Monoclonal Antibodies Against Mature Interleukin-18 Ameliorate Colitis and Repair Goblet Cell Function.

BACKGROUND: Numerous biological interventions and small molecules are used to treat Crohn's disease; however, the effectiveness of these treatments varies largely. Non-responsiveness to biological therapies is associated with interleukin (IL)-18 gene polymorphisms and high IL-18 expression has been implicated in the pathogenesis of Crohn's disease. AIMS: The aim of this study was to elucidate the expression of precursor and mature IL-18 in patients with Crohn's disease who exhibited varied responses to cytokine-targeted treatments and determine whether selective inhibition of mature IL-18 offers a novel therapeutic avenue. METHODS: We generated a monoclonal antibody that specifically recognizes the neoepitope of caspase-cleaved mature IL-18. Expression of precursor and mature IL-18 was analyzed in patients with Crohn's disease. Anti-mature IL-18 monoclonal antibodies were intraperitoneally administered in an acute colitis mouse model, and the disease activity index, body weight loss, tissue pathology, proinflammatory cytokine expression, goblet cell function, and microbiota composition were assessed. RESULTS: Precursor and mature IL-18 expression was upregulated and goblet cell function was impaired in patients with Crohn's disease who were unresponsive to biological therapies. Administration of anti-mature IL-18 antibodies ameliorated induced colitis by repairing goblet cell function and restoring the mucus layer. CONCLUSIONS: The newly developed monoclonal antibody holds promise as a therapeutic alternative for Crohn's disease.

Generation of the novel anti-FXYD5 monoclonal antibody and its application to the diagnosis of pancreatic and lung cancer.

Despite recent advances in cancer treatments, pancreatic cancer has a dismal prognosis globally. Early detection of cancer cells and effective treatments for recalcitrant tumors are required, but the innovative therapeutic tools remain in development. Cancer-specific antigens expressed only on cancer cells may help resolve these problems, and antibodies to such antigens have potential in basic research and clinical applications. To generate specific antibodies that bind to proteins expressed on the surface of pancreatic cancer cells, we immunized mice with human pancreatic cancer MIA PaCa-2 cells, and isolated a hybridoma that produces a monoclonal antibody (mAb), named 12-13.8. This antibody was applied to molecular biological experiments such as immunocytochemistry, immunoblotting, flow cytometry, and immunoprecipitation. In addition, we showed that mAb 12-13.8 could accumulate in tumors, through in vivo experiments using cancer-bearing mice. Immunohistochemical staining of pancreatic and lung tumor tissues indicated that the increase of the staining strength by mAb 12-13.8 positively and inversely correlated with the patients' cancer recurrence and survival rate, respectively. We identified the FXYD5 protein as the target protein of mAb 12-13.8, by a human protein array screening system. The FXYD5 protein is overexpressed in various types of cancer and is modified by O-linked glycosylation. We confirmed the binding of the FXYD5 protein to mAb 12-13.8 by using FXYD5-knockout MIA PaCa-2 cells, and detailed epitope mapping identified amino acid residues 45-52 as the minimal peptide sequence. Our results indicate that mAb 12-13.8 could be a valuable tool for FXYD5 studies, and useful in diagnostic and drug delivery applications for cancer patients.

Generation of antagonistic monoclonal antibodies against the neoepitope of active mouse interleukin (IL)-18 cleaved by inflammatory caspases.

Interleukin 18 (IL-18) is a member of the IL-1 family and plays an important role in both the innate and acquired immune systems. It is constitutively expressed as an inactive precursor (24 kDa) in various cell types, and the mature IL-18 (18 kDa) cleaved by inflammatory caspase-1/4 binds to the interleukin-18 receptor, thereby activating downstream signaling pathways. We previously generated anti-human IL-18 antibodies that specifically recognize the human IL-18 neoepitope cleaved by inflammatory caspase-1/4. Because the N-terminal amino acid sequences of the neoepitopes are different between human IL-18 and mouse IL-18, the anti-human IL-18 neoepitope antibodies do not recognize mouse mature IL-18. We have now generated novel anti-mouse IL-18 neoepitope antibodies. We also confirmed CXCL2 secretion from P-815 mouse cells by mouse IL-18 stimulation, and established a simple assay to evaluate the activity of mouse IL-18. Using this evaluation system, we confirmed that the anti-mouse IL-18 neoepitope antibodies could inhibit mouse IL-18. By demonstrating the therapeutic efficacy of the anti-mouse IL-18 neoepitope and function-blocking mAbs established in the present study in mouse models, corresponding to human inflammatory diseases in which IL-18 may be involved, such as inflammatory bowel diseases, we can provide the proof-of-concept that the previously established anti-human IL-18 neoepitope and function-blocking mAbs work in human inflammatory disorders corresponding to mouse models.

