Known and potential new risk factors for skin cancer in European populations: a multicentre case-control study.

BACKGROUND: During recent years numerous studies have suggested that personal and environmental factors might influence cancer development. OBJECTIVES: To investigate environmental and personal characteristics associated with skin cancer risk. METHODS: A multicentre hospital-based case-control study was performed in Finland, Germany, Greece, Italy, Malta, Poland, Scotland and Spain, including 409 patients with squamous cell carcinoma (SCC), 602 with basal cell carcinoma (BCC) and 360 with cutaneous malignant melanoma (CMM) and 1550 control persons. Exposures were assessed by questionnaires that were partly self-administered, partly completed by dermatologists. Unconditional logistic regression modelling was used to assess associations including the influence of certain drugs and food items on skin cancer risk. RESULTS: The usual associations were observed for sun exposure and pigmentation characteristics, with chronic sun exposure being most strongly associated with SCC risk, and naevi and atypical naevi with CMM risk. Use of ciprofloxacin was associated with a decreased risk of BCC [odds ratio (OR) 0·33] and use of thiazide diuretics was associated with an increased risk of SCC (OR 1·66). Ciprofloxacin was also associated with SCC (OR 0·34) and thiazines with BCC (OR 2·04), but these associations lost significance after correction for multiple testing. Consumption of pomegranate, rich in antioxidants, was associated with decreased BCC and SCC risk, also after correcting for multiple testing. Recent experience of stressful events was associated with increased risk, particularly of CMM. CONCLUSIONS: In this large case-control study from across Europe the expected associations were observed for known risk factors. Some new potential protective factors and potential risk factors were identified for consumption of certain food items, medication use and stress, which deserve further investigation in future studies.

Basal cell carcinomas without histological confirmation and their treatment: an audit in four European regions.

BACKGROUND: Limited data are available on how often basal cell carcinomas (BCCs) are clinically diagnosed without histological confirmation and how they are treated. OBJECTIVES: Within the framework of the EPIDERM project, an audit was conducted in four European countries to study the occurrence of clinically diagnosed BCCs without histological confirmation and to investigate how these are treated. METHODS: In the Netherlands, Scotland, Finland and Malta studies were performed within different timeframes. Patients with one or more BCC(s) were selected and the number of clinically diagnosed BCCs without histological confirmation and their treatment was investigated by (manually) reviewing the (electronic) patient records and checking the (hospital) pathology databases to find evidence of histological confirmation. RESULTS: In the Netherlands, 1089 patients with a first histologically confirmed BCC developed 1974 BCCs of which 1833 (92·9%) were histologically confirmed and 141 (7·1%) were not. A 4-month retrospective study conducted in Scotland selected 294 patients with 344 BCCs; 306 (89·0%) were histologically confirmed and 38 (11·0%) were not. A 3-month prospective study performed at the same centre in Scotland identified 44 patients who developed 58 BCCs; 44 (75·9%) of these were histologically confirmed and 14 (24·1%) were not. In Finland, there were 701 patients who developed 977 BCCs, of which 807 (82·6%) were histologically and 170 (17·4%) nonhistologically confirmed. In Malta, there were 420 patients with 477 BCCs. Only three (0·7%) of them were clinically diagnosed without histological confirmation. In the Netherlands and Finland, clinically diagnosed BCCs without histological confirmation were most often treated with cryotherapy, whereas in Scotland 5% imiquimod cream was the preferred treatment modality. CONCLUSIONS: Although the frequency of clinically diagnosed BCCs without histological confirmation differed between the four European regions (range 0·7-24·1%), this confirms that the burden of BCC in Europe is underestimated when based on data from pathology and/or cancer registries.

Assessing physicians' preferences on skin cancer treatment in Europe.

