Phase 2 trial of crizotinib in Japanese patients with advanced NSCLC harboring a MET gene alteration: a Co-MET study.

BACKGROUND: MET exon 14 skipping mutations occur in 3-4% and MET high amplifications occur in < 1% of patients with non-small-cell lung cancer (NSCLC). Crizotinib, a selective ATP-competitive small-molecule inhibitor of c-Met, ALK, and ROS1 tyrosine kinases, has shown activity in cancer models with various types of MET activation. METHODS: The Co-MET study is a single-arm phase 2 trial to assess the safety and efficacy of crizotinib in MET inhibitor-naïve patients with advanced NSCLC harboring MET exon 14 skipping mutation (cohort 1) or high MET gene copy number of ≥ 7 (cohort 2). The primary endpoint was the objective response rate (ORR) per RECIST v1.1 by independent radiology review in cohort 1. The key secondary endpoints were the duration of response (DoR), progression-free survival (PFS), overall survival (OS), and safety. RESULTS: A total of 28 patients (23 in cohort 1 and 5 in cohort 2) were enrolled between March 2018 and February 2020. The primary endpoint was met as the ORR (90% confidence interval: CI) in cohort 1 was 38.1% (20.6-58.3). Median DoR, PFS, and OS (95% CI) were 7.6 (1.9-NE), 5.7 (2.1-11.3), 9.1 (4.0-19.9) months, respectively, in cohort 1. ORR in cohort 2 was 40.0% (18.9-92.4). The safety signals were generally consistent with the known safety profile of crizotinib. CONCLUSIONS: Crizotinib showed a clinical activity similar to that of tepotinib and capmatinib in patients with NSCLC harboring MET exon 14 skipping mutations. CLINICAL TRIAL INFORMATION: UMIN000031623.

Granulomatosis with Polyangiitis following COVID-19 in an Adolescent.

Granulomatosis with polyangiitis (GPA) is a systemic disease that causes vasculitis in various organs. Although the mechanism of pathogenesis remains unclear, infection has been reported to be a causative factor. We herein report a case of GPA that developed following coronavirus disease 2019 (COVID-19) in an adolescent girl. One month after contracting mild COVID-19, the patient had facial allodynia, a fever, and weight loss and was admitted for multiple nodular shadows on a chest roentgenogram. GPA was diagnosed based on pathological findings of the lung and nasal mucosal biopsies. She received methylprednisolone and rituximab, and her symptoms and radiological findings improved.

ZSWIM8 is a myogenic protein that partly prevents C2C12 differentiation.

Cell adhesion molecule-related/downregulated by oncogenes (Cdon) is a cell-surface receptor that mediates cell-cell interactions and positively regulates myogenesis. The cytoplasmic region of Cdon interacts with other proteins to form a Cdon/JLP/Bnip-2/CDC42 complex that activates p38 mitogen-activated protein kinase (MAPK) and induces myogenesis. However, Cdon complex may include other proteins during myogenesis. In this study, we found that Cullin 2-interacting protein zinc finger SWIM type containing 8 (ZSWIM8) ubiquitin ligase is induced during C2C12 differentiation and is included in the Cdon complex. We knocked-down Zswim8 in C2C12 cells to determine the effect of ZSWIM8 on differentiation. However, we detected neither ZSWIM8-dependent ubiquitination nor the degradation of Bnip2, Cdon, or JLP. In contrast, ZSWIM8 knockdown accelerated C2C12 differentiation. These results suggest that ZSWIM8 is a Cdon complex-included myogenic protein that prevents C2C12 differentiation without affecting the stability of Bnip2, Cdon, and JLP.

A Phase I/II Study of Biweekly Carboplatin and Nab-paclitaxel With Concurrent Radiotherapy for Patients With Locally Advanced Unresectable Stage III Non-small-cell Lung Cancer.

