Discoidin Domain Receptor 1 Activation Research Articles

Lactate supports cell-autonomous ECM production to sustain metastatic behavior in prostate cancer

Extracellular matrix (ECM) is a major component of the tumor environment, promoting the establishment of a pro-invasive behavior. Such environment is supported by both tumor- and stromal-derived metabolites, particularly lactate. In prostate cancer (PCa), cancer-associated fibroblasts (CAFs) are major contributors of secreted lactate, able to impact on metabolic and transcriptional regulation in cancer cells. Here, we describe a mechanism by which CAF-secreted lactate promotes in PCa cells the expression of genes coding for the collagen family. Lactate-exploiting PCa cells rely on increased α-ketoglutarate (α-KG) which activates the α-KG-dependent collagen prolyl-4-hydroxylase (P4HA1) to support collagen hydroxylation. De novo synthetized collagen plays a signaling role by activating discoidin domain receptor 1 (DDR1), supporting stem-like and invasive features of PCa cells. Inhibition of lactate-induced collagen hydroxylation and DDR1 activation reduces the metastatic colonization of PCa cells. Overall, these results provide a new understanding of the link between collagen remodeling/signaling and the nutrient environment exploited by PCa.

#2903 Comprehensive lipidomic analysis reveals further insights into the molecular mechanism of podocyte lipotoxicity in Alport syndrome

Abstract Background and Aims The accumulation of lipids in podocytes has been shown to be a mediator of kidney injury in diabetic kidney disease (DKD). Recent animal studies have shown evidence of podocyte lipotoxicity in Alport syndrome (AS). First, discoidin domain receptor 1 (DDR1) is overactivated by excessive accumulation of α1 chain type 1 collagen in AS resulting in CD36 activation, producing direct podocyte injury by increasing reuptake of free fatty acids (FFAs). Furthermore, local overexpression of glomerular tumor necrosis factor has been observed in AS, which produces suppression of ABCA1, which affects mitochondrial function and decreases cholesterol efflux from podocytes, causing an accumulation of cholesterol and podocyte lipotoxicity. This study aimed to compare serum and urine lipidome variation between patients with AS and patients with DKD compared to healthy controls to explore the underlying molecular mechanisms of podocyte lipotoxicity in AS. Method A total of 63 samples from AS patients (COL4A3/4, n = 50, COL4A5, n = 13) were employed for this study, and compared to 15 samples from DKD patients and 20 samples from healthy volunteers considered as controls. We performed an untargeted lipidomics analysis to cover the broader spectrum of plasma and urine lipidome. Samples were analyzed by using an Agilent 1290 Infinity II Ultra-High-Performance Liquid-Chromatography system coupled to an Agilent 6546 Quadrupole Time-of-Flight Mass Spectrometer equipped with dual Agilent Jet Stream Electrospray ion source. For plasma samples, raw data matrix underwent normalization for sequence intensity correction based on the QC samples by using the support vector regression. For urine samples, normalization was performed using the Probabilistic Quotient Normalization to account for unwanted variance due to sample preparation and the analytical run. Results We generated a heatmap employing hierarchical clustering to visually represent the distinctions in statistically significant lipids across AS COL4A3/4, AS COL4A5, and DKD groups compared to the healthy control group, categorized by classes. Figure 1 summarizes the results of our study. In urine samples, a distinct decrease in acylcarnitines is evident in AS COL4A3/4 and AS COL4A5. Regarding the fatty acid (FA) lipid class, there is an increased general trend. FA 20:3 shows a meaningful increase in AS COL4A3/4 and DKD compared to the healthy control group, whereas in AS COL4A5, the trend of this lipid species is to decline when compared with COL4A3/4 and DKD levels. Concerning plasma samples, different trends were observed in AS COL4A3/4 and DKD depending on specific lipid species, while general reduced levels were reported in AS COL4A5. The phosphatidylcholine (PC) lipid species, implicated in various biological functions, display a drastic increase in the DKD urine group compared to the healthy control. The same trend is followed by AS COL4A3/4 and AS COL4A5 urine groups, with relatively similar data. Among the sphingolipids class, in urine, the overall trend of sphingomyelins (SM) for both AS COL4A3/4 and AS COL4A5 indicates a decrease in the levels of the statistically significant lipid species, with relatively similar levels between them. The neutral sphingolipids (HexCer) experience a general decrease in AS COL4A3/4, AS COL4A5 and DKD urine samples compared to the healthy control group. Lastly, the ceramides (Cer) follow a decreasing trend, where the most remarkable differences could be observed in the DKD urine group compared to the healthy controls. Conclusion Overall, the present study provided new insights into the mechanism of podocyte lipotoxicity in patients with AS. Increased specific plasma Cer and SM that are responsible for correct COL4A1 and COL4A2 formation might be responsible for aberrant COL1 expression DDR1 activation. Furthermore, specific essential FFAs that are involved in collagen synthesis are increased in AS, and might be indicating aberrant CD36 levels increasing their levels and enhancing their accumulation. Increased ABCA1 efflux activity is evident in higher extracellular levels of PC observed in urine samples from patients with AS.

