TGF-β1 promotes linear invadosome formation in hepatocellular carcinoma cells, through DDR1 up-regulation and collagen I cross-linking

Identification of Early Stage Liver Fibrosis by Modifications in the Interstitial Space Diffusive Microenvironment Using Fluorescent Single-Walled Carbon Nanotubes

During liver fibrosis, recurrent hepatic injuries lead to the accumulation of collagen and other extracellular matrix components in the interstitial space, ultimately disrupting liver functions. Early stages of liver fibrosis may be reversible, but opportunities for diagnosis at these stages are currently limited. Here, we show that the alterations of the interstitial space associated with fibrosis can be probed by tracking individual fluorescent single-walled carbon nanotubes (SWCNTs) diffusing in that space. In a mouse model of early liver fibrosis, we find that nanotubes generally explore elongated areas, whose lengths decrease as the disease progresses, even in regions where histopathological examination does not reveal fibrosis yet. Furthermore, this decrease in nanotube mobility is a purely geometrical effect as the instantaneous nanotube diffusivity stays unmodified. This work establishes the promise of SWCNTs both for diagnosing liver fibrosis at an early stage and for more in-depth studies of the biophysical effects of the disease.

Loss of p53 epigenetically modulates epithelial to mesenchymal transition in colorectal cancer

Epithelial to Mesenchymal transition (EMT) drives cancer metastasis and is governed by genetic and epigenetic alterations at multiple levels of regulation. It is well established that loss/mutation of p53 confers oncogenic function to cancer cells and promotes metastasis. Though transcription factors like ZEB1, SLUG, SNAIL and TWIST have been implied in EMT signalling, p53 mediated alterations in the epigenetic machinery accompanying EMT are not clearly understood. This work attempts to explore epigenetic signalling during EMT in colorectal cancer (CRC) cells with varying status of p53. Towards this, we have induced EMT using TGFβ on CRC cell lines with wild type, null and mutant p53 and have assayed epigenetic alterations after EMT induction. Transcriptomic profiling of the four CRC cell lines revealed that the loss of p53 confers more mesenchymal phenotype with EMT induction than its mutant counterparts. This was also accompanied by upregulation of epigenetic writer and eraser machinery suggesting an epigenetic signalling cascade triggered by TGFβ signalling in CRC. Significant agonist and antagonistic relationships observed between EMT factor SNAI1 and SNAI2 with epigenetic enzymes KDM6A/6B and the chromatin organiser SATB1 in p53 null CRC cells suggest a crosstalk between epigenetic and EMT factors. The observed epigenetic regulation of EMT factor SNAI1 correlates with poor clinical outcomes in 270 colorectal cancer patients taken from TCGA-COAD. This unique p53 dependent interplay between epigenetic enzymes and EMT factors in CRC cells may be exploited for development of synergistic therapies for CRC patients presenting to the clinic with loss of p53.

Novel insights into the role of Discoidin domain receptor 2 (DDR2) in cancer progression: a new avenue of therapeutic intervention

Discoidin domain receptors (DDRs), including DDR1 and DDR2, are a unique class of receptor tyrosine kinases (RTKs) activated by collagens at the cell-matrix boundary interface. The peculiar mode of activation makes DDRs as key cellular sensors of microenvironmental changes, with a critical role in all physiological and pathological processes governed by collagen remodeling. DDRs are widely expressed in fetal and adult tissues, and experimental and clinical evidence has shown that their expression is deregulated in cancer. Strong findings supporting the role of collagens in tumor progression and metastasis have led to renewed interest in DDRs.  However, despite an increasing number of studies, DDR biology remains poorly understood, particularly the less studied DDR2, whose involvement in cancer progression mechanisms is undoubted. Thus, the understanding of a wider range of DDR2 functions and related molecular mechanisms is expected. To date, several lines of evidence support DDR2 as a promising target in cancer therapy. Its involvement in key functions in the tumor microenvironment makes DDR2 inhibition particularly attractive to achieve simultaneous targeting of tumor and stromal cells, and tumor regression, which is beneficial for improving the response to different types of anti-cancer therapies, including chemo- and immunotherapy. This review summarizes current research on DDR2, focusing on its role in cancer progression through its involvement in tumor and stromal cell functions, and discusses findings that support the rationale for future development of direct clinical strategies targeting DDR2.

Macrophages and platelets in liver fibrosis and hepatocellular carcinoma

During fibrosis, (myo)fibroblasts deposit large amounts of extracellular matrix proteins, thereby replacing healthy functional tissue. In liver fibrosis, this leads to the loss of hepatocyte function, portal hypertension, variceal bleeding, and increased susceptibility to infection. At an early stage, liver fibrosis is a dynamic and reversible process, however, from the cirrhotic stage, there is significant progression to hepatocellular carcinoma. Both liver-resident macrophages (Kupffer cells) and monocyte-derived macrophages are important drivers of fibrosis progression, but can also induce its regression once triggers of chronic inflammation are eliminated. In liver cancer, they are attracted to the tumor site to become tumor-associated macrophages (TAMs) polarized towards a M2- anti-inflammatory/tumor-promoting phenotype. Besides their role in thrombosis and hemostasis, platelets can also stimulate fibrosis and tumor development by secreting profibrogenic factors and regulating the innate immune response, e.g., by interacting with monocytes and macrophages. Here, we review recent literature on the role of macrophages and platelets and their interplay in liver fibrosis and hepatocellular carcinoma.

TGF-β-p-STAT1-LAIR2 axis has a "self-rescue" role for exhausted CD8+ T cells in hepatocellular carcinoma

BACKGROUND

TGF-β is related to the function of T cells in the tumor microenvironment. However, the characteristics of TGF-β affecting the function of CD8+ T cells in hepatocellular carcinoma (HCC) have not been clearly resolved.

METHODS

In this study, flow cytometry, mass cytometry, immunohistochemistry, RNA-seq, single-cell RNA-seq, assay for transposase-accessible chromatin with high throughput sequencing, chromatin immunoprecipitation, and dual-luciferase reporter gene assay were used to study the regulatory effect and molecular mechanism of TGF-β on HCC infiltrating CD8+ T cells.

