A chondroitin/dermatan sulfate form of CD44 is a receptor for collagen XIV (undulin)

Expression of CD44, Transforming Growth Factor-β, and Matrix Metalloproteinases in Women With Pelvic Organ Prolapse

Background

Defects in the pelvic floor connective tissue may underlie the etiology of pelvic organ prolapse (POP). We hypothesized that the expression of proteins regulating extracellular matrix turnover is altered in the uterosacral ligament of women with POP. We compared the expression of CD44, transforming growth factor (TGF)-β, and matrix metalloproteinases (MMPs) 2/9 in women with and without POP.

Methods and Results

This matched case-control study included 30 postmenopausal women, with POP stage 2 and higher according to the POP quantification system, and 30 postmenopausal women without POP. Immunohistochemical analyses of the uterosacral ligament specimens obtained after hysterectomy were performed to determine CD44, TGF-β, MMP-2, and MMP-9 expression. The expression was quantified using ImageJ software, and the association between prolapse occurrence and risk factors was evaluated using Spearman's correlation analysis. CD44 expressions were significantly lower (p < 0.05), whereas MMP-2 and MMP-9 expression was higher (p < 0.0001 and p < 0.05, respectively), in the POP group than in the control group. The expression of TGF-β was similar in both groups. The occurrence of uterine prolapse was positively correlated with age, postmenopausal age, and MMP-2 and MMP-9 expression (p < 0.01) and negatively correlated with CD44 expression (p < 0.05).

Conclusion

CD44, MMP-2, and MMP-9 may play critical roles in the pathogenesis of POP and may be candidate biomarkers of POP progression.

Interplay between Cell-Surface Receptors and Extracellular Matrix in Skin

Skin consists of the epidermis and dermis, which are connected by a specialized basement membrane-the epidermal basement membrane. Both the epidermal basement membrane and the underlying interstitial extracellular matrix (ECM) created by dermal fibroblasts contain distinct network-forming macromolecules. These matrices play various roles in order to maintain skin homeostasis and integrity. Within this complex interplay of cells and matrices, cell surface receptors play essential roles not only for inside-out and outside-in signaling, but also for establishing mechanical and biochemical properties of skin. Already minor modulations of this multifactorial cross-talk can lead to severe and systemic diseases. In this review, major epidermal and dermal cell surface receptors will be addressed with respect to their interactions with matrix components as well as their roles in fibrotic, inflammatory or tumorigenic skin diseases.

A Novel Splice Variant of HYAL-4 Drives Malignant Transformation and Predicts Outcome in Patients with Bladder Cancer

PURPOSE

Poor prognosis of patients with muscle-invasive bladder cancer that often metastasizes drives the need for discovery of molecular determinants of bladder cancer progression. Chondroitin sulfate proteoglycans, including CD44, regulate cancer progression; however, the identity of a chondroitinase (Chase) that cleaves chondroitin sulfate from proteoglycans is unknown. HYAL-4 is an understudied gene suspected to encode a Chase, with no known biological function. We evaluated HYAL-4 expression and its role in bladder cancer.

EXPERIMENTAL DESIGN

In clinical specimens, HYAL-4 wild-type (Wt) and V1 expression was evaluated by RT-qPCR, IHC, and/or immunoblotting; a novel assay measured Chase activity. Wt and V1 were stably expressed or silenced in normal urothelial and three bladder cancer cell lines. Transfectants were analyzed for stem cell phenotype, invasive signature and tumorigenesis, and metastasis in four xenograft models, including orthotopic bladder.

RESULTS

HYAL-4 expression, specifically a novel splice variant (V1), was elevated in bladder tumors; Wt expression was barely detectable. V1 encoded a truncated 349 amino acid protein that was secreted. In bladder cancer tissues, V1 levels associated with metastasis and cancer-specific survival with high efficacy and encoded Chase activity. V1 cleaved chondroitin-6-sulfate from CD44, increasing CD44 secretion. V1 induced stem cell phenotype, motility/invasion, and an invasive signature. CD44 knockdown abrogated these phenotypes. V1-expressing urothelial cells developed angiogenic, muscle-invasive tumors. V1-expressing bladder cancer cells formed tumors at low density and formed metastatic bladder tumors when implanted orthotopically.

CONCLUSIONS

Our study discovered the first naturally-occurring eukaryotic/human Chase and connected it to disease pathology, specifically cancer. V1-Chase is a driver of malignant bladder cancer and potential predictor of outcome in patients with bladder cancer.

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.

A Consensus Definitive Classification of Scavenger Receptors and Their Roles in Health and Disease

Scavenger receptors constitute a large family of proteins that are structurally diverse and participate in a wide range of biological functions. These receptors are expressed predominantly by myeloid cells and recognize a diverse variety of ligands including endogenous and modified host-derived molecules and microbial pathogens. There are currently eight classes of scavenger receptors, many of which have multiple names, leading to inconsistencies and confusion in the literature. To address this problem, a workshop was organized by the United States National Institute of Allergy and Infectious Diseases, National Institutes of Health, to help develop a clear definition of scavenger receptors and a standardized nomenclature based on that definition. Fifteen experts in the scavenger receptor field attended the workshop and, after extensive discussion, reached a consensus regarding the definition of scavenger receptors and a proposed scavenger receptor nomenclature. Scavenger receptors were defined as cell surface receptors that typically bind multiple ligands and promote the removal of nonself or altered-self targets. They often function by mechanisms that include endocytosis, phagocytosis, adhesion, and signaling that ultimately lead to the elimination of degraded or harmful substances. Based on this definition, nomenclature and classification of these receptors into 10 classes were proposed. This classification was discussed at three national meetings and input from participants at these meetings was requested. The following manuscript is a consensus statement that combines the recommendations of the initial workshop and incorporates the input received from the participants at the three national meetings.

Collagen XIV and a related recombinant fragment protect human vascular smooth muscle cells from calcium-/phosphate-induced osteochondrocytic transdifferentiation

Transdifferentiation of vascular smooth muscle cells (VSMC) promotes the development of vascular calcifications such as arteriosclerosis. The aim was to investigate effects of specific extracellular matrix (ECM) components on transdifferentiation of VSMC to identify novel ECM-based therapeutic tools. Human collagens I & IV (CI, CIV) along with collagen XIV (CXIV) and a CXIV-derived fragment (CXIV-F), both of which induce differentiation, were applied in an in-vitro model of calcium-/phosphate (Ca/P)-induced osteochondrocytic transdifferentiation of human and murine VSMC. Transdifferentiation was determined by RT-PCR and calcium contents of VSMC cultures. Signaling pathways involved were determined by western-blot and luciferase reporter plasmid assays. Under normal culture conditions, CI induced VSMC proliferation and a more epithelioid/synthetic phenotype while CIV and predominantly CXIV provoked opposite effects. CIV and CXIV further blocked Ca/P-induced osteochondrocytic transdifferentiation of VSMC displayed e.g. by reduced gene expressions of Runx2, Sox9, osterix and increased expressions of αSMA and SM22α. This involved impaired activation of ERK1/2, NF-ĸB and Wnt-signaling. Similar preventive effects were achieved by applying CXIV-F. Impaired preventive effects of CXIV by co-treatment with a cluster of differentiation (CD)44 agonist propose CD44 as a CXIV-target structure on VSMC. In conclusion, CXIV and CXIV-F interfere with osteochondrocytic transdifferentiation of VSMC and should be further explored as potential therapeutic tools in vascular calcification.