Endothelial discoidin domain receptor 1 senses flow to modulate YAP activation

Mechanotransduction in endothelial cells is critical to maintain vascular homeostasis and can contribute to disease development, yet the molecules responsible for sensing flow remain largely unknown. Here, we demonstrate that the discoidin domain receptor 1 (DDR1) tyrosine kinase is a direct mechanosensor and is essential for connecting the force imposed by shear to the endothelial responses. We identify the flow-induced activation of endothelial DDR1 to be atherogenic. Shear force likely causes conformational changes of DDR1 ectodomain by unfolding its DS-like domain to expose the buried cysteine-287, whose exposure facilitates force-induced receptor oligomerization and phase separation. Upon shearing, DDR1 forms liquid-like biomolecular condensates and co-condenses with YWHAE, leading to nuclear translocation of YAP. Our findings establish a previously uncharacterized role of DDR1 in directly sensing flow, propose a conceptual framework for understanding upstream regulation of the YAP signaling, and offer a mechanism by which endothelial activation of DDR1 promotes atherosclerosis.

Collagen and Discoidin Domain Receptor 1 Partnership: A Multifaceted Role in the Regulation of Breast Carcinoma Cell Phenotype.

Type I collagen, the major components of breast interstitial stroma, is able to regulate breast carcinoma cell behavior. Discoidin domain receptor 1 (DDR1) is a type I collagen receptor playing a key role in this process. In fact, collagen/DDR1 axis is able to trigger the downregulation of cell proliferation and the activation of BIK-mediated apoptosis pathway. The aim of this review is to discuss the role of two important factors that regulate these processes. The first factor is the level of DDR1 expression. DDR1 is highly expressed in epithelial-like breast carcinoma cells, but poorly in basal-like ones. Moreover, DDR1 undergoes cleavage by MT1-MMP, which is highly expressed in basal-like breast carcinoma cells. The second factor is type I collagen remodeling since DDR1 activation depends on its fibrillar organization. Collagen remodeling is involved in the regulation of cell proliferation and apoptosis through age- and proteolysis-related modifications.

Research Progress of Discoidin Domain Receptor 1 in Breast Cancer and Other Malignant Tumors

Discoidin domain receptor 1(DDR1)is a critical member of the receptor tyrosine kinase family.It may be related to tumor invasion and metastasis,and the abnormal activation of DDR1 can lead to the occurrence and development of malignant tumors,inflammation,and fibrosis.DDR1 are involved in cell adhesion,migration,proliferation,secretion of cytokines,and remodeling of extracellular matrix,thus playing a critical role in various pathophysiological processes of the human body.In this review,we demonstrate the research progress of DDR1 in breast cancer and other malignant tumors,in order to provide a new theoretical basis for the prevention and treatment of breast cancer and other tumors.

