A proteomics-based survey reveals thrombospondin-4 as a ligand regulated by the mannose receptor in the injured lung

Receptor-mediated cellular uptake of specific ligands constitutes an important step in the dynamic regulation of individual protein levels in extracellular fluids. With a focus on the inflammatory lung, we here performed a proteomics-based search for novel ligands regulated by the mannose receptor (MR), a macrophage-expressed endocytic receptor. WT and MR-deficient mice were exposed to lipopolysaccharide, after which the protein content in their lung epithelial lining fluid was compared by tandem mass tag-based mass spectrometry. More than 1200 proteins were identified in the epithelial lining fluid using this unbiased approach, but only six showed a statistically different abundance. Among these, an unexpected potential new ligand, thrombospondin-4 (TSP-4), displayed a striking 17-fold increased abundance in the MR-deficient mice. Experiments using exogenous addition of TSP-4 to MR-transfected CHO cells or MR-positive alveolar macrophages confirmed that TSP-4 is a ligand for MR-dependent endocytosis. Similar studies revealed that the molecular interaction with TSP-4 depends on both the lectin activity and the fibronectin type-II domain of MR and that a closely related member of the TSP family, TSP-5, is also efficiently internalized by the receptor. This was unlike the other members of this protein family, including TSPs -1 and -2, which are ligands for a close MR homologue known as urokinase plasminogen activator receptor-associated protein. Our study shows that MR takes part in the regulation of TSP-4, an important inflammatory component in the injured lung, and that two closely related endocytic receptors, expressed on different cell types, undertake the selective endocytosis of distinct members of the TSP family.

Antibody-Drug Conjugates: The Dynamic Evolution from Conventional to Next-Generation Constructs

Introduced almost two decades ago, ADCs have marked a breakthrough in the targeted therapy era, providing clinical benefits to many cancer patients. While the inherent complexity of this class of drugs has challenged their development and broad application, the experience gained from years of trials and errors and recent advances in construct design and delivery have led to an increased number of ADCs approved or in late clinical development in only five years. Target and payload diversification, along with novel conjugation and linker technologies, are at the forefront of next-generation ADC development, renewing hopes to broaden the scope of these targeted drugs to difficult-to-treat cancers and beyond. This review highlights recent trends in the ADC field, focusing on construct design and mechanism of action and their implications on ADCs' therapeutic profile. The evolution from conventional to innovative ADC formats will be illustrated, along with some of the current hurdles, including toxicity and drug resistance. Future directions to improve the design of next-generation ADCs will also be presented.

Targeted delivery of alcohol-containing payloads with antibody-drug conjugates

We herein describe the cell-specific release of alcohol-containing payloads via a sulfatase-sensitive linker in antibody-drug conjugates (ADCs). The linker shows efficient sulfatase-mediated release and high stability in human and mouse plasma. In vitro evaluation demonstrates potent antigen dependent toxicity towards breast cancer cell lines.

Abstract 5779: A platform utilizing high-grade serous ovarian cancer organoids for prospective patient stratification in functional precision medicine

High-grade serous ovarian cancer (HGSC) is the most prevalent and lethal ovarian cancer type. While HGSC usually responds well to primary treatment, most cases eventually relapse. Functional precision medicine - tailoring individualized treatments based on functional in vitro assays on patient-derived cells - has been recently employed in cancer clinical trials. Cancer organoids - three-dimensional, self-organizing, self-renewing cell cultures that recapitulate original tissue structure and function - have been applied as cellular models in these trials. However, in case of HGSC, organoid derivation has proven time consuming and inefficient, hindering their application in functional precision medicine due to a short time window, in which therapy for each patient needs to be selected.

To address this problem, we aimed to establish whether drug vulnerabilities at HGSC relapse could be predicted using organoids derived from the primary disease cells. We derived sequential organoid models from material sampled during primary treatment and at relapse. Then, for organoid pairs (primary-relapse), we performed large-scale drug response profiling of a library of 370 compounds (approved drugs or drugs in clinical development), in 384-well microplate format, alone or in combination with a standard HGSC chemotherapeutic agent carboplatin. First, we found that HGSC organoid responses to standard chemotherapeutics retrospectively correlated to observed clinical treatment outcomes. But further, for each patient we identified compounds with pronounced cytotoxicity both in the primary and in the relapsed model, amounting to 66% of all hits (7% were primary-specific and 27% relapse-specific). We then focused on identifying patient-specific hits rather than compounds displaying general toxicity in all patient models. Based on a potential clinical applicability, for three patients we selected compounds for validation in organoid outgrowth assay, with prolonged (>1 month) drug-free period post-treatment. In two patients, AZD4573, a selective CDK9 inhibitor in clinical development for hematological malignancies, at nanomolar concentrations caused eradication of organoids when combined with carboplatin. Organoids from the third patient were vulnerable to nitazoxanide, an approved anti-helminthic agent and an inhibitor of mitochondrial oxidative phosphorylation. Importantly, the selected final hits were identified solely based on screening in organoid models from primary disease.

In summary, we here demonstrate that HGSC organoids derived from primary disease material predict a majority of patient-specific drug vulnerabilities of organoids derived from the relapsed HGSC lesions. This indicates that patient stratification in functional precision medicine for treatment of HGSC relapse could be prospectively performed at the primary disease stage.

Citation Format: Wojciech Senkowski, Laura Gall-Mas, Matias M. Falco, Yilin Li, Kari Lavikka, Mette C. Kriegbaum, Jaana Oikkonen, Daria Bulanova, Elin J. Pietras, Karolin Voßgröne, Yan-Jun Chen, Erdogan P. Erkan, Mia K. Høg, Ida M. Larsen, Tarja Lamminen, Katja Kaipio, Jutta Huvila, Anni Virtanen, Lars H. Engelholm, Pernille Christiansen, Eric Santoni Rugiu, Kaisa Huhtinen, Olli Carpén, Johanna Hynninen, Sampsa Hautaniemi, Anna Vähärautio, Krister Wennerberg. A platform utilizing high-grade serous ovarian cancer organoids for prospective patient stratification in functional precision medicine. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5779.

Abstract 1547: The urokinase plasminogen activator receptor-associated protein (uPARAP) is an attractive target for the development of antibody-drug conjugates (ADCs) for treatment of mesenchymal malignancies

Background: Soft tissue sarcoma (STS) is a complex family of rare malignancies with high unmet medical need. uPARAP is an endocytic receptor expressed at low levels on selected mesenchymal cell types, which internalizes fragments of collagen and transfers them to the lysosome for degradation. Besides its physiological role, uPARAP is considered a critical modulator of the tumor microenvironment. Here, for the first time, we explored the molecular epidemiology of uPARAP in sarcoma tissue to validate this receptor as target for the development of ADCs in this indication.

Methods: uPARAP expression was assessed in STS-specific tissue microarrays by immunohistochemistry in tissue samples from more than three hundred individual donors. Stainings were assessed by histopathologic scoring and grouped into high, medium and low expressing subgroups.

Results: uPARAP was found to be strongly over-expressed in a high percentage of cases of common STS, with variations in terms of incidence and level of expression between histological subtypes. High uPARAP expression was found in fibro- (86% of cases), synovial (84%), dedifferentiated lipo- (68%), pleomorphic lipo- (65%), myxofibro- (59%), leiomyo- (49%), and myxoid liposarcoma (24%). Work is ongoing in additional sarcoma subtypes.

Conclusions: Based on protein expression uPARAP is an attractive emerging therapeutic target for the development of uPARAP-binding ADCs in a broad range of mesenchymal malignancies. In addition, expression of uPARAP in STS may serve as a potential marker for patient selection in early clinical studies with uPARAP-targeting ADCs.

Citation Format: Pernille Barkholt, Agnieszka Wozniak, Chao-Chi Wang, Che-Jui Lee, Lore De Kock, Lars H. Engelholm, Carmel Lynch, Dominik Mumberg, Patrick Schöffski. The urokinase plasminogen activator receptor-associated protein (uPARAP) is an attractive target for the development of antibody-drug conjugates (ADCs) for treatment of mesenchymal malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1547.

Abstract 2016: Preclinical evaluation of uPARAP (MRC2) antibody-drug conjugates (ADCE-003,010,011) in osteosarcoma pdx models

Introduction: Antibody-drug Conjugates (ADCs) targeting differentially expressed tumor cell-surface antigens show robust clinical activity in several solid tumor cancers, but none is yet available for osteosarcoma. Due to the high unmet medical need in this indication, there is an urgent requirement to identify respective osteosarcoma cell-surface antigens and evaluate the antitumor activity of an ADC that can deliver tailored cytotoxic payloads to osteosarcoma tumors expressing these targets.