Kinetics of Anti-SARS-CoV-2 Antibody Response Following Two Doses of the BNT162b2 mRNA Vaccine: A Japanese Single-Center Primary Care Clinic Report Involving Volunteers and Patients with Autoimmune Disease.

Despite the promising effectiveness of the coronavirus disease 2019 vaccination using an mRNA vaccine, the short efficacy duration and some poor responses to the vaccination remain major concerns. We aimed to clarify the monthly kinetics of the anti-SARS-CoV-2 spike receptor-binding domain antibody response after two doses of the BNT162b2 vaccine in a Japanese population. A chemiluminescent enzyme immunoassay (CLIA) and an enzyme-linked immunosorbent assay were used to measure the antibody levels in 81 Japanese adults (age, <65 years). The antibody levels increased 10-fold at 2−3 weeks following the second dose of BNT162b2 and declined thereafter to approximately 50%, 20%, and 10% of the peak levels at 2, 3, and 6 months, respectively. To compare the antibody titers among different groups, older adults (age, >65 years; n = 38) and patients with systemic lupus erythematosus (SLE, n = 14) were also investigated. A decline in the mean relative antibody titers was observed in older men compared with younger men and in patients with SLE compared with individuals aged <65 years. Although the antibody levels increased drastically following two BNT162b2 doses, they then declined rapidly. Furthermore, poor responders to the vaccination were observed. Repeated vaccinations are required to maintain high antibody levels.

Nucleus Accumbens-Associated Protein 1 Binds DNA Directly through the BEN Domain in a Sequence-Specific Manner.

Nucleus accumbens-associated protein 1 (NAC1) is a nuclear protein that harbors an amino-terminal BTB domain and a carboxyl-terminal BEN domain. NAC1 appears to play significant and diverse functions in cancer and stem cell biology. Here we demonstrated that the BEN domain of NAC1 is a sequence-specific DNA-binding domain. We selected the palindromic 6 bp motif ACATGT as a target sequence by using a PCR-assisted random oligonucleotide selection approach. The interaction between NAC1 and target DNA was characterized by gel shift assays, pull-down assays, isothermal titration calorimetry (ITC), chromatin-immunoprecipitation assays, and NMR chemical shifts perturbation (CSP). The solution NMR structure revealed that the BEN domain of human NAC-1 is composed of five conserved α helices and two short ß sheets, with an additional hitherto unknown N-terminal α helix. In particular, ITC clarified that there are two sequential events in the titration of the BEN domain of NAC1 into the target DNA. The ITC results were further supported by CSP data and structure analyses. Furthermore, live cell photobleaching analyses revealed that the BEN domain of NAC1 alone was unable to interact with chromatin/other proteins in cells.

Screening of a Panel of Low Molecular Weight Compounds That Inhibit Synovial Fibroblast Invasion in Rheumatoid Arthritis.

Increased invasion of synovial fibroblasts and their involvement in cartilage damage are characteristic phenotypes of rheumatoid arthritis (RA). To identify low molecular weight compounds that suppress synovial fibroblast invasion, a panel of inhibitors (n = 330) was initially screened using a real-time cell analysis system for human synovial fibroblasts that were enzymatically isolated from surgical samples of RA patients. To evaluate the effects of the inhibitors identified in the screen, synovial fibroblast migration was measured using a wound-healing assay, and phosphorylation of intracellular signaling molecules was determined by immunoblots. Several candidate inhibitors were identified in the screen, including inhibitors against platelet-derived growth factor receptor (PDGFR), Akt, PI3K, and glycogen kinase synthetase 3 (GSK-3). These inhibitors strongly suppressed synovial fibroblast migration after 72 h and downregulated phosphorylation of Akt (Ser473) at 48 h. When the inhibitors were removed from the culture conditions, both migration and phosphorylated Akt (Ser473) levels were restored. Furthermore, all the categories of inhibitors except for PDGFR inhibitor IV decreased cell proliferation as well as IL-6 production in synovial fibroblasts. Interestingly, GSK-3 inhibitors increased anti-inflammatory cytokine IL-10 production but suppressed IL-23 production from LPS-primed macrophages obtained from healthy donors. In conclusion, blocking PDGFR, PI3K, or GSK-3 could have therapeutic value as an RA treatment that targets the invasion/migration of synovial fibroblasts.