Two-step release of kinase autoinhibition in discoidin domain receptor 1

Discoidin domain receptor 1 (DDR1) is a collagen-activated receptor tyrosine kinase with important functions in organogenesis and tissue homeostasis. Aberrant DDR1 activity contributes to the progression of human diseases, including fibrosis and cancer. How DDR1 activity is regulated is poorly understood. We investigated the function of the long intracellular juxtamembrane (JM) region of human DDR1 and found that the kinase-proximal segment, JM4, is an important regulator of kinase activity. Crystal structure analysis revealed that JM4 forms a hairpin that penetrates the kinase active site, reinforcing autoinhibition by the activation loop. Using in vitro enzymology with soluble kinase constructs, we established that release from autoinhibition occurs in two distinct steps: rapid autophosphorylation of the JM4 tyrosines, Tyr569 and Tyr586, followed by slower autophosphorylation of activation loop tyrosines. Mutation of JM4 tyrosines abolished collagen-induced DDR1 activation in cells. The insights may be used to develop allosteric, DDR1-specific, kinase inhibitors.

DDR1 (Discoidin Domain Receptor-1)-RhoA (Ras Homolog Family Member A) Axis Senses Matrix Stiffness to Promote Vascular Calcification

Vascular calcification is a pathology characterized by arterial mineralization, which is a common late-term complication of atherosclerosis that independently increases the risk of adverse cardiovascular events by fourfold. A major source of calcifying cells is transdifferentiating vascular smooth muscle cells (VSMCs). Previous studies showed that deletion of the collagen-binding receptor, DDR1 (discoidin domain receptor-1), attenuated VSMC calcification. Increased matrix stiffness drives osteogenesis, and DDR1 has been implicated in stiffness sensing in other cell types; however, the role of DDR1 as a mechanosensor in VSMCs has not been investigated. Here, we test the hypothesis that DDR1 senses increased matrix stiffness and promotes VSMC transdifferentiation and calcification. Approach and Results: Primary VSMCs isolated from Ddr1+/+ (wild-type) and Ddr1-/- (knockout) mice were studied on collagen-I-coated silicon substrates of varying stiffness, culturing in normal or calcifying medium. DDR1 expression and phosphorylation increased with increasing stiffness, as did in vitro calcification, nuclear localization of Runx2 (Runt-related transcription factor 2), and expression of other osteochondrocytic markers. By contrast, DDR1 deficient VSMCs were not responsive to stiffness and did not undergo transdifferentiation. DDR1 regulated stress fiber formation and RhoA (ras homolog family member A) activation through the RhoGEF (rho guanine nucleotide exchange factor), Vav2. Inhibition of actomyosin contractility reduced Runx2 activation and attenuated in vitro calcification in wild-type VSMCs. Finally, a novel positive feedforward loop was uncovered between DDR1 and actomyosin contractility, important in regulating DDR1 expression, clustering, and activation. This study provides mechanistic insights into DDR1 mechanosignaling and shows that DDR1 activity and actomyosin contractility are interdependent in mediating stiffness-dependent increases in VSMC calcification.

The Extracellular Matrix Receptor Discoidin Domain Receptor 1 Regulates Collagen Transcription by Translocating to the Nucleus.

The discoidin domain receptor 1 (DDR1) is activated by collagens, upregulated in injured and fibrotic kidneys, and contributes to fibrosis by regulating extracellular matrix production, but how DDR1 controls fibrosis is poorly understood. DDR1 is a receptor tyrosine kinase (RTK). RTKs can translocate to the nucleus via a nuclear localization sequence (NLS) present on the receptor itself or a ligand it is bound to. In the nucleus, RTKs regulate gene expression by binding chromatin directly or by interacting with transcription factors. To determine whether DDR1 translocates to the nucleus and whether this event is mediated by collagen-induced DDR1 activation, we generated renal cells expressing wild-type or mutant forms of DDR1 no longer able to bind collagen. Then, we determined the location of the DDR1 upon collagen stimulation. Using both biochemical assays and immunofluorescence, we analyzed the steps involved in DDR1 nuclear translocation. We show that although DDR1 and its natural ligand, collagen, lack an NLS, DDR1 is present in the nucleus of injured human and mouse kidney proximal tubules. We show that DDR1 nuclear translocation requires collagen-mediated receptor activation and interaction of DDR1 with SEC61B, a component of the Sec61 translocon, and nonmuscle myosin IIA and β-actin. Once in the nucleus, DDR1 binds to chromatin to increase the transcription of collagen IV, a major collagen upregulated in fibrosis. These findings reveal a novel mechanism whereby activated DDR1 translates to the nucleus to regulate synthesis of profibrotic molecules.