BACKGROUND: Concurrent chemoradiotherapy (CCRT) is the standard treatment for patients with locally advanced non-small-cell lung cell cancer (LA-NSCLC). We conducted a phase I/II study of biweekly carboplatin and nab-paclitaxel (nab-PTX) with radiotherapy (RT). MATERIALS AND METHODS: In the phase I part, patients with inoperable stage IIIA/IIIB NSCLC were treated with carboplatin (area under the time-concentration curve, 4) and nab-PTX (60-100 mg/m2) on days 1, 15, and 29. Thoracic RT was administered from day 1 to a total dose of 60 Gy in 30 fractions. In the phase II part, patients were administered carboplatin and nab-PTX on days 1, 15, and 29 at the recommended dose (RD). The primary endpoint of the phase I part was to determine the maximum tolerated dose and the RD. In the phase II part, the primary endpoint was 2-year overall survival (OS) rate, and secondary endpoints were the objective response rate, progression-free survival, OS, and safety profile. RESULTS: In the phase I part, although maximum tolerated dose was not obtained, the RD was carboplatin (area under the time-concentration curve, 4) and nab-PTX (100 mg/m2). Of the evaluable 28 patients, the rate of 2-year OS was 67.8% (95% confidence interval, 49.3%-82.1%). The objective response rate was 96.4%, and the median follow-up time was 33.2 months. The median progression-free survival was 18.2 months (95% confidence interval, 13.1 months to not reached). The most common toxicities of grade 3 or higher were neutropenia (60.5%), anemia (14.2%), thrombocytopenia (7.2%), and pneumonitis (3.6%). CONCLUSIONS: This study achieved the primary endpoint. Biweekly carboplatin and nab-PTX with concurrent RT was well-tolerated and exerted promising antitumor activity.

A pilot study of adjuvant chemotherapy with carboplatin and oral S-1 for patients with completely resected stage II to IIIA non-small cell lung cancer.

BACKGROUND: Adjuvant chemotherapy with platinum-based regimens for completely resected early-stage non-small cell lung cancer (NSCLC) provides overall survival benefit in several clinical trials. OBJECTIVES: We conducted this prospective study to evaluate the efficacy and safety of adjuvant chemotherapy with carboplatin and S-1 for patients with completely resected stage II to IIIA NSCLC. METHODS: Patients with completely resected stage IIA to IIIA NSCLC were treated with four cycles of carboplatin with area under the concentration time curve of 5 mg/mL/min on day 1 plus S-1 at 80-120 mg/bodyweight per day for two weeks, followed by one-week rest as adjuvant chemotherapy. The primary endpoint was the completion rate of three cycles of the treatment. The secondary endpoints were safety and two-year survival rate. RESULTS: A total of 19 patients were enrolled, until the study was terminated prematurely because of fatal pulmonary embolism in two patients. The median number of treatment cycles was three (range: 1-4). The completion rate of three cycles was 78.9% (95% confidence interval [CI]: 56.6-91.4%). Two-year disease-free survival rate was 57.8%. Grade 3 or 4 hematological toxicities included neutropenia (26.2%), anemia (5.2%), and thrombocytopenia (15.7%). Grade 3 or 4 nonhematological toxicities were anorexia (10.5%) and nausea (10.5%). Febrile neutropenia developed in 5.2%. In two patients (10.5%), grade five pulmonary embolism was observed, and the causal relationship with treatment could not be denied. CONCLUSIONS: Carboplatin and oral S-1 had modest survival benefit, but this regimen was not tolerable in an adjuvant setting because fatal pulmonary embolism occurred in two patients. KEY POINTS: Carboplatin and oral S-1 had modest survival benefit but this regimen was not tolerable. Fatal pulmonary embolism occurred in this regimen.

Cul5-type Ubiquitin Ligase KLHDC1 Contributes to the Elimination of Truncated SELENOS Produced by Failed UGA/Sec Decoding.

The UGA codon signals protein translation termination, but it can also be translated into selenocysteine (Sec, U) to produce selenocysteine-containing proteins (selenoproteins) by dedicated machinery. As Sec incorporation can fail, Sec-containing longer and Sec-lacking shorter proteins co-exist. Cul2-type ubiquitin ligases were recently shown to destabilize such truncated proteins; however, which ubiquitin ligase targets truncated proteins for degradation remained unclear. We report that the Cul5-type ubiquitin ligase KLHDC1 targets truncated SELENOS, a selenoprotein, for proteasomal degradation. SELENOS is involved in endoplasmic reticulum (ER)-associated degradation, which is linked to reactive oxygen species (ROS) production, and the knockdown of KLHDC1 in U2OS cells decreased ER stress-induced cell death. Knockdown of SELENOS increased the cell population with lower ROS levels. Our findings reveal that, in addition to Cul2-type ubiquitin ligases, KLHDC1 is involved in the elimination of truncated oxidoreductase-inactive SELENOS, which would be crucial for maintaining ROS levels and preventing cancer development.