Elucidation of the aberrant 3' splice site selection by cancer-associated mutations on the U2AF1.

The accurate exclusion of introns by RNA splicing is critical for the production of mature mRNA. U2AF1 binds specifically to the 3´ splice site, which includes an essential AG dinucleotide. Even a single amino acid mutation of U2AF1 can cause serious disease such as certain cancers or myelodysplastic syndromes. Here, we describe the first crystal structures of wild-type and pathogenic mutant U2AF1 complexed with target RNA, revealing the mechanism of 3´ splice site selection, and how aberrant splicing results from clinically important mutations. Unexpected features of this mechanism may assist the future development of new treatments against diseases caused by splicing errors.

Generation and characterization of antagonistic anti-human interleukin (IL)-18 monoclonal antibodies with high affinity: Two types of monoclonal antibodies against full-length IL-18 and the neoepitope of inflammatory caspase-cleaved active IL-18.

Interleukin-18 (IL-18) is a pro-inflammatory cytokine that evokes both innate and acquired immune responses. IL-18 is initially synthesized as an inactive precursor and the cleavage for processing into a mature, active molecule is mediated by pro-inflammatory caspases following the activation of inflammasomes. Two types of monoclonal antibodies were raised: anti-IL-1863-68 antibodies which recognize full-length1-193 and cleaved IL-18; and anti-IL-18 neoepitope antibodies which specifically recognize the new N-terminal 37YFGKLESK44 of IL-18 cleaved by pro-inflammatory caspase-1/4. These mAbs were suitable for Western blotting, capillary Western immunoassay (WES), immunofluorescence, immunoprecipitation, and function-blocking assays. WES analysis of these mAbs allowed visualization of the IL-18 bands and provided a molecular weight corresponding to the pro-inflammatory caspase-1/4 cleaved, active form IL-1837-193, and not to the inactive precursor IL-18, in the serum of patients with adult-onset Still's disease (6/14, 42%) and hemophagocytic activation syndrome (2/6, 33%). These monoclonal antibodies will be very useful in IL-18 and inflammasome biology and for diagnostic and therapeutic strategies for inflammatory diseases.

Structural basis for promotion of duodenal iron absorption by enteric ferric reductase with ascorbate.

Dietary iron absorption is regulated by duodenal cytochrome b (Dcytb), an integral membrane protein that catalyzes reduction of nonheme Fe3+ by electron transfer from ascorbate across the membrane. This step is essential to enable iron uptake by the divalent metal transporter. Here we report the crystallographic structures of human Dcytb and its complex with ascorbate and Zn2+. Each monomer of the homodimeric protein possesses cytoplasmic and apical heme groups, as well as cytoplasmic and apical ascorbate-binding sites located adjacent to each heme. Zn2+ coordinates to two hydroxyl groups of the apical ascorbate and to a histidine residue. Biochemical analysis indicates that Fe3+ competes with Zn2+ for this binding site. These results provide a structural basis for the mechanism by which Fe3+ uptake is promoted by reducing agents and should facilitate structure-based development of improved agents for absorption of orally administered iron.

Cancer-related transcription regulator protein NAC1 forms a protein complex with CARM1 for ovarian cancer progression.

NAC1 is a cancer-related transcription regulator protein that is overexpressed in various carcinomas, including ovarian, cervical, breast, and pancreatic carcinomas. NAC1 knock-down was previously shown to result in the apoptosis of ovarian cancer cell lines and to rescue their sensitivity to chemotherapy, suggesting that NAC1 may be a potential therapeutic target, but protein complex formation of intranuclear NAC1 in ovarian cancer cells remain poorly understood. In this study, analysis of ovarian cancer cell lysates by fast protein liquid chromatography on a sizing column showed that the NAC1 peak corresponded to an apparent molecular mass of 300-500 kDa, which is larger than the estimated molecular mass (58 kDa) of the protein. Liquid chromatography-tandem mass spectrometry analysis identified CARM1 as interacting with NAC1 in the protein complex. Furthermore, tissue microarray analysis revealed a significant correlation between CARM1 and NAC1 expression levels. Ovarian cancer patients expressing high levels of NAC1 and CARM1 exhibited poor prognosis after adjuvant chemotherapy. Collectively, our results demonstrate that high expression levels of NAC1 and its novel binding partner CARM1 may serve as an informative prognostic biomarker for predicting resistance to chemotherapy for ovarian cancer.