3D culture enhances chemoresistance of ALL Jurkat cell line by increasing DDR1 expression

Three dimensional (3D) culture has gradually become a research hotspot in the field of drug screening, stem cell research, and tissue engineering due to its more physiological-like morphology and function. In this study, we compared the differences of cell proliferation, population, protein expression and chemoresistance profiles between two dimensional (2D) and 3D culture of acute lymphoblastic leukemia (ALL) Jurkat cell line. Polycaprolactone (PCL) is used for 3D culture owing to its biochemical properties and compatibility. Culturing of ALL Jurkat cell line in collagen type I coated polycaprolactone scaffold for 168 h increased cell proliferation, attachment, as well as the drug resistance to cytarabine (Ara-C) and daunorubicin (DNR) without changing the original CD2+CD3+CD4+dimCD8−CD34−CD45+dim phenotype, compared to uncoated PCL scaffold and tissue culture plate systems. Molecularly, increased chemoresistance is associated with the upregulation of discoidin domain receptor 1 (DDR1) and transcription factor STAT3. Inhibition of DDR1 activity by DDR1-specific inhibitor DDR-IN-1 accelerated cell death in the presence of Ara-C, DNR or their combination. These results demonstrated that 3D culture enhances chemoresistance of ALL Jurkat cell line by increasing DDR1 expression. Importantly, the cell adhesion-mediated drug resistance induced by DDR1 in the scaffold was similar to the clinical situation, indicating the 3D culture of cancer cells recapitulate the in vivo tumor environment and this platform can be used as a promising pre-clinic drug-screen system.

Complement C1q stimulates the progression of hepatocellular tumor through the activation of discoidin domain receptor 1

C1q is known to perform several functions in addition to the role it plays in complement activation. C1q contains a collagen-like portion and DDR1 (discoidin domain receptor 1) is a well-known collagen receptor. Accordingly, we hypothesized C1q might be a novel ligand of DDR1. This study shows for the first time C1q directly induces the activation and upregulation of DDR1, and that this leads to enhanced migration and invasion of HepG2 cells. In addition, C1q was found to induce the activations of mitogen-activated protein kinases (MAPKs) and phosphoinositide 3-kinase (PI3K)/Akt signaling, and to increase the expressions of matrix metalloproteinases (MMP2 and 9). Our results reveal a relationship between C1q and DDR1 and suggest C1q-induced DDR1 activation signaling may be involved in the progression of hepatocellular carcinoma.

Inhibition of Discoidin Domain Receptor 1 Reduces Collagen-mediated Tumorigenicity in Pancreatic Ductal Adenocarcinoma.

The extracellular matrix (ECM), a principal component of pancreatic ductal adenocarcinoma (PDA), is rich in fibrillar collagens that facilitate tumor cell survival and chemoresistance. Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase that specifically binds fibrillar collagens and has been implicated in promoting cell proliferation, migration, adhesion, ECM remodeling, and response to growth factors. We found that collagen-induced activation of DDR1 stimulated protumorigenic signaling through protein tyrosine kinase 2 (PYK2) and pseudopodium-enriched atypical kinase 1 (PEAK1) in pancreatic cancer cells. Pharmacologic inhibition of DDR1 with an ATP-competitive orally available small-molecule kinase inhibitor (7rh) abrogated collagen-induced DDR1 signaling in pancreatic tumor cells and consequently reduced colony formation and migration. Furthermore, the inhibition of DDR1 with 7rh showed striking efficacy in combination with chemotherapy in orthotopic xenografts and autochthonous pancreatic tumors where it significantly reduced DDR1 activation and downstream signaling, reduced primary tumor burden, and improved chemoresponse. These data demonstrate that targeting collagen signaling in conjunction with conventional cytotoxic chemotherapy has the potential to improve outcome for pancreatic cancer patients. Mol Cancer Ther; 16(11); 2473-85. ©2017 AACR.