Insulin-like growth factor 1 receptor stabilizes the ETV6-NTRK3 chimeric oncoprotein by blocking its KPC1/Rnf123-mediated proteasomal degradation.

Many oncogenes, including chimeric oncoproteins, require insulin-like growth factor 1 receptor (IGF1R) for promoting cell transformation. The ETS variant 6 (ETV6)-neurotrophic receptor tyrosine kinase 3 (NTRK3) (EN) chimeric tyrosine kinase is expressed in mesenchymal, epithelial, and hematopoietic cancers and requires the IGF1R axis for transformation. However, current models of IGF1R-mediated EN activation are lacking mechanistic detail. We demonstrate here that IGF-mediated IGF1R stimulation enhances EN tyrosine phosphorylation and that blocking IGF1R activity or decreasing protein levels of the adaptor protein insulin receptor substrate 1/2 (IRS1/2) results in rapid EN degradation. This was observed both in vitro and in vivo in fibroblast and breast epithelial cell line models and in MO91, an EN-expressing human leukemia cell line. Stable isotope labeling with amino acids in cell culture (SILAC)-based MS analysis identified the E3 ligase RING-finger protein 123 (Rnf123, more commonly known as KPC1) as an EN interactor upon IGF1R/insulin receptor (INSR) inhibitor treatment. KPC1/Rnf123 ubiquitylated EN in vitro, and its overexpression decreased EN protein levels. In contrast, KPC1/Rnf123 knockdown rendered EN resistant to IGF1R inhibitor-mediated degradation. These results support a critical function for IGF1R in protecting EN from KPC1/Rnf123-mediated proteasomal degradation. Attempts to therapeutically target oncogenic chimeric tyrosine kinases have traditionally focused on blocking kinase activity to restrict downstream activation of essential signaling pathways. In this study, we demonstrate that IGF1R inhibition results in rapid ubiquitylation and degradation of the EN oncoprotein through a proteasome-dependent mechanism that is reversible, highlighting a potential strategy for targeting chimeric tyrosine kinases in cancer.

Ubiquitin ligase SPSB4 diminishes cell repulsive responses mediated by EphB2.

Eph receptor tyrosine kinases and their ephrin ligands are overexpressed in various human cancers, including colorectal malignancies, suggesting important roles in many aspects of cancer development and progression as well as in cellular repulsive responses. The ectodomain of EphB2 receptor is cleaved by metalloproteinases (MMPs) MMP-2/MMP-9 and released into the extracellular space after stimulation by its ligand. The remaining membrane-associated fragment is further cleaved by the presenilin-dependent γ-secretase and releases an intracellular peptide that has tyrosine kinase activity. Although the cytoplasmic fragment is degraded by the proteasome, the responsible ubiquitin ligase has not been identified. Here, we show that SOCS box-containing protein SPSB4 polyubiquitinates EphB2 cytoplasmic fragment and that SPSB4 knockdown stabilizes the cytoplasmic fragment. Importantly, SPSB4 down-regulation enhances cell repulsive responses mediated by EphB2 stimulation. Altogether, we propose that SPSB4 is a previously unidentified ubiquitin ligase regulating EphB2-dependent cell repulsive responses.

Hypoxia-inducible factor-2α stabilizes the von Hippel-Lindau (VHL) disease suppressor, Myb-related protein 2.

Ubiquitin ligase von Hippel-Lindau tumor suppressor (pVHL) negatively regulates protein levels of hypoxia-inducible factor-α (HIF-α). Loss of pVHL causes HIF-α accumulation, which contributes to the pathogenesis of von Hippel-Lindau (VHL) disease. In contrast, v-Myb avian myeloblastosis viral oncogene homolog-like 2 (MYBL2; B-Myb), a transcription factor, prevents VHL pathogenesis by regulating gene expression of HIF-independent pathways. Both HIF-α and B-Myb are targets of pVHL-mediated polyubiquitination and proteasomal degradation. Here, we show that knockdown of HIF-2α induces downregulation of B-Myb in 786-O cells, which are deficient in pVHL, and this downregulation is prevented by proteasome inhibition. In the presence of pVHL and under hypoxia-like conditions, B-Myb and HIF-2α are both upregulated, and the upregulation of B-Myb requires expression of HIF-2α. We also show that HIF-2α and B-Myb interact in the nucleus, and this interaction is mediated by the central region of HIF-2α and the C-terminal region of B-Myb. These data indicate that oncogenic HIF-2α stabilizes B-Myb to suppress VHL pathogenesis.

