Expression of EDA/EDB isoforms of fibronectin in papillary carcinoma of the thyroid

Shielding and nurturing: Fibronectin as a modulator of cancer drug resistance

Resistance to chemotherapy and targeted therapies constitute a common hallmark of most cancers and represent a dominant factor fostering tumor relapse and metastasis. Fibronectin, an abundant extracellular matrix glycoprotein, has long been proposed to play an important role in the pathobiology of cancer. Recent research has unraveled the role of Fibronectin in the onset of chemoresistance against a variety of antineoplastic drugs including DNA-damaging agents, hormone receptor antagonists, tyrosine kinase inhibitors, microtubule destabilizing agents, etc. The current review summarizes the role played by Fibronectin in mediating drug resistance against diverse anticancer drugs. We have also discussed how the aberrant expression of Fibronectin drives the oncogenic signaling pathways ultimately leading to drug resistance through the inhibition of apoptosis, promotion of cancer cell growth and proliferation.

PET Imaging of Hepatocellular Carcinoma Using ZD2-(68Ga-NOTA)

Purpose

We tested a recently developed short peptide radioligand for PET imaging of hepatocellular carcinoma (HCC) by targeting an oncoprotein, extra-domain B fibronectin (EDB-FN) in the tumor microenvironment.

Methods

The radioligand consists of a small linear peptide ZD2 with 68Ga-NOTA chelator, and specifically binds to EDB-FN. PET images were acquired dynamically for 1 hour after intravenously (i.v.) injecting 37 MBq (1.0 mCi) of the radioligand into the woodchuck model of naturally occurring HCC. Woodchuck HCC originated from chronic viral hepatitis infection, which recapitulates the corresponding human primary liver cancer. The animals were euthanized post-imaging for tissue collection and validation.

Results

For ZD2 avid liver tumors, the radioligand accumulation plateaued a few minutes after injection, while the liver background uptake stabilized 20 min post-injection. The status of EDB-FN in woodchuck HCC was confirmed by histology and validated by PCR and western blocking.

Conclusion

We have showed the viability of using the ZD2 short peptide radioligand targeting EDB-FN in liver tumor tissue for PET imaging of HCC, which can potentially impact the clinical care for HCC patients.

Collateral Damage Intended-Cancer-Associated Fibroblasts and Vasculature Are Potential Targets in Cancer Therapy

After oncogenic transformation, tumor cells rewire their metabolism to obtain sufficient energy and biochemical building blocks for cell proliferation, even under hypoxic conditions. Glucose and glutamine become their major limiting nutritional demands. Instead of being autonomous, tumor cells change their immediate environment not only by their metabolites but also by mediators, such as juxtacrine cell contacts, chemokines and other cytokines. Thus, the tumor cells shape their microenvironment as well as induce resident cells, such as fibroblasts and endothelial cells (ECs), to support them. Fibroblasts differentiate into cancer-associated fibroblasts (CAFs), which produce a qualitatively and quantitatively different extracellular matrix (ECM). By their contractile power, they exert tensile forces onto this ECM, leading to increased intratumoral pressure. Moreover, along with enhanced cross-linkage of the ECM components, CAFs thus stiffen the ECM. Attracted by tumor cell- and CAF-secreted vascular endothelial growth factor (VEGF), ECs sprout from pre-existing blood vessels during tumor-induced angiogenesis. Tumor vessels are distinct from EC-lined vessels, because tumor cells integrate into the endothelium or even mimic and replace it in vasculogenic mimicry (VM) vessels. Not only the VM vessels but also the characteristically malformed EC-lined tumor vessels are typical for tumor tissue and may represent promising targets in cancer therapy.

Magnetic resonance molecular imaging of metastatic breast cancer by targeting extradomain-B fibronectin in the tumor microenvironment

PURPOSE

Non-invasive early accurate detection of malignant breast cancer is paramount to the clinical management of the life-threatening disease. Here, we aim to test a small peptide targeted MRI contrast agent, ZD2-Gd(HP-DO3A), specific to an oncoprotein, extradomain-B fibronectin (EDB-FN), in the tumor microenvironment for MR molecular imaging of breast cancer.