Abstract LB-216: Stroma-induced up-regulation of discoidin domain receptor 1 enhances peritoneal metastasis of gastric carcinomas

Abstract Introduction: Discoidin domain receptor-1 (DDR1), a receptor tyrosine kinase, is expressed by about 50% of gastric tumor cells in previous our study and is activated by fibrillar collagens, which are major components of tumor stroma. Further, it has been proposed that peritoneal metastasis is associated with high stroma content in gastric carcinomas (GCs). In this study we investigated the contribution of DDR1 activity to peritoneal metastasis of GCs. Methods: We performed the immunohistochemistry for DDR1 and Masson’s trichrome staining for accumulation of collagen bundles in 202 human GC tissues. The human GC cell lines (MKN-28 and KATO-III) were co-cultured with GCs-associated fibroblasts (CAFs), and the expression of DDR1 and signal transduction pathways were investigated by Western blot. We evaluated CAF-induced tumorigenesis of GCs cell lines and the effects of DDR1 specific inhibitor in 3D co-culture system and peritoneal seeding in xenograft animal models. Results: High stromal collagen correlated with peritoneal recurrence (P=0.004) and was positively associated with expression of DDR1 in GC tissues (P<0.001). We confirmed that co-culture with CAFs elevated the expression of DDR1 in GC cell lines. CAFs also enhanced GC cell line spheroid formation in vitro in a tumor cell DDR1-dependent manner. Co-implantation of CAFs with GC cells enhanced peritoneal tumor formation in vivo, an effect that was sensitive to pharmacologic inhibition of DDR1. Conclusion: Our findings suggest that CAF-induced elevation of tumor cells DDR1 enhances peritoneal tumorigenesis of GCs and the inhibition of DDR1 signaling is an attractive strategy for the treatment of GC peritoneal metastasis. Citation Format: Hyejin Jin, In-Hye Ham, Hye Jung Oh, Dakeun Lee, Sang-Uk Han, Rolf A. Brekken, Hoon Hur. Stroma-induced up-regulation of discoidin domain receptor 1 enhances peritoneal metastasis of gastric carcinomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-216. doi:10.1158/1538-7445.AM2017-LB-216

Effects of discoidin domain receptor 1 mediated phosphorylation of protein Tau on hypoxic-ischemic brain damage in neonatal rats

Objective To study the effects of discoidin domain receptor 1 (DDR1) mediated phosphorylation of protein Tau on hypoxic-ischemic brain damage (HIBD) in neonatal rats and its possible mechanism. Methods Sixty-four seven-day-old male specific-pathogen-free Wistar rats were randomly divided into four groups with sixteen in each: Sham, HIBD, HIBD with normal saline (HIBD+NS) and HIBD with DDR1 inhibitor (HIBD+DI) groups. A rat model of HIBD was established by subjecting the rats to left common carotid artery ligation, followed by exposing them to hypoxia for two hours. In HIBD+DI group, the inhibitor of DDR1 was immediately injected into lateral cerebroventricles of the rats following modeling. Forty-eight hours after injection, tissues of left cerebral cortex were collected from each rat to evaluate histopathological changes with HE staining. Western-blotting was used to assess the phosphorylation levels of DDR1 and protein Tau. Enzyme-linked immunosorbent assay was performed to detect the concentrations of acetylcholine. Analysis of variance or t test were used for statistical analysis. Results (1) Damages in cerebral cortex: Percentages of abnormal neurons in the rats of HIBD group were higher than those in Sham group [(80.28±4.51)% vs (10.40±2.17)%, t=39.491, P<0.01]. Pyknotic or necrotic neurons in the rats of HIBD+DI group were less than those in HIBD+NS group [(31.91±3.05)% vs (82.01±7.20)%, t=18.123, P<0.01]. (2) Phosphorylation of DDR1 and protein Tau: Levels of phosphorylated DDR1 in the cerebral cortexes of rats in HIBD group were higher than those in Sham group (0.922±0.199 vs 0.095±0.023, t=10.379, P<0.01), and those levels in HIBD+NS group were higher than those in HIBD+DI group (1.200±0.171 vs 0.255±0.111, t=11.901, P<0.01). The phosphorylation of protein Tau was similar to that of DDR1 (0.919±0.228 vs 0.194±0.224 in HIBD and Sham groups, t=7.347; 1.100±0.167 vs 0.291±0.210 in HIBD+NS and HIBD+DI groups, t=9.447; both P<0.01). (3) Levels of acetylcholine: Levels of acetylcholine in cerebral cortexes of rats in HIBD group were lower than those in Sham group [(3.685±0.472) vs (7.429±0.861) ng/g protein, t=10.781, P<0.01], and that levels in HIBD+DI group were higher than those in HIBD+NS group [(7.058±0.915) vs (2.521±0.723) ng/g protein, t=10.989, P<0.01]. Conclusions Activation of DDR1 plays a key role in enhancing the phosphorylation of protein Tau and in reducing the secretion of acetylcholine in cerebral cortexes of rats with HIBD. Inhibitor of DDR1 could protect neonatal rats from HIBD through the decreasing of protein Tau phosphorylation and increasing of acetylcholine release by inhibiting the activation of DDR1. Key words: Hypoxia-ischemia,brain; Discoidin domain receptor 1; Tau proteins; Phosphorylation; Animals, newborn; Rats