G196 epitope tag system: a novel monoclonal antibody, G196, recognizes the small, soluble peptide DLVPR with high affinity.

The recognition specificity of monoclonal antibodies (mAbs) has made mAbs among the most frequently used tools in both basic science research and in clinical diagnosis and therapies. Precise determination of the epitope allows the development of epitope tag systems to be used with recombinant proteins for various purposes. Here we describe a new family of tag derived from the epitope recognized by a highly specific mAb G196. The minimal epitope was identified as the five amino acid sequence Asp-Leu-Val-Pro-Arg. Permutation analysis was used to characterize the binding requirements of mAb G196, and the variable regions of the mAb G196 were identified and structurally analyzed by X-ray crystallography. Isothermal titration calorimetry revealed the high affinity (Kd = 1.25 nM) of the mAb G196/G196-epitope peptide interaction, and G196-tag was used to detect several recombinant cytosolic and nuclear proteins in human and yeast cells. mAb G196 is valuable for developing a new peptide tagging system for cell biology and biochemistry research.

Plant Aurora kinases interact with and phosphorylate transcription factors.

Aurora kinase (AUR) is a well-known mitotic serine/threonine kinase that regulates centromere formation, chromosome segregation, and cytokinesis in eukaryotes. In addition to regulating mitotic events, AUR has been shown to regulate protein dynamics during interphase in animal cells. In contrast, there has been no identification and characterization of substrates and/or interacting proteins during interphase in plants. The Arabidopsis thaliana genome encodes three AUR paralogues, AtAUR1, AtAUR2, and AtAUR3. Among them, AtAUR1 and AtAUR2 are considered to function redundantly. Here, we confirmed that both AtAUR1 and AtAUR3 are localized in the nucleus and cytoplasm during interphase, suggesting that they have functions during interphase. To identify novel interacting proteins, we used AlphaScreen to target 580 transcription factors (TFs) that are mainly functional during interphase, using recombinant A. thaliana TFs and AtAUR1 or AtAUR3. We found 133 and 32 TFs had high potential for interaction with AtAUR1 and AtAUR3, respectively. The highly AtAUR-interacting TFs were involved in various biological processes, suggesting the functions of the AtAURs during interphase. We found that AtAUR1 and AtAUR3 showed similar interaction affinity to almost all TFs. However, in some cases, the interaction affinity differed substantially between the two AtAUR homologues. These results suggest that AtAUR1 and AtAUR3 have both redundant and distinct functions through interactions with TFs. In addition, database analysis revealed that most of the highly AtAUR-interacting TFs contained a detectable phosphopeptide that was consistent with the consensus motifs for human AURs, suggesting that these TFs are substrates of the AtAURs. The AtAURs phosphorylated several highly interacting TFs in the AlphaScreen in vitro. Overall, in line with the regulation of TFs through interaction, our results indicate the possibility of phosphoregulation of several TFs by the AtAURs (280/300).

Protein complex formation and intranuclear dynamics of NAC1 in cancer cells.

Nucleus accumbens-associated protein 1 (NAC1) is a cancer-related transcription regulator protein that is also involved in the pluripotency and differentiation of embryonic stem cells. NAC1 is overexpressed in various carcinomas including ovarian, cervical, breast, and pancreatic carcinomas. NAC1 knock-down was previously shown to result in the apoptosis of ovarian cancer cell lines and to rescue their sensitivity to chemotherapy, suggesting that NAC1 may be a potential therapeutic target, but protein complex formation and the dynamics of intranuclear NAC1 in cancer cells remain poorly understood. In this study, analysis of HeLa cell lysates by fast protein liquid chromatography (FPLC) on a sizing column showed that the NAC1 peak corresponded to an apparent molecular mass of 300-500 kDa, which is larger than the estimated molecular mass (58 kDa) of the protein. Furthermore, live cell photobleaching analyses with green fluorescent protein (GFP)-fused NAC1 proteins revealed the intranuclear dynamics of NAC1. Collectively our results demonstrate that NAC1 forms a protein complex to function as a transcriptional regulator in cancer cells.