METHOD

EDB-FN expression in 4T1 and MDA-MB-231 cancers was analyzed with quantitative real-time PCR and western blot. Primary and metastatic triple negative breast cancer mouse models were developed using 4T1 and MDA-MB-231 cells. Contrast-enhanced MRI was carried out to evaluate the use of ZD2-Gd(HP-DO3A) in detecting 4T1 and MDA-MB-231 primary and metastatic tumors.

RESULTS

EDB-FN was abundantly expressed in the extracellular matrix (ECM) of both the primary and metastatic TNBC tumors. In T₁ -weighted MRI, ZD2-Gd(HP-DO3A) generated superior contrast enhancement in primary TNBC tumors than a nonspecific clinical agent Gd(HP-DO3A), during 30 min after contrast injection. ZD2-Gd(HP-DO3A) also produced a significant increase in contrast-to-noise ratio (CNR) of TNBC metastases, enabling sensitive localization and delineation of metastases that occulted in non-contrast-enhanced or Gd(HP-DO3A)-enhanced MRI.

CONCLUSIONS

These findings potentiate the use of ZD2-Gd(HP-DO3A) for MR molecular imaging of malignant breast cancers to improve the healthcare of breast cancer patients. Magn Reson Med 79:3135-3143, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Tissue stiffness regulates serine/arginine-rich protein-mediated splicing of the extra domain B-fibronectin isoform in tumors

Alternative splicing of proteins gives rise to different isoforms that play a crucial role in regulating several cellular processes. Notably, splicing profiles are altered in several cancer types, and these profiles are believed to be involved in driving the oncogenic process. Although the importance of alternative splicing alterations occurring during cancer is increasingly appreciated, the underlying regulatory mechanisms remain poorly understood. In this study, we use both biochemical and physical tools coupled with engineered models, patient samples, and a murine model to investigate the role of the mechanical properties of the tumor microenvironment in regulating the production of the extra domain-B (EDB) splice variant of fibronectin (FN), a hallmark of tumor angiogenesis. Specifically, we show that the amount of EDB-FN produced by endothelial cells increases with matrix stiffness both in vitro and within mouse mammary tumors. Matrix stiffness regulates splicing through the activation of serine/arginine rich (SR) proteins, the splicing factors involved in the production of FN isoforms. Activation of the SR proteins by matrix stiffness and the subsequent production of EDB-FN are dependent on intracellular contractility and PI3K-AKT signaling. Notably, matrix stiffness-mediated splicing is not limited to EDB-FN, but also affects splicing in the production of PKC βII and the VEGF 165b splice variant. Together, these results demonstrate that the mechanical properties of the microenvironment regulate alternative splicing and establish a previously unidentified mechanism by which cells can adapt to their microenvironment.

Fibronectin splice variation in human knee cartilage, meniscus and synovial membrane: observations in osteoarthritic knee

Fibronectin (FN) is a widely expressed molecule that can participate in development of osteoarthritis (OA) affecting cartilage, meniscus, and synovial membrane (SM). The alternatively spliced isoforms of FN in joint tissues other than cartilage have not been extensively studied previously. The present study compares FN splice variation in patients with varying degrees of osteoarthritic change. Joint tissues were collected from asymptomatic donors and patients undergoing arthroscopic procedures. Total RNA was amplified by PCR using primers flanking alternatively spliced Extra Domain A (EDA), Extra Domain B (EDB) and Variable (V) regions. EDB(+) , EDB(-) and EDA(-) and V(+) variants were present in all joint tissues, while the EDA(+) variant was rarely detected. Expression levels of EDB(+) and EDV(+) variants were similar in cartilage, synovium, and meniscal tissues. Synovial expression of V(+) FN in arthroscopy patients varied with degree of cartilage degeneration. Two V(-) isoforms, previously identified in cartilage, were also present in SM and meniscus. Fibronectin splicing in meniscus and SM bears striking resemblance to that of cartilage. Expression levels of synovial V(+) FN varied with degree of cartilage degeneration. V(+) FN should be investigated as a potential biomarker of disease stage or progression in larger populations.

