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Breast cancer is the second leading cause of cancer-associated mortality among women worldwide. Triple-negative breast cancer (TNBC) accounts for 15-20% of all breast cancers and is defined by its aggressive nature and limited treatment options. Therefore, there is an urgent need to develop effective therapies for TNBC in order to improve breast cancer outcomes, as targeted therapies have done in other subtypes of breast cancer. Discoidin domain receptor tyrosine kinase 1 (DDR1) is activated by collagens, which are important components of the tumor stroma; therefore, DDR1 may serve a critical role in the communication between tumor cells and the tumor microenvironment. The aim of the present study was to determine how tumor DDR1 regulated tumor growth by affecting tumor infiltrated T cells. First, the DDR1 expression levels from a cohort of patients with breast cancer were analyzed. The results revealed that there were higher levels of DDR1 expression in tumor tissues compared with adjacent normal tissues. Overexpression of DDR1 in 4T1 cells promoted tumor growth in vivo, while knockout of DDR1 in EMT6 cells decreased tumor growth in vivo. In addition, it was revealed that DDR1 regulated tumor growth by modulating tumor infiltrating T cells, CD4+ and CD8+. Furthermore, inhibition of DDR1 by neutralizing antibodies decreased breast cancer growth in vivo. To the best of our knowledge, the results of the present study demonstrated for the first time that DDR1 expressed on the tumor cells promoted breast tumor growth by suppressing antitumor immunity. The present findings indicated that DDR1 may not only have a critical role in the progression of breast cancer, but may also serve as a potential therapeutic target for breast cancer, particularly TNBC.

Aim This study aimed to investigate the role of discoidin domain receptor tyrosine kinase 1 (DDR1) in liver hepatocellular carcinoma (LIHC) and to evaluate its prognostic value on patient response to combination therapy. Methods In the current retrospective study, we examined the protein expression of DDR1 in various cancers by standard immunohistochemical (IHC) methods and evaluated its clinical significance in LIHC personalized treatment. Multiple online databases, including The Cancer Genome Atlas (TCGA), TIMER, GEO, ROC Plotter, and Genomics of Drug Sensitivity in Cancer (GDSC), were used. Results DDR1 protein expression was higher in LIHC than in other nine examined cancer types. Additionally, DDR1 exhibited higher expression levels in adjacent normal tissues compared to HBs-positive LIHC tissues. Analysis at single-cell resolution revealed that DDR1 was expressed primarily in epithelial cells but not in stromal and immune cells, and DDR1 expression was lower in HBs-positive LIHC cells in comparison with normal hepatocytes. Correlation of DDR1 upregulation and sorafenib resistance was observed in the patient cohort. Moreover, DDR1 expression positively correlated with the expression of inflammatory response-related genes, ECM-related genes, and collagen formation-related genes, but negatively correlated with the infiltration of CD8+ T cells, NK cells, and dendritic cells in LIHC. Conclusions Our findings suggest that DDR1 expression might be induced by collagen production-related cellular events involved in liver injury and repair, and that DDR1 overexpression might contribute to the resistance to LIHC targeted therapy and immunotherapy, highlighting DDR1 as a potential prognostic biomarker and therapeutic target. Plain Language Summary This study aimed to investigate the role of discoidin domain receptor tyrosine kinase 1 (DDR1) in liver hepatocellular carcinoma (LIHC) and to evaluate its prognostic value on patient response to combination therapy. In the current retrospective study, we examined the protein expression of DDR1 in various cancers by standard immunohistochemical (IHC) methods and evaluated its clinical significance in LIHC personalized treatment. Multiple online databases, including The Cancer Genome Atlas (TCGA), TIMER, GEO, ROC Plotter, and Genomics of Drug Sensitivity in Cancer (GDSC), were used. DDR1 protein expression was higher in LIHC than in other nine examined cancer types. Additionally, DDR1 exhibited higher expression levels in adjacent normal tissues compared to HBs-positive LIHC tissues. Analysis at single-cell resolution revealed that DDR1 was expressed primarily in epithelial cells but not stromal cells and immune cells, and DDR1 expression was lower in HBs-positive LIHC cells in comparison with normal hepatocytes. Correlation of DDR1 upregulation and sorafenib resistance was observed in patient cohort. Moreover, DDR1 expression positively correlated with the expression of inflammatory response-related genes, ECM-related genes, and collagen formation-related genes but negatively correlated with the infiltration of CD8 + T cells, NK cells, and dendritic cells in LIHC. Our findings suggest that DDR1 expression might be induced by collagen production-related cellular events involved in liver injury and repair and that DDR1 overexpression might contribute to the resistance to LIHC targeted therapy and immunotherapy, highlighting DDR1 as a potential prognostic biomarker and therapeutic target.

