Discoidin domain receptor 2 mediates tumor cell cycle arrest induced by fibrillar collagen

Anti-cancer mechanisms of natural isoflavones against melanoma

The incidence of skin-related neoplasms has generally increased in recent years. Melanoma arises from malignant mutations in melanocytes in the basal layer of the epidermis and is a fatal skin cancer that seriously threatens human health. Isoflavones are polyphenolic compounds widely present in legumes and have drawn scientists' attention, because they have good efficacy against a variety of cancers, including melanoma, without significant toxic side effects and resistance. In this review article, we summarize the research progress of isoflavones in melanoma, including anti-melanoma roles and mechanisms of isoflavones via inhibition of tyrosinase activity, melanogenesis, melanoma cell growth, invasion of melanoma cells, and induction of apoptosis in melanoma cells. This information is important for the prevention, clinical treatment, and prognosis and survival of melanoma.

Extracellular matrix remodeling in tumor progression and immune escape: from mechanisms to treatments

The malignant tumor is a multi-etiological, systemic and complex disease characterized by uncontrolled cell proliferation and distant metastasis. Anticancer treatments including adjuvant therapies and targeted therapies are effective in eliminating cancer cells but in a limited number of patients. Increasing evidence suggests that the extracellular matrix (ECM) plays an important role in tumor development through changes in macromolecule components, degradation enzymes and stiffness. These variations are under the control of cellular components in tumor tissue via the aberrant activation of signaling pathways, the interaction of the ECM components to multiple surface receptors, and mechanical impact. Additionally, the ECM shaped by cancer regulates immune cells which results in an immune suppressive microenvironment and hinders the efficacy of immunotherapies. Thus, the ECM acts as a barrier to protect cancer from treatments and supports tumor progression. Nevertheless, the profound regulatory network of the ECM remodeling hampers the design of individualized antitumor treatment. Here, we elaborate on the composition of the malignant ECM, and discuss the specific mechanisms of the ECM remodeling. Precisely, we highlight the impact of the ECM remodeling on tumor development, including proliferation, anoikis, metastasis, angiogenesis, lymphangiogenesis, and immune escape. Finally, we emphasize ECM "normalization" as a potential strategy for anti-malignant treatment.

Discoidin Domain Receptor 2: A New Target in Cancer

BACKGROUND

Discoidin domain receptor is a new and unique type of receptor tyrosine kinases, which binds to collagen, the main compose of an extracellular matrix. DDR1 was identified to mediate cell aggregation, and dysregulation of DDR2 has also been shown to be involved in tumor pathogenesis, although its role in cancer development and progression remains controversial.

SUMMARY

Abnormal expression and mutations of DDR2 have been reported in several cancer types and its participation in different aspects of tumor progression, including proliferation, migration, invasion, metastasis, epithelial-mesenchymal transition, and chemotherapy resistance. Moreover, novel DDR2 inhibitors have been designed and indicate a therapeutic effect for the cancer treatment. Key Messages: In this review, we summarize the current knowledge on the role of DDR2 in cancer promotion and the potential therapeutic value of targeting DDR2.

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.

Complex roles of discoidin domain receptor tyrosine kinases in cancer

Discoidin domain receptors, DDR1 and DDR2 are members of the receptor tyrosine kinase (RTK) family that serves as a non-integrin collagen receptor and were initially identified as critical regulators of embryonic development and cellular homeostasis. In recent years, numerous studies have focused on the role of these receptors in disease development, in particular, cancer where they have been reported to augment ECM remodeling, invasion, drug resistance to facilitate tumor progression and metastasis. Interestingly, accumulating evidence also suggests that DDRs promote apoptosis and suppress tumor progression in various human cancers due to which their functions in cancer remain ill-defined and presents a case of an interesting therapeutic target. The present review has discussed the role of DDRs in tumorigenesis and the metastasis.

Discoidin domain receptors orchestrate cancer progression: A focus on cancer therapies

Discoidin domain receptors (DDR), including DDR1 and DDR2, are special types of the transmembrane receptor tyrosine kinase superfamily. DDR are activated by binding to the triple-helical collagen and, in turn, DDR can activate signal transduction pathways that regulate cell-collagen interactions involved in multiple physiological and pathological processes such as cell proliferation, migration, apoptosis, and cytokine secretion. Recently, DDR have been found to contribute to various diseases, including cancer. In addition, aberrant expressions of DDR have been reported in various human cancers, which indicates that DDR1 and DDR2 could be new targets for cancer treatment. Considerable effort has been made to design DDR inhibitors and several molecules have shown therapeutic effects in pre-clinical models. In this article, we review the recent literature on the role of DDR in cancer progression, the development status of DDR inhibitors, and the clinical potential of targeting DDR in cancer therapies.

Chromatin run-on sequencing analysis finds that ECM remodeling plays an important role in canine hemangiosarcoma pathogenesis

Background

Canine visceral hemangiosarcoma (HSA) is a highly aggressive cancer of endothelial origin that closely resembles visceral angiosarcoma in humans, both clinically and histopathologically. Currently there is an unmet need for new diagnostics and therapies for both forms of this disease. The goal of this study was to utilize Chromatin run-on sequencing (ChRO-seq) and immunohistochemistry (IHC) to identify gene and protein expression signatures that may be important drivers of HSA progression.

Results

ChRO-seq was performed on tissue isolated from 17 HSA samples and 4 normal splenic samples. Computational analysis was then used to identify differentially expressed genes and these factors were subjected to gene ontology analysis. ChRO-seq analysis revealed over a thousand differentially expressed genes in HSA tissue compared with normal splenic tissue (FDR < 0.005). Interestingly, the majority of genes overexpressed in HSA tumor tissue were associated with extracellular matrix (ECM) remodeling. This observation correlated well with our histological analysis, which found that HSA tumors contain a rich and complex collagen network. Additionally, we characterized the protein expression patterns of two highly overexpressed molecules identified in ChRO-seq analysis, podoplanin (PDPN) and laminin alpha 4 (LAMA4). We found that the expression of these two ECM-associated factors appeared to be largely limited to transformed endothelial cells within the HSA lesions.

Conclusion

Outcomes from this study suggest that ECM remodeling plays an important role in HSA progression. Additionally, our study identified two potential novel biomarkers of HSA, PDPN and LAMA4. Interestingly, given that function-blocking anti-PDPN antibodies have shown anti-tumor effects in mouse models of canine melanoma, our studies raise the possibility that these types of therapeutic strategies could potentially be developed for treating canine HSA.

LRP-1 Promotes Colon Cancer Cell Proliferation in 3D Collagen Matrices by Mediating DDR1 Endocytosis

Low density lipoprotein receptor related protein-1 (LRP-1) is a large ubiquitous endocytic receptor mediating the clearance of various molecules from the extracellular matrix. Several studies have shown that LRP-1 plays crucial roles during tumorigenesis functioning as a main signal pathway regulator, especially by interacting with other cell-surface receptors. Discoïdin Domain Receptors (DDRs), type I collagen receptors with tyrosine kinase activity, have previously been associated with tumor invasion and aggressiveness in diverse tumor environments. Here, we addressed whether it could exist functional interplays between LRP-1 and DDR1 to control colon carcinoma cell behavior in three-dimensional (3D) collagen matrices. We found that LRP-1 established tight molecular connections with DDR1 at the plasma membrane in colon cancer cells. In this tumor context, we provide evidence that LRP-1 regulates by endocytosis the cell surface levels of DDR1 expression. The LRP-1 mediated endocytosis of DDR1 increased cell proliferation by promoting cell cycle progression into S phase and decreasing apoptosis. In this study, we identified a new molecular way that controls the cell-surface expression of DDR1 and consequently the colon carcinoma cell proliferation and apoptosis and highlighted an additional mechanism by which LRP-1 carries out its sensor activity of the tumor microenvironment.

