Expression of discoidin domain receptor 1 tyrosine kinase on the human bronchial epithelium

Virtual screening for potential discoidin domain receptor 1 (DDR1) inhibitors based on structural assessment

Discoidin domain receptor 1 (DDR1) (EC Number 2.7.10.1) has recently been considered as a promising therapeutic target for idiopathic pulmonary fibrosis (IPF). However, none of the currently discovered DDR1 inhibitors have been included in clinical studies due to low target specificity or druggability limitations, necessitating various approaches to develop novel DDR1 inhibitors. In this study, to assure target specificity, a docking assessment of the DDR1 crystal structures was undertaken to find the well-differentiated crystal structure, and 4CKR was identified among many crystal structures. Then, using the best pharmacophore model and molecular docking, virtual screening of the ChEMBL database was done, and five potential molecules were identified as promising inhibitors of DDR1. Subsequently, all hit compound complex systems were validated using molecular dynamics simulations and MM/PBSA methods to assess the stability of the system after ligand binding to DDR1. Based on molecular dynamics simulations and hydrogen-bonding occupancy analysis, the DDR1-Cpd2, DDR1-Cpd17, and DDR1-Cpd18 complex systems exhibited superior stability compared to the DDR1-Cpd1 and DDR-Cpd33 complex systems. Meanwhile, when targeting DDR1, the descending order of the five hit molecules' binding free energies was Cpd17 (- 145.820 kJ/mol) > Cpd2 (- 131.818 kJ/mol) > Cpd18 (- 130.692 kJ/mol) > Cpd33 (- 129.175 kJ/mol) > Cpd1 (- 126.103 kJ/mol). Among them, Cpd2, Cpd17, and Cpd18 showed improved binding characteristics, indicating that they may be potential DDR1 inhibitors. In this research, we developed a high-hit rate, effective screening method that serves as a theoretical guide for finding DDR1 inhibitors for the development of IPF therapeutics.

The Extracellular Matrix in Soft Tissue Sarcomas: Pathobiology and Cellular Signalling

Soft tissue sarcomas are rare cancers of mesenchymal origin or differentiation comprising over 70 different histological subtypes. Due to their mesenchymal differentiation, sarcomas are thought to produce and deposit large quantities of extracellular matrix (ECM) components. Interactions between ECM ligands and their corresponding adhesion receptors such as the integrins and the discoidin domain receptors play key roles in driving many fundamental oncogenic processes including uncontrolled proliferation, cellular invasion and altered metabolism. In this review, we focus on emerging studies that describe the key ECM components commonly found in soft tissue sarcomas and discuss preclinical and clinical evidence outlining the important role that these proteins and their cognate adhesion receptors play in sarcomagenesis. We conclude by providing a perspective on the need for more comprehensive in-depth analyses of both the ECM and adhesion receptor biology in multiple histological subtypes in order to identify new drug targets and prognostic biomarkers for this group of rare diseases of unmet need.

The permissive role of TCTP in PM2.5/NNK-induced epithelial-mesenchymal transition in lung cells

Background

Translationally controlled tumor protein (TCTP) is linked to lung cancer. However, upon lung cancer carcinogens stimulation, there were no reports on the relationship between TCTP and lung cell carcinogenic epithelial–mesenchymal transition (EMT). This study was designed to investigate the molecular mechanism of regulation of TCTP expression and its role in lung carcinogens-induced EMT.

Methods

To study the role of TCTP in lung carcinogens [particulate matter 2.5 (PM_2.5) or 4-methylnitrosamino-l-3-pyridyl-butanone (NNK)]-induced EMT, PM_2.5/NNK-treated lung epithelial and non-small cell lung cancer (NSCLC) cells were tested. Cell derived xenografts, human lung cancer samples and online survival analysis were used to confirm the results. MassArray assay, Real-time PCR and Reporter assays were performed to elucidate the mechanism of regulation of TCTP expression. All statistical analyses were performed using GraphPad Prism version 6.0 or SPSS version 20.0.