Therapeutic efficacy of the F8-IL2 immunocytokine in a metastatic mouse model of lung adenocarcinoma

OBJECTIVES

Antibody-cytokine fusion proteins (immunocytokines) represent a novel class of armed antibodies in oncology. In particular, IL2- and TNF-based immunocytokines targeting the EDB domain of fibronectin and the A1 domain of tenascin-C have demonstrated promising anti-tumor activity and are currently investigated in Phase I and Phase II clinical trials. To advance the development of immunocytokines for NSCLC, we here report on the therapeutic efficacy of F8-IL2, an immunocytokine directed against the alternatively spliced EDA domain of fibronectin in a fully immunocompetent, orthotopic model of NSCLC, and the characterization of the target antigen expression in human NSCLC specimens.

MATERIALS AND METHODS

We evaluated the therapeutic efficacy of the F8-IL2 immunocytokine utilizing a K-ras mutant, p53 deficient metastatic mouse model of NSCLC derived from the latest generation of genetically engineered and conditional tumor models. In parallel, we assessed the presence of the EDA domain of fibronectin by immunofluorescence in lung biopsies obtained from patients with NSCLC.

RESULTS

The EDA domain of fibronectin was broadly expressed in lung metastases obtained from our model. Treatment with F8-IL2 induced substantial local changes within immune effector cell populations and demonstrated promising therapeutic efficacy as monotherapy. The target of F8-IL2, the EDA domain of fibronectin, was present in all human lung adenocarcinoma specimens tested.

CONCLUSION

Both the therapeutic efficacy in a metastatic mouse model of NSCLC and the extensive presence of the EDA domain of fibronectin in human NSCLC biopsies support the rational development of therapies based on the F8-IL2 immunocytokine for the treatment of NSCLC.

Application of Immunohistochemistry in Thyroid Pathology

Context

Accurate classification of follicular-patterned thyroid lesions is not always an easy task on routine surgical hematoxylin-eosin–stained or cytologic fine-needle aspiration specimens. The diagnostic challenges are partially due to differential diagnostic criteria that are often subtle and subjective. In the past decades, tremendous advances have been made in molecular gene profiling of tumors and diagnostic immunohistochemistry, aiding in diagnostic accuracy and proper patient management.

Objective

To evaluate the diagnostic utility of the most commonly studied immunomarkers in the field of thyroid pathology by review of the literature, using the database of indexed articles in PubMed (US National Library of Medicine) from 1976–2013.

Data Sources

Literature review, authors' research data, and personal practice experience.

Conclusions

The appropriate use of immunohistochemistry by applying a panel of immunomarkers and using a standardized technical and interpretational method may complement the morphologic assessment and aid in the accurate classification of difficult thyroid lesions.

The Pathogenetic Role of the HGF/c-Met System in Papillary Carcinoma of the Thyroid

The MET oncogene encodes for Met protein, a trans-membrane tyrosine kinase identified as the high affinity receptor for hepatocyte growth factor (HGF). Immunohistochemical studies have demonstrated that Met protein is intensely expressed in tumor cells of >95% cases of thyroid papillary carcinoma. High density of Met protein in tumor cells is the result of increased transcription of a normal MET gene, probably due to a combination of intracellular and extracellular signals. Over-expression of Met protein is more pronounced at the invading front of the tumor and can profoundly affect the tumorigenesis of papillary carcinoma of the thyroid. In fact, Met protein-positive papillary carcinoma cells are highly responsive to hepatocyte growth factor (HGF), which is effective in stimulating tumor cell adhesion, migration and invasiveness. In addition, HGF stimulation of papillary carcinoma of the thyroid (PTC) cells causes up-regulation of COX-2 and down-regulation of CD82/KAI-1; both these molecules have a major role in controlling tumor cell invasiveness. Finally, HGF stimulation of tumor cells may significantly affect the tumor microenvironment. In fact, HGF induces tumor cells to release chemokines active in the recruitment of dendritic cells, and is involved in regulating the production of proangiogenic factors.