Quantitative LC-MS/MS Analysis of Proteins Involved in Metastasis of Breast Cancer

The purpose of this study was to develop quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods for the analysis of proteins involved in metastasis of breast cancer for diagnosis and determining disease prognosis, as well as to further our understand of metastatic mechanisms. We have previously demonstrated that the protein type XIV collagen may be specifically expressed in metastatic tissues by two dimensional LC-MS/MS. In this study, we developed quantitative LC-MS/MS methods for type XIV collagen. Type XIV collagen was quantified by analyzing 2 peptides generated by digesting type XIV collagen using stable isotope-labeled peptides. The individual concentrations were equivalent between 2 different peptides of type XIV collagen by evaluation of imprecise transitions and using the best transition for the peptide concentration. The results indicated that type XIV collagen is highly expressed in metastatic tissues of patients with massive lymph node involvement compared to non-metastatic tissues. These findings were validated by quantitative real-time RT-PCR. Further studies on type XIV collagen are desired to verify its role as a prognostic factor and diagnosis marker for metastasis.

Differences in CD44 Surface Expression Levels and Function Discriminates IL-17 and IFN-γ Producing Helper T Cells

CD44 is a prominent activation marker which distinguishes memory and effector T cells from their naïve counterparts. It also plays a role in early T cell signaling events as it is bound to the lymphocyte-specific protein kinase and thereby enhances T cell receptor signalling. Here, we investigated whether IFN-γ and IL-17 producing T helper cells differ in their CD44 expression and their dependence of CD44 for differentiation. Stimulation of CD4⁺ T cells with allogeneic dendritic cells resulted in the formation of three distinguishable populations: CD44⁺, CD44⁺⁺ and CD44⁺⁺⁺. In vitro and in vivo generated allo-reactive IL-17 producing T helper cells were mainly CD44⁺⁺⁺ as compared to IFN-γ⁺ T helper cells, which were CD44⁺⁺. This effect was enhanced under polarizing conditions. T helper 17 polarization led to a shift towards the CD44⁺⁺⁺ population, whereas T helper 1 polarization diminished this population. Furthermore, blocking CD44 decreased IL-17 secretion, while IFN-γ was barely affected. Titration experiments revealed that low T cell receptor and CD28 stimulation supported T helper 17 rather than T helper 1 development. Under these conditions CD44 could act as a co-stimulatory molecule and replace CD28. Indeed, rested CD44⁺⁺⁺CD4⁺ T cells contained already more total and especially phosphorylated zeta-chain-associated protein kinase 70 as compared to CD44⁺⁺ cells. Our results support the notion, that CD44 enhances T cell receptor signaling strength by delivering lymphocyte-specific protein kinase, which is required for induction of IL-17 producing T helper cells.

Cellular signaling by collagen-binding integrins

The four collagen-binding αI domain integrins form their own subgroup among cell adhesion receptors. The signaling functions of α1β1 and α2β1 integrins have been analyzed in many experimental models, whereas less studies are available about the more recently found α10β1 and α11β1 heterodimers. Interestingly, collagen binding by α1β1 and α2β1 often generates opposite cellular responses. For example α1β1 has often been reported to promote cell proliferation and to suppress collagen synthesis, whereas α2β1 can in many model systems inhibit growth and promote collagen synthesis. There are obviously cell type dependent factors modifying the signaling. Additionally the structure and the organization of collagenous matrix play a critic role. Many recent studies have also stressed the importance of the crosstalk between the integrins and other cell surface receptors.

Zebrafish collagen XIV is transiently expressed in epithelia and is required for proper function of certain basement membranes

We found that zebrafish has two differentially expressed col14a1 paralogs. col14a1a expression peaked between 18-somite stage and 24 hours postfertilization (hpf), whereas col14a1b was first expressed at 32 hpf. To uncover functions of collagen XIV (COLXIV) during early embryogenesis, we focused our study on col14a1a. We characterized the α1 (XIV-A) chain as a collagenase-sensitive 200-kDa protein that formed dimer that could be reduced at high pH. As observed for the transcript, COLXIV-A protein expression peaked between 24 and 48 hpf. Using antisense probes and polyclonal antibodies, we show that col14a1a and its protein product COLXIV-A are transiently expressed in several epithelia, including epithelia undergoing shape changes, such as the fin folds. In contrast, anti-COLXII antibodies stained only connective tissues. COLXIV-A was also detected in the basement membrane (BM), where it co-localized with COLXII. At later developmental stages, COLXIV-A was not expressed in epithelia anymore but persisted in the BM. Morpholino knockdown of COLXIV-A provoked a skin detachment phenotype. Electron microscopy analysis revealed that morpholino-injected embryos lacked a lamina densa and lamina lucida at 24 hpf, and BM defects, such as gaps in the adepidermal granules, were still detected at 48 hpf. These BM defects were accompanied by a rupture of the dermis and detachment of the epidermis. Taken together, these data suggest an unexpected role of COLXIV-A in undifferentiated epithelia and in the formation of embryonic basement membranes.

Application of Collagen-Model Triple-Helical Peptide-Amphiphiles for CD44-Targeted Drug Delivery Systems

Cancer treatment by chemotherapy is typically accompanied by deleterious side effects, attributed to the toxic action of chemotherapeutics on proliferating cells from nontumor tissues. The cell surface proteoglycan CD44 has been recognized as a cancer stem cell marker. The present study has examined CD44 targeting as a way to selectively deliver therapeutic agents encapsulated inside colloidal delivery systems. CD44/chondroitin sulfate proteoglycan binds to a triple-helical sequence derived from type IV collagen, α1(IV)1263–1277. We have assembled a peptide-amphiphile (PA) in which α1(IV)1263–1277 was sandwiched between 4 repeats of Gly-Pro-4-hydroxyproline and conjugated to palmitic acid. The PA was incorporated into liposomes composed of DSPG, DSPC, cholesterol, and DSPE-PEG-2000 (1 : 4 : 5 : 0.5). Doxorubicin-(DOX-)loaded liposomes with and without 10% α1(IV)1263–1277 PA were found to exhibit similar stability profiles. Incubation of DOX-loaded targeted liposomes with metastatic melanoma M14#5 and M15#11 cells and BJ fibroblasts resulted in IC₅₀ values of 9.8, 9.3, and >100 μM, respectively. Nontargeted liposomes were considerably less efficacious for M14#5 cells. In the CD44⁺ B16F10 mouse melanoma model, CD44-targeted liposomes reduced the tumor size to 60% of that of the untreated control, whereas nontargeted liposomes were ineffective. These results suggest that PA targeted liposomes may represent a new class of nanotechnology-based drug delivery systems.

Soluble CD44 interacts with intermediate filament protein vimentin on endothelial cell surface

CD44 is a cell surface glycoprotein that functions as hyaluronan receptor. Mouse and human serum contain substantial amounts of soluble CD44, generated either by shedding or alternative splicing. During inflammation and in cancer patients serum levels of soluble CD44 are significantly increased. Experimentally, soluble CD44 overexpression blocks cancer cell adhesion to HA. We have previously found that recombinant CD44 hyaluronan binding domain (CD44HABD) and its non-HA-binding mutant inhibited tumor xenograft growth, angiogenesis, and endothelial cell proliferation. These data suggested an additional target other than HA for CD44HABD. By using non-HA-binding CD44HABD Arg41Ala, Arg78Ser, and Tyr79Ser-triple mutant (CD443MUT) we have identified intermediate filament protein vimentin as a novel interaction partner of CD44. We found that vimentin is expressed on the cell surface of human umbilical vein endothelial cells (HUVEC). Endogenous CD44 and vimentin coprecipitate from HUVECs, and when overexpressed in vimentin-negative MCF-7 cells. By using deletion mutants, we found that CD44HABD and CD443MUT bind vimentin N-terminal head domain. CD443MUT binds vimentin in solution with a Kd in range of 12–37 nM, and immobilised vimentin with Kd of 74 nM. CD443MUT binds to HUVEC and recombinant vimentin displaces CD443MUT from its binding sites. CD44HABD and CD443MUT were internalized by wild-type endothelial cells, but not by lung endothelial cells isolated from vimentin knock-out mice. Together, these data suggest that vimentin provides a specific binding site for soluble CD44 on endothelial cells.

