Direct binding of hepatocyte growth factor and vascular endothelial growth factor to CD44v6

Quantitative live imaging reveals a direct interaction between CD44v6 and MET in membrane domains upon activation with both MET ligands, HGF and internalin B

Deregulation of the receptor tyrosine kinase MET/hepatocyte growth factor (HGF) pathway results in several pathological processes involved in tumor progression and metastasis. In a different context, MET can serve as an entry point for the bacterium Listeria monocytogenes, when activated by the internalin B (InlB) protein during infection of non-phagocytic cells. We have previously demonstrated that MET requires CD44v6 for its ligand-induced activation. However, the stoichiometry and the steps required for the formation of this complex, are still unknown. In this work, we studied the dynamics of the ligand-induced interaction of CD44v6 with MET at the plasma membrane. Using Förster resonance energy transfer-based fluorescence lifetime imaging microscopy in T-47D cells, we evidenced a direct interaction between MET and CD44v6 promoted by HGF and InlB in live cells. In the absence of MET, fluorescence correlation spectroscopy experiments further showed the dimerization of CD44v6 and the increase of its diffusion induced by HGF and InlB. In the presence of MET, stimulation of the cells by HGF or InlB significantly decreased the diffusion of CD44v6, in line with the formation of a ternary complex of MET with CD44v6 and HGF/InlB. Finally, similarly to HGF/InlB, disruption of liquid-ordered domains (Lo) by methyl-β-cyclodextrin increased CD44v6 mobility suggesting that these factors induce the exit of CD44v6 from the Lo domains. Our data led us to propose a model for MET activation, where CD44v6 dimerizes and diffuses rapidly out of Lo domains to form an oligomeric MET/ligand/CD44v6 complex that is instrumental for MET activation.

Hyaluronan network: a driving force in cancer progression

Hyaluronan is one of the most abundant macromolecules of the extracellular matrix and regulates several physiological cell and tissue properties. However, hyaluronan has been shown to accumulate together with its receptors in various cancers. In tumors, accumulation of hyaluronan system components (hyaluronan synthesizing/degrading enzymes and interacting proteins) associates with poor outcomes of the patients. In this article, we review the main roles of hyaluronan in normal physiology and cancer, and further discuss the targeting of hyaluronan system as an applicable therapeutic strategy.

Coreceptor Functions of Cell Surface Heparan Sulfate Proteoglycans

Receptor-ligand interactions play an important role in many biological processes by triggering specific cellular responses. These interactions are frequently regulated by coreceptors that facilitate, alter, or inhibit signaling. Coreceptors work in parallel with other specific and accessory molecules to coordinate receptor-ligand interactions. Cell surface heparan sulfate proteoglycans (HSPGs) function as unique coreceptors because they can bind to many ligands and receptors through their HS and core protein motifs. Cell surface HSPGs are typically expressed in abundance of the signaling receptors and, thus, are capable of mediating the initial binding of ligands to the cell surface. HSPG coreceptors do not possess kinase domains or intrinsic enzyme activities and, for the most part, binding to cell surface HSPGs does not directly stimulate intracellular signaling. Because of these features, cell surface HSPGs primarily function as coreceptors for many receptor-ligand interactions. Given that cell surface HSPGs are widely conserved, they likely serve fundamental functions to preserve basic physiological processes. Indeed, cell surface HSPGs can support specific cellular interactions with growth factors, morphogens, chemokines, extracellular matrix (ECM) components, and microbial pathogens and their secreted virulence factors. Through these interactions, HSPG coreceptors regulate cell adhesion, proliferation, migration and differentiation, and impact the onset, progression, and outcome of pathophysiological processes, such as development, tissue repair, inflammation, infection, and tumorigenesis. This review seeks to provide an overview of the various mechanisms of how cell surface HSPGs function as coreceptors.

