8 joints (total PD score-8), including bilateral second and third MCP, wrist, and knee joints, showed the highest sensitivity and negative predictive value (98.1% and 96.2%, respectively). Total PD score-8 showed high correlation with the total PD score-24 (rs = 0.97, p < 0.01). Conclusions. Total PD score-8 is simple and efficient enough for monitoring disease activity and judging imaging remission of RA in daily practice.

Bach1 regulates osteoclastogenesis in a mouse model via both heme oxygenase 1–dependent and heme oxygenase 1–independent pathways

OBJECTIVE Reducing inflammation and osteoclastogenesis by heme oxygenase 1 (HO-1) induction could be beneficial in the treatment of rheumatoid arthritis (RA). However, the function of HO-1 in bone metabolism remains unclear. This study was undertaken to clarify the effects of HO-1 and its repressor Bach1 in osteoclastogenesis. METHODS In vitro osteoclastogenesis was compared in Bach1-deficient and wild-type mice. Osteoclasts (OCs) were generated from bone marrow-derived macrophages by stimulation with macrophage colony-stimulating factor and RANKL. Osteoclastogenesis was assessed by tartrate-resistant acid phosphatase staining and expression of OC-related genes. Intracellular signal pathways in OC precursors were also assessed. HO-1 short hairpin RNA (shRNA) was transduced into Bach1(-/-) mouse bone marrow-derived macrophages to examine the role of HO-1 in osteoclastogenesis. In vivo inflammatory bone loss was evaluated by local injection of tumor necrosis factor α (TNFα) into calvaria. RESULTS Transcription of HO-1 was down-regulated by stimulation with RANKL in the early stage of OC differentiation. Bach1(-/-) mouse bone marrow-derived macrophages were partially resistant to the RANKL-dependent HO-1 reduction and showed impaired osteoclastogenesis, which was associated with reduced expression of RANK and components of the downstream TNF receptor-associated factor 6/c-Fos/NF-ATc1 pathway as well as reduced expression of Blimp1. Treatment with HO-1 shRNA increased the number of OCs and expression of OC-related genes except for the Blimp1 gene during in vitro osteoclastogenesis from Bach1(-/-) mouse bone marrow-derived macrophages. TNFα-induced bone destruction was reduced in Bach1(-/-) mice in vivo. CONCLUSION The present findings demonstrate that Bach1 regulates osteoclastogenesis under inflammatory conditions, via both HO-1-dependent and HO-1-independent mechanisms. Bach1 may be worthy of consideration as a target for treatment of inflammatory bone loss in diseases including RA.