Parallel Regulation of von Hippel-Lindau Disease by pVHL-Mediated Degradation of B-Myb and Hypoxia-Inducible Factor α.

pVHL, the protein product of the von Hippel-Lindau (VHL) tumor suppressor gene, is a ubiquitin ligase that targets hypoxia-inducible factor α (HIF-α) for proteasomal degradation. Although HIF-α activation is necessary for VHL disease pathogenesis, constitutive activation of HIF-α alone did not induce renal clear cell carcinomas and pheochromocytomas in mice, suggesting the involvement of an HIF-α-independent pathway in VHL pathogenesis. Here, we show that the transcription factor B-Myb is a pVHL substrate that is degraded via the ubiquitin-proteasome pathway and that vascular endothelial growth factor (VEGF)- and/or platelet-derived growth factor (PDGF)-dependent tyrosine 15 phosphorylation of B-Myb prevents its degradation. Mice injected with B-Myb knockdown 786-O cells developed dramatically larger tumors than those bearing control cell tumors. Microarray screening of B-Myb-regulated genes showed that the expression of HIF-α-dependent genes was not affected by B-Myb knockdown, indicating that B-Myb prevents HIF-α-dependent tumorigenesis through an HIF-α-independent pathway. These data indicate that the regulation of B-Myb by pVHL plays a critical role in VHL disease.

The Ubiquitin Ligase SCF(Ucc1) Acts as a Metabolic Switch for the Glyoxylate Cycle.

Despite the crucial role played by the glyoxylate cycle in the virulence of pathogens, seed germination in plants, and sexual development in fungi, we still have much to learn about its regulation. Here, we show that a previously uncharacterized SCF(Ucc1) ubiquitin ligase mediates proteasomal degradation of citrate synthase in the glyoxylate cycle to maintain metabolic homeostasis in glucose-grown cells. Conversely, transcription of the F box subunit Ucc1 is downregulated in C2-compound-grown cells, which require increased metabolic flux for gluconeogenesis. Moreover, in vitro analysis demonstrates that oxaloacetate regenerated through the glyoxylate cycle induces a conformational change in citrate synthase and inhibits its recognition and ubiquitination by SCF(Ucc1), suggesting the existence of an oxaloacetate-dependent positive feedback loop that stabilizes citrate synthase. We propose that SCF(Ucc1)-mediated regulation of citrate synthase acts as a metabolic switch for the glyoxylate cycle in response to changes in carbon source, thereby ensuring metabolic versatility and flexibility.

Activation of double-stranded RNA-activated protein kinase (PKR) by interferon-stimulated gene 15 (ISG15) modification down-regulates protein translation.

The ubiquitin-like molecule ISG15 (UCRP) and protein modification by ISG15 (ISGylation) are strongly induced by interferon, genotoxic stress, and pathogen infection, suggesting that ISG15 plays an important role in innate immune responses. However, how ISGylation contributes to innate immune responses is not clear. The dsRNA-dependent protein kinase (PKR) inhibits translation by phosphorylating eIF2α to exert its anti-viral effect. ISG15 and PKR are induced by interferon, suggesting that a relationship exists between ISGylation and translational regulation. Here, we report that PKR is ISGylated at lysines 69 and 159. ISG15-modified PKR is active in the absence of virus infection and phosphorylates eIF2α to down-regulate protein translation. The present study describes a novel pathway for the activation of PKR and the regulation of protein translation.

The Role of Elongin BC-Containing Ubiquitin Ligases.

The Elongin complex was originally identified as a positive regulator of RNA polymerase II and is composed of a transcriptionally active subunit (A) and two regulatory subunits (B and C). The Elongin BC complex enhances the transcriptional activity of Elongin A. "Classical" SOCS box-containing proteins interact with the Elongin BC complex and have ubiquitin ligase activity. They also interact with the scaffold protein Cullin (Cul) and the RING domain protein Rbx and thereby are members of the Cullin RING ligase (CRL) superfamily. The Elongin BC complex acts as an adaptor connecting Cul and SOCS box proteins. Recently, it was demonstrated that classical SOCS box proteins can be further divided into two groups, Cul2- and Cul5-type proteins. The classical SOCS box-containing protein pVHL is now classified as a Cul2-type protein. The Elongin BC complex containing CRL family is now considered two distinct protein assemblies, which play an important role in regulating a variety of cellular processes such as tumorigenesis, signal transduction, cell motility, and differentiation.