A novel tumor suppressor role of myosin light chain kinase splice variants through downregulation of the TEAD4/CD44 axis

Myosin light chain kinase (MLCK) regulates actinomyosin contraction. Two splice variants of long MLCK are expressed in epithelial cells and divergently regulate gut barrier functions; reduced MLCK levels in human colorectal cancers (CRC) with unclarified significance have been reported. CRC are solid tumors clonally sustained by stem cells highly expressing CD44 and CD133. The aim was to investigate the role of MLCK splice variants in CRC tumorigenesis. We found lower MLCK1/2 and higher CD44 expression in human CRC, but no change in CD133 or LGR5. Large-scale bioinformatics showed an inverse relationship between MYLK and CD44 in human sample gene datasets. A 3-fold increased tumor burden was observed in MLCK(-/-) mice compared with wild-type (WT) mice in a chemical-induced CRC model. Primary tumorspheres derived from the MLCK(-/-) mice displayed larger sizes and higher CD44 transcript levels than those from the WT mice. Bioinformatics revealed binding of TEAD4 (a transcriptional enhancer factor family member in the Hippo pathway) to CD44 promoter, which was confirmed by luciferase reporter assay. Individually expressing MLCK1 and MLCK2 variants in the MLCK-knockout (KO) Caco-2 cells inhibited the nuclear localization of TEAD4 cofactors, VGLL3 and YAP1, respectively, and both variants reduced the CD44 transcription. Accelerated cell cycle transit was observed in the MLCK-KO cells, whereby expression of MLCK1/2 variants counterbalanced the cell hyperproliferation. In conclusion, MLCK1/2 variants are novel tumor suppressors by downregulating the TEAD4/CD44 axis via reducing nuclear translocation of distinct transcriptional coactivators. The reduction of epithelial MLCKs, especially isoform 2, may drive cancer stemness and tumorigenesis.

A guide to the composition and functions of the extracellular matrix

Extracellular matrix (ECM) is a dynamic 3-dimensional network of macromolecules that provides structural support for the cells and tissues. Accumulated knowledge clearly demonstrated over the last decade that ECM plays key regulatory roles since it orchestrates cell signaling, functions, properties and morphology. Extracellularly secreted as well as cell-bound factors are among the major members of the ECM family. Proteins/glycoproteins, such as collagens, elastin, laminins and tenascins, proteoglycans and glycosaminoglycans, hyaluronan, and their cell receptors such as CD44 and integrins, responsible for cell adhesion, comprise a well-organized functional network with significant roles in health and disease. On the other hand, enzymes such as matrix metalloproteinases and specific glycosidases including heparanase and hyaluronidases contribute to matrix remodeling and affect human health. Several cell processes and functions, among them cell proliferation and survival, migration, differentiation, autophagy, angiogenesis, and immunity regulation are affected by certain matrix components. Structural alterations have been also well associated with disease progression. This guide on the composition and functions of the ECM gives a broad overview of the matrisome, the major ECM macromolecules, and their interaction networks within the ECM and with the cell surface, summarizes their main structural features and their roles in tissue organization and cell functions, and emphasizes the importance of specific ECM constituents in disease development and progression as well as the advances in molecular targeting of ECM to design new therapeutic strategies.

Hepatocyte growth factor/MET and CD44 in colorectal cancer: partners in tumorigenesis and therapy resistance

Intestinal epithelial self-renewal is a tightly controlled process, which is critically dependent on WNT signalling. Aberrant activation of the WNT pathway in intestinal stem cells (ISCs) results in constitutive transcription of target genes, which collectively drive malignant transformation in colorectal cancer (CRC). However, the contribution of individual genes to intestinal homeostasis and tumorigenesis often is incompletely defined. Here, we discuss converging evidence indicating that the receptor tyrosine kinase (RTK) MET and its ligand hepatocyte growth factor (HGF) play a major role in the intestinal damage response, as well as in intestinal tumorigenesis, by controlling the proliferation, survival, motility, and stemness of normal and neoplastic intestinal epithelial cells. These activities of MET are promoted by specific CD44 isoforms expressed by ISCs. The accrued data indicate that MET and the EGFR have overlapping roles in the biology of intestinal epithelium and that metastatic CRCs can exploit this redundancy to escape from EGFR-targeted treatments, co-opting HGF/MET/CD44v signalling. Hence, targeting both pathways may be required for effective treatment of (a subset of) CRCs. The RTK identity of MET, the distinctive 'plasminogen-like' structure and activation mode of its ligand HGF, and the specific collaboration of MET with CD44, provide several unique targeting options, which merit further exploration.