Methods: We used an integrated proteomic and transcriptomic surfaceome profiling approach to identify cell-surface proteins that are highly expressed in osteosarcoma but minimally expressed on normal tissues. uPARAP (MRC2) was found to be enriched in osteosarcoma at both protein and mRNA levels. The cell-surface expression of uPARAP (MRC2) was further validated by IHC and flow cytometry with osteosarcoma cell lines, PDX models, and patient tumor tissue microarray. As a proof of concept, three MRC2 targeted ADCs with different Microtubulin- and alkylating agent types of payloads were tested in 8 osteosarcoma PDX models. uPARAP (MRC2) ADC, control ADC, or vehicle control was administered IV to mice harboring flank tumors at a dose of 3mg/kg, weekly X 3 (ADCE-003), 2mg/kg on Day 1 (ADCE-010), and 10mg/kg weekly X 2 (ADCE-011). EFS for treatment (T) and control (C) groups, minimum relative tumor volume (minRTV), and objective response measures were analyzed.

Results: Western blotting confirmed the expression of uPARAP (MRC2) in 8 osteosarcoma cell lines and 8 PDX models. Flow cytometry further validated cell-surface localization and expression levels of uPARAP (MRC2) in 7 osteosarcoma cell lines. We then performed immunohistochemistry (IHC) staining using an osteosarcoma tissue microarray from 37 patients and 19 PDX models. uPARAP (MRC2) was expressed in 97% of the patient samples and 95% of the PDXs. 51% of the patient samples and 39% of the PDXs had an overall H-score of 100 or higher. Mice tolerated ADCs well with minimal toxicity. All 3 ADCs significantly prolonged EFS in 6/8 osteosarcoma models. Complete response (CR) or maintained CR were observed in 2 models in ADCE-010 and ADCE-011 groups, respectively.

Conclusions: uPARAP (MRC2) is highly expressed in most osteosarcoma samples, which makes it a viable target for respective antigen targeting ADC therapies. Three uPARAP (MRC2) targeting ADCs showed antitumor activities in osteosarcoma preclinical models which warrant further investigation of uPARAP targeting ADC therapies for osteosarcoma.

Citation Format: Yifei Wang, Wendong Zhang, Zhongting Zhang, Xiangjun Tian, Rossana Lazcano, Pooja Hingorani, Michael Roth, Jonathan Gill, Douglas Harrison, Zhaohui Xu, Jing Wang, Niels Behrendt, Christoffer F. Nielsen, Lars H. Engelholm, Richard Gorlick. Preclinical evaluation of uPARAP (MRC2) antibody-drug conjugates (ADCE-003,010,011) in osteosarcoma pdx models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2016.

Abstract 3069: Efficient establishment and utilization of a high-grade serous ovarian cancer organoid biobank

Extensive utilization of organoids from high-grade serous ovarian carcinoma (HGSOC), the most common and lethal ovarian cancer, has been hampered by low success rates of long-term culture and scarcity of fresh tumor material. Here we present the development of a novel method for efficient generation, expansion and use of HGSOC organoids from cryopreserved tumor material.

First, we assessed commonly used organoid media components and found that supplements such as FGF-2, R-Spondin1, Wnt or Noggin had negative impact on the HGSOC organoid derivation. But further, we found that supplementation with FGF-4, which has not been used in cancer organoid culture before, is beneficial for HGSOC organoid growth. Through extensive testing of various supplements and their combinations, we designed two novel HGSOC organoid media formulations - Medium 1 (M1) and Medium 2 (M2). Using M1 and M2 enabled generation and long-term expansion of living HGSOC organoid biobank with markedly improved success rate than in previous reports (55% vs. 23-38%). The organoids were established from cryopreserved tumor material, demonstrating the feasibility of using frozen tissue biobanks for HGSOC organoid derivation. Overall, we generated a collection of 18 expandable HGSOC organoid lines from 11 patients, encompassing samples from different tissue sites and disease progression stages.

We validated the organoids using whole-genome sequencing, immunohistochemistry and single-cell RNA sequencing and demonstrated that they are genetically and phenotypically representative of original patient samples over long-term culture. Based on available patient consents, we deposited 3 organoid lines in a publicly accessible biobank. Finally, we investigated whether organoid drug responses correlate to those observed earlier in the clinic in the corresponding patients. Organoid-based drug-response profiling of clinically used HGSOC drug collection was performed in 384-well microplate format. To explore whether growth conditions impact correlation between organoid drug responses and clinical response, we compared the organoid drug responses in the nutrient-rich M1/M2 growth media to the ones observed in human plasma-like medium (HPLM), supplemented with relevant niche factors from M1/M2. Organoid drug responses correlated with clinical treatment outcomes, but only for organoids maintained in HPLM (Spearman r = 0.987, p=0.007 in HPLM vs 0.607, p=0.167 in growth medium, n=7), highlighting the importance of culture conditions in organoid-based functional assays. Taken together, we introduce a resource for efficient development and use of HGSOC organoids from cryopreserved material in ovarian cancer research.

Citation Format: Wojciech Senkowski, Laura Gall Mas, Matias M. Falco, Yilin Li, Kari Lavikka, Mette C. Kriegbaum, Jaana Oikkonen, Daria Bulanova, Elin J. Pietras, Karolin Voßgröne, Erdogan P. Erkan, Terese K. Høj, Mia K. Høg, Tarja Lamminen, Katja Kaipio, Anni Virtanen, Lars H. Engelholm, Pernille Christiansen, Eric Santoni-Rugiu, Kaisa Huhtinen, Olli Carpén, Johanna Hynninen, Sampsa Hautaniemi, Anna Vähärautio, Krister Wennerberg. Efficient establishment and utilization of a high-grade serous ovarian cancer organoid biobank [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3069.

Uncovering Mediators of Collagen Degradation in the Tumor Microenvironment

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Collagen cleavage in tumors is primarily mediated by FAP⁺ cancer-associated fibroblasts.

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Collagen fibers are cleaved in an MMP-dependent manner.

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Released collagen fragments are internalized by M2-like tumor-associated macrophages and cancer-associated fibroblasts.

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The mannose receptor is central in collagen internalization by tumor-associated macrophages.

Increased remodeling of the extracellular matrix in malignant tumors has been shown to correlate with tumor aggressiveness and a poor prognosis. This remodeling involves degradation of the original extracellular matrix (ECM) and deposition of a new tumor-supporting ECM. The main constituent of the ECM is collagen and collagen turnover mainly occurs in a sequential manner, where initial proteolytic cleavage of the insoluble fibers is followed by cellular internalization of large well-defined collagen fragments for lysosomal degradation. However, despite extensive research in the field, a lack of consensus on which cell types within the tumor microenvironment express the involved proteases still exists. Furthermore, the relative contribution of different cell types to collagen internalization is not well-established. Here, we developed quantitative ex vivo collagen degradation assays and show that the proteases responsible for the initial collagen cleavage in two murine syngeneic tumor models are matrix metalloproteinases produced by cancer-associated fibroblasts and that collagen degradation fragments are endocytosed primarily by tumor-associated macrophages and cancer-associated fibroblasts from the tumor stroma. Using tumors from mannose receptor-deficient mice, we show that this receptor is essential for collagen-internalization by tumor-associated macrophages. Together, these findings identify the cell types responsible for the entire collagen degradation pathway, from initial cleavage to endocytosis of fragments for intracellular degradation.

The Urokinase Receptor (uPAR) as a "Trojan Horse" in Targeted Cancer Therapy: Challenges and Opportunities

Simple Summary

Discovered more than three decades ago, the urokinase-type plasminogen activator receptor (uPAR) has now firmly established itself as a versatile molecular target holding promise for the treatment of aggressive malignancies. The copious abundance of uPAR in virtually all human cancerous tissues versus their healthy counterparts has fostered a gradual shift in the therapeutic landscape targeting this receptor from function inhibition to cytotoxic approaches to selectively eradicate the uPAR-expressing cells by delivering a targeted cytotoxic insult. Multiple avenues are being explored in a preclinical setting, including the more innovative immune- or stroma targeting therapies. This review discusses the current state of these strategies, their potentialities, and challenges, along with future directions in the field of uPAR targeting.