RESULTS

Here, we demonstrated that the overall effect of TGF-β on CD8+ T cells in HCC was to activate p-p38 to induce exhaustion, but it also initiated cell-intrinsic resistance mechanisms: 1) TGF-β upregulated the levels of p-STAT1 (S727) and promoted LAIR2 secretion; 2) the TGF-β-p-STAT1-LAIR2 axis relieved CD8+ T cells from exhaustion, which we called "self-rescue"; 3) this "self-rescue" behavior showed time and dose limitations on TGF-β stimulation, which was easily masked by stronger inhibitory signals; 4) the function of CD8+ T cells was improved by using TAK-981 to amplify "self-rescue" signal.

CONCLUSION

Our study describes a "self-rescue" mechanism of CD8+ T cells in HCC against exhaustion and the good effects from amplifying this signal.

LOXL2 in Cancer: A Two-Decade Perspective

Lysyl Oxidase Like 2 (LOXL2) belongs to the lysyl oxidase (LOX) family, which comprises five lysine tyrosylquinone (LTQ)-dependent copper amine oxidases in humans. In 2003, LOXL2 was first identified as a promoter of tumour progression and, over the course of two decades, numerous studies have firmly established its involvement in multiple cancers. Extensive research with large cohorts of human tumour samples has demonstrated that dysregulated LOXL2 expression is strongly associated with poor prognosis in patients. Moreover, investigations have revealed the association of LOXL2 with various targets affecting diverse aspects of tumour progression. Additionally, the discovery of a complex network of signalling factors acting at the transcriptional, post-transcriptional, and post-translational levels has provided insights into the mechanisms underlying the aberrant expression of LOXL2 in tumours. Furthermore, the development of genetically modified mouse models with silenced or overexpressed LOXL2 has enabled in-depth exploration of its in vivo role in various cancer models. Given the significant role of LOXL2 in numerous cancers, extensive efforts are underway to identify specific inhibitors that could potentially improve patient prognosis. In this review, we aim to provide a comprehensive overview of two decades of research on the role of LOXL2 in cancer.

Multiple Roles of LOXL2 in the Progression of Hepatocellular Carcinoma and Its Potential for Therapeutic Targeting

LOXL2, a copper-dependent amine oxidase, has emerged as a promising therapeutic target in hepatocellular carcinoma (HCC). Increased LOXL2 expression in HCC has been linked with an aggressive phenotype and represents a poor prognostic factor. Here, we focus on the mechanisms through which LOXL2 orchestrates multiple oncogenic functions in HCC development. We performed a review of the current knowledge on the roles LOXL2 performs in the modulation of the HCC tumor microenvironment, formation of premetastatic niches, and epithelial-mesenchymal transition. We also highlighted the complex interplay between LOXL2 and hypoxia, angiogenesis, and vasculogenic mimicry in HCC. At the end of the review, we summarize the current LOXL2 inhibitors and discuss their potential in HCC precision treatment.

Collagen I-DDR1 signaling promotes hepatocellular carcinoma cell stemness via Hippo signaling repression

Cancer stem cells (CSCs) are a minority population of cancer cells with stemness and multiple differentiation potentials, leading to cancer progression and therapeutic resistance. However, the concrete mechanism of CSCs in hepatocellular carcinoma (HCC) remains obscure. We found that in advanced HCC tissues, collagen I was upregulated, which is consistent with the expression of its receptor DDR1. Accordingly, high collagen I levels accompanied by high DDR1 expression are associated with poor prognoses in patients with HCC. Collagen I-induced DDR1 activation enhanced HCC cell stemness in vitro and in vivo. Mechanistically, DDR1 interacts with CD44, which acts as a co-receptor that amplifies collagen I-induced DDR1 signaling, and collagen I-DDR1 signaling antagonized Hippo signaling by facilitating the recruitment of PP2AA to MST1, leading to exaggerated YAP activation. The combined inhibition of DDR1 and YAP synergistically abrogated HCC cell stemness in vitro and tumorigenesis in vivo. A radiomic model based on T2 weighted images can noninvasively predict collagen I expression. These findings reveal the molecular basis of collagen I-DDR1 signaling inhibiting Hippo signaling and highlight the role of CD44/DDR1/YAP axis in promoting cancer cell stemness, suggesting that DDR1 and YAP may serve as novel prognostic biomarkers and therapeutic targets in HCC.

Focusing on discoidin domain receptors in premalignant and malignant liver diseases

Discoidin domain receptors (DDRs) are receptor tyrosine kinases on the membrane surface that bind to extracellular collagens, but they are rarely expressed in normal liver tissues. Recent studies have demonstrated that DDRs participate in and influence the processes underlying premalignant and malignant liver diseases. A brief overview of the potential roles of DDR1 and DDR2 in premalignant and malignant liver diseases is presented. DDR1 has proinflammatory and profibrotic benefits and promotes the invasion, migration and liver metastasis of tumour cells. However, DDR2 may play a pathogenic role in early-stage liver injury (prefibrotic stage) and a different role in chronic liver fibrosis and in metastatic liver cancer. These views are critically significant and first described in detail in this review. The main purpose of this review was to describe how DDRs act in premalignant and malignant liver diseases and their potential mechanisms through an in-depth summary of preclinical in vitro and in vivo studies. Our work aims to provide new ideas for cancer treatment and accelerate translation from bench to bedside.