Involvement of hyaluronan and CD44 in cancer and viral infections

Hyaluronan and its major receptor CD44 are ubiquitously distributed. They have important structural as well as signaling roles, regulating tissue homeostasis, and their expression levels are tightly regulated. In addition to signaling initiated by the interaction of the intracellular domain of CD44 with cytoplasmic signaling molecules, CD44 has important roles as a co-receptor for different types of receptors of growth factors and cytokines. Dysregulation of hyaluronan-CD44 interactions is seen in diseases, such as inflammation and cancer. In the present communication, we discuss the mechanism of hyaluronan-induced signaling via CD44, as well as the involvement of hyaluronan-engaged CD44 in malignancies and in viral infections.

Co-expression of CD44/MyD88 is a poor prognostic factor in advanced epithelial ovarian cancer

Background

Cluster of differentiation 44 (CD44)/myeloid differentiation factor 88 (MyD88) is the molecular characterization of EOC stem cells. An important characteristic of CD44+/MyD88+ epithelial ovarian cancer (EOC) cells, which differentiate them from the CD44-/MyD88- EOC cells, is the presence of a functional TLR4-MyD88-NFkB pathway. The aim of our study is to investigate the clinical significance of CD44/MyD88 co-expression in EOC.

Methods

A total of 138 specimens of ovarian tissues was detected CD44 and MyD88 expression by immunocytochemistry, including EOC (N=108), borderline tumors (N=10), benign cysts (N=10) and normal ovarian tissue (N=10). The association of CD44/MyD88 co-expression with clinicopathological factors and outcomes was analyzed.

Results

The expression of CD44 was showed distinct difference in EOC (53 of 108, 49.1%), in borderline tumors (3 of 10, 30.0%), in benign cysts (2 of 10, 20.0%) and normal ovarian (2 of 10, 20.0%). A total of 41 (38.0%) cancers showed a combined expression of CD44/MyD88. The expression of CD44 and MyD88 had definitely correlativity (r=0.21, P=0.026). CD44/MyD88 co-expression was associated with tumor progression, metastasis, and recurrence in advanced EOC, and an independent prognostic factor for disease-free survival and overall survival.

Conclusions

CD44/MyD88 co-expression has been shown to contribute to EOC progression and outcome directly and has a promising as a therapeutic target in EOC.

CD44-dependent inflammation, fibrogenesis, and collagenolysis regulates extracellular matrix remodeling and tensile strength during cutaneous wound healing

Cutaneous wound healing consists of three main phases: inflammation, re-epithelialization, and tissue remodeling. During normal wound healing, these processes are tightly regulated to allow restoration of skin function and biomechanics. In many instances, healing leads to an excess accumulation of fibrillar collagen (the principal protein found in the extracellular matrix - ECM), and the formation of scar tissue, which has compromised biomechanics, tested using ramp to failure tests, compared to normal skin (Corr and Hart, 2013 [1]). Alterations in collagen accumulation and architecture have been attributed to the reduced tensile strength found in scar tissue (Brenda et al., 1999; Eleswarapu et al., 2011). Defining mechanisms that govern cellular functionality and ECM remodeling are vital to understanding normal versus pathological healing and developing approaches to prevent scarring. CD44 is a cell surface adhesion receptor expressed on nearly all cell types present in dermis. Although CD44 has been implicated in an array of inflammatory and fibrotic processes such as leukocyte recruitment, T-cell extravasation, and hyaluronic acid (the principal glycosaminoglycan found in the ECM) metabolism, the role of CD44 in cutaneous wound healing and scarring remains unknown. We demonstrate that in an excisional biopsy punch wound healing model, CD44-null mice have increased inflammatory and reduced fibrogenic responses during early phases of wound healing. At wound closure, CD44-null mice exhibit reduced collagen degradation leading to increased accumulation of fibrillar collagen, which persists after wound closure leading to reduced tensile strength resulting in a more severe scarring phenotype compared to WT mice. These data indicate that CD44 plays a previously unknown role in fibrillar collagen accumulation and wound healing during the injury response.