Results

Translationally controlled tumor protein and vimentin expression were up-regulated in PM_2.5/NNK-treated lung cells and orthotopic implantation tumors. TCTP expression was positively correlated with vimentin in human NSCLC samples. Patients with high expression of TCTP displayed reduced overall and disease-free survival. TCTP overexpression could increase vimentin expression and promote cell metastasis. Furthermore, PM_2.5/NNK stimulation brought a synergistic effect on EMT in TCTP-transfected cells. TCTP knockdown blocked PM_2.5/NNK carcinogenic effect. Mechanically, PM_2.5/NNK-induced TCTP expression was regulated by one microRNA, namely miR-125a-3p, but not by methylation on TCTP gene promoter. The level of TCTP was regulated by its specific microRNA during the process of PM_2.5/NNK stimulation, which in turn enhanced vimentin expression and played a permissive role in carcinogenic EMT.

Conclusions

Our results provided new insights into the mechanisms of TCTP regulatory expression in lung carcinogens-induced EMT. TCTP and miR-125a-3p might act as potential prognostic biomarkers and therapeutic targets for NSCLC.

Ambient fine particulate matter inhibits 15-lipoxygenases to promote lung carcinogenesis

Background

Epidemiological observations have demonstrated that ambient fine particulate matter with d_p < 2.5 μm (PM_2.5) as the major factor responsible for the increasing incidence of lung cancer in never-smokers. However, there are very limited experimental data to support the association of PM_2.5 with lung carcinogenesis and to compare PM_2.5 with smoking carcinogens.

Methods

To study whether PM_2.5 can contribute to lung tumorigenesis in a way similar to smoking carcinogen 4-methylnitrosamino-l-3-pyridyl-butanone (NNK) via 15-lipoxygenases (15-LOXs) reduction, normal lung epithelial cells and cancer cells were treated with NNK or PM_2.5 and then epigenetically and post-translationally examined the cellular and molecular profiles of the cells. The data were verified in lung cancer samples and a mouse lung tumor model.

Results

We found that similar to smoking carcinogen NNK, PM2.5 significantly enhanced cell proliferation, migration and invasion, but reduced the levels of 15-lipoxygenases-1 (15-LOX1) and 15-lipoxygenases-2 (15-LOX2), both of which were also obviously decreased in lung cancer tissues. 15-LOX1/15-LOX2 overexpression inhibited the oncogenic cell functions induced by PM2.5/NNK. The tumor formation and growth were significantly higher/faster in mice implanted with PM2.5- or NNK-treated NCI-H23 cells, accompanied with a reduction of 15-LOX1/15-LOX2. Moreover, 15-LOX1 expression was epigenetically regulated at methylation level by PM2.5/NNK, while both 15-LOX1 and 15-LOX2 could be significantly inhibited by a set of PM2.5/NNK-mediated microRNAs.

Conclusion

Collectively, PM2.5 can function as the smoking carcinogen NNK to induce lung tumorigenesis by inhibiting 15-LOX1/15-LOX2.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1380-z) contains supplementary material, which is available to authorized users.

Ligand-based pharmacophore mapping and virtual screening for identification of potential discoidin domain receptor 1 inhibitors

AbbreviationsADMEabsorption, distribution, metabolism, and excretionMMGB/SAmolecular mechanics generalized born surface areaIFDinduced fit dockingRTKreceptor tyrosine kinaseNSCLCnon-small-cell lung cancerATPadenosine triphosphateOPLSoptimized potential for liquid stimulationRMSDroot mean square deviationHTVShigh-throughput virtual screeningSPstandard precisionXPextra precisionOPLS-AAoptimized potential for liquid stimulation-all atomMDmolecular simulationMMEmolecular mechanics energiesSGBsurface generalized bornPOPC membrane1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine membranePDBProtein Data BankDDR1discoidin domain receptor 1DDR2discoidin domain receptor 2DDRsdiscoidin domain receptorsECMextracellular matrixTIP4Ptransferable intermolecular potential 4 pointNPTconstant particle number, pressure and temperatureRMSFroot mean square fluctuationCommunicated by Ramaswamy H. Sarma.

Pleural adverse drugs reactions and protein kinase inhibitors: Identification of suspicious targets by disproportionality analysis from VigiBase

AIMS

To evaluate the risk of pleural disorders (PD) associated with 33 protein kinase (PK) inhibitors (PKIs) through a disproportionality analysis and to identify which PKs and pathways are involved in PKI-induced PD.

METHODS

To evaluate the risk of PD, reporting odds ratios (RORs) were calculated for 33 PKIs through data registered in the World Health Organization safety report database (VigiBase). We undertook a literature review to identify PKs that were possibly involved in PD caused by PKIs. Pearson correlation coefficients (r) between RORs and affinity data of 19 PKIs were calculated to identify the cellular target most likely to be involved in PKI-induced PD.