Genetic and pharmacological tools to study the role of discoidin domain receptors in kidney disease

Following injury the kidney undergoes a repair process, which results in replacement of the injured tissue with little evidence of damage. However, repetitive injuries or inability of the kidney to stop the repair process result in abnormal deposition of extracellular matrix (ECM) components leading to fibrosis and organ dysfunction. The synthesis/degradation of ECM components is finely regulated by several factors, including discoidin domain receptors (DDRs). These are receptor tyrosine kinases that are activated by collagens. Upon activation, DDRs control several cell functions that, when exacerbated, contribute to kidney injury and fibrosis. DDRs are undetectable in healthy kidney, but become rapidly upregulated in several kidney fibrotic conditions, thus making them attractive anti-fibrotic targets. DDRs contribute to kidney injury and fibrosis by promoting apoptosis of injured kidney cells, stimulating the production of pro-inflammatory cytokines, and regulating the production of ECM components. They achieve these effects by activating canonical intracellular molecules or by directly interacting with nuclear chromatin and promoting the transcription of pro-fibrotic genes. The goal of this review is to highlight canonical and non-canonical mechanisms whereby DDRs contribute to kidney injury/fibrosis. This review will summarize key findings obtained using cells and mice lacking DDRs and it will discuss the discovery and development of targeted DDR small molecule- and antisense-based inhibitors. Understanding the molecular mechanisms whereby DDRs control kidney injury and fibrosis might enable us to not only develop more selective and potent inhibitors, but to also determine when DDR inhibition needs to be achieved to prevent and/or halt the development of kidney fibrosis.

TGF-β1 and Mechanical-Stretch Induction of Lysyl-Oxidase and Matrix-Metalloproteinase Expression in Synovial Fibroblasts Requires NF-κB Pathways

The imbalance in the expression of matrix metalloproteinases (MMPs) and lysyl oxidases (LOXs) in synovial fibroblasts (SFs) caused by mechanical injury and inflammatory response prevents injured anterior cruciate ligaments (ACLs) from self-healing. However, research on the effect of growth factors on SFs on regulating the microenvironment is limited. In this study, mechanical injury and exogenous transform growth factor-β1 (TGF-β1) were employed to mimic a joint-cavity microenvironment with ACL trauma. The function of the NF-κB transcription factor was further studied. The study found that the gene expression of LOXs (except LOXL-1), MMP-1, -2, and -3 in SFs was promoted by the combination of injurious mechanical stretching and TGF-β1 and that the upregulation of MMPs was higher than that of LOXs. In addition, MMP-2 activity induced by the combination of injurious stretch and TGF-β1 was inhibited by NF-κB inhibitors such as Bay11-7082 and Bay11-7085. The findings concluded that the synovium was an important regulator of the knee joint-cavity microenvironment after ACL injury and that the NF-κB pathway mediated the regulation of MMP-2 in SFs via mechanical factors and TGF-β1.

Hypoxia Alters the Proteome Profile and Enhances the Angiogenic Potential of Dental Pulp Stem Cell-Derived Exosomes

Dental pulp stem cells (DPSCs) and their exosomes (Exos) are effective treatments for regenerative medicine. Hypoxia was confirmed to improve the angiogenic potential of stem cells. However, the angiogenic effect and mechanism of hypoxia-preconditioned DPSC-Exos are poorly understood. We isolated exosomes from DPSCs under normoxia (Nor-Exos) and hypoxia (Hypo-Exos) and added them to human umbilical vein endothelial cells (HUVECs). HUVEC proliferation, migration and angiogenic capacity were assessed by CCK-8, transwell, tube formation assays, qRT-PCR and Western blot. iTRAQ-based proteomics and bioinformatic analysis were performed to investigate proteome profile differences between Nor-Exos and Hypo-Exos. Western blot, immunofluorescence and immunohistochemistry were used to detect the expression of lysyl oxidase-like 2 (LOXL2) in vitro and in vivo. Finally, we silenced LOXL2 in HUVECs and rescued tube formation with Hypo-Exos. Hypo-Exos enhanced HUVEC proliferation, migration and tube formation in vitro superior to Nor-Exos. The proteomics analysis identified 79 proteins with significantly different expression in Hypo-Exos, among which LOXL2 was verified as being upregulated in hypoxia-preconditioned DPSCs, Hypo-Exos, and inflamed dental pulp. Hypo-Exos partially rescued the inhibitory influence of LOXL2 silence on HUVEC tube formation. In conclusion, hypoxia enhanced the angiogenic potential of DPSCs-Exos and partially altered their proteome profile. LOXL2 is likely involved in Hypo-Exos mediated angiogenesis.

Discoidin Domain Receptor 1, a Potential Biomarker and Therapeutic Target in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is still one of the most lethal human cancers in the world due to its high degree of malignancy, easy invasion and metastasis, poor therapeutic effect and poor prognosis. Nowadays, there is no very effective diagnosis and treatment method. It is crucial to elucidate the underlying pathogenesis and mechanisms of HCC for developing new and effective diagnostic/prognostic biomarkers and therapies. Discoidin domain receptors (DDRs) belong to the family of transmembrane receptor tyrosine kinases (RTKs) and are recognized as playing central regulatory roles in a variety of high incidence human diseases, including tumors. DDRs have two members, DDR1 and DDR2. The role of DDR1 in several tumors has been extensively studied, and many researchers have identified it as a powerful candidate target for the development of functional and effective tumor treatment inhibitors. However, its role and mechanism in HCC are ill defined. In this article, we review the advanced insights into the progression of DDR1 in HCC, particularly the ligands and mechanisms in invasion and metastasis, which may open new avenues for the therapeutic utility of HCC.

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.

Inhibition of DDR1 reduces invasive features of human A375 melanoma, HT29 colon carcinoma and SK-HEP hepatoma cells

DDR1 is a receptor tyrosine kinases for collagen and an adverse prognostic factor in primary and metastatic tumors.Despite this, DDR1 signaling and its functional consequences in tumor development remain unclear. RT-PCR and Western blot show that A375, colon carcinoma HT29 and liver carcinoma SK-HEP human cell lines express functional DDR1 that phosphorylates in response to collagen type I. Chemical inhibition of DDR1 phosphorylation or DDR1 mRNA silencing reduced AKT and ERK phosphorylation, expression of ICAM1 and VCAM1, Ki67 and secretion of MMP9. DDR1 silenced cells showed reduced adhesion to collagen type I, MMP-dependent invasion, and chemotactic and proliferative responses to collagen type I. Our work indicates an essential role for DDR1 signaling in key prometastatic features of collagen type I in human carcinoma cells.