The SUMO-targeted ubiquitin ligase RNF4 localizes to etoposide-exposed mitotic chromosomes: implication for a novel DNA damage response during mitosis.

RNF4, a SUMO-targeted ubiquitin ligase (STUbL), localizes to the nucleus and functions in the DNA damage response during interphase of the cell cycle. RNF4 also exists in cells undergoing mitosis, where its regulation and function remain poorly understood. Here we showed that administration of etoposide, an anticancer DNA topoisomerase II poison, to mitotic human cervical cancer HeLa cells induced SUMO-2/3-dependent localization of RNF4 to chromosomes. The FK2 antibody signals, indicative of poly/multi-ubiquitin assembly, were detected on etoposide-exposed mitotic chromosomes, whereas the signals were negligible in cells depleted for RNF4 by RNA interference. This suggests that RNF4 functions as a STUbL in the etoposide-induced damage response during mitosis. Indeed, RNF4-depletion sensitized mitotic HeLa cells to etoposide and increased cells with micronuclei. These results indicate the importance of the RNF4-mediated STUbL pathway during mitosis for the maintenance of chromosome integrity and further implicate RNF4 as a target for topo II poison-based therapy for cancer patients.

PAD4 regulates proliferation of multipotent haematopoietic cells by controlling c-myc expression.

Peptidylarginine deiminase 4 (PAD4) functions as a transcriptional coregulator by catalyzing the conversion of histone H3 arginine residues to citrulline residues. Although the high level of PAD4 expression in bone marrow cells suggests its involvement in haematopoiesis, its precise contribution remains unclear. Here we show that PAD4, which is highly expressed in lineage(-) Sca-1(+) c-Kit(+) (LSK) cells of mouse bone marrow compared with other progenitor cells, controls c-myc expression by catalyzing the citrullination of histone H3 on its promoter. Furthermore, PAD4 is associated with lymphoid enhancer-binding factor 1 and histone deacetylase 1 at the upstream region of the c-myc gene. Supporting these findings, LSK cells, especially multipotent progenitors, in PAD4-deficient mice show increased proliferation in a cell-autonomous fashion compared with those in wild-type mice. Together, our results strongly suggest that PAD4 regulates the proliferation of multipotent progenitors in the bone marrow by controlling c-myc expression.

Nuclear localization signal in a cancer-related transcriptional regulator protein NAC1.

Nucleus accumbens-associated protein 1 (NAC1) might have potential oncogenic properties and participate in regulatory networks for pluripotency. Although NAC1 is described as a transcriptional regulator, the nuclear import machinery of NAC1 remains unclear. We found, using a point mutant, that dimer formation was not committed to the nuclear localization of NAC1 and, using deletion mutants, that the amino-terminal half of NAC1 harbored a potential nuclear localization signal (NLS). Wild type, but not mutants of this region, alone was sufficient to drive the importation of green fluorescent protein (GFP) into the nucleus. Bimax1, a synthetic peptide that blocks the importin α/ß pathway, impaired nuclear localization of NAC1 in cells. We also used the binding properties of importin to demonstrate that this region is an NLS. Furthermore, the transcriptional regulator function of NAC1 was dependent on its nuclear localization activity in cells. Taken together, these results show that the region with a bipartite motif constitutes a functional nuclear import sequence in NAC1 that is independent of NAC1 dimer formation. The identification of an NAC1 NLS thus clarifies the mechanism through which NAC1 translocates to the nucleus to regulate the transcription of genes involved in oncogenicity and pluripotency.

Taurine suppresses platelet-derived growth factor (PDGF) BB-induced PDGF-beta receptor phosphorylation by protein tyrosine phosphatase-mediated dephosphorylation in vascular smooth muscle cells.