Collagen induces activation of DDR1 through lateral dimer association and phosphorylation between dimers.

The collagen-binding receptor tyrosine kinase DDR1 (discoidin domain receptor 1) is a drug target for a wide range of human diseases, but the molecular mechanism of DDR1 activation is poorly defined. Here we co-expressed different types of signalling-incompetent DDR1 mutants ('receiver') with functional DDR1 ('donor') and demonstrate phosphorylation of receiver DDR1 by donor DDR1 in response to collagen. Making use of enforced covalent DDR1 dimerisation, which does not affect receptor function, we show that receiver dimers are phosphorylated in trans by the donor; this process requires the kinase activity of the donor but not that of the receiver. The receiver ectodomain is not required, but phosphorylation in trans is abolished by mutation of the transmembrane domain. Finally, we show that mutant DDR1 that cannot bind collagen is recruited into DDR1 signalling clusters. Our results support an activation mechanism whereby collagen induces lateral association of DDR1 dimers and phosphorylation between dimers.

Discoidin Domain Receptor 1 Mediates Myosin-Dependent Collagen Contraction

Discoidin domain receptor 1 (DDR1) is a tyrosine kinase collagen adhesion receptor that mediates cell migration through association with non-muscle myosin IIA (NMIIA). Because DDR1 is implicated in cancer fibrosis, we hypothesized that DDR1 interacts with NMIIA to enable collagen compaction by traction forces. Mechanical splinting of rat dermal wounds increased DDR1 expression and collagen alignment. In periodontal ligament of DDR1 knockout mice, collagen mechanical reorganization was reduced >30%. Similarly, cultured cells with DDR1 knockdown or expressing kinase-deficient DDR1d showed 50% reduction of aligned collagen. Tractional remodeling of collagen was dependent on DDR1 clustering, activation, and interaction of the DDR1 C-terminal kinase domain with NMIIA filaments. Collagen remodeling by traction forces, DDR1 tyrosine phosphorylation, and myosin light chain phosphorylation were increased on stiff versus soft substrates. Thus, DDR1 clustering, activation, and interaction with NMIIA filaments enhance the collagen tractional remodeling that is important for collagen compaction in fibrosis.

Discoidin domain receptor 1 kinase activity is required for regulating collagen IV synthesis