The biology of CD44 and HCELL in hematopoiesis: the 'step 2-bypass pathway' and other emerging perspectives

PURPOSE OF REVIEW

The homing and egress of hematopoietic stem and progenitor cells (HSPCs) to and from marrow, respectively, and the proliferation and differentiation of HSPCs within marrow are complex processes critically regulated by the ordered expression and function of adhesion molecules that direct key cell-cell and cell-matrix interactions. The integral membrane molecule CD44, known primarily for its role in binding hyaluronic acid, is characteristically expressed on HSPCs. Conspicuously, human HSPCs uniquely display a specialized glycoform of CD44 known as hematopoietic cell E-/L-selectin ligand (HCELL), which is the most potent ligand for both E-selectin and L-selectin expressed on human cells. This review focuses on recent advances in our understanding of the biology of CD44 and HCELL in hematopoiesis.

RECENT FINDINGS

New data indicate that CD44-mediated events in hematopoiesis are more complex than previously imagined. Ex-vivo glycan engineering has established that HCELL serves as a 'bone marrow homing receptor'. Moreover, biochemical studies now show that CD44 forms bimolecular complexes with a variety of membrane proteins, one of which is VLA-4. Engagement of CD44 or of HCELL directly induces VLA-4 activation via G-protein-dependent signaling, triggering a 'step 2-bypass pathway' of cell migration, and extravascular lodgment, in absence of chemokine receptor engagement.

SUMMARY

Recent studies have further clarified the roles of CD44 and its glycoform HCELL in hematopoietic processes, providing key insights on how targeting these molecules may be beneficial in promoting hematopoiesis and in treating hematologic malignancies.

Cell surface glycan-lectin interactions in tumor metastasis

The development of secondary cancers, metastases, requires that a multitude of events are completed in an ordered and sequential manner. This review focuses on the role of cell surface glycans and their binding partners in the metastatic process. A common feature of metastasis is that the steps require adhesive interactions; many of these are mediated by cell surface glycans and their interactions with endogenous carbohydrate binding proteins (lectins). Aberrant glycosylation is a key feature of malignant transformation and the glycans involved influence the adhesive interactions of cancer cells often providing favorable conditions for tumor dissemination. This review focuses on glycans on the cancer cell surface and their association with endogenous lectins. In particular, E-cadherin and siglec-mediated disaggregation of tumor cells from the primary tumor mass; integrins, laminin and CD44-mediated invasion and migration of tumor cells through the connective tissue; the involvement of heparan sulphate in tumor angiogenesis and C-/S-type lectin interactions with the vasculature. The potential role of glycans in cancer cell evasion of immune surveillance is considered.

Differential use of chondroitin sulfate to regulate hyaluronan binding by receptor CD44 in Inflammatory and Interleukin 4-activated Macrophages

CD44 is a cell surface receptor for the extracellular matrix glycosaminoglycan hyaluronan and is involved in processes ranging from leukocyte recruitment to wound healing. In the immune system, the binding of hyaluronan to CD44 is tightly regulated, and exposure of human peripheral blood monocytes to inflammatory stimuli increases CD44 expression and induces hyaluronan binding. Here we sought to understand how mouse macrophages regulate hyaluronan binding upon inflammatory and anti-inflammatory stimuli. Mouse bone marrow-derived macrophages stimulated with tumor necrosis factor α or lipopolysaccharide and interferon-γ (LPS/IFNγ) induced hyaluronan binding by up-regulating CD44 and down-regulating chondroitin sulfation on CD44. Hyaluronan binding was induced to a lesser extent in interleukin-4 (IL-4)-activated macrophages despite increased CD44 expression, and this was attributable to increased chondroitin sulfation on CD44, as treatment with β-d-xyloside to prevent chondroitin sulfate addition significantly enhanced hyaluronan binding. These changes in the chondroitin sulfation of CD44 were associated with changes in mRNA expression of two chondroitin sulfotransferases, CHST3 and CHST7, which were decreased in LPS/IFNγ-stimulated macrophages and increased in IL-4-stimulated macrophages. Thus, inflammatory and anti-inflammatory stimuli differentially regulate the chondroitin sulfation of CD44, which is a dynamic physiological regulator of hyaluronan binding by CD44 in mouse macrophages.

Running GAGs: myxoid matrix in tumor pathology revisited: what's in it for the pathologist?

Ever since Virchow introduced the entity myxoma, abundant myxoid extracellular matrix (ECM) has been recognized in various reactive and neoplastic lesions. Nowadays, the term "myxoid" is commonly used in daily pathological practice. But what do today's pathologists mean by it, and what does the myxoid ECM tell the pathologist? What is known about the exact composition and function of the myxoid ECM 150 years after Virchow? Here, we give an overview of the composition and constituents of the myxoid ECM as known so far and demonstrate the heterogeneity of the myxoid ECM among different tumors. We discuss the possible role of the predominant constituents of the myxoid ECM and attempt to relate them to differences in clinical behavior. Finally, we will speculate on the potential relevance of this knowledge in daily pathological practice.

Cellular/intramuscular myxoma and grade I myxofibrosarcoma are characterized by distinct genetic alterations and specific composition of their extracellular matrix

Cellular myxoma and grade I myxofibrosarcoma are mesenchymal tumours that are characterized by their abundant myxoid extracellular matrix (ECM). Despite their histological overlap, they differ clinically. Diagnosis is therefore difficult though important. We investigated their (cyto) genetics and ECM. GNAS1-activating mutations have been described in intramuscular myxoma, and lead to downstream activation of cFos. KRAS and TP53 mutations are commonly involved in sarcomagenesis whereby KRAS subsequently activates c-Fos. A well-documented series of intramuscular myxoma (three typical cases and seven cases of the more challenging cellular variant) and grade I myxofibrosarcoma (n= 10) cases were karyotyped, analyzed for GNAS1, KRAS and TP53 mutations and downstream activation of c-Fos mRNA and protein expression. ECM was studied by liquid chromatography mass spectrometry and expression of proteins identified was validated by immunohistochemistry and qPCR. Grade I myxofibrosarcoma showed variable, non-specific cyto-genetic aberrations in 83,5% of cases (n= 6) whereas karyotypes of intramuscular myxoma were all normal (n= 7). GNAS1-activating mutations were exclusively found in 50% of intramuscular myxoma. Both tumour types showed over-expression of c-Fos mRNA and protein. No mutations in KRAS codon 12/13 or in TP53 were detected. Liquid chromatography mass spectrometry revealed structural proteins (collagen types I, VI, XII, XIV and decorin) in grade I myxofibrosarcoma lacking in intramuscular myxoma. This was confirmed by immunohistochemistry and qPCR. Intramuscular/cellular myxoma and grade I myxofibrosarcoma show different molecular genetic aberrations and different composition of their ECM that probably contribute to their diverse clinical behaviour. GNAS1 mutation analysis can be helpful to distinguish intramuscular myxoma from grade I myxofibrosarcoma in selected cases.