Coordinated regulation of cell survival and cell cycle pathways by DDR2-dependent SRF transcription factor in cardiac fibroblasts

Relative resistance to apoptosis and the ability to proliferate and produce a collagen-rich scar determine the critical role of cardiac fibroblasts in wound healing and tissue remodeling following myocardial injury. Identification of cardiac fibroblast-specific factors and mechanisms underlying these aspects of cardiac fibroblast function is therefore of considerable scientific and clinical interest. In the present study, gene knockdown and overexpression approaches and promoter binding assays showed that discoidin domain receptor 2 (DDR2), a mesenchymal cell-specific collagen receptor tyrosine kinase localized predominantly in fibroblasts in the heart, acts via ERK1/2 MAPK-activated serum response factor (SRF) transcription factor to enhance the expression of antiapoptotic cIAP2 in cardiac fibroblasts, conferring resistance against oxidative injury. Furthermore, DDR2 was found to act via ERK1/2 MAPK-activated SRF to transcriptionally upregulate Skp2 that in turn facilitated post-translational degradation of p27, the cyclin-dependent kinase inhibitor that causes cell cycle arrest, to promote G₁-S transition, as evidenced by Rb phosphorylation, increased proliferating cell nuclear antigen (PCNA) levels, and flow cytometry. DDR2-dependent ERK1/2 MAPK activation also suppressed forkhead box O 3a (FoxO3a)-mediated transcriptional induction of p27. Inhibition of the binding of collagen type I to DDR2 using WRG-28 indicated the obligate role of collagen type I in the activation of DDR2 and its regulatory role in cell survival and cell cycle protein expression. Notably, DDR2 levels positively correlated with SRF, cIAP2, and PCNA levels in cardiac fibroblasts from spontaneously hypertensive rats. To conclude, DDR2-mediated ERK1/2 MAPK activation facilitates coordinated regulation of cell survival and cell cycle progression in cardiac fibroblasts via SRF.NEW & NOTEWORTHY Relative resistance to apoptosis and the ability to proliferate and produce a collagen-rich scar enable cardiac fibroblasts to play a central role in myocardial response to injury. This study reports novel findings that mitogen-stimulated cardiac fibroblasts exploit a common regulatory mechanism involving collagen receptor (DDR2)-dependent activation of ERK1/2 MAPK and serum response factor to achieve coordinated regulation of apoptosis resistance and cell cycle progression, which could facilitate their survival and function in the injured myocardium.

Modulation of receptor binding to collagen by glycosylated 5-hydroxylysine: Chemical biology approaches made feasible by Carpino's Fmoc group

The creation of the 9-fluorenylmethoxycarbonyl (Fmoc) group by the Carpino laboratory facilitated the synthesis of peptides containing acid-sensitive groups, such as O-linked glycosides. To fully investigative collagen biochemistry, one needs to assemble peptides that possess glycosylated 5-hydroxylysine (Hyl). A convenient method for the synthesis of Fmoc-Hyl(ε-tert-butyloxycarbonyl (Boc),O-tert-butyldimethylsilyl (TBDMS)) and efficient methods for the synthesis of Fmoc-Hyl[ε-Boc,O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)] have been developed. Glycosylated Fmoc-Hyl derivatives were used to construct a series of types I-IV collagen-model triple-helical peptides (THPs) that incorporated known or proposed receptor binding sites. Glycosylation of Hyl was found to strongly down-regulate the binding of CD44 and the α3β1 integrin to collagen, while the impact on α2β1 integrin binding was more modest. Molecular modeling of integrin binding indicated that Hyl glycosylation directly impacted the association between the α3β1 integrin metal ion-dependent adhesion site (MIDAS) and the receptor binding site within type IV collagen. The Fmoc solid-phase strategy ultimately allowed for chemical biology approaches to be utilized to study tumor cell interactions with glycosylated collagen sequences and document the modulation of receptor interactions by Hyl posttranslational modification.

Discoidin Domain Receptors, DDR1b and DDR2, Promote Tumour Growth within Collagen but DDR1b Suppresses Experimental Lung Metastasis in HT1080 Xenografts

The Discoidin Domain Receptors (DDRs) constitute a unique set of receptor tyrosine kinases that signal in response to collagen. Using an inducible expression system in human HT1080 fibrosarcoma cells, we investigated the role of DDR1b and DDR2 on primary tumour growth and experimental lung metastases. Neither DDR1b nor DDR2 expression altered tumour growth at the primary site. However, implantation of DDR1b- or DDR2-expressing HT1080 cells with collagen I significantly accelerated tumour growth rate, an effect that could not be observed with collagen I in the absence of DDR induction. Interestingly, DDR1b, but not DDR2, completely hindered the ability of HT1080 cells to form lung colonies after intravenous inoculation, suggesting a differential role for DDR1b in primary tumour growth and lung colonization. Analyses of tumour extracts revealed specific alterations in Hippo pathway core components, as a function of DDR and collagen expression, that were associated with stimulation of tumour growth by DDRs and collagen I. Collectively, these findings identified divergent effects of DDRs on primary tumour growth and experimental lung metastasis in the HT1080 xenograft model and highlight the critical role of fibrillar collagen and DDRs in supporting the growth of tumours thriving within a collagen-rich stroma.

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.

Discoidin domain receptors: Micro insights into macro assemblies

Assembly of cell-surface receptors into specific oligomeric states and/or clusters before and after ligand binding is an important feature governing their biological function. Receptor oligomerization can be mediated by specific domains of the receptor, ligand binding, configurational changes or other interacting molecules. In this review we summarize our understanding of the oligomeric state of discoidin domain receptors (DDR1 and DDR2), which belong to the receptor tyrosine kinase family (RTK). DDRs form an interesting system from an oligomerization perspective as their ligand collagen(s) can also undergo supramolecular assembly to form fibrils. Even though DDR1 and DDR2 differ in the domains responsible to form ligand-free dimers they share similarities in binding to soluble, monomeric collagen. However, only DDR1b forms globular clusters in response to monomeric collagen and not DDR2. Interestingly, both DDR1 and DDR2 are assembled into linear clusters by the collagen fibril. Formation of these clusters is important for receptor phosphorylation and is mediated in part by other membrane components. We summarize how the oligomeric status of DDRs shares similarities with other members of the RTK family and with collagen receptors. Unraveling the multiple macro-molecular configurations adopted by this receptor-ligand pair can provide novel insights into the intricacies of cell-matrix interactions.