Differential recruitment of CD44 isoforms by ErbB ligands reveals an involvement of CD44 in breast cancer

Members of the CD44 family of transmembrane glycoproteins control cell signaling pathways from numerous cell surface receptors, including receptor tyrosine kinases (RTKs). The decisive factor (ligand, RTKs or both) that controls the recruitment of specific CD44 isoforms is still unknown. We investigated this question by using the EGFR signaling pathway, in which one receptor can be activated by a broad range of ligands. By means of siRNA-mediated downregulation of CD44 expression and blocking experiments, we identified CD44v6 as a co-receptor for EGF- and ER-induced ErbB1 activation and for NRG1-induced ErbB3 and ErbB4 activation. In contrast, TGFα is independent of all CD44 isoforms, even though it addresses the same receptor pairs as EGF. Moreover, the heparin-sulfated CD44v3 isoform is required for HB-EGF-induced EGFR signaling. These data suggest that specific CD44 isoforms are recruited in a ligand-dependent manner as co-receptors in the EGFR signaling pathways and that the specificity is determined by the ligand and not by the receptors themselves. The in vivo relevance of this interplay between CD44 isoforms and EGFR ligands is underlined by the decreased metastatic spreading of mammary carcinomas in mice treated with a CD44v6-specific peptide. Most importantly, we found a clear correlation between the presence of CD44v6/ErbB1 complexes in breast cancer patients and lymph node metastases.

CAR T-cell immunotherapy of MET-expressing malignant mesothelioma

Mesothelioma is an incurable cancer for which effective therapies are required. Aberrant MET expression is prevalent in mesothelioma, although targeting using small molecule-based therapeutics has proven disappointing. Chimeric antigen receptors (CARs) couple the HLA-independent binding of a cell surface target to the delivery of a tailored T-cell activating signal. Here, we evaluated the anti-tumor activity of MET re-targeted CAR T-cells against mesothelioma. Using immunohistochemistry, MET was detected in 67% of malignant pleural mesotheliomas, most frequently of epithelioid or biphasic subtype. The presence of MET did not influence patient survival. Candidate MET-specific CARs were engineered in which a CD28+CD3ζ endodomain was fused to one of 3 peptides derived from the N and K1 domains of hepatocyte growth factor (HGF), which represents the minimum MET binding element present in this growth factor. Using an NIH3T3-based artificial antigen-presenting cell system, we found that all 3 candidate CARs demonstrated high specificity for MET. By contrast, these CARs did not mediate T-cell activation upon engagement of other HGF binding partners, namely CD44v6 or heparan sulfate proteoglycans, including Syndecan-1. NK1-targeted CARs demonstrated broadly similar in vitro potency, indicated by destruction of MET-expressing mesothelioma cell lines, accompanied by cytokine release. In vivo anti-tumor activity was demonstrated following intraperitoneal delivery to mice with an established mesothelioma xenograft. Progressive tumor regression occurred without weight loss or other clinical indicators of toxicity. These data confirm the frequent expression of MET in malignant pleural mesothelioma and demonstrate that this can be targeted effectively and safely using a CAR T-cell immunotherapeutic strategy.

Epidermal-specific deletion of CD44 reveals a function in keratinocytes in response to mechanical stress

CD44, a large family of transmembrane glycoproteins, plays decisive roles in physiological and pathological conditions. CD44 isoforms are involved in several signaling pathways essential for life such as growth factor-induced signaling by EGF, HGF or VEGF. CD44 is also the main hyaluronan (HA) receptor and as such is involved in HA-dependent processes. To allow a genetic dissection of CD44 functions in homeostasis and disease, we generated a Cd44 floxed allele allowing tissue- and time-specific inactivation of all CD44 isoforms in vivo. As a proof of principle, we inactivated Cd44 in the skin epidermis using the K14Cre allele. Although the skin of such Cd44^Δker mutants appeared morphologically normal, epidermal stiffness was reduced, wound healing delayed and TPA induced epidermal thickening decreased. These phenotypes might be caused by cell autonomous defects in differentiation and HA production as well as impaired adhesion and migration on HA by Cd44^Δker keratinocytes. These findings support the usefulness of the conditional Cd44 allele in unraveling essential physiological and pathological functions of CD44 isoforms.