Fibronectins in vascular morphogenesis

Fibronectin is an extracellular matrix protein found only in vertebrate organisms containing endothelium-lined vasculature and is required for cardiovascular development in fish and mice. Fibronectin and its splice variants containing EIIIA and EIIIB domains are highly upregulated around newly developing vasculature during embryogenesis and in pathological conditions including atherosclerosis, cardiac hypertrophy, and tumorigenesis. However, their molecular roles in these processes are not entirely understood. We review genetic studies examining functions of fibronectin and its splice variants during embryonic cardiovascular development, and discuss potential roles of fibronectin in vascular disease and tumor angiogenesis.

Application of immunohistochemistry to thyroid neoplasms

CONTEXT

Thyroid lesions with nodular architecture and follicular pattern of growth often pose difficulties in accurate diagnosis during the assessment of cytologic and histologic specimens. The diagnosis of follicular neoplasm on cytology or of follicular tumor of uncertain malignant potential on histology is likely to cause confusion among clinicians and delay effective management of these lesions. Occasionally, thyroid tumors represent unusual or metastatic lesions and their accurate diagnosis requires immunohistochemical confirmation.

OBJECTIVE

To review the literature on the applications of immunohistochemistry in the differential diagnosis of thyroid tumors.

DATA SOURCES

Relevant articles indexed in PubMed (National Library of Medicine) between 1976 and 2006.

CONCLUSIONS

Our review supports the use of ancillary techniques involving a panel of antibodies suitable for immunohistochemistry and molecular analysis in the assessment of thyroid nodules. These tools can improve diagnostic accuracy when combined with standard morphologic criteria.

The extra-domain A of fibronectin is a vascular marker of solid tumors and metastases

One of the most promising new avenues for the development of more selective and efficacious cancer therapies relies on the antibody-mediated targeted delivery of bioactive agents (e.g., cytokines) to the tumor environment. The identification of quantitative differences in the expression of accessible vascular proteins in metastatic lesions and host organs facilitate the development of antibody-based strategies, which should be highly efficient and selective, considering the fact that an over-exuberant neovasculature is a characteristic feature of aggressive cancers, and that tumor blood vessels are readily accessible for i.v. administered therapeutic agents. Metastasis is the main cause of death in cancer. The availability of metastasis-specific antigens accessible from the bloodstream will allow a selective delivery of therapeutic agents to metastatic lesions using antibodies as vehicles. Using a combination of vascular biotinylation of 129Sv mice bearing F9 liver metastases and mass spectrometry, we have identified 435 accessible proteins in metastasis and host organ specimens, of which 117 were exclusively detected in metastases. In particular, we found that the alternatively spliced extra-domain A (EDA) of fibronectin is strongly expressed in the neovasculature of liver metastases, while being undetectable in most normal organs. A human antibody to EDA was used to show EDA expression in the neovasculature of metastases and primary tumors of human cancer patients and to target mouse liver metastases and subcutaneous tumors in vivo. Human antibody fragments specific to the EDA domain of fibronectin promise to serve as general vehicles for the efficient and selective delivery of imaging agents or therapeutic molecules to metastatic sites.