Rheostatic signaling by CD44 and hyaluronan

Cellular function and adaptive behavior is often driven by signals generated in response to the local tissue microenvironment. Cell surface receptors that detect changes in extracellular matrix composition and modifications to extracellular matrix components, are ideally positioned to provide highly responsive sensors of changes in the microenvironment and mediate changes in cellular function required to maintain tissue integrity. Receptors can act as "on/off" switches, but ligand/receptor complexes that provide "rheostatic" control may be more sensitive, provide a more rapid mechanism of control and allow for fine-tuning of cellular responses to the microenvironment. Herein, we review evidence that transitions in the physiochemical properties of the extracellular glycosaminoglycan hyaluronan and in the function of its major receptor, CD44, differentially regulate ERK and Rac signal transduction pathways to provide critical rheostatic control of mesenchymal cell proliferation.

Involvement of CD44, a molecule with a thousand faces, in cancer dissemination

Tumor progression is substantially dependent on network of multiple factors, including adhesion and homing molecules, which support the malignant metastatic spread. CD44, one of the adhesion/homing molecules, has attracted much attention not only because it is expressed on many types of tumors, but also owing to its numerous functions, such as supporting cell migration and transmitting survival signals, thereby being pro-oncogenic by nature. We have used the mouse malignant LB lymphoma cell line as a model for comprehensive in vitro and in vivo analyses of the interaction between CD44 and hyaluronic acid (HA), and its relevance to tumor dissemination. The in vitro studies revealed that LB cells could not bind HA, either under static or dynamic (i.e., shear flow) conditions, unless their CD44 is activated by phorbol ester, deglycosylated (to increase the CD44 positive net charge) or transfected with CD44 variants. In parallel, in vivo experiments showed that LB cell dissemination could be controlled by injection of anti-CD44 monoclonal antibodies or hyaluronidase. Furthermore, LB cells transfected with CD44v4-v10 variant, rather than standard CD44, displayed enhanced invasion of the peripheral lymph nodes. This effect was completely lost if the HA binding site of CD44 were mutated. LB cell accumulation in the lymph nodes is caused by enhanced migration via the afferent lymphatics rather than by accelerated proliferation within the lymph node. This information can be exploited to tailor a "therapeutic suit" that should be maximally effective in inducing tumor resistance, while minimizing destructive side effects.

Alteration of the expression of CD44 [corrected] isoforms in oral epithelia and saliva from patients with oral lichen planus

Oral lichen planus (OLP) is a chronic inflammatory mucosal disease that cell-mediated immunological mechanisms are involved in pathogenesis. The objective of this study was to investigate the expression of CD44 isoforms including CD44s, CD44v5, and CD44v6 in biopsy specimens and saliva from OLP patients. Thirty-one OLP patients and 30 healthy subjects were enrolled in this study. Immunohistochemical methods were used to detect the expression of CD44 isoforms in oral epithelia, and enzyme-linked immunosorbent assay (ELISA) was performed to measure levels of salivary CD44 isoforms. Our results demonstrated that expression of CD44v6 in oral epithelia from OLP patients was significantly decreased in comparison to controls (p = 0.021). Levels of salivary CD44s and CD44v5 from OLP patients were significantly higher than those from controls (p = 0.007 and p = 0.002, respectively). In summary, our findings provided additional evidence that the pathological stress, such as chronic inflammation, altered the expression of CD44 isoforms in oral epithelia and saliva of OLP patients.

Proteolytic profiling of the extracellular matrix degradome

The profiling of protein function is one of the most challenging scientific tasks in the postgenomic age. Traditional protein expression methodologies have focused only on the quantification of proteins under varying conditions or pathologies. Determining the functional differences between protein populations allows for a more accurate view of the outcomes in normal vs diseased proteomes. Because the presence or absence of a protein's function can affect its complex surroundings (consisting of multiple other proteins and substrates), the study of proteome functionality yields information on protein-protein interactions, amplification cascades, signaling pathways, and posttranslational modifications. Of significant interest are proteinases, as proteolysis is responsible for tight regulation of various cellular and tissue processes. Proteinase activities, or lack there of, alter the proteome makeup by regulating other proteins or by generating cleavage products. This chapter describes current proteolytic profiling technologies using activity or target-based formats. In particular, the analysis of collagenolytic matrix metalloproteinase activity using fluorogenic triple-helical substrates is discussed.

The elongated first fibronectin type III domain of collagen XIV is an inducer of quiescence and differentiation in fibroblasts and preadipocytes

Collagen XIV (CXIV) is a fibril-associated collagen that is mainly expressed in well differentiated tissues and in late embryonic development. Because CXIV is almost absent in proliferating and/or dedifferentiated tissues, a functional role in maintaining cell differentiation is suspected. We demonstrate antiproliferative, quiescence- and differentiation-inducing effects of human CXIV and its recombinant fragments on mesenchymal cells. In primary human fibroblasts, in mouse 3T3 fibroblasts and in 3T3-L1 preadipocytes, CXIV reduced de novo DNA synthesis by 75%, whereas cell numbers and viability remained unaltered. Cells showed no signs of apoptosis, and maximal proliferation was restored when serum was supplemented, thus indicating that CXIV induced reversible cellular quiescence. Exposure of fibroblasts to CXIV in vitro led to cellular bundles and clusters. CXIV also triggered trans-differentiation of 3T3-L1 preadipocytes into adipocytes, as could be shown by lipid accumulation and by expression of the glucose transporter Glut4. These effects were also observed with the amino-terminal recombinant fragment Gln(29)-Pro(154) that harbors the first fibronectin type III domain and a 39-amino-acid extension, whereas no activity was found for all other recombinant CXIV fragments. Based on these finding the development of small molecular analogs that modulate fibroblast cell growth and differentiation, e.g. in wound healing and fibrosis, seems feasible.

Regulation of the release and function of tumor cell-derived soluble CD44

CD44, a major receptor for glycosaminoglycan hyaluronan (HA), is a broadly distributed cell surface glycoprotein implicated in multiple functions, including tumor growth and dissemination. The affinity of surface CD44 for HA is subject to regulation at several levels. CD44 is found in multiple phases, including as an integral transmembrane protein and as soluble fragment of the extracellular domain found in the circulation and other body fluids. Transmembrane CD44 and its ability to interact with HA have been a focus of numerous studies in the past, but the function of soluble CD44 remains obscure. Interestingly, malignant diseases are often associated with an increase in the plasma level of CD44. The delineation of the HA binding capacity of tumor-derived soluble CD44 is an important step toward understanding the biological function of this molecule. In this study, we demonstrate that tumor cells activated to bind HA by cytokines rapidly release CD44 upon treatment with phorbol ester (PMA). The affinity for HA of the soluble CD44 released in response to PMA varied depending on the cytokine pretreatment. These results suggest that the function of tumor-derived soluble CD44, like the transmembrane form of the receptor, can be regulated.

Hyaluronan Cell Surface Binding Is Induced by Type I Collagen and Regulated by Caveolae in Glioma Cells

Hyaluronan (HA) is a component of the brain extracellular matrix environment that is synthesized and secreted by glioma cells. The primary cell surface receptor for HA is CD44, a membrane glycoprotein that is functionally regulated by a membrane type 1 matrix metalloproteinase (MT1-MMP). Both CD44 and MT1-MMP are partially located in Triton X-100-insoluble domains, but no functional link has yet been established between them. In the present study, we studied the regulation of HA cell surface binding in U-87 glioma cells. We show that an MMP-dependent mechanism regulates the intrinsic cell surface binding of HA as ilomastat, a broad MMP inhibitor, increased HA binding to glioma cells. HA binding was also rapidly and specifically up-regulated by 3-fold by type I collagen in U-87 cells, which also induced a significant morphological reorganization associated with the activation of a latent form of MMP-2 through a MT1-MMP-mediated mechanism. Interestingly, caveolae depletion with a cell surface cholesterol-depleting agent beta-cyclodextrin triggered an additional increase (9-fold) in the binding of HA, in synergy with type I collagen. On the other hand, HA cell surface binding was diminished by the MEK inhibitor PD98059 and by the overexpression of a recombinant, wild type MT1-MMP, whereas its cytoplasmic-deleted form had no effect. Taken together, our results suggest that MT1-MMP regulates, through its cytoplasmic domain, the cell surface functions of CD44 in a collagen-rich pericellular environment. Additionally, we describe a new molecular mechanism regulating the invasive potential of glioma cells involving a MT1-MMP/CD44/caveolin interaction, which could represent a potential target for anti-cancer therapies.