RESULTS

A total of 235 110 individual case safety reports were extracted from the database for 33 available PKIs. Among these reports, 5001 concerned PD (2.1%). Significant and positive disproportionality for PD was found for 29 of 33 PKI included in our study with top values for dasatinib [ROR = 115.3; 95% confidence interval (CI): 110.1-120.8], bosutinib (ROR = 20.4; 95% CI: 15.8-26.4) and ponatinib (ROR = 12; 95% CI: 9.2-15.6). Correlation analyses between the product of dissociation constant and ROR highlighted possibly Lyn involvement in PD with PKI (r = 0.73, P = 0.0004).

CONCLUSIONS

Our study showed that 28 of the 33 tested PKIs were associated with PD. Besides, the study highlighted the role of Lyn in PD caused by PKIs through an immune-mediated process.

MiR-199a/b-5p Inhibits Lymphangiogenesis by Targeting Discoidin Domain Receptor 1 in Corneal Injury

Discoidin domain receptor 1 (DDR1) is involved in tumorigenesis and angiogenesis. However, its role in lymphangiogenesis has been unknown. Here, we tested whether downregulation of DDR1 expression by miR-199a/b can suppress lymphangiogenesis. We also aimed to identify miRNA target site(s) in the 3' untranslated region (UTR) of DDR1. Transfection with miR-199a/b-5p mimics reduced expression of DDR1 and tube formation in primary human dermal lymphatic endothelial cells, whereas miR-199a/b-5p inhibitors showed the opposite effects. Critically, injection of miR-199a/b-5p mimics suppressed DDR1 expression and lymphangiogenesis in a corneal alkali-burn rat model. The three well-conserved seed matched sites for miR-199a/b-5p in the DDR1 3'-UTR were targeted, and miRNA binding to at least two sites was required for DDR1 inhibition. Our data suggest that DDR1 promotes enhanced lymphangiogenesis during eye injury, and miR-199a/b-5p suppresses this activity by inhibiting DDR1 expression. Thus, this miRNA may be useful for the treatment of lymphangiogenesis-related eye diseases.

Potential association of DDR1 genetic variant with FEV1 decline by aspirin provocation in asthmatics

BACKGROUND

The discoidin domain receptor tyrosine kinase 1 (DDR1) is positioned within the major histocompatibility complex (MHC) region which plays an important role in the immune system. In addition, DDR1 has been elucidated to be downregulated during the epithelial-mesenchymal transition of bronchial epithelium.

OBJECTIVE

To investigate the potential genetic associations between DDR1 and aspirin-exacerbated respiratory disease (AERD), this study conducted association studies of DDR1 single nucleotide polymorphisms (SNPs) with AERD and the obstructive symptom of forced expiratory volume in 1 s (FEV(1)) decline after aspirin provocation.

METHODS

Nine common SNPs were genotyped in 93 AERD patients and 96 aspirin-tolerant asthma (ATA) controls. The genotype distributions of all loci were in Hardy-Weinberg equilibrium (HWE; p > .05). Results. In the results of logistic analyses using age, sex, smoking status, and atopy as covariates, DDR1 rs1264320 in the intronic region showed a potent association signal with FEV(1) decline by aspirin provocation in asthmatics of this study even after corrections for multiple testing (p = .003 and corrected p = .01). However, the variants of DDR1 were not significantly associated with the AERD development (corrected p > .05). On further comparison of FEV(1) decline by aspirin provocation between AERD and ATA, the variant rs1264320 was found to be associated with the FEV(1) decline of ATA rather than AERD.

CONCLUSION

Despite the need for further functional evaluations and replications, we conclude that DDR1 polymorphisms are not likely to contribute to predispositions of AERD, but may be potentially associated with FEV(1) decline by aspirin provocation in asthmatics.

RNA-Seq quantification of the human small airway epithelium transcriptome

Background

The small airway epithelium (SAE), the cell population that covers the human airway surface from the 6^th generation of airway branching to the alveoli, is the major site of lung disease caused by smoking. The focus of this study is to provide quantitative assessment of the SAE transcriptome in the resting state and in response to chronic cigarette smoking using massive parallel mRNA sequencing (RNA-Seq).