In atherosclerosis, abnormal vascular smooth muscle cell (VSMC) proliferation plays an important role to form fibroproliferative lesions and platelet-derived growth factor (PDGF)-BB is one of the most potent chemoattractants and proliferative factors for VSMCs. Taurine, sulfur-containing beta-amino acid, has been considered to prevent the development of atherosclerosis, although the molecular mechanism remains obscure. Previously, we demonstrated that taurine significantly suppressed PDGF-BB-induced cell proliferation, DNA synthesis, immediate-early gene expressions and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in VSMCs. The present study was aimed at elucidating the precise molecular mechanism of taurine in PDGF-BB signaling pathway. We showed that taurine significantly suppressed PDGF-BB-induced phosphorylation of PDGF-beta receptor and activation of its downstream signaling molecules such as Ras, MAPK/ERK kinase (MEK)1/2 and Akt. Because taurine did not attenuate phorbol 12-myristate 13-acetate (PMA)-induced PDGF-beta receptor-independent ERK1/2 phosphorylation, we further investigated the suppressive mechanism of taurine in PDGF-beta receptor level. Although taurine did not directly affect PDGF receptor autophosphorylation in vitro, taurine promoted PDGF-beta receptor dephosphorylation and restored PDGF-BB-induced suppression of protein tyrosine phosphatase (PTPase) activity. Taken together, we propose that taurine could prevent or delay the progression of atherosclerosis by PTPase-mediated suppression of PDGF-beta receptor phosphorylation, and by decreasing the activation of its downstream signaling molecules in VSMCs.

TGF-beta1 enhances degradation of IFN-gamma-induced iNOS protein via proteasomes in RAW 264.7 cells.

TGF-beta1 is a well-known immunosuppressive cytokine that inhibits inducible nitric oxide synthase (iNOS) gene expression in various cells including macrophages. In this study, we investigated the suppressive mechanisms of TGF-beta1 on IFN-gamma-induced iNOS gene expression using the murine macrophage-like cell line RAW 264.7. TGF-beta1 decreased iNOS protein amount through enhanced degradation, although TGF-beta1 did not affect IFN-gamma-induced iNOS mRNA level or stability. In addition, the enhancement of iNOS protein degradation by TGF-beta1 treatment was almost completely blocked by MG132, a proteasome inhibitor. Furthermore, TGF-beta1 enhanced the trypsin-like activity of proteasomes in the presence of IFN-gamma, although did not enhance the peptidylglutamyl-peptide hydrolyzing and chymotrypsin-like activities of proteasomes. The level of ubiquitinated iNOS protein was not significantly altered by IFN-gamma or IFN-gamma plus TGF-beta1 treatment. Because MG132 inhibited iNOS protein degradation and IFN-gamma plus TGF-beta1 treatment increased the trypsin-like activity of proteasomes, we hypothesized that TGF-beta1 might enhance iNOS protein degradation via the ubiquitin-proteasome pathway in the presence of IFN-gamma. We propose that these mechanisms of TGF-beta1 in the posttranslational regulation of iNOS gene expression may contribute to suppression of excess nitric oxide during inflammatory processes.

Suppressive effect of taurine on platelet-derived growth factor (PDGF) BB-induced c-fos and c-jun mRNA expressions through extracellular signal-regulated kinase (ERK) in mesenchymal cell lines.

Platelet-derived growth factor (PDGF) plays an important role in the pathogenic course of atherosclerosis, pulmonary fibrosis, and glomerulonephritis, and increased activity of the PDGF signaling pathway has been implicated as a contributing factor in the progression of the diseases. Taurine may be a prophylactic amino acid for atherosclerosis not only by decreasing plasma cholesterol level, but also by inhibiting the cell proliferation-signaling pathway. To elucidate how taurine affects the signaling pathway, we investigated the effect of taurine on the expression of immediate-early genes and activation of mitogen-activated protein kinases (MAPKs) in NIH/3T3 cells as standard mesenchymal cells. Taurine inhibited PDGF-BB-induced c-fos and c-jun mRNA expressions dose-dependently, although structural analogues of taurine did not. Taurine decreased the PDGF-induced p44/p42 ERK (extracellular signal-regulated kinase) phosphorylation state dose-dependently, although no phosphorylation was observed on JNK/SAPK (c-Jun N-terminal kinase/stress-activated protein kinase) and p38 MAPK. Further, PDGF-BB-induced tyrosine phosphorylation of the PDGF-beta receptor was not influenced by treatment with taurine, indicating that taurine never affects ligand-receptor interaction, and may act downstream of the PDGF receptor. Thus, the inhibitory mechanism of taurine on PDGF-induced c-fos and c-jun mRNA expressions may depend on the p44/p42 ERK pathway, but not on PDGF-beta receptor tyrosine phosphorylation, JNK/SAPK or p38 MAPK pathway. These results suggest that taurine may suppress the cell proliferation-signaling pathway through the inhibition of ERK activity and immediate-early gene expression.