Fibroblast invasive migration into fibronectin/fibrin gels requires a previously uncharacterized dermatan sulfate-CD44 proteoglycan

After tissue injury, fibroblast migration from the peri-wound collagenous stroma into the fibrin-laden wound is critical for granulation tissue formation and subsequent healing. Recently we found that fibroblast transmigration from a collagen matrix into a fibrin matrix required the presence of fibronectin. Several integrins-alpha 4 beta 1, alpha 5 beta 1, and alpha v beta 3-with known fibronectin binding affinity were necessary for this invasive migration. Here we examined another family of cell surface receptors: the proteoglycans. We found that dermatan sulfate was required for fibroblast migration into a fibronectin/fibrin gel. This conclusion was based on beta-xyloside inhibition of glycanation and specific glycosaminoglycan degradation. CD44, a cell surface receptor known to bind hyaluronan, not infrequently exists as a proteoglycan, decorated with various glycosaminoglycan chains including heparan sulfate and chondroitin sulfate, and as such can bind fibronectin. We found that CD44H, the non-spliced isoform of CD44, was necessary for fibroblast invasion into fibronectin/fibrin gels. Resting fibroblasts expressed mostly nonglycanated CD44H core protein, which became glycanated with chondroitin sulfate and dermatan sulfate, but not heparan sulfate, after a 24 h incubation with platelet-derived growth factor, the stimulus used in the migration assay. These results demonstrate that dermatan sulfate-CD44H proteoglycan is essential for fibroblast migration into fibrin clots and that platelet-derived growth factor, the stimulus for migration, induces the production of chondroitin-sulfate- and dermatan-sulfate-glycanated CD44H.

Characterization of recombinant amino-terminal NC4 domain of human collagen IX: interaction with glycosaminoglycans and cartilage oligomeric matrix protein

The N-terminal NC4 domain of collagen IX is a globular structure projecting away from the surface of the cartilage collagen fibril. Several interactions have been suggested for this domain, reflecting its location and its characteristic high isoelectric point. In an attempt to characterize the NC4 domain in more detail, we set up a prokaryotic expression system to produce the domain. The purified 27.5-kDa product was analyzed for its glycosaminoglycan-binding potential by surface plasmon resonance and solid-state assays. The results show that the NC4 domain of collagen IX specifically binds heparin with a K(d) of 0.6 microm, and the full-length recombinant collagen IX has an even stronger interaction with heparin, with an apparent K(d) of 3.6 nm. The heparin-binding site of the NC4 domain was located in the extreme N terminus, containing a heparin-binding consensus sequence, whereas electron microscopy suggested the presence of at least three additional heparin-binding sites on full-length collagen IX. The NC4 domain was also shown to bind cartilage oligomeric matrix protein. This interaction and the association of cartilage oligomeric matrix protein with other regions of collagen IX were found to be heparin-competitive. Circular dichroism analyses of the NC4 domain indicated the presence of stabilizing disulfide bonds and a thermal denaturation point of about 80 degrees C. The pattern of disulfide bond formation within the NC4 domain was identified by tryptic peptide mass mapping of the NC4 in native and reduced states. A similar pattern was demonstrated for the NC4 domain of full-length recombinant collagen IX.

Cytokines regulate the affinity of soluble CD44 for hyaluronan

CD44, a receptor for the extracellular matrix glycosaminoglycan hyaluronan, has been implicated in many adhesion-dependent cellular processes including tumor growth and metastasis. Soluble CD44 has been identified in the serum of normal individuals. Furthermore, tumor progression is often associated with marked increases in plasma levels of soluble CD44. Release of soluble CD44 by proteolytic cleavage (shedding) of membrane-anchored CD44 is likely to alter cellular responses to the environment due to modification of the cell surface and the potential for soluble CD44 to influence CD44-mediated hyaluronan binding to cell surfaces. Cellular activation is typically required to induce hyaluronan binding to cell surface CD44 but the affinity of endogenous soluble CD44 for hyaluronan remains unknown. In this study, we demonstrate that oncostatin M and transforming growth factor beta1 (TGF-beta1) which stimulate hyaluronan binding to HTB58 lung epithelial-derived tumor cells, also induce the release of soluble CD44. Interestingly, soluble CD44 released by oncostatin M-treated cells retained the ligand-binding properties of the membrane-anchored receptor. In contrast, soluble CD44 released from TGF-beta1-treated HTB58 cells differed in its hyaluronan-binding capacity from cell surface CD44 expressed on TGF-beta1-stimulated cells. These data indicate that the mechanisms that regulate the generation of soluble CD44 may also govern the binding of the released receptor to hyaluronan and therefore determine the impact on CD44-dependent physiologic and pathologic processes.

Purification and characterization of hyaluronic acid from the mollusc bivalve Mytilus galloprovincialis

Hyaluronan (hyaluronic acid, HA) was for the first time extracted, purified and characterized from the species of mollusc bivalve Mytilus galloprovincialis. HA was characterized by agarose-gel electrophoresis, 13C-NMR, HPLC and normal polarity capillary electrophoresis by evaluating the unsaturated disaccharide, DeltaDiHA (Delta-hexuronic acid-N-acetyl-glucosamine) after treatment with chondroitin ABC lyase, and by separating Delta-tetrasaccharide and Delta-hexasaccharide generated by the specific action of hyaluronate lyase from Streptomyces hyalurolyticus. The weight average molecular weight (M(w)) was found to be about 200 kDa as determined by HPSEC. HA from M. galloprovincialis was not able to interact with aggrecan from bovine cartilage to form high molecular mass aggregate and also had a very low specific viscosity, but it showed the same capacity to inhibit cell proliferation (50 microg per 10(3) human fibroblasts inhibit cell proliferation by about 50%) than high molecular mass HA. HA of M. galloprovincialis could have a physiological role in the regulation of cell functions.

Melanoma cell CD44 interaction with the alpha 1(IV)1263-1277 region from basement membrane collagen is modulated by ligand glycosylation

Invasion of the basement membrane is believed to be a critical step in the metastatic process. Melanoma cells have been shown previously to bind distinct triple-helical regions within basement membrane (type IV) collagen. Additionally, tumor cell binding sites within type IV collagen contain glycosylated hydroxylysine residues. In the present study, we have utilized triple-helical models of the type IV collagen alpha1(IV)1263-1277 sequence to (a) determine the melanoma cell receptor for this ligand and (b) analyze the results of single-site glycosylation on melanoma cell recognition. Receptor identification was achieved by a combination of methods, including (a) cell adhesion and spreading assays using triple-helical alpha1(IV)1263-1277 and an Asp(1266)Abu variant, (b) inhibition of cell adhesion and spreading assays, and (c) triple-helical alpha1(IV)1263-1277 affinity chromatography with whole cell lysates and glycosaminoglycans. Triple-helical alpha1(IV)1263-1277 was bound by melanoma cell CD44/chondroitin sulfate proteoglycan receptors and not by the collagen-binding integrins or melanoma-associated proteoglycan. Melanoma cell adhesion to and spreading on the triple-helical alpha1(IV)1263-1277 sequence was then compared for glycosylated (replacement of Lys(1265) with Hyl(O-beta-d-galactopyranosyl)) versus non-glycosylated ligand. Glycosylation was found to strongly modulate both activities, as adhesion and spreading were dramatically decreased due to the presence of galactose. CD44/chondroitin sulfate proteoglycan did not bind to glycosylated alpha1(IV)1263-1277. Overall, this study (a) is the first demonstration of the prophylactic effects of glycosylation on tumor cell interaction with the basement membrane, (b) provides a rare example of an apparent unfavorable interaction between carbohydrates, and (c) suggests that sugars may mask "cryptic sites" accessible to tumor cells with cell surface or secreted glycosidase activities.