BACKGROUND: A wide variety of both surgical and nonsurgical therapies is currently available for patients with skin cancer. OBJECTIVES: This part of the EPIDERM (European Prevention Initiative for Dermatological Malignancies) project is aimed at the evaluation of the treatment preferences for skin cancer in eight countries of the European Union. METHODS: A multicentre hospital-based case-control study was carried out at dermatology departments in Finland, Germany, Greece, Italy, Malta, Poland, Scotland and Spain. Patients with skin cancer (basal cell carcinoma, actinic keratosis, squamous cell carcinoma, cutaneous malignant melanoma and Bowen disease) were consecutively enrolled between July 2008 and July 2010. Information on the study variables (sex, age, country, tumour type, anatomical location and treatment) was obtained from questionnaires designed by the EPIDERM project. RESULTS: In total, 1708 patients with skin cancer were included. Surgery was the first treatment option in 76·5% of the patients (P = 0·001). Actinic keratosis was the only tumour type in which nonsurgical treatment was more frequent than surgery (91·4%). Tumours on the head were less likely to be surgically excised than those at other locations (odds ratio 0·25, P = 0·001). Simple excision or curettage was the most common surgical procedure (65·4%), followed by graft and flaps (22·4%). Cryotherapy was the most common nonsurgical option (52·4%), followed by imiquimod (18·0%), photodynamic therapy (PDT; 12·0%), 5-fluorouracil (5-FU; 5·7%), and diclofenac with hyaluronic acid (4·0%). CONCLUSIONS: Surgery remains the first-choice treatment of skin cancer. Regarding nonsurgical treatments, the conservative treatments available (imiquimod, 5-FU, PDT and diclofenac gel) have not yet exceeded the use of ablative options such as cryotherapy despite their accepted benefit of treating field cancerization.

Risk factors for actinic keratosis in eight European centres: a case-control study.

BACKGROUND: There are limited data regarding the association of actinic keratosis (AK) and other types of nonmelanoma skin cancer (NMSC); studies investigating possible correlation of AK with melanocytic naevi are even scarcer. To our knowledge, there are no data examining the risk of AK in people using specific medications. OBJECTIVE: To investigate constitutional and exposure risk factors leading to AK and the coexistence of AK with NMSC and melanoma. METHODS: A multicentre hospital-based case-control study was performed in Finland, Germany, Greece, Italy, Malta, Poland, Scotland and Spain, including 343 patients with actinic keratosis (AK), 409 with squamous cell carcinoma (SCC), 602 with basal cell carcinoma (BCC), 360 with invasive melanoma and 119 with in situ melanoma, and 686 control subjects. Exposures were assessed by questionnaires that were partly self-administered and partly filled out by dermatologists. Unconditional logistic regression modelling was used to assess associations including the influence of phenotypic characteristics, presence of naevi, sun-exposure habits and certain drugs on AK risk. RESULTS: Differences in hair and eye coloration variably influenced the risk for AK, with red hair signifying a seven times higher risk [odds ratio (OR) 6·9, 95% confidence interval (CI) 4·34-11·00), and brown - compared with blue - eyes, about a 40% reduced risk (OR 0·61, 95% CI 0·13-0·92). The darker the skin phototype, the lower the risk for AK, with phototype IV exhibiting nine times less risk of developing AK. Some and many freckles on the arms were associated with an OR of 1·8 (95% CI 1·08-2·81) and 3·0 (95% CI 1·10-3·54), respectively, while overall number of naevi and high educational level were inversely associated with AK. Sun exposure, thiazide diuretics and cardiac drugs had a higher risk for AK. SCC was the most frequent (58%) skin neoplasm coexisting with AKs, followed by BCC (30%), melanoma in situ (12%) and invasive melanoma (6%). CONCLUSION: In this large case-control study from across Europe the expected associations were confirmed for known risk factors. Some possible new risk factors, including cardiac and diuretic drugs, were identified, creating a new field for further investigation in future studies.

The patient journey: a report of skin cancer care across Europe.