Fibronectin as target for tumor therapy

During cancer progression, the extracellular matrix (ECM) of the tissue in which the tumor grows is extensively remodeled, both by degradation of preexisting ECM molecules and by the neosynthesis of ECM components, which in many cases are not present in the ECM of normal tissues. Fibronectin (FN), a class of high-molecular-weight adhesive glycoproteins, plays a prominent role in mediating ECM function, because of its high abundance and its interaction with cellular components. Furthermore, the generation of tumor-associated FN isoforms allows the development of specific ligands (e.g., antibodies), which can be used for the selective delivery of therapeutic agents to the tumor environment. In view of these considerations, it is not surprising that FN is being used as a target for biomolecular intervention, both for the development of inhibitory molecules that block the interaction of FN with integrins and other receptors on the cell surface, and for the development of ligand-based targeted imaging and therapeutic strategies. In this review, we briefly present the essential properties of FN, and we then focus on the therapeutic strategies that are currently in preclinical or clinical development and feature FN as a target, or that are based on FN fragments so as to promote tumor-growth inhibition.

Fetal cell carcinogenesis of the thyroid: theory and practice

A novel hypothesis of thyroid carcinogenesis, the "fetal cell carcinogenesis" hypothesis, in which cancer cells are derived from the remnants of three types of fetal thyroid cells, instead of normal thyroid follicular cells, is proposed. In this hypothesis, thyroid cancer cells are generated from fetal cells by proliferation without differentiation and oncogenes play an oncogenic role by preventing fetal cells from differentiating. This hypothesis explains well the clinical and biological features and recent molecular evidence of thyroid carcinoma. It underscores the importance of clarifying the molecular mechanism of thyroid development and the identification of fetal thyroid cells, especially thyroid stem cells (TSCs), since such data will lead to better understanding of thyroid carcinoma and other thyroid diseases.

Fetal cell carcinogenesis: a new hypothesis for better understanding of thyroid carcinoma

Modern advances in molecular technology have given us the chance to establish a new insight into thyroid carcinogenesis. Gene expression in thyroid malignancies usually reveals highly consistent profiles, which leads to questioning of the classic concept of multistep carcinogenesis, in which cancer cells are produced from well-differentiated benign cells by transformation caused by accumulating damage to their genome. We propose a novel hypothesis of thyroid carcinogenesis, the fetal cell carcinogenesis hypothesis, in which cancer cells are derived from the remnants of three types of fetal thyroid cells, instead of normal thyroid follicular cells. This hypothesis explains well the clinical and biologic features and recent molecular evidence of thyroid carcinoma. It suggests the importance of clarifying the molecular mechanism of thyroid development and the identification of fetal thyroid cells, especially thyroid stem cells (TSCs), because such data will lead to better understanding of thyroid carcinogenesis and thyroid regeneration.

Gene Expression Profile of Papillary Thyroid Cancer: Sources of Variability and Diagnostic Implications

The study looked for an optimal set of genes differentiating between papillary thyroid cancer (PTC) and normal thyroid tissue and assessed the sources of variability in gene expression profiles. The analysis was done by oligonucleotide microarrays (GeneChip HG-U133A) in 50 tissue samples taken intraoperatively from 33 patients (23 PTC patients and 10 patients with other thyroid disease). In the initial group of 16 PTC and 16 normal samples, we assessed the sources of variability in the gene expression profile by singular value decomposition which specified three major patterns of variability. The first and the most distinct mode grouped transcripts differentiating between tumor and normal tissues. Two consecutive modes contained a large proportion of immunity-related genes. To generate a multigene classifier for tumor-normal difference, we used support vector machines-based technique (recursive feature replacement). It included the following 19 genes: DPP4, GJB3, ST14, SERPINA1, LRP4, MET, EVA1, SPUVE, LGALS3, HBB, MKRN2, MRC2, IGSF1, KIAA0830, RXRG, P4HA2, CDH3, IL13RA1, and MTMR4, and correctly discriminated 17 of 18 additional PTC/normal thyroid samples and all 16 samples published in a previous microarray study. Selected novel genes (LRP4, EVA1, TMPRSS4, QPCT, and SLC34A2) were confirmed by Q-PCR. Our results prove that the gene expression signal of PTC is easily detectable even when cancer cells do not prevail over tumor stroma. We indicate and separate the confounding variability related to the immune response. Finally, we propose a potent molecular classifier able to discriminate between PTC and nonmalignant thyroid in more than 90% of investigated samples.