Tissue remodeling by invadosomes

One of the strategies used by cells to degrade and remodel the extracellular matrix (ECM) is based on invadosomes, actin-based force-producing cell–ECM contacts that function in adhesion and migration and are characterized by their capacity to mediate pericellular proteolysis of ECM components. Invadosomes found in normal cells are called podosomes, whereas invadosomes of invading cancer cells are named invadopodia. Despite their broad involvement in cell migration and in protease-dependent ECM remodeling and their detection in living organisms and in fresh tumor tissue specimens, the specific composition and dynamic behavior of podosomes and invadopodia and their functional relevance in vivo remain poorly understood. Here, we discuss recent findings that underline commonalities and peculiarities of podosome and invadopodia in terms of organization and function and propose an updated definition of these cellular protrusions, which are increasingly relevant in patho-physiological tissue remodeling.

The Yin and Yang of Discoidin Domain Receptors (DDRs): Implications in Tumor Growth and Metastasis Development

Simple Summary

The tumor microenvironment plays an important role in tumor development and metastasis. Collagens are major components of the extracellular matrix and can influence tumor development and metastasis by activating discoidin domain receptors (DDRs). This work shows the different roles of DDRs in various cancers and highlights the complexity of anti-DDR therapies in cancer treatment.

Abstract

The tumor microenvironment is a complex structure composed of the extracellular matrix (ECM) and nontumoral cells (notably cancer-associated fibroblasts (CAFs) and immune cells). Collagens are the main components of the ECM and they are extensively remodeled during tumor progression. Some collagens are ligands for the discoidin domain receptor tyrosine kinases, DDR1 and DDR2. DDRs are involved in different stages of tumor development and metastasis formation. In this review, we present the different roles of DDRs in these processes and discuss controversial findings. We conclude by describing emerging DDR inhibitory strategies, which could be used as new alternatives for the treatment of patients.

TGFβ-1 Induced Cross-Linking of the Extracellular Matrix of Primary Human Dermal Fibroblasts

Excessive cross-linking is a major factor in the resistance to the remodelling of the extracellular matrix (ECM) during fibrotic progression. The role of TGFβ signalling in impairing ECM remodelling has been demonstrated in various fibrotic models. We hypothesised that increased ECM cross-linking by TGFβ contributes to skin fibrosis in Systemic Sclerosis (SSc). Proteomics was used to identify cross-linking enzymes in the ECM of primary human dermal fibroblasts, and to compare their levels following treatment with TGFβ-1. A significant upregulation and enrichment of lysyl-oxidase-like 1, 2 and 4 and transglutaminase 2 were found. Western blotting confirmed the upregulation of lysyl hydroxylase 2 in the ECM. Increased transglutaminase activity in TGFβ-1 treated ECM was revealed from a cell-based assay. We employed a mass spectrometry-based method to identify alterations in the ECM cross-linking pattern caused by TGFβ-1. Cross-linking sites were identified in collagens I and V, fibrinogen and fibronectin. One cross-linking site in fibrinogen alpha was found only in TGFβ-treated samples. In conclusion, we have mapped novel cross-links between ECM proteins and demonstrated that activation of TGFβ signalling in cultured dermal fibroblasts upregulates multiple cross-linking enzymes in the ECM.

Roles of Lysyl Oxidase Family Members in the Tumor Microenvironment and Progression of Liver Cancer

The lysyl oxidase (LOX) family members are secreted copper-dependent amine oxidases, comprised of five paralogues: LOX and LOX-like l-4 (LOXL1-4), which are characterized by catalytic activity contributing to the remodeling of the cross-linking of the structural extracellular matrix (ECM). ECM remodeling plays a key role in the angiogenesis surrounding tumors, whereby a corrupt tumor microenvironment (TME) takes shape. Primary liver cancer includes hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), ranked as the seventh most common cancer globally, with limited therapeutic options for advanced stages. In recent years, a growing body of evidence has revealed the key roles of LOX family members in the pathogenesis of liver cancer and the shaping of TME, indicating their notable potential as therapeutic targets. We herein review the clinical value and novel biological roles of LOX family members in tumor progression and the TME of liver cancers. In addition, we highlight recent insights into their mechanisms and their potential involvement in the development of target therapy for liver cancer.

Defective membrane repair machinery impairs survival of invasive cancer cells

Cancer cells are able to reach distant tissues by migration and invasion processes. Enhanced ability to cope with physical stresses leading to cell membrane damages may offer to cancer cells high survival rate during metastasis. Consequently, down-regulation of the membrane repair machinery may lead to metastasis inhibition. We show that migration of MDA-MB-231 cells on collagen I fibrils induces disruptions of plasma membrane and pullout of membrane fragments in the wake of cells. These cells are able to reseal membrane damages thanks to annexins (Anx) that are highly expressed in invasive cancer cells. In vitro membrane repair assays reveal that MDA-MB-231 cells respond heterogeneously to membrane injury and some of them possess a very efficient repair machinery. Finally, we show that silencing of AnxA5 and AnxA6 leads to the death of migrating MDA-MB-231 cells due to major defect of the membrane repair machinery. Disturbance of the membrane repair process may therefore provide a new avenue for inhibiting cancer metastasis.

LOXL2 in cancer: regulation, downstream effectors and novel roles

Lysyl oxidase-like 2 (LOXL2) is a copper and lysine tyrosyl-quinone (LTQ)-dependent amine oxidase belonging to the lysyl oxidase (LOX) family, the canonical function of which is to catalyze the crosslinking of elastin and collagen in the extracellular matrix (ECM). Many studies have revealed that the aberrant expression of LOXL2 in multiple cancers is associated with epithelial-mesenchymal transition (EMT), metastasis, poor prognosis, chemoradiotherapy resistance, and tumor progression. LOXL2 is regulated in many ways, such as transcriptional regulation, alternative splicing, microRNA regulation, posttranslational modification, and cleavage. Beyond affecting the extracellular environment, various intracellular roles, such as oxidation and deacetylation activities in the nucleus, have been reported for LOXL2. Additionally, LOXL2 contributes to tumor cell invasion by promoting cytoskeletal reorganization. Targeting LOXL2 has become a potential therapeutic strategy to combat many types of cancers. Here, we provide an overview of the regulation and downstream effectors of LOXL2 and discuss the intracellular role of LOXL2 in cancer.