BACKGROUND: There are poorly documented variations in the journey a skin cancer patient will follow from diagnosis to treatment in the European Union. OBJECTIVES: To investigate the possible difficulties or obstacles that a person with a skin malignancy in the European Union may have to overcome in order to receive adequate medical screening and care for his/her condition. In addition, we wished to explore differences in European health systems, which may lead to health inequalities and health inequities within Europe. METHODS: Ten European countries took part in this investigation (in alphabetical order): Finland, Germany, Greece, Italy, Malta, Poland, Romania, Spain, the Netherlands and the U.K. The individual participants undertook local and national enquiries within their own country and completed a questionnaire. RESULTS: This exercise has identified important differences in the management of a skin cancer patient, reflecting major disparities in health care between European countries. CONCLUSIONS: Further investigation of health disparities and efforts to address health inequalities should lead to improvements in European health care quality and reduction in morbidity from skin cancer.

Short incubation with methyl aminolevulinate for photodynamic therapy of actinic keratoses.

BACKGROUND: Photodynamic therapy (PDT) using methyl aminolevulinate (MAL) is an effective first-line treatment for actinic keratoses. A reduced incubation period may have practical advantages. OBJECTIVE: This study aims to evaluate the effect of incubation time (1 vs. 3 h), MAL concentration (160 mg/g vs. 80 mg/g) and lesion preparation in the setting of MAL-PDT for treatment of actinic keratosis (AK). DESIGN: Open, randomized, parallel-group multicentre study. SETTING: Outpatient dermatology clinics. SUBJECTS: One hundred and twelve patients with 384 previously untreated AK. Most lesions (87%) were located on the face and scalp and were thin (55%) or moderately thick (34%). METHODS: Lesions were debrided, and MAL cream (160 mg/g or 80 mg/g) was applied before illumination with red light (570-670 nm; light dose, 75 J/cm2). Patients were followed up at 2 and 3 months. Sixty patients (54%) were re-treated and assessed at 6 months. MAIN OUTCOME: Complete lesion response rates 3 and 12 months after last treatment. RESULTS: For lesions on the face/scalp, lesion complete response rates were 78% for thin AK and 74% for moderately thick AK lesions after 1 h vs. 96% and 87% after 3 h incubation with MAL 160 mg/g. Lesion recurrence rates at 12 months after two treatments were similar [19% (3 of 16) with 1 h vs. 17% (3 of 18) with 3 h 160 mg/kg MAL-PDT] and lower than for 80 mg/g MAL-PDT (44-45%). CONCLUSION: MAL-PDT using a 1-h incubation may be sufficient for successful treatment of selected AK lesions.

Systematic search for the best gene expression markers for melanoma micrometastasis detection.

Melanoma is notorious for its high tendency to metastasize and its refractoriness to treatment thereafter. Metastasis is believed to occur mostly through the lymphatic system, and the status of sentinel lymph nodes is currently recognized as the best prognostic indicator. Unfortunately, the lymphatic metastatic process is still poorly understood and the occurrence of sentinel node metastases (micrometastases) may be underestimated. We performed genome-wide gene expression analyses of melanoma lymph node micrometastases and macrometastases, and of primary melanomas and benign naevi, to characterize the early metastatic cells molecularly and to disclose the best diagnostic markers and rational targets for therapy. Significance analysis of microarrays identified 22 over- and five under-expressed genes with > or = four-fold changes in the micrometastases. Of these genes, MLANA, TYR, MIA, ERBB3, PRAME, and SPP1 were tested as potential markers by RT-PCR and immunohistochemistry. In a prospective study of 160 patients, our graded MLANA and TYR RT-PCR analyses disclosed clinically significant metastases, as assessed by disease recurrence, better than histological and immunohistochemical examinations. These results strongly suggest the clinical implementation of quantifiable RT-PCR assays to confirm and complement the pathological examination of sentinel node metastases. Furthermore, SPP1 and PRAME proved valuable as melanoma-specific markers capable of differentiating melanoma cells from benign naevi in the sentinel lymph nodes. Importantly, these two genes may also prove to be ideal targets for drug development and therapy. Most molecular traits of the micrometastases were already present in the primary tumours, suggesting that micrometastasis to sentinel lymph nodes is a fairly non-selective process.