Hepatocyte growth factor (HGF) downregulates thrombospondin 1 (TSP-1) expression in thyroid papillary carcinoma cells

This study investigates the expression of thrombospondin-1 in papillary carcinoma of the thyroid and the role of Met-HGF interaction in TSP-1 regulation. In tissue sections, immunostaining for TSP-1 was associated with the fibrous tumour stroma, and showed areas of marked intensity adjacent to the basal membrane of tumour cells. Investigation of TSP-1 RNA expression showed that, in 10 of 14 cases, TSP-1 mRNA levels were significantly lower in tumour tissue (20-100% reduction; mean = 55% +/- 20; p = 0.001) than in the corresponding normal thyroid. Since it has been reported that HGF can downregulate the expression of TSP-1 mRNA, TSP-1 mRNA levels were measured in 7 primary cultures, established from thyroid papillary carcinomas (TPC), and in 1 TPC cell line prior to, or after, stimulation with HGF. A marked decrease in TSP-1 mRNA levels was observed after HGF stimulation in 6/7 primary cultures (60-100% decrease (mean = 79 +/- 15%; p = 0.006) and in the TPC cell line; moreover, the decrease in TSP-1 mRNA in cell extracts was associated with a decrease in TSP-1 protein in culture supernatants. The HGF activity was dose dependent and the downregulation lasted for at least 48 h after stimulation. The high-level expression of Met protein, the high-affinity receptor for HGF, in most cases of papillary carcinoma of the thyroid is consistent with the possibility that HGF-Met interaction plays a crucial role in regulating the expression of TSP-1 in this tumour type.

Direct test of potential roles of EIIIA and EIIIB alternatively spliced segments of fibronectin in physiological and tumor angiogenesis

Fibronectin splice variants containing the EIIIA and/or EIIIB exons are prominently expressed in the vasculature of a variety of human tumors but not in normal adult tissues. To understand the functions of these splice variants in physiological and tumor angiogenesis, we used EIIIB-null and EIIIA-null strains of mice to examine neovascularization of mouse retinas, pancreatic tumors in Rip-Tag transgenic mice, and transplanted melanomas. Contrary to expectations, physiological and tumor angiogenesis was not significantly affected by the absence of either EIIIA or EIIIB splice variants. Tumor growth was also not affected. In addition, the expression levels of smooth muscle alpha actin, believed to be modulated by EIIIA-containing fibronectins, were not affected either. Our experiments show that despite their tight regulation during angiogenesis, the presence of EIIIA or EIIIB splice variants individually is not essential for neovascularization.

"Stromatogenesis" and tumor progression

"Stromatogenesis" is the formation of new stroma occurring, in parallel with the neoplastic process, at sites of active tumor invasion, i.e., at the free surface of a developing exophytic tumor, at the invading tumor front of an advancing endophytic tumor, and at sites of tumor metastasis, wherein the newly formed stroma disrupts the continuity of normal structures, cleaving paths for the invading tumor cells. Stroma is also present at the heart of the tumor, but only as a secondary event following tumor advancement and subsequent incorporation of its periphery into inner tumor areas. The new stroma, composed of stromal cells and extracellular matrix (ECM), is loose and edematous at the expanding tumor fronts, and rather dense in central tumor areas and sites of tumor metastasis. The stromal cells facing tumor invasion are intensely proliferating (high MIB-1 index) spindle-shaped cells, alpha-smooth muscle actin positive, and loaded with thymidine phosphorylase (TP) and SPARC (secreted protein acidic and rich in cysteine). The associated ECM is rich in collagen III, SPARC, and new blood vessels (CD31) but is depleted of collagen I and fibronectin. These constitutional changes render stromatogenesis amenable to tumor cell invasion and are, in cases of incipient neoplasia, a prospective criterion of early stromal invasion. Other stromal cell or ECM constituents, such as the lactate dehydrogenase-5 (LDH-5), the acidic fibroblast growth factor (aFGF), the basic FGF (bFGF), and the collagens II and IV, remain unchanged, and others are negative: myosin, desmin, S-100 protein and epidermal growth factor receptor (EGFR). The mechanism of stromatogenesis is obscure but is probably stimulated by specific stromatogenic growth factors, released by neoplastic and inflammatory cells. It appears that the process is neither neoplastic nor reactive, but rather is a, hereto unexplained, phenomenon of host's complicity in tumor progression.