Abstract

One of the largest challenges to the implementation of precision oncology is identifying and validating selective tumor-driving targets to enhance the therapeutic efficacy while limiting off-target toxicity. In this context, the urokinase-type plasminogen activator receptor (uPAR) has progressively emerged as a promising therapeutic target in the management of aggressive malignancies. By focalizing the plasminogen activation cascade and subsequent extracellular proteolysis on the cell surface of migrating cells, uPAR endows malignant cells with a high proteolytic and migratory potential to dissolve the restraining extracellular matrix (ECM) barriers and metastasize to distant sites. uPAR is also assumed to choreograph multiple other neoplastic stages via a complex molecular interplay with distinct cancer-associated signaling pathways. Accordingly, high uPAR expression is observed in virtually all human cancers and is frequently associated with poor patient prognosis and survival. The promising therapeutic potential unveiled by the pleiotropic nature of this receptor has prompted the development of distinct targeted intervention strategies. The present review will focus on recently emerged cytotoxic approaches emphasizing the novel technologies and related limits hindering their application in the clinical setting. Finally, future research directions and emerging opportunities in the field of uPAR targeting are also discussed.

The collagen receptor uPARAP/Endo180 regulates collectins through unique structural elements in its FNII domain

C-type lectins that contain collagen-like domains are known as collectins. These proteins are present both in the circulation and in extravascular compartments and are central players of the innate immune system, contributing to first-line defenses against viral, bacterial, and fungal pathogens. The collectins mannose-binding lectin (MBL) and surfactant protein D (SP-D) are regulated by tissue fibroblasts at extravascular sites via an endocytic mechanism governed by urokinase plasminogen activator receptor-associated protein (uPARAP or Endo180), which is also a collagen receptor. Here, we investigated the molecular mechanisms that drive the uPARAP-mediated cellular uptake of MBL and SP-D. We found that the uptake depends on residues within a protruding loop in the fibronectin type-II (FNII) domain of uPARAP that are also critical for collagen uptake. Importantly, however, we also identified FNII domain residues having an exclusive role in collectin uptake. We noted that these residues are absent in the related collagen receptor, the mannose receptor (MR or CD206), which consistently does not interact with collectins. We also show that the second C-type lectin-like domain (CTLD2) is critical for the uptake of SP-D, but not MBL, indicating an additional level of complexity in the interactions between collectins and uPARAP. Finally, we demonstrate that the same molecular mechanisms enable uPARAP to engage MBL immobilized on the surface of pathogens, thereby expanding the potential biological implications of this interaction. Our study reveals molecular details of the receptor-mediated cellular regulation of collectins and offers critical clues for future investigations into collectin biology and pathology.

Cellular uptake of collagens and implications for immune cell regulation in disease

As the dominant constituent of the extracellular matrix (ECM), collagens of different types are critical for the structural properties of tissues and make up scaffolds for cellular adhesion and migration. Importantly, collagens also directly modulate the phenotypic state of cells by transmitting signals that influence proliferation, differentiation, polarization, survival, and more, to cells of mesenchymal, epithelial, or endothelial origin. Recently, the potential of collagens to provide immune regulatory signals has also been demonstrated, and it is believed that pathological changes in the ECM shape immune cell phenotype. Collagens are themselves heavily regulated by a multitude of structural modulations or by catabolic pathways. One of these pathways involves a cellular uptake of collagens or soluble collagen-like defense collagens of the innate immune system mediated by endocytic collagen receptors. This cellular uptake is followed by the degradation of collagens in lysosomes. The potential of this pathway to regulate collagens in pathological conditions is evident from the increased extracellular accumulation of both collagens and collagen-like defense collagens following endocytic collagen receptor ablation. Here, we review how endocytic collagen receptors regulate collagen turnover during physiological conditions and in pathological conditions, such as fibrosis and cancer. Furthermore, we highlight the potential of collagens to regulate immune cells and discuss how endocytic collagen receptors can directly regulate immune cell activity in pathological conditions or do it indirectly by altering the extracellular milieu. Finally, we discuss the potential collagen receptors utilized by immune cells to directly detect ECM-related changes in the tissues which they encounter.

CCL2/MCP-1 signaling drives extracellular matrix turnover by diverse macrophage subsets

Macrophage plasticity, cellular origin, and phenotypic heterogeneity are perpetual challenges for studies addressing the biology of this pivotal immune cell in development, homeostasis, and tissue remodeling/repair. Consequently, a myriad of macrophage subtypes has been described in these contexts. To facilitate the identification of functional macrophage subtypes in vivo, here we used a flow cytometry-based assay that allows for detailed phenotyping of macrophages engaged in extracellular matrix (ECM) degradation. Of the five macrophage subtypes identified in the remodeling dermis by using this assay, collagen degradation was primarily executed by Ly6C⁻CCR2⁺ and Ly6C⁻CCR2^low macrophages via mannose receptor-dependent collagen endocytosis, while Ly6C⁺CCR2⁺ macrophages were the dominant fibrin-endocytosing cells. Unexpectedly, the CCL2/MCP1-CCR2 signaling axis was critical for both collagen and fibrin degradation, while collagen degradation was independent of IL-4Ra signaling. Furthermore, the cytokine GM-CSF selectively enhanced collagen degradation by Ly6C⁺CCR2⁺ macrophages. This study reveals distinct subsets of macrophages engaged in ECM turnover and identifies novel wound healing-associated functions for CCL2 and GM-CSF inflammatory cytokines.

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Phenotypically diverse subsets of dermal macrophages undertake the degradation of extracellular matrix

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C-C motif chemokine Ligand 2 (CCL2) signaling is critical for macrophage-mediated endocytosis of collagen and fibrin.

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Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) and Interleukin (IL)-13 stimulate collagen endocytosis.

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The wound healing-associated IL4-IL4 Receptor a (IL4Ra) signaling is dispensable for collagen endocytosis by macrophages.

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The mannose receptor is the principal endocytic collagen receptor utilized by resident dermal macrophages.

Collagen density regulates the activity of tumor-infiltrating T cells

Background

Tumor progression is accompanied by dramatic remodeling of the surrounding extracellular matrix leading to the formation of a tumor-specific ECM, which is often more collagen-rich and of increased stiffness. The altered ECM of the tumor supports cancer growth and metastasis, but it is unknown if this effect involves modulation of T cell activity. To investigate if a high-density tumor-specific ECM could influence the ability of T cells to kill cancer cells, we here studied how T cells respond to 3D culture in different collagen densities.

Methods

T cells cultured in 3D conditions surrounded by a high or low collagen density were imaged using confocal fluorescent microscopy. The effects of the different collagen densities on T cell proliferation, survival, and differentiation were examined using flow cytometry. Cancer cell proliferation in similar 3D conditions was also measured. Triple-negative breast cancer specimens were analyzed for the number of infiltrating CD8+ T cells and for the collagen density. Whole-transcriptome analyses were applied to investigate in detail the effects of collagen density on T cells. Computational analyses were used to identify transcription factors involved in the collagen density-induced gene regulation. Observed changes were confirmed by qRT-PCR analysis.

Results

T cell proliferation was significantly reduced in a high-density matrix compared to a low-density matrix and prolonged culture in a high-density matrix led to a higher ratio of CD4+ to CD8+ T cells. The proliferation of cancer cells was unaffected by the surrounding collagen-density. Consistently, we observed a reduction in the number of infiltrating CD8+ T-cells in mammary tumors with high collagen-density indicating that collagen-density has a role in regulating T cell abundance in human breast cancer.

Whole-transcriptome analysis of 3D-cultured T cells revealed that a high-density matrix induces downregulation of cytotoxic activity markers and upregulation of regulatory T cell markers. These transcriptional changes were predicted to involve autocrine TGF-β signaling and they were accompanied by an impaired ability of tumor-infiltrating T cells to kill autologous cancer cells.

Conclusions

Our study identifies a new immune modulatory mechanism, which could be essential for suppression of T cell activity in the tumor microenvironment.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0556-6) contains supplementary material, which is available to authorized users.