Blood-derived gene-expression profiling in unravelling susceptibility to recessive disease.

Identification of new disease predisposition genes with chip-based technologies typically requires extensive financial and sample resources. We have recently shown that combining peripheral blood genome and transcriptome (BGT) information in highly selected materials can be a successful low-cost approach to unravelling dominant tumour susceptibility. In this study, we extended our investigations to recessively inherited tumour predisposition, and identified a homozygous germline mutation in the damage-specific DNA binding protein 2 (DDB2) gene in a patient with several facial tumours, for which doctors had been unable to provide a diagnosis. Our results provide proof of principle that BGT is a powerful approach for both dominant and recessive genes. In addition to tumour susceptibility, the method may be useful in characterising genetic defects underlying other disease phenotypes.

Switch to an invasive growth phase in melanoma is associated with tenascin-C, fibronectin, and procollagen-I forming specific channel structures for invasion.

Malignant melanomas are characterized by their high propensity to invade and metastasize, but the molecular mechanisms of these traits have remained elusive. Our DNA microarray analyses of benign nevi and melanoma tissue specimens revealed that the genes encoding extracellular matrix proteins tenascin-C (TN-C), fibronectin (FN), and procollagen-I (PCOL-I) are highly upregulated in invasive and metastatic melanomas. The expression and distribution of these proteins were further studied by immunohistochemistry in benign nevi, radially and vertically growing melanomas, sentinel node micrometastases, and macrometastases. TN-C was increased in all invasive tumours and metastases, especially at invasion fronts, but not in benign nevi or non-invasive melanomas. Significantly, the intensity of TN-C staining correlated with metastasis to sentinel lymph nodes, better than tumour thickness (Breslow). Moreover, TN-C, FN, and PCOL-I appeared to co-localize in the tumours and form tubular meshworks and channels ensheathing the melanoma cells. Our data suggest that melanoma invasion is associated with the formation of special channel-like structures, providing a new concept, structured tumour cell spreading. Altogether, these data provide potential new prognostic markers and therapeutic targets/strategies for preventing melanoma dissemination.

Transforming growth factor beta1 induces apoptosis in normal melanocytes but not in nevus cells grown in type I collagen gel.

We used type I collagen gel cultures to compare the growth requirements of melanocytes and dermal nevus cells. Melanocytes but not nevus cells undergo apoptosis in collagen unless supplied with growth stimulators such as fibroblast growth factor 2. To characterize the mechanism of melanocyte apoptosis in collagen, we tested the effects of transforming growth factor beta1, known to be functionally active in the skin. When picomolar amounts of transforming growth factor beta1 were added to normal melanocytes grown in type I collagen gel, their apoptosis was dramatically accelerated. In contrast, the apoptotic rate of nevus cells and melanoma cells grown under similar conditions was not affected by transforming growth factor beta1. The increased apoptosis of normal melanocytes was effectively counteracted by addition of either neutralizing transforming growth factor beta1 antibodies or fibroblast growth factor 2 to the collagen gel. Interestingly, the background apoptosis of normal melanocytes was also inhibited by transforming growth factor beta1 antibodies. By Western blotting we detected transforming growth factor beta-like immunoreactivity in melanocyte, nevus cell, and melanoma cell lysates. A sensitive bioassay confirmed that their medium contained considerable amounts of heat-activatable growth inhibitory activity that could partly be neutralized by transforming growth factor beta1 antibodies. It is evident that apoptosis of melanocytes grown in type I collagen gel can be mediated by both endogenous and exogenous transforming growth factor beta. We suggest that the balance between inhibitory growth factors such as transforming growth factor beta and stimulatory growth factors like fibroblast growth factor 2 has the potential to regulate the growth, localization, and survival of normal melanocytes also in vivo. The resistance of nevus cells to transforming-growth-factor-beta-mediated apoptosis may facilitate their ability to grow in the dermal compartment of the skin.

