Tumour Suppressor Neuron Navigator 3 and Matrix Metalloproteinase 14 are Co-expressed in Most Melanomas but Downregulated in Thick Tumours

Melanoma is a highly metastatic tumour originating from neural crest-derived melanocytes. The aim of this study was to analyse the expression of neuron navigator 3 (NAV3) in relation to membrane type-1 matrix metalloproteinase MMP14, a major regulator of invasion, in 40 primary melanomas, 15 benign naevi and 2 melanoma cell lines. NAV3 copy number changes were found in 18/27 (67%) primary melanomas, so that deletions dominated (16/27 of samples, 59%). NAV3 protein was found to be localized at the leading edge of migrating melanoma cells in vitro. Silencing of NAV3 reduced both melanoma cell migration in 2-dimensional conditions, as well as sprouting in 3-dimensional collagen I. NAV3 protein expression correlated with MMP14 in 26/37 (70%) primary melanomas. NAV3 and MMP14 were co-expressed in all tumours with Breslow thickness < 1 mm, in 11/23 of mid-thickness tumours (1-5 mm), but in only 1/6 samples of thick (> 5 mm) melanomas. Altogether, NAV3 number changes are frequent in melanomas, and NAV3 and MMP14, while expressed in all thin melanomas, are often downregulated in thicker tumours, suggesting that the lack of both NAV3 and MMP14 favours melanoma progression.

Prolyl 4-hydroxylase subunit alpha 1 (P4HA1) is a biomarker of poor prognosis in primary melanomas, and its depletion inhibits melanoma cell invasion and disrupts tumor blood vessel walls

Melanoma is an unpredictable, highly metastatic malignancy, and treatment of advanced melanoma remains challenging. Novel molecular markers based on the alterations in gene expression and the molecular pathways activated or deactivated during melanoma progression are needed for predicting the course of the disease already in primary tumors and for providing new targets for therapy. Here, we sought to identify genes whose expression in primary melanomas correlate with patient disease‐specific survival using global gene expression profiling. Many of the identified potential markers of poor prognosis were associated with the epithelial–mesenchymal transition, extracellular matrix formation, and angiogenesis. We studied further the significance of one of the genes, prolyl 4‐hydroxylase subunit alpha 1 (P4HA1), in melanoma progression. P4HA1 depletion in melanoma cells reduced cell adhesion, invasion, and viability in vitro. In melanoma xenograft assays, we found that P4HA1 knockdown reduced melanoma tumor invasion as well as the deposition of collagens, particularly type IV collagen, in the interstitial extracellular matrix and in the basement membranes of tumor blood vessels, leading to vessel wall rupture and hemorrhages. Further, P4HA1 knockdown reduced the secretion of collagen triple helix repeat containing 1 (CTHRC1), an important mediator of melanoma cell migration and invasion, in vitro and its deposition around tumor blood vessels in vivo. Taken together, P4HA1 is an interesting potential prognostic marker and therapeutic target in primary melanomas, influencing many aspects of melanoma tumor progression.

Gene expression analyses of primary melanomas reveal CTHRC1 as an important player in melanoma progression

Melanoma is notorious for its high tendency to metastasize and its refractoriness to conventional treatments after metastasis, and the responses to most targeted therapies are short-lived. A better understanding of the molecular mechanisms behind melanoma development and progression is needed to develop more effective therapies and to identify new markers to predict disease behavior. Here, we compared the gene expression profiles of benign nevi, and non-metastatic and metastatic primary melanomas to identify any common changes in disease progression. We identified several genes associated with inflammation, angiogenesis, and extracellular matrix modification to be upregulated in metastatic melanomas. We selected one of these genes, collagen triple helix repeat containing 1 (CTHRC1), for detailed analysis, and found that CTHRC1 was expressed in both melanoma cells and the associated fibroblasts, as well as in the endothelium of tumor blood vessels. Knockdown of CTHRC1 expression by shRNAs in melanoma cells inhibited their migration in Transwell assays and their invasion in three-dimensional collagen and Matrigel matrices. We also elucidated the possible down-stream effectors of CTHRC1 by gene expression profiling of the CTHRC1-knockdown cells. Our analyses showed that CTHRC1 is regulated coordinately with fibronectin and integrin β3 by the pro-invasive and -angiogenic transcription factor NFATC2. We also found CTHRC1 to be a target of TFGβ and BRAF. These data highlight the importance of tumor stroma in melanoma progression. Furthermore, CTHRC1 was recognized as an important mediator of melanoma cell migration and invasion, providing together with its regulators-NFATC2, TGFβ, and BRAF-attractive therapeutic targets against metastatic melanomas.