Results

The data demonstrate that 48% of SAE expressed genes are ubiquitous, shared with many tissues, with 52% enriched in this cell population. The most highly expressed gene, SCGB1A1, is characteristic of Clara cells, the cell type unique to the human SAE. Among other genes expressed by the SAE are those related to Clara cell differentiation, secretory mucosal defense, and mucociliary differentiation. The high sensitivity of RNA-Seq permitted quantification of gene expression related to infrequent cell populations such as neuroendocrine cells and epithelial stem/progenitor cells. Quantification of the absolute smoking-induced changes in SAE gene expression revealed that, compared to ubiquitous genes, more SAE-enriched genes responded to smoking with up-regulation, and those with the highest basal expression levels showed most dramatic changes. Smoking had no effect on SAE gene splicing, but was associated with a shift in molecular pattern from Clara cell-associated towards the mucus-secreting cell differentiation pathway with multiple features of cancer-associated molecular phenotype.

Conclusions

These observations provide insights into the unique biology of human SAE by providing quantit-ative assessment of the global transcriptome under physiological conditions and in response to the stress of chronic cigarette smoking.

Expression of the tyrosine kinase discoidin domain receptor 1 (DDR1) in human central nervous system myelin

During development of the mouse brain, the protein kinase discoidin domain receptor 1 (DDR1) is present prenatally in neurons of the proliferative areas, and postnatally, DDR1 expression is no longer detected in neurons, but a spatial-temporal expression pattern in oligodendrocytes that overlaps with the dynamics of the myelination process is detected. Notably, oligodendrocytic DDR1 expression is upregulated in mice during experimentally induced remyelination. Recently, we demonstrated that DDR1 expression is high in human brain and that there is an association between the gene and schizophrenia in a case-control study. However, data regarding expression of DDR1 in the human brain are scarce. Here, we describe the expression pattern of DDR1 in the human adult cerebral cortex. Using several immunohistological techniques and in situ hybridization, we identified DDR1 in the following: a) myelin, b) capillary endothelial cells in the gray as well as white matter, and c) in the soma of some oligodendrocytes and astrocytes in the white matter. The most important overall finding in this study was that DDR1 is present in myelin and is expressed by oligodendrocyte cells. We detected the presence of DDR1 mRNA and protein in myelin and observed that DDR1 co-localized with the classical myelin basic protein (MBP). Moreover, we found a strong positive correlation between expression levels of DDR1 and two myelin-associated genes, myelin-associated glycoprotein (MAG) and oligodendrocyte transcription factor 2 (OLIG2). These observations suggest that DDR1 could be an important constituent of myelin. Because defects in myelination are linked to several mental disorders such as schizophrenia, the function of DDR1 in the process of myelination warrants further investigation.

In vitro cardiomyogenic differentiation of adipose-derived stromal cells using transforming growth factor-beta1

Transplanting stem cells differentiated towards a cardiac lineage can regenerate cardiac muscle tissues to treat myocardial infarction. In this study, we tested the hypothesis that transforming growth factor-beta1 (TGF-beta1) induces cardiomyogenic differentiation of adipose- derived stromal cells (ADSCs) in vitro. Rat ADSCs were cultured with TGF-beta1 (10 ng ml(-1)) for 2 weeks in vitro. ADSCs cultured without TGF-beta1 served as a control. The mRNA expression of cardiac-specific gene was induced by TGF-beta1, while the control culture did not show cardiac-specific gene expression. Immunocytochemical analyses showed that a small fraction of ADSCs cultured with TGF-beta1 for 2 weeks stained positively for cardiac myosin heavy chain (MHC) and alpha-sarcomeric actin. Flow cytometric analyses showed that the proportion of cells expressing cardiac MHC increased with TGF-beta1. However, no mesenchymal differentiation (e.g., osteogenic and adipogenic differentiation) was detected other than cardiomyogenic differentiation. These results showed that TGF-beta1 induce ADSC cardiomyogenic differentiation in vitro, which could be useful for myocardial infarction stem cell therapy.