Immune regulation by fibroblasts in tissue injury depends on uPARAP-mediated uptake of collectins

Collectins such as mannose-binding lectin (MBL) and surfactant protein D (SP-D) become temporarily deposited in extravascular compartments after tissue injury and perform immune-stimulatory or inflammation-limiting functions. However, their turnover mechanisms, necessary to prevent excessive tissue damage, are virtually unknown. In this study, we show that fibroblasts in injured tissues undertake the clearance of collectins by using the endocytic collagen receptor uPARAP. In cellular assays, several types of collectins were endocytosed in a highly specific uPARAP-dependent process, not shared by the closely related receptor MR/CD206. When introduced into dermis or bleomycin-injured lungs of mice, collectins MBL and SP-D were endocytosed and routed for lysosomal degradation by uPARAP-positive fibroblasts. Fibroblast-specific expression of uPARAP governed endogenous SP-D levels and overall survival after lung injury. In lung tissue from idiopathic pulmonary fibrosis patients, a strong up-regulation of uPARAP was observed in fibroblasts adjacent to regions with SP-D secretion. This study demonstrates a novel immune-regulatory function of fibroblasts and identifies uPARAP as an endocytic receptor in immunity.

CRISPR/Cas9 Engineering of Adult Mouse Liver Demonstrates That the Dnajb1-Prkaca Gene Fusion Is Sufficient to Induce Tumors Resembling Fibrolamellar Hepatocellular Carcinoma

BACKGROUND & AIMS

Fibrolamellar hepatocellular carcinoma (FL-HCC) is a primary liver cancer that predominantly affects children and young adults with no underlying liver disease. A somatic, 400 Kb deletion on chromosome 19 that fuses part of the DnaJ heat shock protein family (Hsp40) member B1 gene (DNAJB1) to the protein kinase cAMP-activated catalytic subunit alpha gene (PRKACA) has been repeatedly identified in patients with FL-HCC. However, the DNAJB1-PRKACA gene fusion has not been shown to induce liver tumorigenesis. We used the CRISPR/Cas9 technique to delete in mice the syntenic region on chromosome 8 to create a Dnajb1-Prkaca fusion and monitored the mice for liver tumor development.

METHODS

We delivered CRISPR/Cas9 vectors designed to juxtapose exon 1 of Dnajb1 with exon 2 of Prkaca to create the Dnajb1-Prkaca gene fusion associated with FL-HCC, or control Cas9 vector, via hydrodynamic tail vein injection to livers of 8-week-old female FVB/N mice. These mice did not have any other engineered genetic alterations and were not exposed to liver toxins or carcinogens. Liver tissues were collected 14 months after delivery; genomic DNA was analyzed by PCR to detect the Dnajb1-Prkaca fusion, and tissues were characterized by histology, immunohistochemistry, RNA sequencing, and whole-exome sequencing.

RESULTS

Livers from 12 of the 15 mice given the vectors to induce the Dnajb1-Prkaca gene fusion, but none of the 11 mice given the control vector, developed neoplasms. The tumors contained the Dnajb1-Prkaca gene fusion and had histologic and cytologic features of human FL-HCCs: large polygonal cells with granular, eosinophilic, and mitochondria-rich cytoplasm, prominent nucleoli, and markers of hepatocytes and cholangiocytes. In comparing expression levels of genes between the mouse tumor and non-tumor liver cells, we identified changes similar to those detected in human FL-HCC, which included genes that affect cell cycle and mitosis regulation. Genomic analysis of mouse neoplasms induced by the Dnajb1-Prkaca fusion revealed a lack of mutations in genes commonly associated with liver cancers, as observed in human FL-HCC.

CONCLUSIONS

Using CRISPR/Cas9 technology, we found generation of the Dnajb1-Prkaca fusion gene in wild-type mice to be sufficient to initiate formation of tumors that have many features of human FL-HCC. Strategies to block DNAJB1-PRKACA might be developed as therapeutics for this form of liver cancer.

Early reversal cells in adult human bone remodeling: osteoblastic nature, catabolic functions and interactions with osteoclasts

The mechanism coupling bone resorption and formation is a burning question that remains incompletely answered through the current investigations on osteoclasts and osteoblasts. An attractive hypothesis is that the reversal cells are likely mediators of this coupling. Their nature is a big matter of debate. The present study performed on human cancellous bone is the first one combining in situ hybridization and immunohistochemistry to demonstrate their osteoblastic nature. It shows that the Runx2 and CD56 immunoreactive reversal cells appear to take up TRAcP released by neighboring osteoclasts. Earlier preclinical studies indicate that reversal cells degrade the organic matrix left behind by the osteoclasts and that this degradation is crucial for the initiation of the subsequent bone formation. To our knowledge, this study is the first addressing these catabolic activities in adult human bone through electron microscopy and analysis of molecular markers. Periosteoclastic reversal cells show direct contacts with the osteoclasts and with the demineralized resorption debris. These early reversal cells show (1) ¾-collagen fragments typically generated by extracellular collagenases of the MMP family, (2) MMP-13 (collagenase-3) and (3) the endocytic collagen receptor uPARAP/Endo180. The prevalence of these markers was lower in the later reversal cells, which are located near the osteoid surfaces and morphologically resemble mature bone-forming osteoblasts. In conclusion, this study demonstrates that reversal cells colonizing bone surfaces right after resorption are osteoblast-lineage cells, and extends to adult human bone remodeling their role in rendering eroded surfaces osteogenic.

Targeting a novel bone degradation pathway in primary bone cancer by inactivation of the collagen receptor uPARAP/Endo180

In osteosarcoma, a primary mesenchymal bone cancer occurring predominantly in younger patients, invasive tumour growth leads to extensive bone destruction. This process is insufficiently understood, cannot be efficiently counteracted and calls for novel means of treatment. The endocytic collagen receptor, uPARAP/Endo180, is expressed on various mesenchymal cell types and is involved in bone matrix turnover during normal bone growth. Human osteosarcoma specimens showed strong expression of this receptor on tumour cells, along with the collagenolytic metalloprotease, MT1-MMP. In advanced tumours with ongoing bone degeneration, sarcoma cells positive for these proteins formed a contiguous layer aligned with the degradation zones. Remarkably, osteoclasts were scarce or absent from these regions and quantitative analysis revealed that this scarcity marked a strong contrast between osteosarcoma and bone metastases of carcinoma origin. This opened the possibility that sarcoma cells might directly mediate bone degeneration. To examine this question, we utilized a syngeneic, osteolytic bone tumour model with transplanted NCTC-2472 sarcoma cells in mice. When analysed in vitro, these cells were capable of degrading the protein component of surface-labelled bone slices in a process dependent on MMP activity and uPARAP/Endo180. Systemic treatment of the sarcoma-inoculated mice with a mouse monoclonal antibody that blocks murine uPARAP/Endo180 led to a strong reduction of bone destruction. Our findings identify sarcoma cell-resident uPARAP/Endo180 as a central player in the bone degeneration of advanced tumours, possibly following an osteoclast-mediated attack on bone in the early tumour stage. This points to uPARAP/Endo180 as a promising therapeutic target in osteosarcoma, with particular prospects for improved neoadjuvant therapy.

The collagen receptor uPARAP/Endo180 in tissue degradation and cancer (Review)

The collagen receptor uPARAP/Endo180, the product of the MRC2 gene, is a central component in the collagen turnover process governed by various mesenchymal cells. Through the endocytosis of collagen or large collagen fragments, this recycling receptor serves to direct basement membrane collagen as well as interstitial collagen to lysosomal degradation. This capacity, shared only with the mannose receptor from the same protein family, endows uPARAP/Endo180 with a critical role in development and homeostasis, as well as in pathological disruptions of the extracellular matrix structure. Important pathological functions of uPARAP/Endo180 have been identified in various cancers and in several fibrotic conditions. With a particular focus on matrix turnover in cancer, this review presents the necessary background for understanding the function of uPARAP/Endo180 at the molecular and cellular level, followed by an in-depth survey of the available knowledge of the expression and role of this receptor in various types of cancer and other degenerative diseases.

Complex determinants in specific members of the mannose receptor family govern collagen endocytosis

Members of the well-conserved mannose receptor (MR) protein family have been functionally implicated in diverse biological and pathological processes. Importantly, a proposed common function is the internalization of collagen for intracellular degradation occurring during bone development, cancer invasion, and fibrosis protection. This functional relationship is suggested by a common endocytic capability and a candidate collagen-binding domain. Here we conducted a comparative investigation of each member's ability to facilitate intracellular collagen degradation. As expected, the family members uPARAP/Endo180 and MR bound collagens in a purified system and internalized collagens for degradation in cellular settings. In contrast, the remaining family members, PLA2R and DEC-205, showed no collagen binding activity and were unable to mediate collagen internalization. To pinpoint the structural elements discriminating collagen from non-collagen receptors, we constructed a series of receptor chimeras and loss- and gain-of-function mutants. Using this approach we identified a critical collagen binding loop in the suggested collagen binding region (an FN-II domain) in uPARAP/Endo180 and MR, which was different in PLA2R or DEC-205. However, we also found that an active FN-II domain was not a sufficient determinant to allow collagen internalization through these receptors. Nevertheless, this ability could be acquired by the transfer of a larger segment of uPARAP/Endo180 (the Cys-rich domain, the FN-II domain and two CTLDs) to DEC-205. These data underscore the importance of the FN-II domain in uPARAP/Endo180 and MR-mediated collagen internalization but at the same time uncover a critical interplay with flanking domains.