A Complex and Evolutive Character: Two Face Aspects of ECM in Tumor Progression

Tumor microenvironment, including extracellular matrix (ECM) and stromal cells, is a key player during tumor development, from initiation, growth and progression to metastasis. During all of these steps, remodeling of matrix components occurs, changing its biochemical and physical properties. The global and basic cancer ECM model is that tumors are surrounded by activated stromal cells, that remodel physiological ECM to evolve into a stiffer and more crosslinked ECM than in normal conditions, thereby increasing invasive capacities of cancer cells. In this review, we show that this too simple model does not consider the complexity, specificity and heterogeneity of each organ and tumor. First, we describe the general ECM in context of cancer. Then, we go through five invasive and most frequent cancers from different origins (breast, liver, pancreas, colon, and skin), and show that each cancer has its own specific matrix, with different stromal cells, ECM components, biochemical properties and activated signaling pathways. Furthermore, in these five cancers, we describe the dual role of tumor ECM: as a protective barrier against tumor cell proliferation and invasion, and as a major player in tumor progression. Indeed, crosstalk between tumor and stromal cells induce changes in matrix organization by remodeling ECM through invadosome formation in order to degrade it, promoting tumor progression and cell invasion. To sum up, in this review, we highlight the specificities of matrix composition in five cancers and the necessity not to consider the ECM as one general and simple entity, but one complex, dynamic and specific entity for each cancer type and subtype.

Epithelial-Mesenchymal Transition: Role in Cancer Progression and the Perspectives of Antitumor Treatment

About 90% of all malignant tumors are of epithelial nature. The epithelial tissue is characterized by a close interconnection between cells through cell-cell interactions, as well as a tight connection with the basement membrane, which is responsible for cell polarity. These interactions strictly determine the location of epithelial cells within the body and are seemingly in conflict with the metastatic potential that many cancers possess (the main criteria for highly malignant tumors). Tumor dissemination into vital organs is one of the primary causes of death in patients with cancer. Tumor dissemination is based on the so-called epithelial-mesenchymal transition (EMT), a process when epithelial cells are transformed into mesenchymal cells possessing high mobility and migration potential. More and more studies elucidating the role of the EMT in metastasis and other aspects of tumor progression are published each year, thus forming a promising field of cancer research. In this review, we examine the most recent data on the intracellular and extracellular molecular mechanisms that activate EMT and the role they play in various aspects of tumor progression, such as metastasis, apoptotic resistance, and immune evasion, aspects that have usually been attributed exclusively to cancer stem cells (CSCs). In conclusion, we provide a detailed review of the approved and promising drugs for cancer therapy that target the components of the EMT signaling pathways.

Integration of biochemical and topographic cues for the formation and spatial distribution of invadosomes in nasopharyngeal epithelial cells

Invadosomes are invasive protrusions generated by cells which can secrete matrix metalloproteinases for focal digestion of extracellular matrix. They also aid invasive cancer cells in their transmigration through vascular endothelium. However, how the physical and chemical cues in a three-dimensional (3D) system signal the spatial localization of invadosomes remains largely unknown. Here we study the topographic guidance of invadosome formation in invasive nasopharyngeal cells under the stimulation of an inflammatory cytokine, TGF-β1, using engineered gratings with different width and depth. We first report that TGF-β1 can act as an external signal to upregulate the formation of invadosomes with a random distribution on a plane 2D surface. When the cells were seeded on parallel 3D gratings of 5 µm width and 1 µm depth, most of the invadosomes aligned to the edges of the gratings, indicating a topographic cue to the control of invadosome localization. While the number of invadosomes per cell were not upregulated when the cells were seeded on 3D topography, guidance of invadosomes localization to edges is correlated with cell migration directionality on 1 µm deep gratings. Invadosomes preferentially form at edges when the cells move at a lower speed and are guided along narrow gratings. The invadosomes forming at 3D edges also have a longer half-life than those forming on a plane surface. These data suggest that there are integrated biochemical and 3D geometric cues underlying the spatial regulation of invasive structures so as to elicit efficient invasion or metastasis of cells. STATEMENT OF SIGNIFICANCE: Nasopharyngeal cells were integrated with the biological cues and matrix topography to govern the activity and spatial distribution of invadosomes. The biochemical induction of invadosome formation by TGF-β1 in nasopharyngeal cells was observed. When the cells were seeded on parallel 3D gratings, most of the invadosomes aligned to the edges of the gratings due to topographical induced invadosome localization. While the number of invadosomes per cell were not upregulated, guidance of invadosomes localization to edges is correlated with cell migration directionality on 1 µm deep gratings. Invadosomes preferentially form at edges with a higher stability when the cells are guided along narrow gratings. The integrated biochemical and 3D geometric cues could elicit efficient invasion or metastasis of cells.

Location and dynamic changes of inflammation, fibrosis, and expression levels of related genes in SiO2-induced pulmonary fibrosis in rats in vivo

Silicosis is a serious occupational disease characterized by pulmonary fibrosis, and its mechanism and progression have not been fully elucidated yet. In this study, silicosis models of rat were established by a one-time dusting method, and the rats were sacrificed after 30, 60, and 120 days (herein referred to as the 30, 60, and 120 days groups, respectively). The rats without dust exposure were used as the control. The lungs were removed to observe pathological changes using hematoxylin and eosin and Masson’s trichrome staining and transmission electron microscopy, and the degree of collagen type I and III deposition in the lung was evaluated by enzyme‐linked immunosorbent assay. The levels of malondialdehyde and superoxide dismutase were measured by spectrophotometry, and the expression levels of fibrosis-related genes (transforming growth factor beta 1, type I collagen, type III collagen) were assessed by real-time quantitative polymerase chain reaction. The results suggested that the rats in the model groups exhibited obvious collagen fibrosis and that the severity of the lung injury increased as the time after exposure to SiO₂ increased. There was a significant response to lung inflammation in the model rats, especially in the 30 days group. The degree of lipid peroxidation in bronchoalveolar lavage fluid cells and lung tissues in experiment group rats significantly increased. Among the three fibrosis-related genes, transforming growth factor beta 1was elevated in both bronchoalveolar lavage fluid cells and lung tissues of the experiment group rats, while collagen type I and III were only elevated in lung tissues. Hence, we concluded that as silicosis progressed, inflammation, fibrosis, and the expression of fibrosis-related genes showed different time-dependent changes and that a number of causal relationships existed among them.