The collagen receptor DDR1 regulates cell spreading and motility by associating with myosin IIA

The spreading and migration of cells on adhesive substrates is regulated by the counterbalance of contractile and protrusive forces. Non-muscle myosin IIA, an ubiquitously expressed contractile protein and enzyme, is implicated in the regulation of cell spreading and directional migration in response to various stimuli. Here we show that discoidin domain receptor 1 (DDR1), a tyrosine kinase receptor activated by type I collagen, associates with the non-muscle myosin IIA heavy chain (NMHC-IIA) upon ligand stimulation. An association was also indicated by coimmunoprecipitation of NMHC-IIA with full-length DDR1, but not with the truncated DDR1d-isoform lacking the kinase domain. DDR1 was important for assembly of NMHC-IIA into filaments on cells plated on collagen. DDR1 expression inhibited cell spreading over collagen but promoted cell migration. By contrast, blockade of non-muscle myosin II activity by blebbistatin enhanced cell spreading but inhibited migration over collagen. We propose that myosin and DDR1 impact cell spreading and migration by regulating adhesive contacts with collagen.

Serosal inflammation (pleural and pericardial effusions) related to tyrosine kinase inhibitors

Tyrosine kinase inhibitors (TKIs) have dramatically changed the treatment of chronic myeloid leukemia (CML) and are increasingly used in other malignancies. Despite the apparent selectivity of these agents significant side effects can occur mainly due to off target kinase inhibition. Clinical consequences of serosal inflammation, including pleural and pericardial effusions, have emerged as a frequent adverse event associated with dasatinib while occurring much less frequently during imatinib and nilotinib therapy. The pathogenesis is uncertain but may involve inhibition of platelet derived growth factor or expansion of cytotoxic T and natural killer cells. The development of serosal inflammation with dasatinib poses a significant challenge to physicians, as it cannot be predicted, the time of onset is variable, and management frequently requires repeat invasive procedures.

Chemical proteomic profiles of the BCR-ABL inhibitors imatinib, nilotinib, and dasatinib reveal novel kinase and nonkinase targets

The BCR-ABL tyrosine kinase inhibitor imatinib represents the current frontline therapy in chronic myeloid leukemia. Because many patients develop imatinib resistance, 2 second-generation drugs, nilotinib and dasatinib, displaying increased potency against BCR-ABL were developed. To predict potential side effects and novel medical uses, we generated comprehensive drug-protein interaction profiles by chemical proteomics for all 3 drugs. Our studies yielded 4 major findings: (1) The interaction profiles of the 3 drugs displayed strong differences and only a small overlap covering the ABL kinases. (2) Dasatinib bound in excess of 30 Tyr and Ser/Thr kinases, including major regulators of the immune system, suggesting that dasatinib might have a particular impact on immune function. (3) Despite the high specificity of nilotinib, the receptor tyrosine kinase DDR1 was identified and validated as an additional major target. (4) The oxidoreductase NQO2 was bound and inhibited by imatinib and nilotinib at physiologically relevant drug concentrations, representing the first nonkinase target of these drugs.

Enhancement of pituitary adenoma cell invasion and adhesion is mediated by discoidin domain receptor-1

The discoidin domain receptor-1 (DDR1) tyrosine kinases are a family of cell surface receptors that bind to several types of collagen and facilitate cell adhesion that is known association with several cancers. However, no previous study has examined the expression and function of DDR1 in pituitary adenoma. Tissue microarray analysis of DDR1 expression levels in 52 pituitary adenoma tissues revealed that DDR1 expression was significantly related to hormonal background (Kruskal-Wallis test; P < 0.0001). To further elucidate the function of DDR1 in pituitary adenoma, we developed DDR1 over- and under-expressing cell lines using DDR1 clone transfection and short interfering ribonucleic acids (siRNA)-based DDR1 gene silencing, respectively, in a human pituitary adenoma cell line (HP-75). Real-time reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting confirmed that expression of both DDR1 isoforms (DDR1a and DDR1b) was elevated by clone transfection and diminished by siRNA. Matrigel invasion assays revealed that cell invasion was increased in HP-75 cells over-expressing DDR1 and decreased in cells under-expressing DDR1. Consistent with this, zymography revealed that the activation levels of matrix metalloproteinase (MMP)-2 and -9 were increased and decreased in cells over- and under-expressing DDR1, respectively. Examination of in vitro cell adhesion to collagen types I, II, III, and IV with respect to MMP-2 and -9 expression revealed that DDR1 regulated cell adhesion to collagen type I, which was responsible for accelerating secretion of MMP-2 and -9 in DDR1 over-expressing cells. Taken together, these results strongly suggest that DDR1 mediates cell invasion-related signaling between collagen type I and MMP-2 and -9 in pituitary adenoma cells.