Monitoring mammary tumor progression and effect of tamoxifen treatment in MMTV-PymT using MRI and magnetic resonance spectroscopy with hyperpolarized [1-13C]pyruvate

PURPOSE

To use dynamic magnetic resonance spectroscopy (MRS) of hyperpolarized (13)C-pyruvate to follow the progress over time in vivo of breast cancer metabolism in the MMTV-PymT model, and to follow the response to the anti-estrogen drug tamoxifen.

METHODS

Tumor growth was monitored by anatomical MRI by measuring tumor volumes. Dynamic MRS of hyperpolarized (13)C was used to measure an "apparent" pyruvate-to-lactate rate constant (kp) of lactate dehydrogenase (LDH) in vivo. Further, ex vivo pathology and in vitro LDH initial reaction velocity were evaluated.

RESULTS

Tamoxifen significantly halted the tumor growth measured as tumor volume by MRI. In the untreated animals, kp correlated with tumor growth. The kP was somewhat but not significantly lower in the treated group. Studies in vitro confirmed the effects of tamoxifen on tumor growth, and here the LDH reaction velocity was reduced significantly in the treated group.

CONCLUSION

These hyperpolarized (13)C MRS findings indicate that tumor metabolic changes affects kP. The measured kp did not relate to treatment response to the same extent as did tumor growth, histological evaluation, and in vitro determination of LDH activity.

Loss of miR-10a activates lpo and collaborates with activated Wnt signaling in inducing intestinal neoplasia in female mice

miRNAs are small regulatory RNAs that, due to their considerable potential to target a wide range of mRNAs, are implicated in essentially all biological process, including cancer. miR-10a is particularly interesting considering its conserved location in the Hox cluster of developmental regulators. A role for this microRNA has been described in developmental regulation as well as for various cancers. However, previous miR-10a studies are exclusively based on transient knockdowns of this miRNA and to extensively study miR-10a loss we have generated a miR-10a knock out mouse. Here we show that, in the Apc^min mouse model of intestinal neoplasia, female miR-10a deficient mice develop significantly more adenomas than miR-10^+/+ and male controls. We further found that Lpo is extensively upregulated in the intestinal epithelium of mice deprived of miR-10a. Using in vitro assays, we demonstrate that the primary miR-10a target KLF4 can upregulate transcription of Lpo, whereas siRNA knockdown of KLF4 reduces LPO levels in HCT-116 cells. Furthermore, Klf4 is upregulated in the intestines of miR-10a knockout mice. Lpo has previously been shown to have the capacity to oxidize estrogens into potent depurinating mutagens, creating an instable genomic environment that can cause initiation of cancer. Therefore, we postulate that Lpo upregulation in the intestinal epithelium of miR-10a deficient mice together with the predominant abundance of estrogens in female animals mainly accounts for the sex-related cancer phenotype we observed. This suggests that miR-10a could be used as a potent diagnostic marker for discovering groups of women that are at high risk of developing colorectal carcinoma, which today is one of the leading causes of cancer-related deaths.

Posttranscriptional regulation by microRNA molecules constitutes an important mechanism for gene regulation and numerous studies have demonstrated a correlation between deregulated microRNA levels and diseases, such as cancer. However, genetics studies linking individual microRNAs to the etiology of cancer remain scarce. Here, we provide causal evidence for the involvement of the conserved microRNA miR-10a in the development of intestinal adenomas in the face of activated Wnt signaling. Interestingly, we find that loss of miR-10a mediates an increase in intestinal adenomas in female mice only and delineate the pathway to involve aberrant upregulation of the miR-10a target Klf4 and subsequent transcriptional activation of the Lpo gene encoding the antibacterial protein Lactoperoxidase. Lpo, in turn, has previously been demonstrated to oxidize estrogens into DNA-damaging mutagens.

M2-like macrophages are responsible for collagen degradation through a mannose receptor-mediated pathway

Tissue remodeling processes critically depend on the timely removal and remodeling of preexisting collagen scaffolds. Nevertheless, many aspects related to the turnover of this abundant extracellular matrix component in vivo are still incompletely understood. We therefore took advantage of recent advances in optical imaging to develop an assay to visualize collagen turnover in situ and identify cell types and molecules involved in this process. Collagen introduced into the dermis of mice underwent cellular endocytosis in a partially matrix metalloproteinase-dependent manner and was subsequently routed to lysosomes for complete degradation. Collagen uptake was predominantly executed by a quantitatively minor population of M2-like macrophages, whereas more abundant Col1a1-expressing fibroblasts and Cx3cr1-expressing macrophages internalized collagen at lower levels. Genetic ablation of the collagen receptors mannose receptor (Mrc1) and urokinase plasminogen activator receptor-associated protein (Endo180 and Mrc2) impaired this intracellular collagen degradation pathway. This study demonstrates the importance of receptor-mediated cellular uptake to collagen turnover in vivo and identifies a key role of M2-like macrophages in this process.

Differential actions of the endocytic collagen receptor uPARAP/Endo180 and the collagenase MMP-2 in bone homeostasis

A well-coordinated remodeling of uncalcified collagen matrices is a pre-requisite for bone development and homeostasis. Collagen turnover proceeds through different pathways, either involving extracellular reactions exclusively, or being dependent on endocytic processes. Extracellular collagen degradation requires the action of secreted or membrane attached collagenolytic proteases, whereas the alternative collagen degradation pathway proceeds intracellularly after receptor-mediated uptake and delivery to the lysosomes. In this study we have examined the functional interplay between the extracellular collagenase, MMP-2, and the endocytic collagen receptor, uPARAP, by generating mice with combined deficiency of both components. In both uPARAP-deficient and MMP-2-deficient adult mice the length of the tibia and femur was decreased, along with a reduced bone mineral density and trabecular bone quality. An additional decrease in bone length was observed when combining the two deficiencies, pointing to both components being important for the remodeling processes in long bone growth. In agreement with results found by others, a different effect of MMP-2 deficiency was observed in the distinct bone structures of the calvaria. These membranous bones were found to be thickened in MMP-2-deficient mice, an effect likely to be related to an accompanying defect in the canalicular system. Surprisingly, both of the latter defects in MMP-2-deficient mice were counteracted by concurrent uPARAP deficiency, demonstrating that the collagen receptor does not support the same matrix remodeling processes as the MMP in the growth of the skull. We conclude that both uPARAP and MMP-2 take part in matrix turnover processes important for bone growth. However, in some physiological situations, these two components do not support the same step in the growth process.

Tumor MMP-1 activates endothelial PAR1 to facilitate vascular intravasation and metastatic dissemination

Intravasation, the active entry of primary tumor cells into the vasculature, remains the least studied step in the metastatic cascade. Protease-mediated escape and stromal invasion of tumor cells represent widely accepted processes leading up to the intravasation step. However, molecular factors that contribute directly to tumor cell vascular penetration have not been identified. In this study, the in vivo role of the collagenolytic protease, MMP-1, in cancer cell intravasation and metastasis was analyzed by using a highly disseminating variant of human HEp3 epidermoid carcinoma, HEp3-hi/diss. Although naturally acquired or experimentally induced MMP-1 deficiency substantially suppressed HEp3-hi/diss intravasation, supplementation of recombinant MMP-1 to MMP-1-silenced primary tumors restored their impaired vascular dissemination. Surprisingly, abrogation of MMP-1 production and activity did not significantly affect HEp3-hi/diss migration or matrix invasion, suggesting noncollagenolytic mechanisms underlying MMP-1-dependent cell intravasation. In support of such noncollagenolytic mechanisms, MMP-1 silencing in HEp3-hi/diss cells modulated the microarchitecture and integrity of the angiogenic vasculature in a novel microtumor model. Concomitantly, MMP-1 deficiency led to decreased levels of intratumoral vascular permeability, tumor cell intravasation, and metastatic dissemination. Taking advantage of PAR1 deficiency of HEp3-hi/diss cells, we further show that endothelial PAR1 is a putative nontumor-cell/nonmatrix target, activation of which by carcinoma-produced MMP-1 regulates endothelial permeability and transendothelial migration. The inhibitory effects of specific PAR1 antagonists in live animals have also indicated that the mechanisms of MMP-1-dependent vascular permeability in tumors involve endothelial PAR1 activation. Together, our findings mechanistically underscore the contribution of a tumor MMP-1/endothelial PAR1 axis to actual intravasation events manifested by aggressive carcinoma cells.