Stimulation of extracellular matrix remodeling by the first type III repeat in fibronectin

The fibronectin matrix contains cryptic sites which are thought to modulate cellular biological responses. One of these sites, located in fibronectin's first type III repeat (III1c), influences signaling pathways that are relevant to cytoskeletal organization and cell cycle progression. The purpose of this study was to identify possible mechanisms responsible for the effects of III1c on cell behavior. Recombinant peptides representing various type III repeats of fibronectin were compared for their effects on fibronectin matrix organization and activation of intracellular signaling pathways. III1c and III13 but not III11c or III10 bound to monolayers of human skin fibroblasts in a dose- and time-dependent manner and were localized to the extracellular matrix. Binding of III13, but not III1c, to matrix was sensitive to heparitinase, suggesting that the association of III1c with the matrix was not dependent on heparan sulfate proteoglycans. Quantitative and morphological assessment indicated that, in contrast to previously published reports, the binding of III1c to cell layers did not result in the loss or disruption of matrix fibronectin. Binding of III1c but not III13 to the extracellular matrix did result in the loss of a conformationally sensitive epitope present within the EDA type III module of cellular fibronectin. III1c-induced loss of the EDA epitope did not require the presence of cells, occurred within 1 hour and was associated with the activation of p38 mitogen-activated protein kinase (MAPK) followed by the formation of filopodia. Maximal phosphorylation of p38 MAPK occurred within 1 hour, whereas cytoskeletal changes did not appear until 12 hours later. These findings are consistent with a model in which the binding of III1c to the extracellular matrix results in a conformational remodeling of the fibronectin matrix, which has both short- and long-term effects on cell physiology.

Papillary carcinoma of the thyroid: evidence for a role for hepatocyte growth factor (HGF) in promoting tumour angiogenesis

The pattern of vascularization of papillary carcinoma was investigated in tumour sections from 31 cases and in primary cultures from 12 cases. Tumour sections were immunostained for von Willebrand Factor (vWF) to visualize blood vessels; for endothelial-specific nitric-oxide-synthase (EC-NOS), as a marker of endothelial cell activation; and for Ki-67 to evaluate endothelial cell proliferation. It was found that endothelial cells lining venous vessels located in peritumoural fibrous tissue were intensely EC-NOS-positive and occasionally Ki-67-positive. Capillary vessels of tumour papillae were not stained for Ki-67 and were weakly EC-NOS-positive. Primary cultures of papillary carcinoma cells were used as a potential source of factors active on endothelial cells. It was found that thyroid tumour cells contain RNAs for angiopoietin, vascular endothelial growth factor (VEGF), and VEGF-C; moreover, they release large amounts of VEGF into culture supernatants and exert chemotactic activity in vitro for the endothelial cell line SIEC. The ability of papillary carcinoma cells to release angiogenic factors could be stimulated in vitro. Hepatocyte growth factor (HGF; 25 ng/ml) induced a 1.2- to 5-fold increase in the amount of VEGF released by tumour cells and a 1.2- to 4.2-fold increase in the amount of chemotactic activity present in culture supernatants. Met protein, the high affinity HGF-receptor, is overexpressed in a large proportion of cases of papillary carcinoma. These findings are consistent with the possibility that HGF-Met protein interaction is one of the molecular mechanisms promoting the vascularization of papillary carcinoma of the thyroid.