DDR1 and MT1-MMP Expression Levels Are Determinant for Triggering BIK-Mediated Apoptosis by 3D Type I Collagen Matrix in Invasive Basal-Like Breast Carcinoma Cells

Type I collagen is the major adhesive component in breast interstitial stroma, which represents the first barrier against tumor cell invasion after basement-membrane degradation. Among cellular receptors, type I collagen is able to activate discoidin domain receptors DDR1 and DDR2. We have previously shown that in 3D collagen matrix, DDR1 plays a key role as it promotes cell growth suppression and apoptosis through the upregulation of the pro-apoptotic mediator BIK in noninvasive luminal-like breast carcinoma cells. We have also shown that MT1-MMP is able to rescue these cells and protect them against the effects induced by collagen/DDR1/BIK axis. Our data suggested that the protective effect of MT1-MMP might be mediated through the degradation of type I collagen and/or DDR1 cleavage. Decreased DDR1 expression has been associated with the epithelial to mesenchymal transition process in breast cancer, and its overexpression in aggressive basal-like breast cancer cells reduces their invasiveness in 3D cultures and in vivo. In the present work, we propose to study the role of MT1-MMP in the resistance against collagen-induced apoptosis in basal-like breast carcinoma MDA-MB-231 cells. We aimed to investigate whether MT1-MMP depletion is able to restore apoptosis mediated by collagen/DDR1/BIK axis and to verify if such depletion is able to restore full-length DDR1 expression and phosphorylation. ShRNA strategy against MT1-MMP mRNA was able to partially restore full length DDR1 expression and phosphorylation. This was accompanied by a decrease in cell growth and an upregulation of BIK expression. This suggested that MT1-MMP expression in basal-like breast carcinoma cells, in addition to a low basal level of DDR1 expression, protects these cells against collagen-induced apoptosis via DDR1 cleavage. Since DDR1 was moderately expressed in MDA-MB-231 cells, we then investigated whether overexpression of DDR1 could be able to increase its ability to suppress cell growth and to induce apoptosis. Data showed that overexpression of DDR1 induced a decrease in cell growth and an increase in BIK expression, suggesting that moderate expression level of full length DDR1 in basal-like breast carcinoma provides them with a capacity to resist to collagen-induced cell growth suppression and apoptosis. Finally, the combined overexpression of DDR1 and depletion of MT1-MMP in MDA-MB-231 cells synergistically increased collagen-induced cell growth suppression and apoptosis to a level similar to that observed in luminal breast carcinoma. Taken together, our data suggest that during the acquisition of mesenchymal features, the low level of DDR1 expression should be considered as an important biomarker in the prognosis of basal-like breast carcinoma, conferring them a high rate of cell growth and resistance to BIK-mediated apoptosis induced by the stromal collagen.

A structural prospective for collagen receptors such as DDR and their binding of the collagen fibril

The structure of the collagen fibril surface directly effects and possibly assists the management of collagen receptor interactions. An important class of collagen receptors, the receptor tyrosine kinases of the Discoidin Domain Receptor family (DDR1 and DDR2), are differentially activated by specific collagen types and play important roles in cell adhesion, migration, proliferation, and matrix remodeling. This review discusses their structure and function as it pertains directly to the fibrillar collagen structure with which they interact far more readily than they do with isolated molecular collagen. This prospective provides further insight into the mechanisms of activation and rational cellular control of this important class of receptors while also providing a comparison of DDR-collagen interactions with other receptors such as integrin and GPVI. When improperly regulated, DDR activation can lead to abnormal cellular proliferation activities such as in cancer. Hence how and when the DDRs associate with the major basis of mammalian tissue infrastructure, fibrillar collagen, should be of keen interest.

DDR1 and DDR2 in skin

DDR1 and DDR2 are expressed in skin but their expression differs according to the skin compartment, epidermis, dermis, hypodermis and to the embryonic origin of the cells. In skin, it seems that during physiological processes such as wound healing or pathological processes such as tumorigenesis or systemic sclerosis development only one of the DDR is dysregulated. Furthermore, the altered DDR in pathological process is not necessarily the DDR implicated in basal homeostasis. Indeed, in epidermis, while DDR1 is the main DDR involved in melanocyte homeostasis, DDR2 seems to be the main DDR implicated in melanoma. On the contrary, in dermis, while DDR2 is necessary for normal wound healing, dysregulation of DDR1 is associated with abnormal wound healing leading to keloid. In conclusion, targeting DDR could be a therapeutic solution, however side effects have to be managed carefully.

Age-related modifications of type I collagen impair DDR1-induced apoptosis in non-invasive breast carcinoma cells

Type I collagen and DDR1 axis has been described to decrease cell proliferation and to initiate apoptosis in non-invasive breast carcinoma in three-dimensional cell culture matrices. Moreover, MT1-MMP down-regulates these effects. Here, we address the effect of type I collagen aging and MT1-MMP expression on cell proliferation suppression and induced-apoptosis in non-invasive MCF-7 and ZR-75-1 breast carcinoma. We provide evidence for a decrease in cell growth and an increase in apoptosis in the presence of adult collagen when compared to old collagen. This effect involves a differential activation of DDR1, as evidenced by a higher DDR1 phosphorylation level in adult collagen. In adult collagen, inhibition of DDR1 expression and kinase function induced an increase in cell growth to a level similar to that observed in old collagen. The impact of aging on the sensitivity of collagen to MT1-MMP has been reported recently. We used the MT1-MMP expression strategy to verify whether, by degrading adult type I collagen, it could lead to the same phenotype observed in old collagen 3D matrix. MT1-MMP overexpression abrogated the proliferation suppression and induced-apoptosis effects only in the presence of adult collagen. This suggests that differential collagen degradation by MT1-MMP induced a structural disorganization of adult collagen and inhibits DDR1 activation. This could in turn impair DDR1-induced cell growth suppression and apoptosis. Taken together, our data suggest that modifications of collagen structural organization, due to aging, contribute to the loss of the growth suppression and induced apoptosis effect of collagen in luminal breast carcinoma. MT1-MMP-dependent degradation and aging of collagen have no additive effects on these processes.

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.

Type I collagen aging impairs discoidin domain receptor 2-mediated tumor cell growth suppression

Tumor cells are confronted to a type I collagen rich environment which regulates cell proliferation and invasion. Biological aging has been associated with structural changes of type I collagen. Here, we address the effect of collagen aging on cell proliferation in a three-dimensional context (3D).

We provide evidence for an inhibitory effect of adult collagen, but not of the old one, on proliferation of human fibrosarcoma HT-1080 cells. This effect involves both the activation of the tyrosine kinase Discoidin Domain Receptor 2 (DDR2) and the tyrosine phosphatase SHP-2. DDR2 and SHP-2 were less activated in old collagen. DDR2 inhibition decreased SHP-2 phosphorylation in adult collagen and increased cell proliferation to a level similar to that observed in old collagen.

In the presence of old collagen, a high level of JAK2 and ERK1/2 phosphorylation was observed while expression of the cell cycle negative regulator p21^CIP1 was decreased. Inhibition of DDR2 kinase function also led to an increase in ERK1/2 phosphorylation and a decrease in p21^CIP1 expression. Similar signaling profile was observed when DDR2 was inhibited in adult collagen. Altogether, these data suggest that biological collagen aging could increase tumor cell proliferation by reducingthe activation of the key matrix sensor DDR2.

Matrix-regulated integrin αvβ5 maintains α5β1-dependent desmoplastic traits prognostic of neoplastic recurrence

Desmoplasia, a fibrotic mass including cancer-associated fibroblasts (CAFs) and self-sustaining extracellular matrix (D-ECM), is a puzzling feature of pancreatic ductal adenocarcinoma (PDACs). Conflicting studies have identified tumor-restricting and tumor-promoting roles of PDAC-associated desmoplasia, suggesting that individual CAF/D-ECM protein constituents have distinguishable tumorigenic and tumor-repressive functions. Using 3D culture of normal pancreatic versus PDAC-associated human fibroblasts, we identified a CAF/D-ECM phenotype that correlates with improved patient outcomes, and that includes CAFs enriched in plasma membrane-localized, active α₅β₁-integrin. Mechanistically, we established that TGFβ is required for D-ECM production but dispensable for D-ECM-induced naïve fibroblast-to-CAF activation, which depends on α_vβ₅-integrin redistribution of pFAK-independent active α₅β₁-integrin to assorted endosomes. Importantly, the development of a simultaneous multi-channel immunofluorescence approach and new algorithms for computational batch-analysis and their application to a human PDAC panel, indicated that stromal localization and levels of active SMAD2/3 and α₅β₁-integrin distinguish patient-protective from patient-detrimental desmoplasia and foretell tumor recurrences, suggesting a useful new prognostic tool.