TRIM67 protein negatively regulates Ras activity through degradation of 80K-H and induces neuritogenesis.

Tripartite motif (TRIM)-containing proteins, which are defined by the presence of a common domain structure composed of a RING finger, one or two B-box motifs and a coiled-coil motif, are involved in many biological processes including innate immunity, viral infection, carcinogenesis, and development. Here we show that TRIM67, which has a TRIM motif, an FN3 domain and a SPRY domain, is highly expressed in the cerebellum and that TRIM67 interacts with PRG-1 and 80K-H, which is involved in the Ras-mediated signaling pathway. Ectopic expression of TRIM67 results in degradation of endogenous 80K-H and attenuation of cell proliferation and enhances neuritogenesis in the neuroblastoma cell line N1E-115. Furthermore, morphological and biological changes caused by knockdown of 80K-H are similar to those observed by overexpression of TRIM67. These findings suggest that TRIM67 regulates Ras signaling via degradation of 80K-H, leading to neural differentiation including neuritogenesis.

TRIM6 interacts with Myc and maintains the pluripotency of mouse embryonic stem cells.

The proto-oncogene product Myc is a master regulator of cell proliferation through its specific binding to the E-box motif in genomic DNA. It has been reported that Myc has an important role in the proliferation and maintenance of the pluripotency of embryonic stem (ES) cells and that the transcriptional activity of Myc is regulated by several post-translational modifications, including ubiquitination. In this study, we showed that tripartite motif containing 6 (TRIM6), one of the TRIM family ubiquitin ligases, was selectively expressed in ES cells and interacted with Myc followed by attenuation of the transcriptional activity of Myc. Knockdown of TRIM6 in ES cells enhanced the transcriptional activity of Myc and repressed expression of NANOG, resulting in the promotion of ES cell differentiation. These findings indicate that TRIM6 regulates the transcriptional activity of Myc during the maintenance of ES cell pluripotency, suggesting that TRIM6 functions as a novel regulator for Myc-mediated transcription in ES cells.

TRIM32 promotes retinoic acid receptor α-mediated differentiation in human promyelogenous leukemic cell line HL60.

Ubiquitination, one of the posttranslational modifications, appears to be involved in the transcriptional activity of nuclear receptors including retinoic acid receptor α (RARα). We previously reported that an E3 ubiquitin ligase, TRIM32, interacts with several important proteins including RARα and enhances transcriptional activity of RARα in mouse neuroblastoma cells and embryonal carcinoma cells. Retinoic acid (RA), which acts as a ligand to nuclear receptors including RARα, plays crucial roles in development, differentiation, cell cycles and apoptosis. In this study, we found that TRIM32 enhances RARα-mediated transcriptional activity even in the absence of RA and stabilizes RARα in the human promyelogenous leukemic cell line HL60. Moreover, we found that overexpression of TRIM32 in HL60 cells suppresses cellular proliferation and induces granulocytic differentiation even in the absence of RA. These findings suggest that TRIM32 functions as one of the coactivators for RARα-mediated transcription in acute promyelogenous leukemia (APL) cells, and thus TRIM32 may become a potentially therapeutic target for APL.

TRIM32 promotes neural differentiation through retinoic acid receptor-mediated transcription.

Retinoic acid (RA), a metabolite of vitamin A, plays versatile roles in development, differentiation, cell cycles and regulation of apoptosis by regulating gene transcription through nuclear receptor activation. Ubiquitinylation, which is one of the post-translational modifications, appears to be involved in the transcriptional activity of intranuclear receptors including retinoic acid receptor α (RARα). Mutations in the tripartite motif-containing protein 32 gene (TRIM32; also known as E3 ubiquitin-protein ligase) have been reported to be responsible for limb-girdle muscular dystrophy type 2H in humans, and its encoded protein has been shown to interact with several other important proteins. In this study, we found that TRIM32 interacts with RARα and enhances its transcriptional activity in the presence of RA. We also found that overexpression of TRIM32 in mouse neuroblastoma cells and embryonal carcinoma cells promoted stability of RARα, resulting in enhancement of neural differentiation. These findings suggest that TRIM32 functions as one of the co-activators for RARα-mediated transcription, and thereby TRIM32 is a potential therapeutic target for developmental disorders and RA-dependent leukemias.

TRIM40 promotes neddylation of IKKγ and is downregulated in gastrointestinal cancers.