FGF expression allows nevus cells to survive in three-dimensional collagen gel under conditions that induce apoptosis in normal human melanocytes.

Melanocytes, the pigment forming cells of the skin, form an almost nonproliferating cell population located to the lowermost part of the epidermis. Normally melanocytes are not found higher in the epidermis or in the dermis. Nevi consist of melanocytes with altered growth characteristics and localization. The common pigmented nevus, a benign skin lesion, develops when melanocytes proliferate in the dermo-epidermal junction or in the dermis. Here we report growth characteristics of in vitro cultured normal human melanocytes and dermal nevus-derived melanocytes. As previously reported, nevus cells have a moderate to high FGF-2 expression level. Here we demonstrate that dermal nevus cells are able to survive in three-dimensional type 1 collagen culture, while normal human melanocytes rapidly undergo apoptosis. Melanocytes also, however, survive in collagen cultures in the presence of exogenous FGF-2. The survival of nevus cells in collagen is suppressed by protamine, an inhibitor of FGF-mediated cell stimulation. The in vivo growth environment of dermal nevus cells consists largely of type I and type III collagens. The results suggest that FGF-2 expression by nevus cells allows them to adapt to grow in the dermis. FGF-2 obviously has importance as a melanocyte survival factor and probably also in the development of malignant melanoma.

Induction of proliferation in isolated guinea pig gastric epithelium during restitution after superficial injury.

Immediate repair of the gastrointestinal epithelium after superficial injury is called restitution. It is based on the migration of the surviving mucoid neck cells over the area of injury. The involvement of growth factors in the process has been recently documented. They are known to enhance the process (ie, EGF, FGF, TGF-beta) and to activate the basolateral Na+-H+-antiport (EGF). They may exert their effect by activating intracellular tyrosine kinases or by inducing chemotaxis. Yet, their precise mechanism of action in the process is unknown. The aim of the present study was to investigate the effect of modulation of the signal transduction pathway on the occurrence of proliferative mucoid neck and foveolar cells in guinea pig gastric epithelium. Therefore guinea pig gastric epithelium was mounted in Ussing chambers in vitro and perfused 4 hr after superficial injury with 1.25 M NaCl. The potential difference over the epithelium and tissue resistance were recorded simultaneously. The tissue was exposed either to cycloheximide, genistein, or to 4-phorbol myristate 13-acetate (PMA) during the 4-hr recovery, and the expression of proliferative cells was assessed by staining the tissue for proliferative cells (Ki-67). The mean proliferative index of tissues subjected to NaCl injury was significantly higher than that of uninjured control tissues after 4 hr of restitution. Inhibition of the signaling pathway with genistein decreased the proliferative index significantly, while its stimulation with phorbol myristate increased it. Both electrophysiologic and morphologic restitution were sensitive to genistein, but not to PMA or cycloheximide. Superficial epithelial injury results in a significantly increased occurrence of proliferative cells in isolated guinea pig gastric epithelium. This endogenous activation of the tissue is sensitive to inhibition by tyrosine kinases and to stimulation by protein kinases. Electrophysiologic and morphologic recovery are also affected by the modulation of the signaling pathway. This suggests that it is involved in the immediate repair process.

A recombinant mutant vascular endothelial growth factor-C that has lost vascular endothelial growth factor receptor-2 binding, activation, and vascular permeability activities.