Serglycin in tumor microenvironment promotes non-small cell lung cancer aggressiveness in a CD44-dependent manner

Tumor microenvironment (TME) plays an active role in promoting tumor progression. To further understand the communication between TME and tumor cells, this study aimed at investigating the involvement of CD44, a type I cell surface receptor, in the crosstalk between tumor cells and TME. We have previously shown that chondroitin sulfate proteoglycan serglycin (SRGN), a CD44-interacting factor, was preferentially secreted by cancer-associated fibroblasts (CAFs) for promoting tumor growth in breast cancer patients. In this study, we show that SRGN is overexpressed in primary non-small cell lung cancers (NSCLCs), by both carcinoma and stromal cells. Using gain-of-function and loss-of-function approaches, we show that SRGN promotes NSCLC cell migration and invasion as well as colonization in the lung and liver in a CD44-dependent manner. SRGN induces lung cancer cell stemness, as demonstrated by its ability to enhance NSCLC cell sphere formation via Nanog induction, accompanied with increased chemoresistance and anoikis-resistance. SRGN promotes epithelial-mesenchymal transition by enhancing vimentin expression via CD44/NF-κB/claudin-1 (CLDN1) axis. In support, CLDN1 and SRGN expression are tightly linked together in primary NSCLC. Most importantly, increased expression of SRGN and/or CLDN1 predicts poor prognosis in primary lung adenocarcinomas. In summary, we demonstrate that SRGN secreted by tumor cells and stromal components in the TME promotes malignant phenotypes through interacting with tumor cell receptor CD44, suggesting that a combined therapy targeting both CD44 and its ligands in the TME may be an attractive approach for cancer therapy.

The prognostic value and clinicopathological significance of CD44 expression in ovarian cancer: a meta-analysis

PURPOSE

The prognostic value and clinicopathological significance of CD44 in ovarian cancer (OC) remain unclear. This meta-analysis, therefore, aims to evaluate the correlation between CD44 expression and OC.

METHODS

Studies published until March 2016 were searched in PubMed, EMBASE, and ISI Web of Knowledge databases. The odds ratio (OR) and the hazard ratio (HR) with 95 % confidence interval (CI) were used to assess the effects.

RESULTS

Twenty-four studies that include 2267 OC patients were identified for the final analysis. Sixteen studies investigated the expression difference of CD44 standard (CD44s) in 1848 patients. Results showed that high CD44s expression is associated with chemoresistance (OR 5.94, 95 % CI 1.91-18.47) and short disease-free survival (DFS) time (HR 2.57, 95 % CI 1.34-4.91). In addition, CD44s expression is not associated with tumor differentiation grade, residual mass, lymphoid nodal metastasis, and overall survival (OS). Ten studies investigated the expression difference of CD44v6 in 724 patients. Results showed that the CD44v6 expression is not correlated with FIGO stage, tumor differentiation grade, lymphoid nodal metastasis, and OS.

CONCLUSION

High CD44s expression possibly indicates poor prognosis in OC patients given that high CD44s expression initiates chemotherapy resistance, although this expression pattern is not an independent predictive factor for OS. Meanwhile, high CD44s expression may be related to poor DFS of OC, but this relationship must be further confirmed. In addition, the result in which CD44v6 is not associated with OS of OC patients should be interpreted with caution.

Expression and Function of CD44 in Epithelial Ovarian Carcinoma

CD44, a cell surface glycoprotein, has been increasingly implicated in the pathogenesis and progression of epithelial ovarian cancer, the deadliest gynecologic malignancy in women. Here, we review recent reports on the expression and function of CD44 in epithelial ovarian carcinoma. Further functional data for CD44 in peritoneal adhesion and metastatic progression and its association with stem cells is highlighted. Recent studies utilizing CD44 for therapeutic targeting are also discussed.