DOI:http://dx.doi.org/10.7554/eLife.20600.001

Tumors are not entirely made out of cancerous cells. They contain many other components – referred to as tumor stroma – that may either encourage or hinder the tumor’s growth. Tumor stroma includes non-cancerous cells and a framework of fibrous sugary proteins, called the extracellular matrix, which surround and signal to cells while providing physical support.

In the most common and aggressive form of pancreatic cancer, the stroma often makes up the majority of the tumor’s mass. Sometimes the stroma of these pancreatic tumors can protect the cancer cells from anti-cancer drugs. Researchers have therefore been interested in finding out exactly which aspects of the tumor stroma shield and support cancer cells, and which impede their growth and progression. Answering these questions could make it possible to develop new drugs that will change a tumor-supporting stroma into one that hinders the tumor’s growth and spread.

The most abundant cells in the stroma of pancreatic tumors are called cancer-associated fibroblasts. Healthy specialized fibroblasts – known as pancreatic stellate cells – help to build and maintain the ‘normal’ extracellular matrix and so these cells normally restrict a tumor’s development. However, cancer cells can adapt healthy fibroblasts into cancer-associated fibroblasts, which produce an altered extracellular matrix that could allow the tumor to grow.

Franco-Barraza et al. have now compared healthy and cancer-associated fibroblasts from patients’ pancreatic tumors. One of the main differences between these two cell types was the location of the activated form of a molecule called α₅β₁-integrin. Healthy fibroblasts, in a normal extracellular matrix, have active α₅β₁-integrin on the surface of the cell. However, a number of tumor-promoting signals, including some from the altered extracellular matrix, could force the active α₅β₁-integrins to relocate inside the fibroblasts instead. In further experiments, where the activated integrin was retained at the cell surface, the fibroblasts were able to resist the influence of the cancer-associated extracellular matrix. Then again, if the active α₅β₁-integrins were directed inside the cells, healthy cells turned into cancer-associated fibroblasts.

With this information in hand, Franco-Barraza et al. examined tumor samples from over a hundred pancreatic cancer patients using a new microscopy-based technique that distinguishes cancer cells from stroma cells. The analysis confirmed the pattern observed in the laboratory: those patients who appeared to produce more normal extracellular matrix and have active α₅β₁-integrin localized mostly to the surface of the cells survived longer without the cancer returning than those patients who lacked these stroma traits. Samples from patients with kidney cancer also showed similar results and, as before, an altered extracellular matrix was linked to a worse outcome of the disease.

Together these findings suggest that if future studies uncover ways to relocate or maintain active α₅β₁-integrin to the cell surface of fibroblasts they could lead to new treatments to restrict the growth of tumors in cancer patients.

DOI:http://dx.doi.org/10.7554/eLife.20600.002

Novel phase I study combining G1 phase, S phase, and G2/M phase cell cycle inhibitors in patients with advanced malignancies

PURPOSE

Cancer is a manifestation of aberrant cellular proliferation, and the cell cycle is one of the most successfully drugged targets in oncology. No prior study has been reported that simultaneously targets the 3 principal cell cycle phases populated by proliferating cells--G1, S, and G2/M.

METHODS

Temsirolimus (G1 inhibitor), topotecan (S inhibitor), and bortezomib (G2/M inhibitor) were administered in combination to patients with advanced malignancies using a 3+3 dose escalation schedule to assess the safety and establish the maximum tolerated dose (primary endpoints) of this cell cycle targeting approach. An in silico pharmacodynamic model using established effects of each of these agents on the cell cycle was used to validate the regimen and to guide the dosing regimen.

RESULTS

Sixty-two subjects were enrolled. The most common adverse events and dose-limiting toxicities were cytopenias, consistent with the cell cycle targeting approach employed. All cytopenias resolved to baseline values upon holding study drug administration. The maximum tolerated dose was temsirolimus 15 mg/kg IV D1, 8, 15; topotecan 2.8 mg/m(2) IV D1, 8; and bortezomib 0.6 mg/m2 IV D1, 4, 8, 11 [DOSAGE ERROR CORRECTED] of a 21-day cycle. In silico modeling suggests the regimen induces cell population shifts from G2/M and S phases to G1 phase and the quiescent G0 phase. Eighteen percent of subjects (11/62) achieved partial response (n = 2, serous ovarian and papillary thyroid) or stable disease for > 6 months (n = 9).

CONCLUSION

Combining drugs with inhibitory activity of G1 phase, S phase, and G2/M phase is safe and warrants further evaluation.

Tyrosine Kinase Receptor Landscape in Lung Cancer: Therapeutical Implications

Lung cancer is a heterogeneous disease responsible for the most cases of cancer-related deaths. The majority of patients are clinically diagnosed at advanced stages, with a poor survival rate. For this reason, the identification of oncodrivers and novel biomarkers is decisive for the future clinical management of this pathology. The rise of high throughput technologies popularly referred to as “omics” has accelerated the discovery of new biomarkers and drivers for this pathology. Within them, tyrosine kinase receptors (TKRs) have proven to be of importance as diagnostic, prognostic, and predictive tools and, due to their molecular nature, as therapeutic targets. Along this review, the role of TKRs in the different lung cancer histologies, research on improvement of anti-TKR therapy, and the current approaches to manage anti-TKR resistance will be discussed.

Prognostic significance of discoidin domain receptor 2 (DDR2) expression in ovarian cancer

Increasing evidence has suggested that discoidin domain receptor 2 (DDR2) plays an important role in cancer development and metastasis. However, the correlation between DDR2 expression and clinical outcome in ovarian cancer has not been investigated. In this study, DDR2 expression was examined by Real-time PCR in surgically resected ovarian cancer and normal ovary tissues. Besides, DDR2 expression was analyzed immunohistochemically in 103 ovarian cancer patients, and the correlation between DDR2 expression with clinicopathologic factors was analyzed. The result showed that DDR2 mRNA expression was upregulated in ovarian cancer tissues compared with normal ovary tissues. Statistical analysis revealed that DDR2 expression correlated with tumor stage (P = 0.008) and peritoneal metastasis (P = 0.009). Patients with high DDR2 expression showed poorer 5-year overall survival (P = 0.005), and DDR2 remained an independent prognostic marker for OS (P = 0.013) in multivariate analysis. Our results suggest that DDR2 might be closely associated with ovarian cancer progression and metastasis. Its high expression may serve as a potential prognostic biomarker in human ovarian cancer.