Delineating margins of lentigo maligna using a hyperspectral imaging system

Lentigo maligna (LM) is an in situ form of melanoma which can progress into invasive lentigo maligna melanoma (LMM). Variations in the pigmentation and thus visibility of the tumour make assessment of lesion borders challenging. We tested hyperspectral imaging system (HIS) in in vivo preoperative delineation of LM and LMM margins. We compared lesion margins delineated by HIS with those estimated clinically, and confirmed histologically. A total of 14 LMs and 5 LMMs in 19 patients were included. HIS analysis matched the histo-pathological analysis in 18/19 (94.7%) cases while in 1/19 (5.3%) cases HIS showed lesion extension not confirmed by histopathology (false positives). Compared to clinical examination, HIS defined lesion borders more accurately in 10/19 (52.6%) of cases (wider, n = 7 or smaller, n = 3) while in 8/19 (42.1%) cases lesion borders were the same as delineated clinically as confirmed histologically. Thus, HIS is useful for the detection of subclinical LM/LMM borders.

[Diagnosis and treatment of actinic keratosis]

Actinic keratoses are premalignant skin lesions with the risk of converting into squamous cell carcinoma, and therefore they should be treated. Treatment modalities include cryotherapy, photodynamic therapy, carbon dioxide laser and also topical treatments such as imiquimode, ingenol mebutate, 5-fluorouracil and diclophenac. In the future, the treatment of actinic keratosis can be more often done in primary health care. The most favorable treatment modality depends on patient age, general health, and the thickness, size and localization of the lesion.

Detecting field cancerization using a hyperspectral imaging system

BACKGROUND

Field cancerization denotes subclinical abnormalities in a tissue chronically exposed to UV radiation. These abnormalities can be found surrounding the clinically visible actinic keratoses.

OBJECTIVES

The aim of this study was to test the feasibility of a hyperspectral imaging system in the detection of multiple clinical and subclinical AKs for early treatment of the affected areas.

MATERIALS AND METHODS

Altogether 52 clinical AKs in 12 patients were included in this study. In six patients digital photos were taken of the naive AKs, and again after methylaminolevulinate(MAL)-fluorescence diagnosis which was used to teach HIS to find subclinical lesions. After 2-3 days when the MAL had vanished, the hyperspectral images were taken. Biopsies were taken from clinical AKs, healthy-looking skin and several suspected subclinical AKs. In the other six patients digital and hyperspectral images were taken of the naive AKs followed by one biopsy per patient.

RESULTS

HIS detected all clinically visible 52 AKs and numerous subclinical lesions. The histopathology of the 33 biopsied lesions were concordant with the HIS results showing either AK (n = 28) or photodamage (n = 5). Of the 28 histopathologically confirmed AKs, 16 were subclinical. A specific diffuse reflectance spectrum of an AK and healthy skin was defined.

CONCLUSION

The hyperspectral imaging system offers a new, non-invasive method for early detection of field cancerization. Lasers Surg. Med. 45:410-417, 2013. © 2013 Wiley Periodicals, Inc.

Osteopontin promotes the invasive growth of melanoma cells by activating integrin αvβ3 and down-regulating tetraspanin CD9

Overexpression of osteopontin (OPN) is strongly associated with the invasiveness/metastasis of many cancers, including melanomas. However, the molecular mechanisms of OPN in these processes remain poorly understood. We found that forced expression of OPN in early vertical-growth-phase melanoma cells dramatically increased their migration/invasion and growth/survival in a three-dimensional collagen I gel. Neutralizing antibodies to OPN, integrin β1, and integrin αvβ3, but not to CD44, negated the effects of OPN. Conversely, knocking down OPN in metastatic melanoma cells abrogated the invasive growth. OPN overexpression activated and OPN knockdown inactivated αvβ3 and αvβ5 integrins, negligibly affecting their expression. We further found OPN expression to inversely correlate with tetraspanin CD9 expression. Early-stage melanoma cells displayed low OPN and high CD9 expression, and conversely, metastatic cells displayed high OPN and low CD9 expression. Overexpression of OPN in vertical-growth-phase melanoma cells induced down-regulation of CD9, and knockdown of OPN in metastatic melanoma cells up-regulated CD9. Reversion of these CD9 changes abolished the effects of OPN. Furthermore, knockdown of CD9 in early-stage melanoma cells stimulated their invasive capacity in three-dimensional collagen. Similarly, microarray analyses of benign nevi and primary melanomas from different stages revealed an inverse correlation between OPN and CD9. These data suggest that OPN promotes melanoma cell invasion by activating integrin αvβ3 and down-regulating CD9, a putative metastasis suppressor.