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase that binds to and is activated by collagens. DDR1 expression increases following kidney injury and accumulating evidence suggests that it contributes to the progression of injury. To this end, deletion of DDR1 is beneficial in ameliorating kidney injury induced by angiotensin infusion, unilateral ureteral obstruction, or nephrotoxic nephritis. Most of the beneficial effects observed in the DDR1-null mice are attributed to reduced inflammatory cell infiltration to the site of injury, suggesting that DDR1 plays a pro-inflammatory effect. The goal of this study was to determine whether, in addition to its pro-inflammatory effect, DDR1 plays a deleterious effect in kidney injury by directly regulating extracellular matrix production. We show that DDR1-null mice have reduced deposition of glomerular collagens I and IV as well as decreased proteinuria following the partial renal ablation model of kidney injury. Using mesangial cells isolated from DDR1-null mice, we show that these cells produce significantly less collagen compared to DDR1-null cells reconstituted with wild type DDR1. Moreover, mutagenesis analysis revealed that mutations in the collagen binding site or in the kinase domain significantly reduce DDR1-mediated collagen production. Finally, we provide evidence that blocking DDR1 kinase activity with an ATP-competitive small molecule inhibitor reduces collagen production. In conclusion, our studies indicate that the kinase activity of DDR1 plays a key role in DDR1-induced collagen synthesis and suggest that blocking collagen-mediated DDR1 activation may be beneficial in fibrotic diseases.

DDR1 promotes E-cadherin stability via inhibition of integrin-β1-Src activation-mediated E-cadherin endocytosis.

Discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase of collagen, is primarily expressed in epithelial cells. Activation of DDR1 stabilises E-cadherin located on the cell membrane; however, the detailed mechanism of DDR1-stabilised E-cadherin remains unclear. We performed DDR1 knockdown (Sh-DDR1) on Mardin-Darby canine kidney cells to investigate the mechanism of DDR1-stabilised E-cadherin. Sh-DDR1 decreased junctional localisation, increased endocytosis of E-cadherin, and increased physical interactions between E-cadherin and clathrin. Treatment of the dynamin inhibitor Dyngo 4a suppressed Sh-DDR1-induced E-cadherin endocytosis. In addition, the phosphorylation level of Src tyrosine 418 was increased in Sh-DDR1 cell junctions, and inhibition of Src activity decreased Sh-DDR1-induced E-cadherin endocytosis. To characterise the molecular mechanisms, blocking integrin β1 decreased Src activity and E-cadherin junctional localisation in Sh-DDR1 cells. Photoconversion results showed that inhibition of Src activity rescued E-cadherin membrane stability and that inhibition of integrin β1-Src signalling decreased stress fibres and rescued E-cadherin membrane stability in Sh-DDR1 cells. Taken together, DDR1 stabilised membrane localisation of E-cadherin by inhibiting the integrin β1-Src-mediated clathrin-dependent endocytosis pathway.

Abstract B14: Discoidin domain receptor 1 activity drives an aggressive phenotype in gastric adenocarcinoma

Abstract Purpose: Stromal content in gastric cancer patients inversely correlates with outcome. However, underlying molecular mechanisms for these clinical observations have not been determined. Here, we investigated the contribution of the collagen receptor, discoidin domain receptor-1 (DDR1), in the aggressive phenotype of gastric cancer induced by tumor stroma. Experimental Design: We conducted immunohistochemical analyses with a tissue microarray of 217 gastric cancer specimens. We examined the effect of collagen-induced activation of DDR1 on cell signaling, tumorigenesis and cell migration in gastric cancer, and evaluated the effects of DDR1 inhibition in organotypic culture and xenograft animal models of gastric cancer. Results: High DDR1 expression in gastric cancer tissue significantly correlated with poor prognosis. Gastric cancer patients were classified into two groups based on the stromal collagen and the expression of DDR1 was significantly associated with cancer invasion and lymph node metastasis in the collagen-positive group. Decreased expression of E-cadherin was associated with cancer progression in the collagen and DDR1 positive groups. We also demonstrated that collagen activated DDR1 and increased clonogenicity and cell migration. Importantly, we demonstrated that a DDR1 inhibitor, 7rh benzamide, reduced the invasiveness of gastric cancer in organotypic culture system and suppressed tumor growth in gastric cancer xenografts. Conclusions: Taken together, these findings suggest that collagen enhances the aggressive phenotype of gastric cancer through the DDR1 signaling pathway and that inhibition of DDR1 is an attractive candidate for the therapy of aggressive gastric cancer. Citation Format: Hoon Hur, In-hye Ham, Da Keun Lee, Hye-Jin Jin, Aguilera Kristina Y., Hae Jeong Oh, Sang-Uk Han, Ji-Eun Kwon, Young Bae Kim, Ke Ding, Rolf Brekken. Discoidin domain receptor 1 activity drives an aggressive phenotype in gastric adenocarcinoma. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr B14.