Discoidin Domain Receptors: Potential Actors and Targets in Cancer

The extracellular matrix critically controls cancer cell behavior by inducing several signaling pathways through cell membrane receptors. Besides conferring structural properties to tissues around the tumor, the extracellular matrix is able to regulate cell proliferation, survival, migration, and invasion. Among these receptors, the integrins family constitutes a major class of receptors that mediate cell interactions with extracellular matrix components. Twenty years ago, a new class of extracellular matrix receptors has been discovered. These tyrosine kinase receptors are the two discoidin domain receptors DDR1 and DDR2. DDR1 was first identified in the Dictyostelium discoideum and was shown to mediate cell aggregation. DDR2 shares highly conserved sequences with DDR1. Both receptors are activated upon binding to collagen, one of the most abundant proteins in extracellular matrix. While DDR2 can only be activated by fibrillar collagen, particularly types I and III, DDR1 is mostly activated by type I and IV collagens. In contrast with classical growth factor tyrosine kinase receptors which display a rapid and transient activation, DDR1 and DDR2 are unique in that they exhibit delayed and sustained receptor phosphorylation upon binding to collagen. Recent studies have reported differential expression and mutations of DDR1 and DDR2 in several cancer types and indicate clearly that these receptors have to be taken into account as new players in the different aspects of tumor progression, from non-malignant to highly malignant and invasive stages. This review will discuss the current knowledge on the role of DDR1 and DDR2 in malignant transformation, cell proliferation, epithelial to mesenchymal transition, migratory, and invasive processes, and finally the modulation of the response to chemotherapy. These new insights suggest that DDR1 and DDR2 are new potential targets in cancer therapy.

Functional Analyses of Mutations in Receptor Tyrosine Kinase Genes in Non-Small Cell Lung Cancer: Double-Edged Sword of DDR2

PURPOSE

This study investigated whether mutations of receptor tyrosine kinase (RTK) genes detected using next-generation sequencing (NGS) are suitable therapeutic targets.

EXPERIMENTAL DESIGN

Fifty surgically resected non-small cell lung cancer (NSCLC) samples were target resequenced using NGS. We then investigated the functions of the identified RTK gene mutations, including their oncogenic potential, in vitro

RESULTS

Mutations in RTK genes were found in 20 samples (EGFR, 15; ERBB4, 1; ALK, 1; DDR2, 2; FGFR1, 1), mutations in MAPK pathway genes were found in nine samples (KRAS, 7; NRAS, 1; BRAF, 2), and mutations in PI3K pathway genes were found in three samples (PIK3CA, 1; PTEN, 3). Among the mutations in RTKs, the functions of four mutations were unclear (ERBB4 D245G; DDR2 H246R and E655K; FGFR1 A263V). These mutations did not exhibit any transformational activities. Neither the phosphorylation nor the protein expressions of RTKs were changed by the DDR2 H246R, ERBB4 D245G, and FGFR1 A263V mutations, although the expression level of the DDR2 protein harboring the E655K mutation was particularly low. Collagen stimulation decreased cellular proliferation through p38 activation in the DDR2 wild-type-overexpressed cell lines, whereas the growth-suppressive effect was weakened in DDR2 E655K-overexpressed cell lines. Furthermore, the DDR2 E655K protein strongly bound to ubiquitin ligase E3 (Cbl-b), and the mutant protein expression was increased after treatment with a proteasome inhibitor.

CONCLUSIONS

Our experimental findings suggest that RTK mutations are not always suitable as therapeutic targets. The DDR2 E655K mutation can play a role in cancer progression by reducing the growth-inhibitory effect of collagen. Clin Cancer Res; 22(14); 3663-71. ©2016 AACR.

Immunogenic, cellular, and angiogenic drivers of tumor dormancy--a melanoma view

In tumor cells, the ability to maintain viability over long time periods without proliferation is referred to as a state of dormancy. Maintenance of dormancy is controlled by numerous cellular and environmental factors, from immune surveillance and tumor-stroma interaction to intracellular signaling. Interference of dormancy (to an 'awaken' state) is associated with reduced response to therapy, resulting in relapse or in metastatic burst. Thus, maintaining a dormant state should prolong therapeutic responses and delay metastasis. Technical obstacles in studying tumor dormancy have limited our understanding of underlying mechanisms and hampered our ability to target dormant cells. In this review, we summarize the progress of research in the field of immunogenic, angiogenic, and cellular dormancy in diverse malignancies with particular attention to our current understanding in melanoma.

Discoidin domain receptor functions in physiological and pathological conditions

The discoidin domain receptors, DDR1 and DDR2, are nonintegrin collagen receptors that are members of the receptor tyrosine kinase family. Both DDRs bind a number of different collagen types and play important roles in embryo development. Dysregulated DDR function is associated with progression of various human diseases, including fibrosis, arthritis, and cancer. By interacting with key components of the extracellular matrix and displaying distinct activation kinetics, the DDRs form a unique subfamily of receptor tyrosine kinases. DDR-facilitated cellular functions include cell migration, cell survival, proliferation, and differentiation, as well as remodeling of extracellular matrices. This review summarizes the current knowledge of DDR-ligand interactions, DDR-initiated signal pathways and the molecular mechanisms that regulate receptor function. Also discussed are the roles of DDRs in development and disease progression.

Discoidin domain receptor 2 signaling networks and therapy in lung cancer

Discoidin domain receptor 2 (DDR2) is an atypical receptor tyrosine kinase that binds to and is activated by collagen in the extracellular matrix. Recent exon sequencing studies have identified DDR2 to be mutated with a 3% to 4% incidence in squamous cell cancers of the lung. This article summarizes the current state of knowledge of DDR2 biology and signaling in lung squamous cell cancer. It also explores the context-dependent role of this receptor as both an oncogene and a tumor suppressor in cancer cells. Promising therapeutic opportunities based on existing and novel targeted small molecule inhibitors against DDR2 may provide new strategies for treating lung squamous cell cancer patients.

Phosphoproteomics of collagen receptor networks reveals SHP-2 phosphorylation downstream of wild-type DDR2 and its lung cancer mutants

Collagen is an important extracellular matrix component that directs many fundamental cellular processes including differentiation, proliferation and motility. The signalling networks driving these processes are propagated by collagen receptors such as the β1 integrins and the DDRs (discoidin domain receptors). To gain an insight into the molecular mechanisms of collagen receptor signalling, we have performed a quantitative analysis of the phosphorylation networks downstream of collagen activation of integrins and DDR2. Temporal analysis over seven time points identified 424 phosphorylated proteins. Distinct DDR2 tyrosine phosphorylation sites displayed unique temporal activation profiles in agreement with in vitro kinase data. Multiple clustering analysis of the phosphoproteomic data revealed several DDR2 candidate downstream signalling nodes, including SHP-2 (Src homology 2 domain-containing protein tyrosine phosphatase 2), NCK1 (non-catalytic region of tyrosine kinase adaptor protein 1), LYN, SHIP-2 [SH2 (Src homology 2)-domain-containing inositol phosphatase 2], PIK3C2A (phosphatidylinositol-4-phosphate 3-kinase, catalytic subunit type 2α) and PLCL2 (phospholipase C-like 2). Biochemical validation showed that SHP-2 tyrosine phosphorylation is dependent on DDR2 kinase activity. Targeted proteomic profiling of a panel of lung SCC (squamous cell carcinoma) DDR2 mutants demonstrated that SHP-2 is tyrosine-phosphorylated by the L63V and G505S mutants. In contrast, the I638F kinase domain mutant exhibited diminished DDR2 and SHP-2 tyrosine phosphorylation levels which have an inverse relationship with clonogenic potential. Taken together, the results of the present study indicate that SHP-2 is a key signalling node downstream of the DDR2 receptor which may have therapeutic implications in a subset of DDR2 mutations recently uncovered in genome-wide lung SCC sequencing screens.