Proteinase-mediated release of epithelial cell-associated CD44. Extracellular CD44 complexes with components of cellular matrices

CD44 is a receptor for the matrix glycosaminoglycan hyaluronan. Proteoglycan forms of CD44 also exhibit affinity for fibronectin and collagen as well as chemokines and growth factors. CD44 plays a role in autoimmunity, inflammation, and tumor progression. Soluble CD44 (sCD44) is found in plasma, and the levels of sCD44 correlate with immune function and some malignancies. The mechanisms by which sCD44 is generated and its function are unknown. We demonstrate here that normal bronchial epithelial cells spontaneously release sCD44. Exposure to phagocyte- and bacterium-derived proteinases markedly increased the release of sCD44 from epithelial cells. The spontaneously released sCD44 was incorporated into high molecular mass complexes derived from the matrix that also contained chondroitin sulfate, fibronectin, hyaluronan, and collagens I and IV. Enzymatic digestion with proteinases liberated sCD44 from the high molecular mass complex. Consistent with the homology of CD44 to proteoglycan core and link proteins, these data suggest that CD44 spontaneously released from normal bronchial epithelial cells can accumulate as an integral component of the matrix, where it may play a role in the organization of matrices and in anchoring growth factors and chemokines to the matrix. Increases in plasma CD44 during immune activation and tumor progression therefore may be a manifestation of the matrix remodeling that occurs in the face of the enhanced proteolytic activity associated with infection, inflammation, and tumor metastasis, leading to alterations in cell-matrix interactions.

CD44 in cancer

CD44 is a multistructural and multifunctional cell surface molecule involved in cell proliferation, cell differentiation, cell migration, angiogenesis, presentation of cytokines, chemokines, and growth factors to the corresponding receptors, and docking of proteases at the cell membrane, as well as in signaling for cell survival. All these biological properties are essential to the physiological activities of normal cells, but they are also associated with the pathologic activities of cancer cells. Experiments in animals have shown that targeting of CD44 by antibodies, antisense,and CD44-soluble proteins markedly reduces the malignant activities of various neoplasms, stressing the therapeutic potential of anti-CD44 agents. Furthermore, because alternative splicing and posttranslational modifications generate many different CD44 sequences, including, perhaps, tumor-specific sequences, the production of anti-CD44 tumor-specific agents may be a realistic therapeutic approach. However, in many cancers (renal cancer and non-Hodgkin's lymphomas are exceptions), a high level of CD44 expression is not always associated with an unfavorable outcome. On the contrary, in some neoplams CD44 upregulation is associated with a favorable outcome. Even worse, in many cases different research grows analyzing the same neoplastic disease reached contradictory conclusions regarding the correlation between CD44 expression and disease prognosis, possibly due to differences in methodology. These problems must be resolved before applying anti-CD44 therapy to human cancers.

TNF- increases the carbohydrate sulfation of CD44: induction of 6-sulfo N-acetyl lactosamine on N- and O-linked glycans

CD44 and sulfation have both been implicated in leukocyte adhesion. In monocytes, the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha) stimulates CD44 sulfation, and this correlates with the induction of CD44-mediated adhesion events. However, little is known about the sulfation of CD44 or its induction by inflammatory cytokines. We determined that TNF-alpha induces the carbohydrate sulfation of CD44. CD44 was established as a major sulfated cell surface protein on myeloid cells. In the SR91 myeloid cell line, the majority of CD44 sulfation was attributed to the glycosaminoglycan chondroitin sulfate. However, TNF-alpha stimulation increased CD44 sulfation two- to threefold, largely attributed to the increased sulfation of N- and O-linked glycans on CD44. Therefore, TNF-alpha induced a decrease in the percentage of CD44 sulfation due to chondroitin sulfate and an increase due to N- and O-linked sulfation. Furthermore, TNF-alpha induced the expression of 6-sulfo N-acetyl lactosamine (LacNAc)/Lewis x on these cells, which was detected by a monoclonal antibody after neuraminidase treatment. This 6-sulfo LacNAc/Lewis x epitope was induced on N-linked and (to a lesser extent) on O-linked glycans present on CD44. This demonstrates that CD44 is modified by sulfated carbohydrates in myeloid cells and that TNF-alpha modifies both the type and amount of carbohydrate sulfation occurring on CD44. In addition, it demonstrates that TNF-alpha can induce the expression of 6-sulfo N-acetyl glucosamine on both N- and O-linked glycans of CD44 in myeloid cells.

Capillary electrophoresis for the analysis of glycosaminoglycans and glycosaminoglycan-derived oligosaccharides

Glycosaminoglycans are a family of polydisperse, highly sulfated complex mixtures of linear polysaccharides that are involved in many life processes. Defining the structure of glycosaminoglycans is an important factor in elucidating their structure-activity relationship. Capillary electrophoresis has emerged as a highly promising technique consuming an extremely small amount of sample and capable of rapid, high-resolution separation, characterization and quantitation of analytes. Numerous capillary electrophoresis methods for analysis of intact glycosaminoglycans and glycosaminoglycan-derived oligosaccharides have been developed. These methods allow for both qualitative and quantitative analysis with a high level of sensitivity. This review is concerned with separation methods of capillary electrophoresis, detection methods and applications to several aspects of research into glycosaminoglycans and glycosaminoglycan-derived oligosaccharides. The importance of capillary electrophoresis in biological and pharmaceutical samples in glycobiology and carbohydrate biochemistry and its possible applications in disease diagnosis and monitoring chemical synthesis are described.

Differences in mesenchymal tissue repair

Variations in certain mesenchymal tissue healing processes are not widely recognized. The current review summarizes key differences in healing mechanisms and healing potential after injury to soft tissues having different healing outcomes.

Collagenous Sequence Governs the Trimeric Assembly of Collagen XII

A minicollagen containing the COL1 and NC1 domains of chicken collagen XII has been produced in insect cells. Significant amounts of trimers contain a triple-helical domain in which the cysteines are not involved in inter- but in intrachain bonds. In reducing conditions, providing that the triple-helix is maintained, disulfide exchange between intra- and interchain bonding is observed, suggesting that the triple-helix forms first and that in favorable redox conditions interchain bonding occurs to stabilize the molecule. This hypothesis is verified by in vitro reassociation studies performed in the presence of reducing agents, demonstrating that the formation of interchain disulfide bonds is not a prerequisite to the trimeric association and triple-helical folding of the collagen XII molecule. Shortening the COL1 domain of minicollagen XII to its five C-terminal GXY triplets results in an absence of trimers. This can be explained by the presence of a collagenous domain that is too short to form a stable triple-helix. In contrast, the presence of five additional C-terminal triplets in COL1 allows the formation of triple-helical disulfide-bonded trimers, suggesting that the presence of a triple-helix is essential for the assembly of collagen XII.