Discoidin Domain Receptor 1–deficient Mice Are Resistant to Bleomycin-induced Lung Fibrosis

RATIONALE

Discoidin domain receptor 1 (DDR1) is a tyrosine kinase activated by native collagens. Based on previous findings showing increased DDR1 expression in bronchoalveolar lavage cells from patients with idiopathic pulmonary fibrosis, we hypothesized that DDR1 mediates disease progression after lung injury.

OBJECTIVES

To investigate the inflammatory and fibrotic responses of DDR1 knockout and wild-type mice to bleomycin-induced lung injury.

METHODS

Age- and sex-matched DDR1 knockout and wild-type C57BL/6 mice received a single intratracheal instillation of 2 U/kg bleomycin or saline, respectively. After 2 wk, lung inflammation and fibrosis were assessed using immunohistochemistry, real-time polymerase chain reaction, TUNEL assay, ELISA, fluorescence-activated cell sorting, and Western blot analysis.

MEASUREMENTS AND MAIN RESULTS

Compared with wild-type animals, DDR1-null mice were largely protected against bleomycin-induced injury. Bleomycin-induced increases in collagen protein levels and tenascin-C mRNA levels were abrogated in knockout animals. Furthermore, myofibroblast expansion and apoptosis were much lower in these animals compared with their wild-type counterparts. Absence of inflammation in knockout mice was confirmed by lavage cell count and a cytokine ELISA. Western blot analysis of injured lung tissue revealed that DDR1-null mice failed to respond to the bleomycin insult with p38 MAPK activation, which was readily observed in wild-type mice.

CONCLUSIONS

DDR1 expression is a prerequisite for the development of lung inflammation and fibrosis. Blockade of DDR1 may therefore be a novel therapeutic intervention in patients with pulmonary fibrosis.

Suppression of discoidin domain receptor 1 by RNA interference attenuates lung inflammation

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase whose ligand is collagen. Recently, we have reported the association of DDR1 in the cytokine production of human leukocytes in in vitro and in vivo expression in idiopathic pulmonary fibrosis. However, its role in in vivo inflammation has not been fully elucidated. Small interference RNA (siRNA) can induce specific suppression of in vitro and in vivo gene expression. In this study, using a bleomycin-induced pulmonary fibrosis mouse model, we administered siRNA against DDR1 transnasally and evaluated histological changes, cytokine expression, and signaling molecule activation in the lungs. Histologically, siRNA against DDR1 successfully reduced in vivo DDR1 expression and attenuated bleomycin-induced infiltration of inflammatory cells. Furthermore, it significantly reduced inflammatory cell counts and concentrations of cytokines such as MCP-1, MIP-1alpha, and MIP-2 in bronchoalveolar lavage fluid. Subsequently, bleomycin-induced up-regulation of TGF-beta in bronchoalveolar lavage fluid was significantly inhibited, and collagen deposition in the lungs was reduced. Furthermore, siRNA against DDR1 significantly inhibited bleomycin-induced P38 MAPK activation in the lungs. Considered together, we propose that DDR1 contributes to the development of bleomycin-induced pulmonary inflammation and fibrosis.

Sensing extracellular matrix: an update on discoidin domain receptor function

Discoidin Domain Receptors (DDRs) have recently emerged as non-integrin-type receptors for collagen. The two mammalian gene products Discoidin Domain Receptor 1 and -2 constitute a subfamily of tyrosine kinase receptors that are selectively expressed in a number of different cell types and organs. Upon collagen activation, DDRs regulate cell adhesion, proliferation and extracellular matrix remodeling. Here we review the various signaling pathways and cellular responses evoked by activated DDRs. Additionally, we give an overview of the more recent advances in understanding the role of DDRs in various human diseases, in particular during tumor progression, atherosclerosis, inflammation and tissue fibrosis. Furthermore, we discuss potential roles of genes homologous to mammalian DDRs identified in flies, worms and sponges. We show that the structural organization of these DDR-related genes is highly conserved throughout evolution suggesting that invertebrate DDRs may also function as receptors for collagen. By highlighting current questions about these unusual collagen receptors, we hope to attract new research on DDRs from a variety of different fields.