Targeting a single function of the multifunctional matrix metalloprotease MT1-MMP: impact on lymphangiogenesis

The group of matrix metalloproteases (MMPs) is responsible for multiple processes of extracellular matrix remodeling in the healthy body but also for matrix and tissue destruction during cancer invasion and metastasis. The understanding of the contributions from each individual MMP, both in healthy and pathological events, has been complicated by the lack of specific inhibitors and the fact that some of the potent MMPs are multifunctional enzymes. These factors have also hampered the setup of therapeutic strategies targeting MMP activity. A tempting target is the membrane-associated MT1-MMP, which has well-documented importance in matrix degradation but which takes part in more than one pathway in this regard. In this report, we describe the selective targeting of a single function of this enzyme by means of a specific monoclonal antibody against MT1-MMP, raised in an MT1-MMP knock-out mouse. The antibody blocks the enzyme ability to activate proMMP-2 without interfering with the collagenolytic function or the general proteolytic activity of MT1-MMP. Using this antibody, we have shown that the MT1-MMP-catalyzed activation of proMMP-2 is involved in the outgrowth of cultured lymphatic endothelial cells in a collagen matrix in vitro, as well as in lymphatic vessel sprouting assayed ex vivo. This is the first example of the complete inactivation of a single function of a multifunctional MMP and the use of this strategy to pursue its role.

Inhibitory Monoclonal Antibodies against Mouse Proteases Raised in Gene-Deficient Mice Block Proteolytic Functions in vivo

Identification of targets for cancer therapy requires the understanding of the in vivo roles of proteins, which can be derived from studies using gene-targeted mice. An alternative strategy is the administration of inhibitory monoclonal antibodies (mAbs), causing acute disruption of the target protein function(s). This approach has the advantage of being a model for therapeutic targeting. mAbs for use in mouse models can be obtained through immunization of gene-deficient mice with the autologous protein. Such mAbs react with both species-specific epitopes and epitopes conserved between species. mAbs against proteins involved in extracellular proteolysis, including plasminogen activators urokinase plasminogen activator (uPA), tissue-type plasminogen activator (tPA), their inhibitor PAI-1, the uPA receptor (uPAR), two matrix metalloproteinases (MMP9 and MMP14), as well as the collagen internalization receptor uPARAP, have been developed. The inhibitory mAbs against uPA and uPAR block plasminogen activation and thereby hepatic fibrinolysis in vivo. Wound healing, another plasmin-dependent process, is delayed by an inhibitory mAb against uPA in the adult mouse. Thromboembolism can be inhibited by anti-PAI-1 mAbs in vivo. In conclusion, function-blocking mAbs are well-suited for targeted therapy in mouse models of different diseases, including cancer.

No effect of NGAL/lipocalin-2 on aggressiveness of cancer in the MMTV-PyMT/FVB/N mouse model for breast cancer

NGAL/lipocalin-2 is a siderophore-binding protein that is highly expressed in several cancers. It is suggested to confer a proliferative advantage to cancer cells. Its expression has been correlated with aggressiveness of breast cancer as determined both in patients and in mouse breast cancer models. This was recently confirmed in two mouse models of spontaneous breast cancer in wild-type and lipocalin-2-deficient mice. We used a similar strategy using a different mouse strain. Lipocalin-2-deficient mice and mouse mammary tumor virus-polyoma middle T antigen (MMTV-PyMT) mice were crossed into the same FVB/N background. All mice developed tumors by week 8. The mice were sacrificed on week 13 and tissue was processed for biochemical and histological analysis. The total tumor volume and number of metastases were quantitated in 26 lipocalin-2-deficient mice and 34 wild-type controls. Lipocalin-2 expression in tumors of MMTV-PyMT-positive and wild-type mice was assessed by quantitative real-time PCR and by immunohistochemistry. The expression of the lipocalin-2 receptors 24p3R and megalin and of Mmp-9, transferrin receptor, and Bdh2 (a producer of a mammalian siderophore) were quantitated by real-time PCR. No significant difference was observed between wild-type and lipocalin-2-deficient mice. Lipocalin-2 was highly expressed in tumors from wild-type mice, but the expression did not correlate with tumor size. No effect of lipocalin-2 was observed with respect to time to tumor appearance, total tumor volume, or to the number of metastases. Histology and gelatinolytic activity of the mammary tumors did not differ between wild-type and lipocalin-2-deficient mice. We conclude that NGAL/lipocalin-2 does not invariably affect the aggressiveness of breast cancers as assessed in mouse models, thus questioning the role of lipocalin-2 in cancer development.

Endocytic collagen degradation: a novel mechanism involved in protection against liver fibrosis

Fibrosis of the liver and its end-stage, cirrhosis, represent major health problems worldwide. In these fibrotic conditions, activated fibroblasts and hepatic stellate cells display a net deposition of collagen. This collagen deposition is a major factor leading to liver dysfunction, thus making it crucially important to understand both the collagen synthesis and turnover mechanisms in this condition. Here we show that the endocytic collagen receptor, uPARAP/Endo180, is a major determinant in governing the balance between collagen deposition and degradation. Cirrhotic human livers displayed a marked up-regulation of uPARAP/Endo180 in activated fibroblasts and hepatic stellate cells located close to the collagen deposits. In a hepatic stellate cell line, uPARAP/Endo180 was shown to be active in, and required for, the uptake and intracellular degradation of collagen. To evaluate the functional importance of this collagen receptor in vivo, liver fibrosis was induced in uPARAP/Endo180-deficient mice and littermate wild-type mice by chronic CCl(4) administration. A strong up-regulation of uPARAP/Endo180 was observed in wild-type mice, and a quantitative comparison of collagen deposits in the two groups of mice clearly revealed a fibrosis protective role of uPARAP/Endo180. This effect appeared to directly reflect the activity of the collagen receptor, since no compensatory events were noted when comparing the mRNA expression profiles of the two groups of mice in an array system focused on matrix-degrading components. This function of uPARAP/Endo180 defines a novel role of intracellular collagen turnover in fibrosis protection.

A novel functional role of collagen glycosylation: interaction with the endocytic collagen receptor uparap/ENDO180

Collagens make up the most abundant component of interstitial extracellular matrices and basement membranes. Collagen remodeling is a crucial process in many normal physiological events and in several pathological conditions. Some collagen subtypes contain specific carbohydrate side chains, the function of which is poorly known. The endocytic collagen receptor urokinase plasminogen activator receptor-associated protein (uPARAP)/Endo180 plays an important role in matrix remodeling through its ability to internalize collagen for lysosomal degradation. uPARAP/Endo180 is a member of the mannose receptor protein family. These proteins all include a fibronectin type II domain and a series of C-type lectin-like domains, of which only a minor part possess carbohydrate recognition activity. At least two of the family members, uPARAP/Endo180 and the mannose receptor, interact with collagens. The molecular basis for this interaction is known to involve the fibronectin type II domain but nothing is known about the function of the lectin domains in this respect. In this study, we have investigated a possible role of the single active lectin domain of uPARAP/Endo180 in the interaction with collagens. By expressing truncated recombinant uPARAP/Endo180 proteins and analyzing their interaction with collagens with high and low levels of glycosylation we demonstrated that this lectin domain interacts directly with glycosylated collagens. This interaction is functionally important because it was found to modulate the endocytic efficiency of the receptor toward highly glycosylated collagens such as basement membrane collagen IV. Surprisingly, this property was not shared by the mannose receptor, which internalized glycosylated collagens independently of its lectin function. This role of modulating its uptake efficiency by a specific receptor is a previously unrecognized function of collagen glycosylation.