A crucial role for CD44 in inflammation

Current therapies for chronic inflammatory diseases typically act through the nonspecific downregulation of immune cell activation. However, it is becoming increasingly evident that parenchymal cells are also active participants in the inflammatory process. Future prospects for the treatment of inflammation should therefore include the targeting of specific inflammatory pathways in both immune cells and parenchymal cells. CD44, a cell-adhesion molecule that is ubiquitously expressed on leukocytes and parenchymal cells, has been implicated, together with its ligand hyaluronan (HA), in several inflammatory diseases. The mechanisms of action of CD44-HA interactions in inflammation might provide potential targets for therapy.

Alternative splicing of the first F3 domain from chicken collagen XIV affects cell adhesion and heparin binding

The N terminus of chicken collagen XIV is subject to alternative splicing. The longer isoform contains a fibronectin type III (F3) domain at its N terminus, whereas the shorter isoform is lacking this domain. Alternative splicing of the F3 domain is developmentally regulated. At early embryonic stages, both isoforms are expressed, whereas after hatching only the longer isoform is expressed. When immobilized on plastic dishes, the recombinant F3 domain promotes the adhesion of mesenchymal cells. Attachment to this domain is specifically inhibited by heparin but not by other glycosaminoglycans. Molecular modeling studies illustrate that the first F3 domain harbors a positively charged groove, which may accommodate the negatively charged heparin chain. Site-directed mutagenesis of a single lysine residue within this groove abolishes the cell binding activity but does not affect the heparin binding activity. Cell binding and heparin binding are therefore two functionally distinct properties shared by the N-terminal F3 domain. When full-length collagen XIV polypeptides that either contain or lack the first F3 domain are tested on heparin-Sepharose, a pronounced difference in their relative affinity is observed. Thus, alternative splicing of the N-terminal F3 domain influences the interaction of this FACIT (fibril-associated collagens with interrupted triple helices) collagen with cells and with glycosaminoglycans.

Development of a peptide inhibitor of hyaluronan-mediated leukocyte trafficking

Hyaluronan (HA), a high molecular weight glycosaminoglycan, is expressed abundantly in the extracellular matrix and on cell surfaces. Although HA is known to bind many adhesion molecules, little information has been available with respect to its direct physiological role. In this study, we developed a novel 12-mer (GAHWQFNALTVR) peptide inhibitor of HA, termed "Pep-1," by using phage display technology. Pep-1 showed specific binding to soluble, immobilized, and cell-associated forms of HA, and it inhibited leukocyte adhesion to HA substrates almost completely. Systemic, local, or topical administration of Pep-1 inhibited the expression of contact hypersensitivity responses in mice by blocking skin-directed homing of inflammatory leukocytes. Pep-1 also inhibited the sensitization phase by blocking hapten-triggered migration of Langerhans cells from the epidermis. These observations document that HA plays an essential role in "two-way" trafficking of leukocytes to and from an inflamed tissue, and thus provide technical and conceptual bases for testing the potential efficacy of HA inhibitors (e.g., Pep-1) for inflammatory disorders.

Expression of type XIV collagen in developing chicken tendons: association with assembly and growth of collagen fibrils

Collagen fibril assembly is a multistep process involving multiple macromolecular interactions. Type XIV collagen contains multiple domains and is capable of interacting with collagen fibrils and other extracellular matrix components. During tendon development, naturally changing expression of type XIV collagen and its variants may modulate such interactions. Type XIV collagen was studied using immunochemical and molecular approaches. Western analysis demonstrated that type XIV collagen content was high between days 14 and 19, decreasing sharply at hatching. Immunoelectron microscopy demonstrated that type XIV collagen was fibril-associated, with a periodicity of 67 nm, indicating specific interactions. Decreased fibril-associated reactivity for type XIV collagen was seen at hatching, indicating a removal of collagen XIV from the fibril surface. The expression of two NC1 splice variants was analyzed. Overall, type XIV collagen mRNA decreased significantly from day 14 to hatching. The long NC1 splice variant was the predominant species at 14 days; at 19 days the two variants were expressed in lower amounts at nearly a 1:1 ratio; at hatching, both variants were expressed minimally. Changes in splice variant expression, suggest that different functional forms of type XIV collagen are present, allowing modified interactions with fibrils during development. In conclusion, type XIV collagen is fibril-associated and developmentally regulated. Modulation of expression of the NC1 splice variants may mediate the fibril interactions that allow the transition from growing fibril intermediates to mature fibrils.

A role for the cell adhesion molecule CD44 and sulfation in leukocyte-endothelial cell adhesion during an inflammatory response?

CD44 is a widely expressed cell adhesion molecule that has been implicated in a variety of biological processes including lymphopoiesis, angiogenesis, wound healing, leukocyte extravasation at inflammatory sites, and tumor metastasis. The adhesive function of CD44, like other molecules involved in inducible adhesion, is tightly regulated. Post-translational modifications, isoform expression, aggregation state, and protein associations all can affect the ligand binding properties of CD44, and these can vary depending on the cell type and the activation state of the cell. The most extensively characterized ligand for CD44 is hyaluronan, a component of the extracellular matrix. Interactions between CD44 and hyaluronan can mediate both cell-cell and cell-extracellular matrix adhesion. In the immune system, both the selectin molecules and CD44 have been implicated in the initial binding of leukocytes to endothelial cells at an inflammatory site. Sulfation is required for selectin-mediated leukocyte-endothelial cell interactions, and, recently, inducible sulfation also was shown to regulate CD44-mediated leukocyte adhesion to endothelial cells. Sulfation, therefore, may be important in the regulation of cell adhesion at inflammatory sites. In this commentary we have reviewed the molecular aspects of CD44 and the mechanisms that regulate its binding to hyaluronan. In addition, we have summarized the role of CD44 and hyaluronan in mediating leukocyte-endothelial cell interactions and have discussed how this interaction may be regulated. Finally, we examined the potential role of sulfation as an inducible means to regulate CD44-mediated leukocyte adhesion and as a more general mechanism to regulate leukocyte-endothelial cell interactions.

Biomimetic transport and rational drug delivery

Medicine and pharmaceutics are encountering critical needs and opportunities for transvascular drug delivery that improves site targeting and tissue permeation by mimicking natural tissue addressing and transport mechanisms. This is driven by the accelerated development of genomic agents requiring targeted controlled release. Although rationally designed for in vitro activity, such agents are not highly effective in vivo, due to opsonization and degradation by plasma constituents, and failure to transport across the local vascular endothelium and tissue matrix. A growing knowledge of the addresses of the body can be applied to engineer "Bio-Logically" staged delivery systems with sequential bioaddressins complementary to the discontinuous compartments encountered--termed discontinuum pharmaceutics. Effective tissue targeting is accomplished by leukocytes, bacteria, and viruses. We are increasingly able to mimic their bioaddressins by genomic means. Approaches described in this commentary include: (a) endothelial-directed adhesion mediated by oligosaccharides and carbohydrates (e.g. dermatan sulfate as a mimic of sulfated CD44) and peptidomimetics interacting with adhesins, selectins, integrins, hyaluronans, and locally induced growth factors (e.g. vascular endothelial growth factor, VEGF) and coagulation factors (e.g. factor VIII antigen); (b) improved tissue permeation conferred by hydrophilically "cloaked" carrier systems; (c) "uncloaking" by matrix dilution or selective triggering near the target cells; and (d) target binding-internalization by terminally exposed hydrophobic moieties, cationic polymers, and receptor-binding lectins, peptides, or carbohydrates. This commentary also describes intermediate technology solutions (e.g. "hybrid drugs"), and highlights the high-resolution, dynamic magnetic resonance imaging and radiopharmaceutical imaging technologies plus the groups and organizations capable of accelerating these important initiatives.