Insulin/IGF signaling and discoidin domain receptors: An emerging functional connection

The insulin/insulin-like growth factor system (IIGFs) plays a fundamental role in the regulation of prenatal and postnatal growth, metabolism and homeostasis. As a consequence, dysregulation of this axis is associated with growth disturbance, type 2 diabetes, chronic inflammation and tumor progression. A functional crosstalk between IIGFs and discoidin domain receptors (DDRs) has been recently discovered. DDRs are non-integrin collagen receptors that canonically undergo slow and long-lasting autophosphorylation after binding to fibrillar collagen. While both DDR1 and DDR2 functionally interact with IIGFs, the crosstalk with DDR1 is so far better characterized. Notably, the IIGFs-DDR1 crosstalk presents a feed-forward mechanism, which does not require collagen binding, thus identifying novel non-canonical action of DDR1. Further studies are needed to fully explore the role of this IIGFs-DDRs functional loop as potential target in the treatment of inflammatory and neoplastic disorders.

Targeting of DDR1 with antibody-drug conjugates has antitumor effects in a mouse model of colon carcinoma

DDR1 has been identified as a cancer‐associated receptor tyrosine kinase that is highly expressed in several malignancies relative to normal tissues. Clinically approved multi‐kinase inhibitors, such as nilotinib, inhibit DDR1‐mediated tumor growth in xenograft models, suggesting DDR1 might be a potential target for cancer treatments. Here, we employed an antibody‐based strategy with a novel anti‐DDR1 antibody‐drug conjugate (ADC) for colon carcinoma treatment. We developed T₄H₁₁‐DM4, an ADC targeting DDR1 which carries the tubulin inhibitor payload DM4. Immunohistochemical analysis of a tissue microarray containing 100 colon cancer specimens revealed that DDR1 was highly expressed in 81% of tumor tissues. Meanwhile, high expression of DDR1 was associated with poor survival in patients. In vitro, T₄H₁₁‐DM4 exhibited potent anti‐proliferative activity with half maximal inhibitory concentration (IC₅₀) values in the nanomolar range in a panel of colon cancer cell lines. In vivo, the antitumor efficacy of T₄H₁₁‐DM4 was evaluated in three colon cancer cell lines expressing different levels of DDR1. T₄H₁₁‐DM4 achieved complete tumor regression at doses of 5 and 10 mg·kg⁻¹ in HT‐29 and HCT116 tumor models. Moreover, a correlation between in vivo efficacy of T₄H₁₁‐DM4 and the levels of DDR1 expression on the cell surface was observed. Tumor cell proliferation was caused by the induction of mitotic arrest, indicating that the antitumor effect in vivo was mediated by DM4. In addition, T₄H₁₁‐DM4 was efficacious in oxaliplatin‐resistant colon cancer models. In exploratory safety studies, T₄H₁₁‐DM4 exhibited no overt toxicities when multi‐doses were administered at 10 mg·kg⁻¹ into BALB/c nude mice or when a single dose up to 50 mg·kg⁻¹ was administered into BALB/c mice. Overall, our findings highlight the potential of DDR1‐targeted ADC and may facilitate the development of a new effective therapeutic strategy for colon cancer.

Quantitative proteomic profiling of extracellular matrix and site-specific collagen post-translational modifications in an in vitro model of lung fibrosis

Lung fibrosis is characterized by excessive deposition of extracellular matrix (ECM), in particular collagens, by fibroblasts in the interstitium. Transforming growth factor-β1 (TGF-β1) alters the expression of many extracellular matrix (ECM) components produced by fibroblasts, but such changes in ECM composition as well as modulation of collagen post-translational modification (PTM) levels have not been comprehensively investigated. Here, we performed mass spectrometry (MS)-based proteomics analyses to assess changes in the ECM deposited by cultured lung fibroblasts from idiopathic pulmonary fibrosis (IPF) patients upon stimulation with transforming growth factor β1 (TGF-β1). In addition to the ECM changes commonly associated with lung fibrosis, MS-based label-free quantification revealed profound effects on enzymes involved in ECM crosslinking and turnover as well as multiple positive and negative feedback mechanisms of TGF-β1 signaling. Notably, the ECM changes observed in this in vitro model correlated significantly with ECM changes observed in patient samples. Because collagens are subject to multiple PTMs with major implications in disease, we implemented a new bioinformatic platform to analyze MS data that allows for the comprehensive mapping and site-specific quantitation of collagen PTMs in crude ECM preparations. These analyses yielded a comprehensive map of prolyl and lysyl hydroxylations as well as lysyl glycosylations for 15 collagen chains. In addition, site-specific PTM analysis revealed novel sites of prolyl-3-hydroxylation and lysyl glycosylation in type I collagen. Interestingly, the results show, for the first time, that TGF-β1 can modulate prolyl-3-hydroxylation and glycosylation in a site-specific manner. Taken together, this proof of concept study not only reveals unanticipated TGF-β1 mediated regulation of collagen PTMs and other ECM components but also lays the foundation for dissecting their key roles in health and disease.

The proteomic data has been deposited to the ProteomeXchange Consortium via the MassIVE partner repository with the data set identifier MSV000082958.

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Quantitative proteomics of TGF-β-induced changes in ECM composition and collagen PTM in pulmonary fibroblasts

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TGF-β promotes crosslinking and turnover as well as complex feedback mechanisms that alter fibroblast ECM homeostasis.