The non-phagocytic route of collagen uptake: a distinct degradation pathway

The degradation of collagens, the most abundant proteins of the extracellular matrix, is involved in numerous physiological and pathological conditions including cancer invasion. An important turnover pathway involves cellular internalization and degradation of large, soluble collagen fragments, generated by initial cleavage of the insoluble collagen fibers. We have previously observed that in primary mouse fibroblasts, this endocytosis of collagen fragments is dependent on the receptor urokinase plasminogen activator receptor-associated protein (uPARAP)/Endo180. Others have identified additional mechanisms of collagen uptake, with different associated receptors, in other cell types. These receptors include β1-integrins, being responsible for collagen phagocytosis, and the mannose receptor. We have now utilized a newly developed monoclonal antibody against uPARAP/Endo180, which down-regulates the receptor protein level on treated cells, to examine the role of uPARAP/Endo180 as a mediator of collagen internalization by a wide range of cultured cell types. With the exception of macrophages, all cells that proved capable of efficient collagen internalization were of mesenchymal origin and all of these utilized uPARAP/Endo180 for their collagen uptake process. Macrophages internalized collagen in a process mediated by the mannose receptor, a protein belonging to the same protein family as uPARAP/Endo180. β1-Integrins were found not to be involved in the endocytosis of soluble collagen, irrespectively of whether this was mediated by uPARAP/Endo180 or the mannose receptor. This further distinguishes these pathways from the phagocytic uptake of particulate collagen.

Fibroblast growth factor receptor 4 regulates tumor invasion by coupling fibroblast growth factor signaling to extracellular matrix degradation

Aberrant expression and polymorphism of fibroblast growth factor receptor 4 (FGFR4) has been linked to tumor progression and anticancer drug resistance. We describe here a novel mechanism of tumor progression by matrix degradation involving epithelial-to-mesenchymal transition in response to membrane-type 1 matrix metalloproteinase (MT1-MMP, MMP-14) induction at the edge of tumors expressing the FGFR4-R388 risk variant. Both FGFR4 and MT1-MMP were upregulated in tissue biopsies from several human cancer types including breast adenocarcinomas, where they were partially coexpressed at the tumor/stroma border and tumor invasion front. The strongest overall coexpression was found in prostate carcinoma. Studies with cultured prostate carcinoma cell lines showed that the FGFR4-R388 variant, which has previously been associated with poor cancer prognosis, increased MT1-MMP-dependent collagen invasion. In this experimental model, knockdown of FGFR4-R388 or MT1-MMP by RNA interference blocked tumor cell invasion and growth in collagen. This was coupled with impaired phosphorylation of FGFR substrate 2 and Src, upregulation of E-cadherin, and suppression of cadherin-11 and N-cadherin. These in vitro results were substantiated by reduced MT1-MMP content and in vivo growth of prostate carcinoma cells after the FGFR4-R388 gene silencing. In contrast, knockdown of the alternative FGFR4-G388 allele enhanced MT1-MMP and invasive tumor cell growth in vivo and within three-dimensional collagen. These results will help to explain the reported association of the FGFR4-R388 variant with the progression and poor prognosis of certain types of tumors.

Mesenchymal cells reactivate Snail1 expression to drive three-dimensional invasion programs

Epithelial–mesenchymal transition (EMT) is required for mesodermal differentiation during development. The zinc-finger transcription factor, Snail1, can trigger EMT and is sufficient to transcriptionally reprogram epithelial cells toward a mesenchymal phenotype during neoplasia and fibrosis. Whether Snail1 also regulates the behavior of terminally differentiated mesenchymal cells remains unexplored. Using a Snai1 conditional knockout model, we now identify Snail1 as a regulator of normal mesenchymal cell function. Snail1 expression in normal fibroblasts can be induced by agonists known to promote proliferation and invasion in vivo. When challenged within a tissue-like, three-dimensional extracellular matrix, Snail1-deficient fibroblasts exhibit global alterations in gene expression, which include defects in membrane type-1 matrix metalloproteinase (MT1-MMP)-dependent invasive activity. Snail1-deficient fibroblasts explanted atop the live chick chorioallantoic membrane lack tissue-invasive potential and fail to induce angiogenesis. These findings establish key functions for the EMT regulator Snail1 after terminal differentiation of mesenchymal cells.

The collagen receptor uPARAP/Endo180

The uPAR-associated protein (uPARAP/Endo180), a type-1 membrane protein belonging to the mannose receptor family, is an endocytic receptor for collagen. Through this endocytic function, the protein takes part in a previously unrecognized mechanism of collagen turnover. uPARAP/Endo180 can bind and internalize both intact and partially degraded collagens. In some turnover pathways, the function of the receptor probably involves an interplay with certain matrix-degrading proteases whereas, in other physiological processes, redundant mechanisms involving both endocytic and pericellular collagenolysis seem to operate in parallel. On certain cell types, uPARAP/Endo180 occurs in a complex with the urokinase plasminogen activator receptor (uPAR) where it seems to fulfill other functions in addition to collagenolysis. uPARAP/Endo180 is expressed on various mesenchymal cells, including subpopulations of fibroblasts, osteoblasts and chondrocytes, generally in conjunction with matrix turnover and collagenolysis. A striking expression is found in developing bone where the collagenolytic function of uPARAP/Endo180 is one of the rate-limiting steps in growth. In murine breast tumors, the endocytic function of the receptor in collagen breakdown seems to be involved in invasive tumor growth.

Dimerization of endogenous MT1-MMP is a regulatory step in the activation of the 72-kDa gelatinase MMP-2 on fibroblasts and fibrosarcoma cells

The secreted gelatinase matrix metalloprotease-2 (MMP-2) and the membrane-anchored matrix metalloprotease MT1-MMP (MMP-14), are central players in pericellular proteolysis in extracellular matrix degradation. In addition to possessing a direct collagenolytic and gelatinolytic activity, these enzymes take part in a cascade pathway in which MT1-MMP activates the MMP-2 proenzyme. This reaction occurs in an interplay with the matrix metalloprotease inhibitor, TIMP-2, and the proposed mechanism involves two molecules of MT1-MMP in complex with one TIMP-2 molecule. We provide positive evidence that proMMP-2 activation is governed by dimerization of MT1-MMP on the surface of fibroblasts and fibrosarcoma cells. Even in the absence of transfection and overexpression, dimerization of MT1-MMP markedly stimulated the formation of active MMP-2 products. The effect demonstrated here was brought about by a monoclonal antibody that binds specifically to MT1-MMP as shown by immunofluorescence experiments. The antibody has no effect on the catalytic activity. The effect on proMMP-2 activation involves MT1-MMP dimerization because it requires the divalent monoclonal antibody, with no effect obtained with monovalent Fab fragments. Since only a negligible level of proMMP-2 activation was obtained with MT1-MMP-expressing cells in the absence of dimerization, our results identify the dimerization event as a critical level of proteolytic cascade regulation.

A composite role of vitronectin and urokinase in the modulation of cell morphology upon expression of the urokinase receptor

The urokinase receptor, urokinase receptor (uPAR), is a glycosylphosphatidylinositol-anchored membrane protein engaged in pericellular proteolysis and cellular adhesion, migration, and modulation of cell morphology. A direct matrix adhesion is mediated through the binding of uPAR to vitronectin, and this event is followed by downstream effects including changes in the cytoskeletal organization. However, it remains unclear whether the adhesion through uPAR-vitronectin is the only event capable of initiating these morphological rearrangements or whether lateral interactions between uPAR and integrins can induce the same response. In this report, we show that both of these triggering mechanisms can be operative and that uPAR-dependent modulation of cell morphology can indeed occur independently of a direct vitronectin binding. Expression of wild-type uPAR on HEK293 cells led to pronounced vitronectin adhesion and cytoskeletal rearrangements, whereas a mutant uPAR, uPAR(W32A) with defective vitronectin binding, failed to induce both phenomena. However, upon saturation of uPAR(W32A) with the protease ligand, pro-uPA, or its receptor-binding domain, the ability to induce cytoskeletal rearrangements was restored, although this did not rescue the uPAR-vitronectin binding and adhesion capability. On the other hand, using other uPAR variants, we could show that uPAR-vitronectin adhesion is indeed capable and sufficient to induce the same morphological rearrangements. This was shown with cells expressing a different single-site mutant, uPAR(Y57A), in the presence of a synthetic uPAR-binding peptide, as well as with wild-type uPAR, which underwent cytoskeletal rearrangements even when cultivated in uPA-deficient serum. Blocking of integrins with an Arg-Gly-Asp-containing peptide counteracted the matrix contacts necessary to initiate the uPAR-dependent cytoskeletal rearrangements, whereas inactivation of the Rac signaling pathway in all cases suppressed the occurrence of the same events.