Triple negative breast cancer (TNBC) has received increasing attention from oncologists worldwide due to its poor prognosis and paucity of targeted therapies. MicroRNAs (miRs) are a group of small non-coding RNAs that are responsible for the post-transcriptional regulation of various target genes. The present study demonstrated that the expression of miR-199b-5p in breast cancer tissue was significantly reduced compared with that in normal breast tissues by reverse transcription-quantitative polymerase chain reaction. In addition, western blot analysis and luciferase reporter assays revealed that miR-199b-5p in TNBC cells inhibited discoidin domain receptor tyrosine kinase 1 expression by directly targeting its 3′-untranslated region. Furthermore, miR-199b-5p markedly suppressed the proliferation and invasion of TNBC cells, as demonstrated by using wound-healing, migration, invasion and proliferation assays. Collectively, these results indicate that miR-199b-5p may be a novel alternative therapeutic target for TNBC.

Immune exclusion predicts poor patient outcomes in multiple malignancies, including triple-negative breast cancer (TNBC) 1 . The extracellular matrix (ECM) contributes to immune exclusion 2 . However, strategies to reduce ECM abundance are largely ineffective or generate undesired outcomes 3 , 4 . Here we show that discoidin domain receptor 1 (DDR1), a collagen receptor with tyrosine kinase activity 5 , instigates immune exclusion by promoting collagen fibre alignment. Ablation of Ddr1 in tumours promotes the intratumoral penetration of T cells and obliterates tumour growth in mouse models of TNBC. Supporting this finding, in human TNBC the expression of DDR1 negatively correlates with the intratumoral abundance of anti-tumour T cells. The DDR1 extracellular domain (DDR1-ECD), but not its intracellular kinase domain, is required for immune exclusion. Membrane-untethered DDR1-ECD is sufficient to rescue the growth of Ddr1 -knockout tumours in immunocompetent hosts. Mechanistically, the binding of DDR1-ECD to collagen enforces aligned collagen fibres and obstructs immune infiltration. ECD-neutralizing antibodies disrupt collagen fibre alignment, mitigate immune exclusion and inhibit tumour growth in immunocompetent hosts. Together, our findings identify a mechanism for immune exclusion and suggest an immunotherapeutic target for increasing immune accessibility through reconfiguration of the tumour ECM. In mouse models of triple-negative breast cancer, the extracellular domain of the collagen receptor DDR1 has a role in tumour defence against the immune system, by aligning collagen fibres to obstruct immune infiltration.

The discoidin domain receptor tyrosine kinases DDR1 and DDR2 are distinguished from other kinase enzymes by their extracellular domains, which interact with collagen rather than with peptidic growth factors, before initiating signaling via tyrosine phosphorylation. They share significant sequence and structural homology with both the c-Kit and Bcr-Abl kinases, and so many inhibitors of those kinases are also effective. Nevertheless, there has been an extensive research effort to develop potent and specific DDR inhibitors. A key interaction for many of these compounds is H-bonding to Met-704 in a hydrophobic pocket of the DDR enzyme. The most widespread use of DDR inhibitors has been for cancer therapy, but they have also shown effectiveness in animal models of inflammatory conditions such as Alzheimer’s and Parkinson’s diseases, and in chronic renal failure and glomerulonephritis.

Discoidin domain receptor 1 (DDR1) is a member of the receptor tyrosine kinase family, and its ligand is collagen. Previous studies demonstrated that DDR1 is highly expressed in many tumors. However, its role in hepatocellular carcinoma (HCC) remains obscure. In this study, we found that DDR1 was upregulated in HCC tissues, and the expression of DDR1 in TNM stage II-IV was higher than that in TNM stage I in HCC tissues, and high DDR1 expression was associated with poor prognosis. Gene expression analysis showed that DDR1 target genes were functionally involved in HCC metastasis. DDR1 positively regulated the migration and invasion of HCC cells and promoted lung metastasis. Human Phospho-Kinase Array showed that DDR1 activated ERK/MAPK signaling pathway. Mechanically, DDR1 interacted with ARF6 and activated ARF6 through recruiting PSD4. The kinase activity of DDR1 was required for ARF6 activation and its role in metastasis. High expression of PSD4 was associated with poor prognosis in HCC. In summary, our findings indicate that DDR1 promotes HCC metastasis through collagen induced DDR1 signaling mediated PSD4/ARF6 signaling, suggesting that DDR1 and ARF6 may serve as novel prognostic biomarkers and therapeutic targets for metastatic HCC.

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.