Gastrointestinal neoplasia seems to be a common consequence of chronic inflammation in the gastrointestinal epithelium. Nuclear factor-kappaB (NF-κB) is an important transcription factor for carcinogenesis in chronic inflammatory diseases and plays a key role in promoting inflammation-associated carcinoma in the gastrointestinal tract. Activation of NF-κB is regulated by several posttranslational modifications including phosphorylation, ubiquitination and neddylation. In this study, we showed that tripartite motif (TRIM) 40 is highly expressed in the gastrointestinal tract and that TRIM40 physically binds to Nedd8, which is conjugated to target proteins by neddylation. We also found that TRIM40 promotes the neddylation of inhibitor of nuclear factor kappaB kinase subunit gamma, which is a crucial regulator for NF-κB activation, and consequently causes inhibition of NF-κB activity, whereas a dominant-negative mutant of TRIM40 lacking the RING domain does not inhibit NF-κB activity. Knockdown of TRIM40 in the small intestinal epithelial cell line IEC-6 caused NF-κB activation followed by increased cell growth. In addition, we found that TRIM40 is highly expressed in normal gastrointestinal epithelia but that TRIM40 is downregulated in gastrointestinal carcinomas and chronic inflammatory lesions of the gastrointestinal tract. These findings suggest that TRIM40 inhibits NF-κB activity via neddylation of inhibitor of nuclear factor kappaB kinase subunit gamma and that TRIM40 prevents inflammation-associated carcinogenesis in the gastrointestinal tract.

MDA-9/syntenin interacts with ubiquitin via a novel ubiquitin-binding motif.

Ubiquitination appears to be involved in proteasome-dependent proteolysis and in the membrane trafficking system including endocytosis and exocytosis. In this study, we identified MDA-9/syntenin as a novel ubiquitin-binding protein by a yeast two-hybrid system using modified ubiquitin in which lysine 48 is substituted by arginine. It has been reported that MDA-9/syntenin is a membrane-associated protein and regulates a cellular process involving endocytosis and intracellular transport. We found that MDA-9/syntenin binds to ubiquitin by a non-covalent bond and is ubiquitinated covalently. MDA-9/syntenin has no ubiquitin-binding motifs that have so far been reported, suggesting that MDA-9/syntenin physically interacts with ubiquitin via a novel binding motif. MDA-9/syntenin is stable in the cell, suggesting that ubiquitin binding of MDA-9/syntenin or ubiquitination of MDA-9/syntenin is not related to proteolysis. Furthermore, we showed that overexpression of wild-type MDA-9/syntenin enhances formation of filopodia, whereas MDA-9/syntenin lacking the PDZ domain inhibits the formation of filopodia, suggesting that MDA-9/syntenin plays an important role via interaction with ubiquitin in the regulation of cancer metastasis and invasion.

Plasma gelsolin facilitates interaction between ß2 glycoprotein I and α5ß1 integrin.

Antiphospholipid syndrome (APS) is characterized by thrombosis and the presence of antiphospholipid antibodies (aPL) that directly recognizes plasma ß(2)-glycoprotein I (ß(2) GPI). Tissue factor (TF), the major initiator of the extrinsic coagulation system, is induced on monocytes by aPL in vitro, explaining in part the pathophysiology in APS. We previously reported that the mitogen-activated protein kinase (MAPK) pathway plays an important role in aPL-induced TF expression on monocytes. In this study, we identified plasma gelsolin as a protein associated with ß(2) GPI by using immunoaffinity chromatography and mass spectrometric analysis. An in vivo binding assay showed that endogenous ß(2) GPI interacts with plasma gelsolin, which binds to integrin a(5) ß(1) through fibronectin. The tethering of ß(2) GPI to monoclonal anti-ß(2) GPI autoantibody on the cell surface was enhanced in the presence of plasma gelsolin. Immunoblot analysis demonstrated that p38 MAPK protein was phosphorylated by monoclonal anti-ß(2) GPI antibody treatment, and its phosphorylation was attenuated in the presence of anti-integrin a(5) ß(1) antibody. Furthermore, focal adhesion kinase, a downstream molecule of the fibronectin-integrin signalling pathway, was phosphorylated by anti-ß(2) GPI antibody treatment. These results indicate that molecules including gelsolin and integrin are involved in the anti-ß(2) GPI antibody-induced MAPK pathway on monocytes and that integrin is a possible therapeutic target to modify a prothrombotic state in patients with APS.