Abstract 743: Tyrosine kinase discoidin domain receptor-1 (DDR1) regulates cytotoxicity of recombinant immunotoxin for cancer therapy

Abstract Discoidin domain receptor 1 (DDR1) is a collagen-activated tyrosine kinase that facilitates cell adhesion, migration, proliferation and matrix remodeling. The collagen/DDR1 axis is also thought to modulate tumor-stromal interaction and potentially affects tumor response to therapy. Mesothelin is a cell-surface protein over-expressed in several human cancers including mesothelioma, ovarian, lung, breast, and pancreatic cancers with limited expression on normal cells. RG7787 is a clinically optimized recombinant immunotoxin (RIT) consisting of a humanized anti-mesothelin Fab fused to domain III of Pseudomonas exotoxin A in which immunogenic B cell epitopes are silenced. To enhance therapeutic efficacy of RITs we conducted a kinome RNAi sensitization screen which identified DDR1 as a potential target. We hypothesized that DDR1 regulates RIT activity and its inhibition might enhance cell killing by RG7787. Knockdown of DDR1 by siRNA or treatment with inhibitor, ‘7rh’, greatly enhanced the cytotoxic activity of RG7787 in several cancer cell lines. Investigation into the mechanism of action showed DDR1 silencing was associated with a decrease in several ribosomal proteins and enhanced inhibition of protein synthesis. Induction of DDR1 expression or stimulation of DDR1 activity by collagen protected cancer cells from RG7787 killing, while DDR1 inhibition enhanced killing by RG7787. Moreover, the combination of immunotoxin and DDR1 inhibitor caused significantly more shrinkage of epithelial A431/H9 and pancreatic KLM1 tumor xenografts than either agent alone. These data demonstrate that DDR1 has a critical role in modulating immunotoxin activity. Inhibition of DDR1 represents a novel strategy to enhance therapeutic efficacy of RITs targeting mesothelin-expressing cancers. Citation Format: Fatima Ali-Rahmani, David Fitzgerald, Scott Martin, Paresma Patel, Marco Prunotto, Pinar Ormanoglu, Craig Thomas, Ira Pastan. Tyrosine kinase discoidin domain receptor-1 (DDR1) regulates cytotoxicity of recombinant immunotoxin for cancer therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 743.

Anticancer Effects of Mesothelin-Targeted Immunotoxin Therapy Are Regulated by Tyrosine Kinase DDR1.

Recombinant immunotoxins (RIT) have been highly successful in cancer therapy due, in part, to the high cancer-specific expression of cell surface antigens such as mesothelin, which is overexpressed in mesothelioma, ovarian, lung, breast, and pancreatic cancers, but is limited in normal cells. RG7787 is a clinically optimized RIT consisting of a humanized anti-mesothelin Fab fused to domain III of Pseudomonas exotoxin A, in which immunogenic B-cell epitopes are silenced. To enhance the therapeutic efficacy of RITs, we conducted a kinome RNAi sensitization screen, which identified discoidin domain receptor 1 (DDR1), a collagen-activated tyrosine kinase, as a potential target. The collagen/DDR1 axis is implicated in tumor-stromal interactions and potentially affects tumor response to therapy. Therefore, we investigated the effects of DDR1 on RIT. Knockdown of DDR1 by siRNA or treatment with inhibitor, 7rh, greatly enhanced the cytotoxic activity of RG7787 in several cancer cell lines. Investigation into the mechanism of action showed DDR1 silencing was associated with decreased expression of several ribosomal proteins and enhanced inhibition of protein synthesis. Conversely, induction of DDR1 expression or collagen-stimulated DDR1 activity protected cancer cells from RG7787 killing. Moreover, the combination of RG7787 and DDR1 inhibitor caused greater shrinkage of tumor xenografts than either agent alone. These data demonstrate that DDR1 is a key modulator of RIT activity and represents a novel therapeutic strategy to improve targeting of mesothelin-expressing cancers.