Extracellular matrix collagen alters cell proliferation and cell cycle progression of human uterine leiomyoma smooth muscle cells

Uterine leiomyomas (ULs) are benign tumors occurring in the majority of reproductive aged women. Despite the high prevalence of these tumors, little is known about their etiology. A hallmark of ULs is the excessive deposition of extracellular matrix (ECM), primarily collagens. Collagens are known to modulate cell behavior and function singularly or through interactions with integrins and growth factor-mediated mitogenic pathways. To better understand the pathogenesis of ULs and the role of ECM collagens in their growth, we investigated the interaction of leiomyoma smooth muscle cells (LSMCs) with two different forms of collagen, non-polymerized collagen (monomeric) and polymerized collagen (fibrillar), in the absence or presence of platelet-derived growth factor (PDGF), an abundant growth factor in ULs. Primary cultures of human LSMCS from symptomatic patients were grown on these two different collagen matrices and their morphology, cytoskeletal organization, cellular proliferation, and signaling pathways were evaluated. Our results showed that LSMCs had distinct morphologies on the different collagen matrices and their basal as well as PDGF-stimulated proliferation varied on these matrices. These differences in proliferation were accompanied by changes in cell cycle progression and p21, an inhibitory cell cycle protein. In addition we found alterations in the phosphorylation of focal adhesion kinase, cytoskeletal reorganization, and activation of the mitogen activated protein kinase (MAPK) signaling pathway. In conclusion, our results demonstrate a direct effect of ECM on the proliferation of LSMCs through interplay between the collagen matrix and the PDGF-stimulated MAPK pathway. In addition, these findings will pave the way for identifying novel therapeutic approaches for ULs that target ECM proteins and their signaling pathways in ULs.

Multiphase modelling of desmoplastic tumour growth

It is well-known that the microenvironment of solid tumours is a significant component of the processes of tumour growth and invasion. Interactions between tumour cells and stromal components play a crucial role in tumour progression as well as suppression. We describe a mathematical model of tumour growth within a host tissue which takes into account both cell-extracellular matrix interactions and tissue compression effects. This multiphase model consisting of three coupled partial differential equations captures the dynamics of tumour progression, particularly of a desmoplastic tumour (i.e. a tumour rich in fibrous connective tissue). The model is analysed in terms of stability in a spatially homogenous case. Computer simulations agree with the biological picture of the disease and may help to understand the process leading to the pathology.

RNA interference against discoidin domain receptor 2 ameliorates alcoholic liver disease in rats

Discoidin domain receptor 2 (DDR2) is involved in fibrotic disease. However, the exact pathogenic implications of the receptor in early alcoholic liver disease are still controversial. We constructed plasmid vectors encoding short-hairpin RNA against DDR2 to investigate its role in alcoholic liver disease in an immortalized rat hepatic stellate cell line, HSC-T6, and in rats by MTT, RT-PCR and western blot analyses; immunohistochemistry and electron microscopy. Alcohol-induced upregulation of DDR2 was associated with the expression of matrix metalloproteinase 2, the transforming growth factor β1 signaling pathway and tissue inhibitor of metalloproteinase 1; collagen deposition; and extracellular matrix remodeling. Inhibition of DDR2 decreased HSC-T6 cell proliferation and liver injury in rats with 10-week-induced alcoholic liver disease. DDR2 may have an important role in the pathogenesis of early-stage alcoholic liver disease. Silencing DDR2 may be effective in preventing early-stage alcoholic liver disease.

Discoidin domain receptors: unique receptor tyrosine kinases in collagen-mediated signaling

The discoidin domain receptors (DDRs) are receptor tyrosine kinases that recognize collagens as their ligands. DDRs display unique structural features and distinctive activation kinetics, which set them apart from other members of the kinase superfamily. DDRs regulate cell-collagen interactions in normal and pathological conditions and thus are emerging as major sensors of collagen matrices and potential novel therapeutic targets. New structural and biological information has shed light on the molecular mechanisms that regulate DDR signaling, turnover, and function. This minireview provides an overview of these areas of DDR research with the goal of fostering further investigation of these intriguing and unique receptors.

Discoidin domain receptor tyrosine kinases: new players in cancer progression

Almost all human cancers display dysregulated expression and/or function of one or more receptor tyrosine kinases (RTKs). The strong causative association between altered RTK function and cancer progression has been translated into novel therapeutic strategies that target these cell surface receptors in cancer. Yet, the full spectrum of RTKs that may alter the oncogenic process is not completely understood. Accumulating evidence suggests that a unique set of RTKs known as the discoidin domain receptors (DDRs) play a key role in cancer progression by regulating the interactions of tumor cells with their surrounding collagen matrix. The DDRs are the only RTKs that specifically bind to and are activated by collagen. DDRs control cell and tissue homeostasis by acting as collagen sensors, transducing signals that regulate cell polarity, tissue morphogenesis, and cell differentiation. In cancer, DDRs are hijacked by tumor cells to disrupt normal cell-matrix communication and initiate pro-migratory and pro-invasive programs. Importantly, several cancer types exhibit DDR mutations, which are thought to alter receptor function and contribute to cancer progression. Other evidence suggests that the actions of DDRs in cancer are complex, either promoting or suppressing tumor cell behavior in a DDR type/isoform specific- and context-dependent manner. Thus, there is still a considerable gap in our knowledge of DDR actions in cancer tissues. This review summarizes and discusses the current knowledge on DDR expression and function in cancer. It is hoped that this effort will encourage more research into these poorly understood but unique RTKs, which have the potential of becoming novel therapeutic targets in cancer.

Discoidin domain receptor 2-microRNA 196a-mediated negative feedback against excess type I collagen expression is impaired in scleroderma dermal fibroblasts

Systemic sclerosis (SSc) is characterized by excess collagen deposition in the skin, due to intrinsic transforming growth factor-β (TGF-β) activation. We tried to determine the expression and the role of discoidin domain receptor 2 (DDR2) in SSc. The expression of DDR2 mRNA and protein was significantly decreased in SSc dermal fibroblasts, which was recovered by knocking down TGF-β. The knockdown of DDR2 in normal fibroblasts induced microRNA-196a expression, which led to type I collagen downregulation, indicating that DDR2 itself has a negative effect on microRNA-196a expression and inducible effect on collagen expression. In SSc fibroblasts, however, the DDR2 knockdown did not affect TGF-β signaling and microRNA-196a expression. The microRNA-196a levels were significantly decreased in normal fibroblasts treated with TGF-β and in SSc fibroblasts. Taken together our data indicate that, in SSc fibroblasts, intrinsic TGF-β stimulation induces type I collagen expression, and also downregulates DDR2 expression. This probably acts as a negative feedback mechanism against excess collagen expression, as a decreased DDR2 expression is supposed to stimulate the microRNA-196a expression and further change the collagen expression. However, in SSc fibroblasts the microRNA-196a expression was downregulated by TGF-β signaling. DDR2-microRNA-196a pathway may be a previously unreported negative feedback system, and its impairment may be involved in the pathogenesis of SSc.

Deletion of discoidin domain receptor 2 does not affect smooth muscle cell adhesion, migration, or proliferation in response to type I collagen

Collagen receptors expressed on vascular smooth muscle cells include the discoidin domain receptors (DDR1 and DDR2). DDR1 is known to play important roles in mediating smooth muscle cell responses to vascular injury, including neointimal hyperplasia, but much less is known about the function of DDR2. In this study, we harvested smooth muscle cells from DDR2 wild-type and knockout mice and studied the cells using in vitro models of migration and growth. There were no significant differences in the ability of Ddr2(+/+) or Ddr2(-/-) smooth muscle cells to attach to, migrate, or proliferate on type I collagen. Furthermore, neither matrix metalloproteinase (MMP) 2 nor MMP-9 activity nor type I collagen expression was different between the cell types. We conclude that in vitro, endogenous DDR2 is not required for smooth muscle cell hyperplastic responses to collagen.