Complementary roles of intracellular and pericellular collagen degradation pathways in vivo

Collagen degradation is essential for cell migration, proliferation, and differentiation. Two key turnover pathways have been described for collagen: intracellular cathepsin-mediated degradation and pericellular collagenase-mediated degradation. However, the functional relationship between these two pathways is unclear and even controversial. Here we show that intracellular and pericellular collagen turnover pathways have complementary roles in vivo. Individual deficits in intracellular collagen degradation (urokinase plasminogen activator receptor-associated protein/Endo180 ablation) or pericellular collagen degradation (membrane type 1-matrix metalloproteinase ablation) were compatible with development and survival. Their combined deficits, however, synergized to cause postnatal death by severely impairing bone formation. Interestingly, this was mechanistically linked to the proliferative failure and poor survival of cartilage- and bone-forming cells within their collagen-rich microenvironment. These findings have important implications for the use of pharmacological inhibitors of collagenase activity to prevent connective tissue destruction in a variety of diseases.

Extracellular collagenases and the endocytic receptor, urokinase plasminogen activator receptor-associated protein/Endo180, cooperate in fibroblast-mediated collagen degradation

The collagens of the extracellular matrix are the most abundant structural proteins in the mammalian body. In tissue remodeling and in the invasive growth of malignant tumors, collagens constitute an important barrier, and consequently, the turnover of collagen is a rate-limiting process in these events. A recently discovered turnover route with importance for tumor growth involves intracellular collagen degradation and is governed by the collagen receptor, urokinase plasminogen activator receptor-associated protein (uPARAP or Endo180). The interplay between this mechanism and extracellular collagenolysis is not known. In this report, we demonstrate the existence of a new, composite collagen breakdown pathway. Thus, fibroblast-mediated collagen degradation proceeds preferentially as a sequential mechanism in which extracellular collagenolysis is followed by uPARAP/Endo180-mediated endocytosis of large collagen fragments. First, we show that collagen that has been pre-cleaved by a mammalian collagenase is taken up much more efficiently than intact, native collagen by uPARAP/Endo180-positive cells. Second, we demonstrate that this preference is governed by the acquisition of a gelatin-like structure by the collagen, occurring upon collagenase-mediated cleavage under native conditions. Third, we demonstrate that the growth of uPARAP/Endo180-deficient fibroblasts on a native collagen matrix leads to substantial extracellular accumulation of well defined collagen fragments, whereas, wild-type fibroblasts possess the ability to direct an organized and complete degradation sequence comprising both the initial cleavage, the endocytic uptake, and the intracellular breakdown of collagen.

Increased expression of the collagen internalization receptor uPARAP/Endo180 in the stroma of head and neck cancer

Local growth, invasion, and metastasis of malignancies of the head and neck involve extensive degradation and remodeling of the underlying, collagen-rich connective tissue. Urokinase plasminogen activator receptor-associated protein (uPARAP)/Endo180 is an endocytic receptor recently shown to play a critical role in the uptake and intracellular degradation of collagen by mesenchymal cells. As a step toward determining the putative function of uPARAP/Endo180 in head and neck cancer progression, we used immunohistochemistry to determine the expression of this collagen internalization receptor in 112 human squamous cell carcinomas and 19 normal or tumor-adjacent head and neck tissue samples from the tongue, gingiva, cheek, tonsils, palate, floor of mouth, larynx, maxillary sinus, upper jaw, nasopharynx/nasal cavity, and lymph nodes. Specificity of detection was verified by staining of serial sections with two different monoclonal antibodies against two non-overlapping epitopes on uPARAP/Endo180 and by the use of isotype-matched non-immune antibodies. uPARAP/Endo180 expression was observed in stromal fibroblast-like, vimentin-positive cells. Furthermore, expression of the collagen internalization receptor was increased in tumor stroma compared with tumor-adjacent connective tissue or normal submucosal connective tissue and was most prominent in poorly differentiated tumors. These data suggest that uPARAP/Endo180 participates in the connective tissue destruction during head and neck squamous cell carcinoma progression by mediating cellular uptake and lysosomal degradation of collagen.

Intracellular collagen degradation mediated by uPARAP/Endo180 is a major pathway of extracellular matrix turnover during malignancy

We recently reported that uPARAP/Endo180 can mediate the cellular uptake and lysosomal degradation of collagen by cultured fibroblasts. Here, we show that uPARAP/Endo180 has a key role in the degradation of collagen during mammary carcinoma progression. In the normal murine mammary gland, uPARAP/Endo180 is widely expressed in periductal fibroblast-like mesenchymal cells that line mammary epithelial cells. This pattern of uPARAP/Endo180 expression is preserved during polyomavirus middle T-induced mammary carcinogenesis, with strong uPARAP/Endo180 expression by mesenchymal cells embedded within the collagenous stroma surrounding nests of uPARAP/Endo180-negative tumor cells. Genetic ablation of uPARAP/Endo180 impaired collagen turnover that is critical to tumor expansion, as evidenced by the abrogation of cellular collagen uptake, tumor fibrosis, and blunted tumor growth. These studies identify uPARAP/Endo180 as a key mediator of collagen turnover in a pathophysiological context.

Quantification of tissue inhibitor of metalloproteinases 2 in plasma from healthy donors and cancer patients

Tissue inhibitor of metalloproteinases (TIMP)-2 is a highly conserved molecule, which binds both active and latent matrix metalloproteinase (MMP)-2. TIMP-2 is also involved in the activation of MMP-2 on the cell surface. A quantitative enzyme-linked immunosorbent assay (ELISA) was established and optimized for measurement of TIMP-2 in plasma. The capturing antibody in the ELISA was a monoclonal, while the detecting antibody was a chicken polyclonal antibody recognizing the native form of human TIMP-2. The levels of TIMP-2 were measured in ethylenediaminetetraacetic acid (EDTA) and citrate plasma from healthy donors. The median values were determined as 163 ng/ml (n = 186) with a range of 109-253 ng/ml for EDTA plasma and 139 ng/ml (n = 77) with a range of 95-223 ng/ml for citrate plasma. The TIMP-2 concentration in citrate plasma from 15 patients with advanced, stage IV breast cancer had a median value of 160 ng/ml, only slightly higher but statistically distinguishable from the level found in citrate plasma from the healthy donors. In addition, the TIMP-2 concentration in EDTA plasma from colorectal cancer patients revealed a significantly higher level in plasma from patients with Dukes stage A (P = 0.01) compared with patients with more advanced Dukes stages.

uPARAP/endo180 directs lysosomal delivery and degradation of collagen IV

Collagen turnover is crucial for tissue homeostasis and remodeling and pathological processes such as cancer invasion, but the underlying molecular mechanisms are poorly understood. A major pathway appears to be internalization and degradation by fibroblasts. We now show that the endocytic transmembrane glycoprotein urokinase plasminogen activator receptor-associated protein (uPARAP/endo180) directs collagen IV for lysosomal delivery and degradation. In wild-type fibroblasts, fluorescently labeled collagen IV was first internalized into vesicular structures with diffuse fluorescence eventually appearing uniformly within the wild-type cells after longer incubation times. In these cells, some collagen-containing vesicles were identified as lysosomes by staining for LAMP-1. In contrast, collagen IV remained extracellular and associated with fiber-like structures on uPARAP/endo180-deficient fibroblasts. Blocking lysosomal cysteine proteases with the inhibitor E64d resulted in strong accumulation of collagen IV in lysosomes in wild-type cells, but only very weak intracellular fluorescence accumulation in uPARAP/endo180-deficient fibroblasts. We conclude that uPARAP/endo180 is critical for targeted delivery of collagen IV to lysosomes for degradation implicating the receptor in normal and malignant extracellular matrix degradation. A similar localization pattern was observed for collagen V, suggesting that uPARAP/endo180 might be generally involved in collagen degradation.

uPARAP/Endo180 is essential for cellular uptake of collagen and promotes fibroblast collagen adhesion

The uptake and lysosomal degradation of collagen by fibroblasts constitute a major pathway in the turnover of connective tissue. However, the molecular mechanisms governing this pathway are poorly understood. Here, we show that the urokinase plasminogen activator receptor-associated protein (uPARAP)/Endo180, a novel mesenchymally expressed member of the macrophage mannose receptor family of endocytic receptors, is a key player in this process. Fibroblasts from mice with a targeted deletion in the uPARAP/Endo180 gene displayed a near to complete abrogation of collagen endocytosis. Furthermore, these cells had diminished initial adhesion to a range of different collagens, as well as impaired migration on fibrillar collagen. These studies identify a central function of uPARAP/Endo180 in cellular collagen interactions.