The vascular endothelial growth factor (VEGF) and the VEGF-C promote growth of blood vessels and lymphatic vessels, respectively. VEGF activates the endothelial VEGF receptors (VEGFR) 1 and 2, and VEGF-C activates VEGFR-3 and VEGFR-2. Both VEGF and VEGF-C are also potent vascular permeability factors. Here we have analyzed the receptor binding and activating properties of several cysteine mutants of VEGF-C including those (Cys156 and Cys165), which in other platelet-derived growth factor/VEGF family members mediate interchain disulfide bonding. Surprisingly, we found that the recombinant mature VEGF-C in which Cys156 was replaced by a Ser residue is a selective agonist of VEGFR-3. This mutant, designated DeltaNDeltaC156S, binds and activates VEGFR-3 but neither binds VEGFR-2 nor activates its autophosphorylation or downstream signaling to the ERK/MAPK pathway. Unlike VEGF-C, DeltaNDeltaC156S neither induces vascular permeability in vivo nor stimulates migration of bovine capillary endothelial cells in culture. These data point out the critical role of VEGFR-2-mediated signal transduction for the vascular permeability activity of VEGF-C and strongly suggest that the redundant biological effects of VEGF and VEGF-C depend on binding and activation of VEGFR-2. The DeltaNDeltaC156S mutant may provide a valuable tool for the analysis of VEGF-C effects mediated selectively via VEGFR-3. The ability of DeltaNDeltaC156S to form homodimers also emphasizes differences in the structural requirements for VEGF and VEGF-C dimerization.

Proteolytic processing regulates receptor specificity and activity of VEGF-C.

The recently identified vascular endothelial growth factor C (VEGF-C) belongs to the platelet-derived growth factor (PDGF)/VEGF family of growth factors and is a ligand for the endothelial-specific receptor tyrosine kinases VEGFR-3 and VEGFR-2. The VEGF homology domain spans only about one-third of the cysteine-rich VEGF-C precursor. Here we have analysed the role of post-translational processing in VEGF-C secretion and function, as well as the structure of the mature VEGF-C. The stepwise proteolytic processing of VEGF-C generated several VEGF-C forms with increased activity towards VEGFR-3, but only the fully processed VEGF-C could activate VEGFR-2. Recombinant 'mature' VEGF-C made in yeast bound VEGFR-3 (K[D] = 135 pM) and VEGFR-2 (K[D] = 410 pM) and activated these receptors. Like VEGF, mature VEGF-C increased vascular permeability, as well as the migration and proliferation of endothelial cells. Unlike other members of the PDGF/VEGF family, mature VEGF-C formed mostly non-covalent homodimers. These data implicate proteolytic processing as a regulator of VEGF-C activity, and reveal novel structure-function relationships in the PDGF/VEGF family.

Human ornithine decarboxylase-overproducing NIH3T3 cells induce rapidly growing, highly vascularized tumors in nude mice.

Overexpression of human ornithine decarboxylase (ODC) under the control of strong promoters induces morphological transformation of immortalized NIH3T3 and Rat-1 fibroblasts [M. Auvinen et al., Nature (Lond.), 360: 355-358, 1992]. We demonstrate here that ODC-overproducing NIH3T3 cells are tumorigenic in nude mice, giving rise to rapidly growing, large fibrosarcomas at the site of inoculation. The tumors are capable of invading host fat and muscle tissues and are vascularized abundantly. To disclose the molecular mechanism(s) driving the tumorigenic, invasive, and angiogenic phenotype of the tumors, the ODC-overproducing cell lines and tumor tissues were analyzed for the expression of various potential regulators and mediators of cell proliferation, matrix degradation, and angiogenesis. The tumorigenicity of ODC transformants was associated with elevated polyamine levels and down-regulated growth factor receptors. The invasiveness of the ODC-induced tumors could not be attributed to overexpression of various known extracellular matrix-degrading proteases or matrix metalloproteinases. The induction of the tumor neovascularization proved not to be elicited by vascular endothelial growth factor or basic fibroblast growth factor. Instead, the ODC-overexpressing cells appeared to secrete a novel angiogenic factor(s) that was able to promote migration of bovine capillary endothelial cells in collagen gels and increase the proliferation of human endothelial cells in vitro. In parallel, ODC-transformed cells displayed down-regulation of thrombospondin-1 and -2, the negative regulators of angiogenesis. Thus, the induction of the angiogenic phenotype of the ODC transformants is likely due both to increased expression and secretion of the new angiogenesis-stimulating factor(s) and decreased production and release of the antiangiogenic thrombospondins.