Transmembrane collagen receptors

Collagen, the most abundant protein in animals, is a key component of extracellular matrices. Not only do collagens provide essential structural support for connective tissues, but they are also intimately involved in controlling a spectrum of cellular functions such as growth, differentiation, and morphogenesis. All collagens possess triple-helical regions through which they interact with a host of other proteins including cell surface receptors. A structurally diverse group of transmembrane receptors mediates the recognition of the collagen triple helix: integrins, discoidin domain receptors, glycoprotein VI, and leukocyte-associated immunoglobulin-like receptor-1. These collagen receptors regulate a wide range of behaviors including cell adhesion and migration, hemostasis, and immune function. Here these collagen receptors are discussed in terms of their molecular basis of collagen recognition, their signaling and developmental functions, and their roles in disease.

Analysis of kinase gene expression patterns across 5681 human tissue samples reveals functional genomic taxonomy of the kinome

Kinases play key roles in cell signaling and represent major targets for drug development, but the regulation of their activation and their associations with health and disease have not been systematically analyzed. Here, we carried out a bioinformatic analysis of the expression levels of 459 human kinase genes in 5681 samples consisting of 44 healthy and 55 malignant human tissues. Defining the tissues where the kinase genes were transcriptionally active led to a functional genomic taxonomy of the kinome and a classification of human tissues and disease types based on the similarity of their kinome gene expression. The co-expression network around each of the kinase genes was defined in order to determine the functional context, i.e. the biological processes that were active in the cells and tissues where the kinase gene was expressed. Strong associations for individual kinases were found for mitosis (69 genes, including AURKA and BUB1), cell cycle control (73 genes, including PLK1 and AURKB), DNA repair (49 genes, including CHEK1 and ATR), immune response (72 genes, including MATK), neuronal (131 genes, including PRKCE) and muscular (72 genes, including MYLK2) functions. We then analyzed which kinase genes gain or lose transcriptional activity in the development of prostate and lung cancers and elucidated the functional associations of individual cancer associated kinase genes. In summary, we report here a systematic classification of kinases based on the bioinformatic analysis of their expression in human tissues and diseases, as well as grouping of tissues and tumor types according to the similarity of their kinome transcription.

Dynamic interplay between the collagen scaffold and tumor evolution

The extracellular matrix (ECM) is a key regulator of cell and tissue function. Traditionally, the ECM has been thought of primarily as a physical scaffold that binds cells and tissues together. However, the ECM also elicits biochemical and biophysical signaling. Controlled proteolysis and remodeling of the ECM network regulate tissue tension, generate pathways for migration, and release ECM protein fragments to direct normal developmental processes such as branching morphogenesis. Collagens are major components of the ECM of which basement membrane type IV and interstitial matrix type I are the most prevalent. Here we discuss how abnormal expression, proteolysis and structure of these collagens influence cellular functions to elicit multiple effects on tumors, including proliferation, initiation, invasion, metastasis, and therapy response.

KLF6 Gene and early melanoma development in a collagen I-rich extracellular environment

BACKGROUND

A putative tumor suppressor gene at chromosome 10p15, which contains KLF6 and other genes, is predicted to be lost during melanoma development, and its identity is unknown. In this study, we investigated the biological roles and identity of this tumor suppressor gene.

METHODS

The human UACC 903 melanoma cell line containing introduced DNA fragments from the 10p15 region with (10E6/3, 10E6/11, and 10E6/18) and without (10ER4S.2/1) the tumor suppressor gene was used. Xenograft tumors were generated in a total of 40 mice with melanoma cell lines, and tumor size was measured. Cells were cultured on plastic or a gel of type I collagen. Viability, proliferation, and apoptosis were assessed. Expression of KLF6 protein was assessed by immunohistochemistry and immunoblot analysis. Expression of phosphorylated Erk1/2 and cyclin D1 was assessed by immunoblot analysis. Protein expression of KLF6 was inhibited with small interfering RNA (siRNA). KLF6 protein expression was assessed in 17 human nevi and human melanoma specimens from 29 patients. Statistical analyses were adjusted for multiple comparisons by use of Dunnett method. All statistical tests were two-sided.

RESULTS

Melanoma cells containing KLF6 generated smaller subcutaneous xenograft tumors with fewer proliferating cells than control cells. When grown on collagen 1, viability of cells with ectopic KLF6 expression (72%) was lower than that of control cells (100%) (group difference = -28%, 95% confidence interval = -31.3% to -25.2%, P < .001). Viability of melanoma cells with or without the KLF6 tumor suppressor gene on plastic dishes was similar. When KLF6 expression was inhibited with KLF6 siRNA, viability of cells with the tumor suppressor gene on collagen I gel increased compared with that of control cells carrying scrambled siRNA. KLF6 protein was detected in all nevi examined but not in human metastatic melanoma tissue examined. Ectopic expression of KLF6 protein in melanoma cells grown on collagen I decreased levels of phosphorylated Erk1/2 and cyclin D1 in the mitogen-activated protein kinase signaling pathway.

CONCLUSIONS

In melanoma cells, the tumor suppressor gene at 10p15 appears to be KLF6. Signaling from the collagen I-rich extracellular matrix appears to be involved in the tumor suppressive activity of KLF6 protein.

Crystallographic insight into collagen recognition by discoidin domain receptor 2

The discoidin domain receptors, DDR1 and DDR2, are widely expressed receptor tyrosine kinases that are activated by triple-helical collagen. They control important aspects of cell behavior and are dysregulated in several human diseases. The major DDR2-binding site in collagens I–III is a GVMGFO motif (O is hydroxyproline) that also binds the matricellular protein SPARC. We have determined the crystal structure of the discoidin domain of human DDR2 bound to a triple-helical collagen peptide. The GVMGFO motifs of two collagen chains are recognized by an amphiphilic pocket delimited by a functionally critical tryptophan residue and a buried salt bridge. Collagen binding results in structural changes of DDR2 surface loops that may be linked to the process of receptor activation. A comparison of the GVMGFO-binding sites of DDR2 and SPARC reveals a striking case of convergent evolution in collagen recognition.

Alternatively activated macrophages and collagen remodeling characterize the postpartum involuting mammary gland across species

Recent pregnancy correlates with decreased survival for breast cancer patients compared with non-pregnancy-associated breast cancer. We hypothesize that postpartum mammary involution induces metastasis through wound-healing programs known to promote cancer. It is unknown whether alternatively activated M2 macrophages, immune cells important in wound-healing and experimental tumorigenesis that also predict poor prognosis for breast cancer patients, are recruited to the normal involuting gland. Macrophage markers CD68, CSF-1R, and F4/80 were examined across the pregnancy and involution cycle in rodent and human mammary tissues. Quantitative immunohistochemistry revealed up to an eightfold increase in macrophage number during involution, which returned to nulliparous levels with full regression. The involution macrophages exhibit an M2 phenotype as determined by high arginase-1 and low inducible nitric oxide synthase staining in rodent tissue, and by mannose receptor expression in human breast tissue. M2 cytokines IL-4 and IL-13 also peaked during involution. Extracellular matrix (ECM) isolated from involuting rat mammary glands was chemotactic for macrophages compared with nulliparous mammary ECM. Fibrillar collagen levels and proteolysis increased dramatically during involution, and denatured collagen I acted as a strong chemoattractant for macrophages in cell culture, suggesting proteolyzed fibrillar collagen as a candidate ECM mediator of macrophage recruitment. M2 macrophages, IL-4, IL-13, fibrillar collagen accumulation, and proteolysis of collagen are all components of tumor promotional microenvironments, and thus may mediate promotion of breast cancers arising in the postpartum setting.