The extracellular matrix (ECM) provides critical biochemical and biophysical cues that regulate cell behavior in health and disease. Collagens dominate in abundance and structural importance, shaping tissue-specific ECM signatures that guide cellular behavior. Two major and distinct transmembrane receptor families, integrins and discoidin domain receptors (DDRs), serve as primary sensors for collagens, yet they employ fundamentally distinct binding mechanisms and signaling kinetics. While both can activate shared downstream pathways, their functional interplay remains complex and context-dependent, with the potential to fine-tune cellular responses to ECM cues. This review deciphers the nuanced crosstalk between integrin β1 and DDRs, with a particular focus on the understudied DDR2, across physiological and pathological processes. We discuss how this interplay, which evolves from cooperative to compensatory or even antagonistic signaling, is influenced by variables,  such as tissue specificity, developmental timing, and pathological context, dictating cell adhesion, migration, and ECM remodeling. Key examples include DDRs acting as allosteric regulators to license integrin activation, their partnership in mechanotransduction during development, and their divergent roles in aging tissues, where altered collagen mechanics shift the receptor hierarchy. In pathology, the DDR-integrin axis is pivotal in fibrosis and cancer, influencing fibroblast activation, drug resistance, metastatic outgrowth, and immune suppression within the tumor microenvironment. Notably, the receptors can function both independently and synergistically; for instance, DDR2 in cancer-associated fibroblasts regulates integrin-mediated mechanosignaling to promote metastasis, while in other contexts, both receptors activate distinct survival pathways. Understanding the signaling dynamics and mechanisms of these receptors is necessary for deciphering how cells interpret ECM signals and how these mechanisms contribute to disease progression, especially in those diseases marked by collagen remodeling. This comprehension is crucial for developing novel therapeutic strategies. Emerging evidence suggests that combined targeting DDRs and integrins can synergistically overcome ECM-mediated therapy resistance, enhance immune infiltration, and reprogram pathological microenvironments, offering a promising approach for treating fibrosis and collagen-rich cancers.

The clinical management of metastatic colorectal cancer (mCRC) faces major challenges. Here, we show that nilotinib, a clinically approved drug for chronic myeloid leukaemia, strongly inhibits human CRC cell invasion in vitro and reduces their metastatic potential in intrasplenic tumour mouse models. Nilotinib acts by inhibiting the kinase activity of DDR1, a receptor tyrosine kinase for collagens, which we identified as a RAS‐independent inducer of CRC metastasis. Using quantitative phosphoproteomics, we identified BCR as a new DDR1 substrate and demonstrated that nilotinib prevents DDR1‐mediated BCR phosphorylation on Tyr177, which is important for maintaining β‐catenin transcriptional activity necessary for tumour cell invasion. DDR1 kinase inhibition also reduced the invasion of patient‐derived metastatic and circulating CRC cell lines. Collectively, our results indicate that the targeting DDR1 kinase activity with nilotinib may be beneficial for patients with mCRC. Synopsis The clinical management of metastatic colorectal cancer (mCRC) faces major challenges. Targeting the receptor for collagens DDR1 by nilotinib inhibits mCRC cells properties and paves the way to a new therapeutic strategy for mCRC. DDR1 tyrosine kinase activity promotes colorectal cancer cell invasion and metastatic properties in nude mice. BCR is a central substrate of DDR1. DDR1 activation maintains a high level of β‐catenin transcriptional activity necessary for cell invasion and metastatic progression. DDR1 pharmacological inhibition by nilotinib inhibits colorectal cancer cell invasion and metastatic properties in nude mice. Nilotinib may be of clinical interest for treatment of metastatic colorectal cancer. Graphical Abstract The clinical management of metastatic colorectal cancer (mCRC) faces major challenges. Targeting the receptor for collagens DDR1 by nilotinib inhibits mCRC cells properties and paves the way to a new therapeutic strategy for mCRC.

The tyrosine kinase family receptor of discoidin domain receptors (DDR1 and DDR2) is known to be activated by extracellular matrix collagen catalytic binding protein receptors. They play a remarkable role in cell proliferation, differentiation, migration, and cell survival. DDR1 of the DDR family regulates matrix-metalloproteinase, which causes extracellular matrix (ECM) remodeling and reconstruction during unbalanced homeostasis. Collagenous-rich DDR1 triggers the ECM of cartilage to regenerate the cartilage tissue in osteoarthritis (OA) and temporomandibular disorder (TMD). Moreover, DDR2 is prominently present in the fibroblasts, smooth muscle cells, myofibroblasts, and chondrocytes. It is crucial in generating and breaking collagen vital cellular activities like proliferation, differentiation, and adhesion mechanisms. However, the deficiency of DDR1 rather than DDR2 was detrimental in cases of OA and TMDs. DDR1 stimulated the ECM cartilage and improved bone regeneration. Based on the above information, we made an effort to outline the advancement of the utmost promising DDR1 and DDR2 regulation in bone and cartilage, also summarizing their structural, biological activity, and selectivity.