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A novel bioinformatic workflow for MS data analysis enabled global mapping and quantitation of known and novel collagen PTMs

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Quantitative assessment of prolyl-3-hydroxylation site occupancy and lysine-O-glycosylation microheterogeneity

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TGF-β1 modulates collagen PTMs in a site-specific manner that may favor collagen accumulation in lung fibrosis

Dichotomy of the function of DDR1 in cells and disease progression

Discoidin domain receptors DDR1 and DDR2 are collagen receptor tyrosine kinases that have many roles in tissue development and disease progression. Under physiological conditions, DDR1 is predominantly expressed in epithelial cells and functions to maintain cell differentiation and tissue homeostasis. A switch in expression from DDR1 to DDR2 occurs during epithelial-to-mesenchymal transition. However, opposite effects of DDR1 are reported to be involved in the progression of cancer and fibrotic diseases. Accumulating evidence suggests that DDR1 is involved in pro-metastasis and pro-survival signals. This review summarizes the roles of DDR1 in epithelial cell differentiation, cell migration, cancer progression and tissues fibrosis and highlights how the dichotomous functions of DDR1 may relevant to different cell types and statues. Elucidation of the underlying mechanism of the dichotomous functions of DDR1 will help to develop DDR1 as a therapeutic target.

Downregulation of lysyl oxidase and lysyl oxidase-like protein 2 suppressed the migration and invasion of trophoblasts by activating the TGF-β/collagen pathway in preeclampsia

Preeclampsia is a pregnancy-specific disorder that is a major cause of maternal and fetal morbidity and mortality with a prevalence of 6–8% of pregnancies. Although impaired trophoblast invasion in early pregnancy is known to be closely associated with preeclampsia, the underlying mechanisms remain elusive. Here we revealed that lysyl oxidase (LOX) and LOX-like protein 2 (LOXL2) play a critical role in preeclampsia. Our results demonstrated that LOX and LOXL2 expression decreased in preeclamptic placentas. Moreover, knockdown of LOX or LOXL2 suppressed trophoblast cell migration and invasion. Mechanistically, collagen production was induced in LOX- or LOXL2-downregulated trophoblast cells through activation of the TGF-β1/Smad3 pathway. Notably, inhibition of the TGF-β1/Smad3 pathway could rescue the defects caused by LOX or LOXL2 knockdown, thereby underlining the significance of the TGF-β1/Smad3 pathway downstream of LOX and LOXL2 in trophoblast cells. Additionally, induced collagen production and activated TGF-β1/Smad3 were observed in clinical samples from preeclamptic placentas. Collectively, our study suggests that the downregulation of LOX and LOXL2 leading to reduced trophoblast cell migration and invasion through activation of the TGF-β1/Smad3/collagen pathway is relevant to preeclampsia. Thus, we proposed that LOX, LOXL2, and the TGF-β1/Smad3/collagen pathway can serve as potential markers and targets for clinical diagnosis and therapy for preeclampsia.

Cancer-associated proteins play a role in preeclampsia, a potentially life-threatening disorder of pregnancy marked by high blood pressure and protein in the urine. The causes of preeclampsia are poorly understood, but the tissue that nourishes the fetus, the placenta, is known to be involved. Knowing that for healthy placenta formation, cells called trophoblasts must show cancer cell-like behavior and invade the developing tissue, Li-Ping Jin and Kai Wang at Tongji University School of Medicine in Shanghai, China, and co-workers investigated the role of cancer-associated LOX proteins, previously linked to cell invasiveness. Preeclamptic placentas showed low LOX levels, poor trophoblast invasion, and excessive formation of collagen, an important connective tissue. Further analysis showed that this excessive collagen is broken down, becoming the diagnostic urinary protein. These results illuminate potential markers for early diagnosis and treatment of preeclampsia.

Multitasking discoidin domain receptors are involved in several and specific hallmarks of cancer

Discoidin domain receptors, DDR1 and DDR2, are two members of collagen receptor family that belong to tyrosine kinase receptor subgroup. Unlike other matrix receptor-like integrins, these collagen receptors have not been extensively studied. However, more and more studies are focusing on their involvement in cancer. These two receptors are present in several subcellular localizations such as intercellular junction or along type I collagen fibers. Consequently, they are involved in multiple cellular functions, for instance, cell cohesion, proliferation, adhesion, migration and invasion. Furthermore, various signaling pathways are associated with these multiple functions. In this review, we highlight and characterize hallmarks of cancer in which DDRs play crucial roles. We discuss recent data from studies that demonstrate the involvement of DDRs in tumor proliferation, cancer mutations, drug resistance, inflammation, neo-angiogenesis and metastasis. DDRs could be potential targets in cancer and we conclude this review by discussing the different ways to inhibits them.

Targeting invadopodia for blocking breast cancer metastasis

Dissemination of cancer cells from the primary tumor and their spread to distant sites of the body is the leading cause of mortality in metastatic cancer patients. Metastatic cancer cells invade surrounding tissues and blood vessels by forming F-actin-rich protrusions known as invadopodia, which degrade the extracellular matrix and enable invasion of tumor cells through it. Invadopodia have now been observed in vivo, and recent evidence demonstrates direct molecular links between assembly of invadopodia and cancer metastasis in both mouse models and in human patients. While significant progress has been achieved in the last decade in understanding the molecular mechanisms and signaling pathways regulating invadopodia formation and function, the application of this knowledge to development of prognostic and therapeutic approaches for cancer metastasis has not been discussed before. Here, we provide a detailed overview of current prognostic markers and tests for cancer metastasis and discuss their advantages, disadvantages, and their predicted efficiency. Using bioinformatic patient database analysis, we demonstrate, for the first time, a significant correlation between invadopodia-associated genes to breast cancer metastasis, suggesting that invadopodia could be used as both a prognostic marker and as a therapeutic target for blocking cancer metastasis. We include here a novel network interaction map of invadopodia-associated proteins with currently available inhibitors, demonstrating a central role for the recently identified EGFR-Pyk2-Src-Arg-cortactin invadopodial pathway, to which re-purposing of existent inhibitors could be used to block breast cancer metastasis. We then present an updated overview of current cancer-related clinical trials, demonstrating the negligible number of trials focusing on cancer metastasis. We also discuss the difficulties and complexity of performing cancer metastasis clinical trials, and the possible development of anti-metastasis drug resistance when using a prolonged preventive treatment with invadopodia inhibitors. This review presents a new perspective on invadopodia-mediated tumor invasiveness and may lead to the development of novel prognostic and therapeutic approaches for cancer metastasis.