Navigating ECM barriers at the invasive front: the cancer cell-stroma interface

A seminal event in cancer progression is the ability of the neoplastic cell to mobilize the necessary machinery to breach surrounding extracellular matrix barriers while orchestrating a host stromal response that ultimately supports tissue-invasive and metastatic processes. With over 500 proteolytic enzymes identified in the human genome, interconnecting webs of protease-dependent and protease-independent processes have been postulated to drive the cancer cell invasion program via schemes of daunting complexity. Increasingly, however, a body of evidence has begun to emerge that supports a unifying model wherein a small group of membrane-tethered enzymes, termed the membrane-type matrix metalloproteinases (MT-MMPs), plays a dominant role in regulating cancer cell, as well as stromal cell, traffic through the extracellular matrix barriers assembled by host tissues in vivo. Understanding the mechanisms that underlie the regulation and function of these metalloenzymes as host cell populations traverse the dynamic extracellular matrix assembled during neoplastic states should provide new and testable theories regarding cancer invasion and metastasis.

Dormancy of metastatic melanoma

Metastatic dormancy of melanoma has not received sufficient attention, most likely because once detectable, metastasis is almost invariably fatal and, understandably, the focus has been on finding ways to prolong life of patients with overt recurrences. Nevertheless, analysis of the published clinical and experimental data on melanoma indicates that some aspect of melanoma biology imitate traits recently associated with dormancy in other solid cancers. Among them the ability of some melanomas to disseminate early during primary tumor progression and once disseminated, to remain undetected (dormant) for years. Comparison of cutaneous and uveal melanoma indicates that, in spite of being of the same origin, they differ profoundly in their clinical progression. Importantly for this discussion, between 40 and 50% of uveal melanoma remain undetected for longer than a decade, while less than 5% of cutaneous melanoma show this behavior. Both types of melanoma have activating oncogene mutations that provide autonomous pro-proliferative signals, yet the consensus is that those are not sufficient for tumor progression. If that is the case, it is possible to envision that signals from outside the tumor cell, (microenvironment) shape the fate of an individual disseminated cell, regardless of an oncogene mutation, to progress or to pause in a state of dormancy. To stimulate further debate and inquiry we describe here a few examples of potential signals that might modify the fate of disseminated cell and provide brief description of the current knowledge on dormancy in other cancers. Our hope is to convince the reader that disseminated melanoma cells do enter periods of prolonged dormancy and that finding ways to induce it, or to prolong it, might mean an extension of symptoms-free life for melanoma patients. Ultimately, understanding the biology of dormancy and the mechanisms of dormant cell survival, might allow for their specific targeting and elimination.

The relative roles of collagen adhesive receptor DDR2 activation and matrix stiffness on the downregulation of focal adhesion kinase in vascular smooth muscle cells

Cells within tissues derive mechanical anchorage and specific molecular signals from the insoluble extracellular matrix (ECM) that surrounds them. Understanding the role of different cues that extracellular matrices provide cells is critical for controlling and predicting cell response to scaffolding materials. Using an engineered extracellular matrix of Type I collagen we examined how the stiffness, supramolecular structure, and glycosylation of collagen matrices influence the protein levels of cellular FAK and the activation of myosin II. Our results show that (1) cellular FAK is downregulated on collagen fibrils, but not on a non-fibrillar monolayer of collagen, (2) the downregulation of FAK is independent of the stiffness of the collagen fibrils, and (3) FAK levels are correlated with levels of tyrosine phosphorylation of the collagen adhesion receptor DDR2. Further, siRNA depletion of DDR2 blocks FAK downregulation. Our results suggest that the collagen receptor DDR2 is involved in the regulation of FAK levels in vSMC adhered to Type I collagen matrices, and that regulation of FAK levels in these cells appears to be independent of matrix stiffness.

Tamoxifen induces pleiotrophic changes in mammary stroma resulting in extracellular matrix that suppresses transformed phenotypes

INTRODUCTION

The functional unit of the mammary gland has been defined as the epithelial cell plus its microenvironment, a hypothesis that predicts changes in epithelial cell function will be accompanied by concurrent changes in mammary stroma. To test this hypothesis, the question was addressed of whether mammary stroma is functionally altered by the anti-oestrogen drug tamoxifen.

METHODS

Forty female rats at 70 days of age were randomised to two groups of 20 and treated with 1.0 mg/kg tamoxifen or vehicle subcutaneously daily for 30 days, followed by a three-day wash out period. Mammary tissue was harvested and effects of tamoxifen on mammary epithelium and stroma determined.

RESULTS

As expected, tamoxifen suppressed mammary alveolar development and mammary epithelial cell proliferation. Primary mammary fibroblasts isolated from tamoxifen-treated rats displayed a three-fold decrease in motility and incorporated less fibronectin in their substratum in comparison to control fibroblasts; attributes indicative of fibroblast quiescence. Immunohistochemistry analysis of CD68, a macrophage lysosomal marker, demonstrated a reduction in macrophage infiltration in mammary glands of tamoxifen-treated rats. Proteomic analyses by mass spectrometry identified several extracellular matrix (ECM) proteins with expression levels with tamoxifen treatment that were validated by Western blot. Mammary tissue from tamoxifen-treated rats had decreased fibronectin and increased collagen 1 levels. Further, ECM proteolysis was reduced in tamoxifen-treated rats as detected by reductions in fibronectin, laminin 1, laminin 5 and collagen 1 cleavage fragments. Consistent with suppression in ECM proteolysis with tamoxifen treatment, matrix metalloproteinase-2 levels and activity were decreased. Biochemically extracted mammary ECM from tamoxifen-treated rats suppressed in vitro macrophage motility, which was rescued by the addition of proteolysed collagen or fibronectin. Mammary ECM from tamoxifen-treated rats also suppressed breast tumour cell motility, invasion and haptotaxis, reduced organoid size in 3-dimensional culture and blocked tumour promotion in an orthotopic xenograft model; effects which could be partially reversed by the addition of exogenous fibronectin.

CONCLUSIONS

These data support the hypothesis that mammary stroma responds to tamoxifen treatment in concert with the epithelium and remodels to a microenvironment inhibitory to tumour cell progression. Reduced fibronectin levels and reduced ECM turnover appear to be hallmarks of the quiescent mammary microenvironment. These data may provide insight into attributes of a mammary microenvironment that facilitate tumour dormancy.

Type I collagen expression contributes to angiogenesis and the development of deeply invasive cutaneous melanoma

Tumors are complex tissues composed of neoplastic cells, soluble and insoluble matrix components and stromal cells. Here we report that in melanoma, turn-over of type I collagen (Col(I)), the predominant matrix protein in dermal stroma affects melanoma progression. Fibroblasts juxtaposed to melanoma cell nests within the papillary dermis display high levels of Col(I) mRNA expression. These nests are enveloped by collagen fibers. In contrast, melanoma-associated fibroblasts within the reticular dermis express Col(I) mRNA at a level that is comparable to its expression in uninvolved dermis and reduced amount of collagen protein can be observed. To determine the significance of Col(I) expression in melanoma, we pharmacologically inhibited its transcription in a porcine cutaneous melanoma model by oral administration of halofuginone. When administered before melanoma development, it reduced melanoma incidence and diminished the transition from microinvasive toward deeply invasive growth by limiting the development of a tumor vasculature. Whereas invasive melanoma growth has been correlated with increased blood vessel density previously, our data for the first time demonstrate that the proangiogenic effect of Col(I) expression by fibroblasts and vascular cells precedes the development of invasive melanomas in a de novo tumor model.