Fibrogenesis and fibrolysis in collagenous colitis. Patterns of procollagen types I and IV, matrix-metalloproteinase-1 and -13, and TIMP-1 gene expression

Collagenous colitis is characterized by the deposition of a superficial subepithelial collagenous layer, the pathogenesis of which is unknown. Because the excess matrix deposition is potentially reversible, a labile imbalance between fibrogenesis and fibrolysis may be suspected. Expression of procollagen alpha1(I) and alpha1(IV), matrix-metalloproteinase (MMP)-1 and -13, and tissue inhibitor of metalloproteinase (TIMP)-1 genes was semiquantitated by in situ hybridization on serial biopsies of 12 patients with collagenous colitis and compared to controls. Collagen types I, III, IV, and VI, tenascin, undulin/collagen XIV, and alpha-actin were localized by immunohistology. The superficial collagen layer stained strongly for collagen types I, III, and VI, and particularly for tenascin, but not for undulin. Elevated procollagen alpha1(I), procollagen alpha1(IV), and TIMP-1 transcript levels were found in alpha-actin-positive cells with linear distribution underneath the superficial collagenous layer, whereas MMP-1 RNA expression was variable and restricted to cell clusters. MMP-13 expression was undetectable. The patterns of procollagen alpha1(I)- and alpha1(IV)-specific labeling, combined with an intense tenascin- but absent undulin-specific staining, indicate deposition of an immature interstitial matrix that may be susceptible to degradation. The restricted MMP-1 RNA expression, counteracted by increased TIMP-1 expression, suggests locally impaired fibrolysis as a relevant factor in the pathogenesis of collagenous colitis.

Increased expression of tenascin C by keloids in vivo and in vitro

Tenascin C, undulin, collagen XIV and fibronectin are extracellular matrix glycoproteins with a partial DNA sequence homology. During embryogenesis, tenascin C is abundant in mesenchymal tissues but its distribution in human adult tissue is severely restricted. The levels of tenascin C expression are enhanced with skin inflammation, wound healing and hyperproliferative skin diseases and return to normal in normal scar tissue after wound contraction is completed. Undulin/collagen XIV is associated with collagen fibrils and fibronectin is present throughout the dermis in adult skin but it is produced by keloidal fibroblasts in an increased amount. In this study we investigated by immunohistochemistry the expression of the three extracellular matrix proteins in keloids and normal skin as well as in keloidal and normal fibroblasts in vitro. In keloids, increased tenascin C expression was observed especially in the reticular dermis associated with collagen fibrils sharply demarcating the limit of the lesion. In normal tissue, tenascin C was only expressed beneath the basal lamina and dermal-epidermal junction. Corresponding to the in vivo findings, tenascin C expression was increased in keloidal fibroblasts compared with normal fibroblasts in vitro (P < 0.003), whereas undulin/collagen XIV and fibronectin expression in keloids and keloidal fibroblasts was similar to that in normal tissue and normal fibroblasts, respectively. Therefore, tenascin C is a marker associated with keloids and we suggest that keloidal fibroblasts, once stimulated, continue to produce tenascin C independently from circulating factors.

An alternative insert of three amino acids is incorporated into collagen XIV in a developmentally regulated fashion

We have identified a novel splice variant of chicken collagen XIV which contains an insert of three amino acids (Val-Arg-Thr) in the sixth fibronectin type III-like (FNIII) domain. The codons for these amino acids are inserted into the mRNA by skipping of a splice donor site and usage of another donor site 9 bp further downstream in the collagen XIV gene. The percentage of the new splice variant in the total collagen XIV mRNA varies between 22 and 46% in different embryonic tissues. After hatching, however, this percentage increases dramatically and reaches 86% in adult skeletal muscle and 58% in adult gizzard, indicating developmental regulation of this splicing event. Computer modeling suggests that the three extra amino acids cause an increase in the size of a flexible loop connecting two beta-strands in the sixth FNIII domain. This increase might affect the exact arrangement of the FNIII domain in the collagen XIV molecule, thereby modulating its interactions with other matrix molecules.

Predominant expression of CD44 splice variant v10 in malignant and reactive human skin lymphocytes

The remarkable functional diversity of the cell surface receptor CD44 may be due to expression of multiple variant isoforms generated by alternative splicing of variant exons. Functional and correlative data implicate a role of CD44 variant isoforms in adhesion dependent processes such as lymphocyte recirculation and tumor progression and metastasis. We have analyzed 25 primary cutaneous lymphomas and 35 reactive lymphoid cell skin infiltrates or T cell-mediated skin diseases for the expression of CD44 variant isoforms. Irrespective of histologic typing, staging, and grading, cutaneous lymphomas as well as nonmalignant skin-infiltrating CD3+ CD4+ and CD8+ T and CD19+ B lymphocytes exhibited a strong expression of CD44v10 and a moderate expression of CD44v3 as determined by immunohistochemistry, immunofluorescence microscopy, and mRNA analysis. Expression of v5, v6, v7, and v9-containing CD44 variant isoforms was not detected. Furthermore, flow cytometry revealed expression of CD44v10 on a significant proportion of peripheral blood lymphocytes from Sézary's syndrome patients and a remarkable co-expression with cutaneous lymphocyte antigen. These results indicate a distinct CD44 variant isoform expression pattern associated with skin-homing lymphocytes different to lymphatic cells at noncutaneous sites. This differential expression pattern of CD44 variant isoforms may contribute to the development of lymphocyte skin infiltrates and/or the unique biologic behavior of cutaneous lymphomas.

Localization of a cell adhesion site on collagen XIV (undulin)

Cell adhesion to collagen XIV is implied to be mediated by proteoglycans as cellular receptors (T. Ehnis et al., 1996, Exp. Cell Res. 229, 388-397). In order to define the cell binding region(s), fusion proteins expressed in Escherichia coli and covering the large noncollagenous domain NC3 of collagen XIV were used as substrates for the adhesion of skin fibroblasts. A prominent cell binding site could be localized in the N-terminal fibronectin type III repeat of collagen XIV and its immediate C-terminal extension. Since this region also mediates the binding of the small chondroitin/dermatan sulfate proteoglycan decorin (T. Ehnis et al., 1997, J. Biol. Chem. 272, 20414-20419), our finding could provide the molecular basis for the observation that decorin serves as inhibitor and potential modulator of cellular interactions with collagen XIV.

Cell binding properties of collagen type XIV for human hematopoietic cells

Collagen XIV, which belongs to the subclass of fibril-associated collagens with interrupted triple helices (FACITs), is a homotrimeric molecule consisting of three alpha 1 (XIV) chains. Collagen type XIV is strongly expressed in the native human bone marrow, as shown by immunofluorescence staining and immunoblotting with an affinity-purified antibody. Hematopoietic cell lines of myeloid (KG1a, U937, K562) and lymphoid (U266, IM-9) origin were able to attach firmly to purified human collagen XIV preparations. Attachment of these cells was shown to be concentration-dependent. However, other hematopoietic cell lines tested were unable to adhere to collagen XIV, indicating restriction of this cellular interaction. The cellular receptors involved in cell binding to collagen type XIV are probably membrane-bound heparansulfate proteoglycans, since only the the addition of heparin inhibited attachment of the hematopoietic cells to collagen XIV in a concentration-dependent manner. Antibodies against the beta 1-integrin subunit could not interfere with binding to collagen type XIV. Using purified fragments of collagen XIV, it could be demonstrated that at least two different heparin-sensitive adhesion sites are present in the N-terminal globular domain and in the triple-helical domain. These data indicate that collagen XIV represents another collagen type expressed in human bone marrow with strong cell binding properties for defined populations of hematopoietic cells.