Mechanical signaling through the discoidin domain receptor 1 plays a central role in tissue fibrosis

The preservation of tissue and organ architecture and function depends on tightly regulated interactions of cells with the extracellular matrix (ECM). These interactions are maintained in a dynamic equilibrium that balances intracellular, myosin-generated tension with extracellular resistance conferred by the mechanical properties of the extracellular matrix. Disturbances of this equilibrium can lead to the development of fibrotic lesions that are associated with a wide repertoire of high prevalence diseases including obstructive cardiovascular diseases, muscular dystrophy and cancer. Mechanotransduction is the process by which mechanical cues are converted into biochemical signals. At the core of mechanotransduction are sensory systems, which are frequently located at sites of cell-ECM and cell-cell contacts. As integrins (cell-ECM junctions) and cadherins (cell-cell contacts) have been extensively studied, we focus here on the properties of the discoidin domain receptor 1 (DDR1), a tyrosine kinase that mediates cell adhesion to collagen. DDR1 expression is positively associated with fibrotic lesions of heart, kidney, liver, lung and perivascular tissues. As the most common end-point of all fibrotic disorders is dysregulated collagen remodeling, we consider here the mechanical signaling functions of DDR1 in processing of fibrillar collagen that lead to tissue fibrosis.

A novel functional crosstalk between DDR1 and the IGF axis and its relevance for breast cancer

In the last decades increasing importance has been attributed to the Insulin/Insulin-like Growth Factor signaling (IIGFs) in cancer development, progression and resistance to therapy. In fact, IIGFs is often deregulated in cancer. In particular, the mitogenic insulin receptor isoform A (IR-A) and the insulin-like growth factor receptor (IGF-1R) are frequently overexpressed in cancer together with their cognate ligands IGF-1 and IGF-2. Recently, we identified discoidin domain receptor 1 (DDR1) as a new IR-A interacting protein. DDR1, a non-integrin collagen tyrosine kinase receptor, is overexpressed in several malignancies and plays a role in cancer progression and metastasis. Herein, we review recent findings indicating that DDR1 is as a novel modulator of IR and IGF-1R expression and function. DDR1 functionally interacts with IR and IGF-1R and enhances the biological actions of insulin, IGF-1 and IGF-2. Conversely, DDR1 is upregulated by IGF-1, IGF-2 and insulin through the PI3K/AKT/miR-199a-5p circuit. Furthermore, we discuss the role of the non-canonical estrogen receptor GPER1 in the DDR1-IIGFs crosstalk. These data suggest a wider role of DDR1 as a regulator of cell response to hormones, growth factors, and signals coming from the extracellular matrix.

Involvement of bone morphogenetic protein-related pathways in the effect of aucubin on the promotion of osteoblast differentiation in MG63 cells

Aucubin, an iridoid glycoside found in several plants, such as Eucommia ulmoide and Rehmannia, has various pharmacological effects. Bone formation is a complex process in which osteoblast differentiation plays an important role. This study aimed to investigate the promotion effects of aucubin on osteoblast differentiation in MG63 cells, a human osteoblast-like cell line. Aucubin not only improved osteoblast differentiation, as shown by enhanced ALP (alkaline phosphatase) concentration and mineralization in cells, but increased the expression of various cytokines, including collagen I, osteocalcin, osteopontin, integrin β1, and Osterix. Aucubin strongly enhanced the levels of BMP2 (bone morphogenetic proteins-2) in MG63 cells, which play a central role during osteoblast differentiation. Further data show that aucubin exposure after 1 day, 7 days, and 14 days enhanced the expression of Smad1, 5, and 8, and the phosphoresced levels of MAPKs (mitogen-activated protein kinases) family Erk (extracellular signal-regulated kinases), JNK (c-Jun-NH2-terminal kinases), P38, and Akt (serine/threonine protein kinase)/mTOR (mammalian target of rapamycin)/p70s6k in MG63 cells. This study shows the improved effects of aucubin on osteoblast differentiation in MG63 cells, related to the signaling of BMP2-mediated Smads (drosophila mothers against decapentaplegic proteins), MAPKs, and Akt/mTOR/p70S6K. This study indicates the potential of aucubin for osteoporosis treatment.

Functional importance of lysyl oxidase family propeptide regions

The lysyl oxidase family of proteins is primarily known for its critical role in catalyzing extracellular oxidative deamination of hydroxylysine and lysine residues in collagens, and lysine residues in elastin required for connective tissue structure and function. Lysyl oxidases have additional important biological functions in health and disease. While the enzyme domains are highly conserved, the propeptide regions are less uniform, and have biological activity, some of which are independent of their respective enzymes. This review summarizes what has been published regarding the functions of the propeptide regions of this family of proteins in the context of extracellular matrix biosynthesis, fibrosis and cancer biology. Although much has been learned, there is a need for greater attention to structure/function relationships and mechanisms to more fully understand these multifunctional proteins.

Role of the extracellular matrix in cancer-associated epithelial to mesenchymal transition phenomenon

The epithelial to mesenchymal transition (EMT) program is a crucial component in the processes of morphogenesis and embryonic development. The transition of epithelial to mesenchymal phenotype is associated with numerous structural and functional changes, including loss of cell polarity and tight cell-cell junctions, the acquisition of invasive abilities, and the expression of mesenchymal proteins. The switch between the two phenotypes is involved in human pathology and is crucial for cancer progression. Extracellular matrices (ECMs) are multi-component networks that surround cells in tissues. These networks are obligatory for cell survival, growth, and differentiation as well as tissue organization. Indeed, the ECM suprastructure, in addition to its supportive role, can process and deliver a plethora of signals to cells, which ultimately regulate their behavior. Importantly, the ECM derived signals are critically involved in the process of EMT during tumorigenesis. This review discusses the multilayer interaction between the ECM and the EMT process, focusing on contributions of discrete mediators, a strategy that may identify novel potential target molecules. Developmental Dynamics 247:368-381, 2018. © 2017 Wiley Periodicals, Inc.

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.