Expression of extradomain-B-containing fibronectin in subretinal choroidal neovascular membranes

PURPOSE

To investigate the presence of the fibronectin isoform containing the extradomain B (B-FN), a marker-protein of angiogenesis, in surgically excised human choroidal neovascular membranes (CNVM) to evaluate whether B-FN could be used as a therapeutic target for specific antibody-photosensitizer immunoconjugates.

DESIGN

Laboratory investigation.

METHODS

The setting was an institutional practice. The study population consisted of 15 eyes (15 patients) with CNVM undergoing membrane excision (four eyes with age-related macular degeneration, seven with pathologic myopia and four with multifocal choroiditis). The control group consisted of eight eye bank eyes (four subjects) without choroidal neovascularization. Light microscopic immunohistochemistry on cryostat sections of tissues was obtained. B-FN was detected by a human recombinant antibody, CGS-1, and compared with immunostaining for endothelial cells with factor VIII-related antigen. The main outcome measure was the presence of CGS-1 positively stained cells or areas of the extracellular matrix. Staining of CGS-1 was scored on a scale from 0 to 3.

RESULTS

Fourteen of 15 neovascular membranes stained strongly with CGS-1 (score 2 or 3). One membrane from a patient with pathologic myopia was negatively stained (score 0). CGS-1 positive staining was detected around endothelial cells and in the extracellular matrix of CNVMs. The retina of eyes without choroidal neovascularization was negative with CGS-1 in all eight donor eyes, while the choroid contained some weakly CGS-1 positive cells (score 0 and 1, respectively).

CONCLUSIONS

The extradomain B is abundantly expressed in CNVMs, but its expression is more restricted in eyes harboring no apparent choroidal neovascularization. In the future, B-FN might serve as a target for the delivery of antibody-photosensitizer immunoconjugates to newly developed vessels to enhance the selectivity of photodynamic therapy.

Met protein and hepatocyte growth factor (HGF) in papillary carcinoma of the thyroid: evidence for a pathogenetic role in tumourigenesis

In the last 10 years, evidence has accumulated that overexpression of Met protein is a distinguishing feature of almost every case of well-differentiated papillary carcinoma. Increased expression of the protein is probably due to enhanced transcription of the MET gene and/or to post-transcriptional mechanisms. So far, alterations of the MET gene have not been recognized, but evidence has been provided that activated RAS and RET can cause accumulation of MET RNA. Thus, the possibility exists that dysregulation of MET is the final result of different molecular pathways capable of inducing thyroid cell transformation; RET rearrangements might account for some of the cases, but the demonstration that the majority of papillary carcinomas do not have recognized alterations of the RET gene strongly suggests that MET gene dysregulation can also be achieved through other molecular pathways. Dysregulation of MET causes marked accumulation of Met protein in tumour cells that is promptly detected by immunohistochemistry. Thus, overexpression of Met protein might represent an immunohistochemical marker of papillary carcinoma, potentially helpful in problematic cases, but caution is required; moderate expression of Met protein is observed in non-neoplastic thyroid diseases, such as Graves' and Hashimoto's thyroiditis, and reagents active on paraffin sections may have a low affinity and/or low specificity for Met protein, leading to artifactual staining. Met protein-positive papillary carcinoma cells may produce hepatocyte growth factor (HGF) and may activate HGF through the urokinase-type plasminogen activator (uPA) bound to urokinase-type plasminogen activator receptor (uPA-R). Thus, papillary carcinoma cells possess the molecular machinery necessary for a productive HGF/Met interaction. In vitro studies have demonstrated that HGF enhances the motility and invasiveness of tumour cells and induces the synthesis and release of chemokines active in the recruitment of dendritic cells. These observations provide a rational basis for the understanding of two distinguishing features of papillary carcinoma. First, the tumour is often characterized by early metastatic spread to regional lymph nodes and by multifocal involvement of the gland, which suggests highly invasive behaviour. Second, a prominent peritumoural inflammatory reaction is often observed, which suggests cross-talk between tumour cells and the immune system.