Involvement of discoidin domain receptor 1 in the deterioration of pulmonary sarcoidosis

The prognosis of sarcoidosis with pulmonary infiltrates differs in each case, and several cytokines are reported to contribute to its deterioration. However, the detailed mechanism has not been fully elucidated. Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase activated by collagen and associated with cytokine production from inflammatory cells. We previously reported the functional expression of DDR1 on CD14-positive bronchoalveolar lavage fluid (BALF) cells in vivo. In this study, we hypothesized that DDR1 might be associated with the deterioration of pulmonary sarcoidosis (PS), and investigated 33 patients with sarcoidosis with pulmonary infiltrates, prospectively. We found that patients with deteriorated PS showed significantly higher DDR1 expression in CD14-positive BALF cells predominant with DDR1b isoforms. Activation of DDR1 induced monocyte chemoattractant protein-1 (MCP-1) and matrix metalloproteinase-9 (MMP-9) production in a p38 mitogen-activated protein kinase-dependent manner from CD14-positive BALF cells of patients with deteriorated sarcoidosis. DDR1 activation also induced NF-kappaB nuclear translocation in CD14-positive BALF cells of patients with deteriorated PS. The inhibitor of NF-kappaB inhibited the production of MCP-1 and MMP-9. We propose that DDR1 is associated with the deterioration of pulmonary sarcoidosis.

Activation of Discoidin Domain Receptor 1 on CD14-Positive Bronchoalveolar Lavage Fluid Cells Induces Chemokine Production in Idiopathic Pulmonary Fibrosis

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase activated by collagen. We previously reported the functional expression of DDR1 on human monocyte-derived macrophages in vitro; however, information regarding its role in diseases is limited. Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease, and the lesions contain an abundance of collagen. In this study, we examined DDR1 expression on bronchoalveolar lavage fluid (BALF) cells and investigated its functionality using samples obtained from 28 IPF patients, 13 chronic obstructive pulmonary disease patients, and 14 healthy volunteers. The DDR1 expression level in CD14-positive BALF cells was higher in IPF patients than in chronic obstructive pulmonary disease patients or healthy volunteers. The predominant isoform was DDR1b in the IPF group, while DDR1a was predominant in the other two groups. Using immunohistochemical analysis, we also detected DDR1 expression on infiltrating inflammatory cells in the IPF lesion. In IPF patients, DDR1 activation induced the production of MCP-1, IL-8, MIP-1 alpha, and matrix metalloproteinase-9 (MMP-9) from CD14-positive BALF cells in a p38 MAPK-dependent manner. In contrast, DDR1 activation of CD14-positive BALF cells in the other groups did not induce the production of these chemokines or MMP-9. These chemokines and MMP-9 contribute to the development of IPF and, therefore, we suggest that DDR1 might be associated with the pathogenesis of IPF in the tissue microenvironment.

Localization of Discoidin Domain Receptors in Rat Kidney

BACKGROUND/AIM

The discoidin domain receptors (DDRs) DDR1 and DDR2 are cardinal members of a receptor tyrosine kinase subfamily, activated by collagens. They are candidate effectors in tissue injury and fibrosis. We investigated the DDR expression in normal and remnant rat kidneys.

METHODS

The DDR expression in kidney and other tissues was examined by indirect immunofluorescence, immunoblotting, and ribonuclease protection assays. The expression patterns in remnant and control kidneys were compared at 2-, 4-, and 8-week time points, following induction of injury.

RESULTS

DDR1 is expressed in basolateral membranes of select nephron segments, from the connecting tubule to the renal papilla. DDR2 is expressed in apical membranes of select nephron segments, from the loop of Henle to the macula densa. The DDR1 protein expression is upregulated within the glomeruli of remnant kidneys. The distribution of DDR2 in remnant kidneys is similar to that in controls. The DDR mRNA levels in remnant and control kidneys were not significantly different, at any time point.

CONCLUSIONS

The DDR1 localization in the rat kidney is consistent with roles in cell-matrix interactions. Upregulation within glomeruli of remnant kidneys suggests the possibility of additional roles in kidney injury. The DDR2 localization in adult rat kidneys is inconsistent with roles in cell-matrix interactions.