FGF-2 inhibits apoptosis in human teratocarcinoma cells during differentiation on collagen substratum.

Tera-2 is a human teratocarcinoma cell line, which is induced to differentiate into neuronal direction by retinoic acid. Once differentiated, the cells form an almost nondividing population that can be maintained for weeks under conventional culture conditions. If differentiation by retinoic acid is induced while the cells are growing on type I collagen or if the already-differentiated cells are transferred onto collagen, they survive only a few days unless the cultures are repeatedly supplied with FGF-2. Lack of this growth factor induces programmed cell death (apoptosis) detectable after 24-48 h, as marked by DNA cleavage and nuclear fragmentation. The undifferentiated stem cells survive and proliferate readily on collagen without addition of FGF-2. Tera-2 cells express two members of the FGF family, FGF-2 and FGF-4. The expression of both FGFs is turned off during differentiation on collagen substratum, whereas when cultivated on plain tissue culture dish, the expression of only FGF-4 becomes undetectable. The results indicate that signaling through cell surface FGF receptors is vital for the cells, and differentiation on collagen substratum results in complete extinction of the autocrine stimulatory loop. In vivo, such induction of growth factor dependency upon differentiation would result in apoptotic death of those cells which fail to find adequate conditions for continuing FGF stimulation.

Vascular endothelial growth factor B, a novel growth factor for endothelial cells.

We have isolated and characterized a novel growth factor for endothelial cells, vascular endothelial growth factor B (VEGF-B), with structural similarities to vascular endothelial growth factor (VEGF) and placenta growth factor. VEGF-B was particularly abundant in heart and skeletal muscle and was coexpressed with VEGF in these and other tissues. VEGF-B formed cell-surface-associated disulfide-linked homodimers and heterodimerized with VEGF when coexpressed. Conditioned medium from transfected 293EBNA cells expressing VEGF-B stimulated DNA synthesis in endothelial cells. Our results suggest that VEGF-B has a role in angiogenesis and endothelial cell growth, particularly in muscle.

A novel vascular endothelial growth factor, VEGF-C, is a ligand for the Flt4 (VEGFR-3) and KDR (VEGFR-2) receptor tyrosine kinases.

Angiogenesis, the sprouting of new blood vessels from pre-existing ones, and the permeability of blood vessels are regulated by vascular endothelial growth factor (VEGF) via its two known receptors Flt1 (VEGFR-1) and KDR/Flk-1 (VEGFR-2). The Flt4 receptor tyrosine kinase is related to the VEGF receptors, but does not bind VEGF and its expression becomes restricted mainly to lymphatic endothelia during development. In this study, we have purified the Flt4 ligand, VEGF-C, and cloned its cDNA from human prostatic carcinoma cells. While VEGF-C is homologous to other members of the VEGF/platelet derived growth factor (PDGF) family, its C-terminal half contains extra cysteine-rich motifs characteristic of a protein component of silk produced by the larval salivary glands of the midge, Chironomus tentans. VEGF-C is proteolytically processed, binds Flt4, which we rename as VEGFR-3 and induces tyrosine autophosphorylation of VEGFR-3 and VEGFR-2. In addition, VEGF-C stimulated the migration of bovine capillary endothelial cells in collagen gel. VEGF-C is thus a novel regulator of endothelia, and its effects may extend beyond the lymphatic system, where Flt4 is expressed.