Exploring the Collagen-binding Site of the DDR1 Tyrosine Kinase Receptor

Discoidin domain receptors 1 and 2 (DDR1 and DDR2) are tyrosine kinase receptors activated by triple-helical collagens. Aberrant expression and signaling of these receptors have been implicated in several human diseases linked to accelerated matrix degradation and remodeling including tumor invasion, atherosclerosis and liver fibrosis. The objective of this study is to characterize the collagen-binding sites in the discoidin domains of DDR1 and DDR2 at a molecular level. We expressed glutathione S-transferase fusion proteins containing the discoidin and extracellular domains of DDR1 and DDR2 in insect cells and subjected them to a solid-phase collagen-binding assay. We found high affinity binding of the DDR extracellular domains to immobilized type I collagen and confirmed the discoidin-collagen interaction with an enzyme-linked immunosorbent assay-based read-out. Furthermore, we created a three-dimensional model of the DDR1 discoidin domain based on the related domains of blood coagulation factors V and VIII. This model predicts the presence of four neighboring, surface-exposed loops that are topologically equivalent to a major phospholipid-binding site in factors V and VIII. To test the involvement of these loops in collagen binding, we mutated individual amino acid residues to alanine or deleted short sequence stretches within these loops. We found that several residues within loop 1 (Ser-52-Thr-57) and loop 3 (Arg-105-Lys-112) as well as Ser-175 in loop 4 are critically involved in collagen binding. Our structure-function analysis of the DDR discoidin domains provides new insights into this non-integrin-mediated collagen-signaling mechanism and may ultimately lead to the design of small molecule inhibitors that interfere with aberrant DDR function.

Discoidin domain receptor 1 controls growth and adhesion of mesangial cells

Various types of collagen are known as modulators of mesangial cell proliferation. Here the function of the collagen-binding tyrosine kinase receptor discoidin domain receptor 1 (DDR1) in mesangial cells is investigated. The expression of DDR1 in the mouse kidney is confirmed by Northern analysis. In primary mesangial cells isolated from wild-type and DDR1-null mice, tyrosine phosphorylation in response to collagen-stimulation, adhesion to collagen, and cellular proliferation were measured. DDR1 phosphorylation was induced after overnight incubation of cells with type I collagen. Compared with wild-type cells, the adhesion of DDR1-null cells was drastically reduced. In contrast, DDR1-knockout cells showed significantly enhanced proliferation compared with wild-type cells. Both effects were largely independent of the collagen-binding alpha1/beta1 integrin function. This study found that the increased proliferation rate of DDR1-null cells is caused by a constitutive upregulation of p42/p44 and p38 mitogen-activated protein kinases (MAPK) activity. This is the first evidence indicating that DDR1 could be involved in the proliferative stage of renal disorders.

Ligand-induced shedding of discoidin domain receptor 1

Tyrosine kinases belonging to the discoidin domain receptor (DDR) family are activated upon stimulation with various types of collagen. In response to collagen treatment, immunoprecipitation of DDR1 with an antibody specific to the juxtamembrane region results in co-purification of a previously unrecognized tyrosine phosphorylated protein of 62 kDa molecular weight. Here, this protein is identified as C-terminal cleavage product of the full-length DDR1 receptor and a DDR1-specific shedding enzyme postulated. Shedding of DDR1 can be partially blocked by the furin inhibitor decanoyl-RVKR-chloromethylketone and completely inhibited by the hydroxamate-based inhibitor batimastat. The characteristic of the DDR1 sheddase to be blocked by batimastat suggests that it belongs to the membrane-bound matrix metalloproteinase or disintegrin and metalloproteinase family of proteases.

Mapping of epitopes in discoidin domain receptor 1 critical for collagen binding

The binding and activation of the discoidin domain receptor 1 by collagen has led to the conclusion that proteins from the extracellular matrix can directly induce receptor tyrosine kinase-mediated signaling cascades. A region in the extracellular domain of DDR1 homologous to the Dictyostelium discoideum protein discoidin-I is also present in the secreted human protein RS1. Mutations in RS1 cause retinoschisis, a genetic disorder characterized by ablation of the retina. By introducing point mutations into the discoidin domain of DDR1 at positions homologous to the retinoschisis mutations, ligand binding epitopes in the discoidin domain of DDR1 were mapped. Surprisingly, some residues only affected receptor phosphorylation, whereas others influenced both collagen-binding and receptor activation. Furthermore, two truncated DDR1 variants, lacking either the discoidin domain or the stalk region between the discoidin and transmembrane domain, were generated. We showed that (i) the discoidin domain was necessary and sufficient for collagen binding, (ii) only the region between discoidin and transmembrane domain was glycosylated, and (iii) the entire extracellular domain was essential for transmembrane signaling. Using these results, we were able to predict key sites in the collagen-binding epitope of DDR1 and to suggest a potential mechanism of signaling.