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.

TGF-β signaling, activated stromal fibroblasts, and cysteine cathepsins B and L drive the invasive growth of human melanoma cells

Accumulating evidence indicates that interactions between cancer cells and stromal cells are important for the development/progression of many cancers. Herein, we found that the invasive growth of melanoma cells in three-dimensional-Matrigel/collagen-I matrices is dramatically increased on their co-culture with embryonic or adult skin fibroblasts. Studies with fluorescent-labeled cells revealed that the melanoma cells first activate the fibroblasts, which then take the lead in invasion. To identify the physiologically relevant invasion-related proteases involved, we performed genome-wide microarray analyses of invasive human melanomas and benign nevi; we found up-regulation of cysteine cathepsins B and L, matrix metalloproteinase (MMP)-1 and -9, and urokinase- and tissue-type plasminogen activators. The mRNA levels of cathepsins B/L and plasminogen activators, but not MMPs, correlated with metastasis. The invasiveness/growth of the melanoma cells with fibroblasts was inhibited by cell membrane-permeable inhibitors of cathepsins B/L, but not by wide-spectrum inhibitors of MMPs. The IHC analysis of primary melanomas and benign nevi revealed cathepsin B to be predominantly expressed by melanoma cells and cathepsin L to be predominantly expressed by the tumor-associated fibroblasts surrounding the invading melanoma cells. Finally, cathepsin B regulated TGF-β production/signaling, which was required for the activation of fibroblasts and their promotion of the invasive growth of melanoma cells. These data provide a basis for testing inhibitors of TGF-β signaling and cathepsins B/L in the therapy of invasive/metastatic melanomas.

Transforming growth factor beta-induced (TGFBI) is an anti-adhesive protein regulating the invasive growth of melanoma cells

Melanoma is a malignancy characterized by high invasive/metastatic potential, with no efficient therapy after metastasis. Understanding the molecular mechanisms underlying the invasive/metastatic tendency is therefore important. Our genome-wide gene expression analyses revealed that human melanoma cell lines WM793 and especially WM239 (vertical growth phase and metastatic cells, respectively) overexpress the extracellular matrix (ECM) protein transforming growth factor β induced (TGFBI). In adhesion assays, recombinant TGFBI was strongly anti-adhesive for both melanoma cells and skin fibroblasts. TGFBI further impaired the adhesion of melanoma cells to the adhesive ECM proteins fibronectin, collagen-I, and laminin, known to interact with it. Unexpectedly, WM239 cells migrated/invaded more effectively in three-dimensional collagen-I and Matrigel cultures after knockdown of TGFBI by shRNA expression. However, in the physiological subcutaneous microenvironment in nude mice, after TGFBI knockdown, these cells showed markedly impaired tumor growth and invasive capability; the initially formed small tumors later underwent myxoid degeneration and completely regressed. By contrast, the expanding control tumors showed intense TGFBI staining at the tumor edges, co-localizing with the fibrillar fibronectin/tenascin-C/periostin structures that characteristically surround melanoma cells at invasion fronts. Furthermore, TGFBI was found in similar fibrillar structures in clinical human melanoma metastases as well, co-localizing with fibronectin. These data imply an important role for TGFBI in the ECM deposition and invasive growth of melanoma cells, rendering TGFBI a potential target for therapeutic interventions.

Metastatic outgrowth encompasses COL-I, FN1, and POSTN up-regulation and assembly to fibrillar networks regulating cell adhesion, migration, and growth

Although the outgrowth of micrometastases into macrometastases is the rate-limiting step in metastatic progression and the main determinant of cancer fatality, the molecular mechanisms involved have been little studied. Here, we compared the gene expression profiles of melanoma lymph node micro- and macrometastases and unexpectedly found no common up-regulation of any single growth factor/cytokine, except for the cytokine-like SPP1. Importantly, metastatic outgrowth was found to be consistently associated with activation of the transforming growth factor-beta signaling pathway (confirmed by phospho-SMAD2 staining) and concerted up-regulation of POSTN, FN1, COL-I, and VCAN genes-all inducible by transforming growth factor-beta. The encoded extracellular matrix proteins were found to together form intricate fibrillar networks around tumor cell nests in melanoma and breast cancer metastases from various organs. Functional analyses suggested that these newly synthesized protein networks regulate adhesion, migration, and growth of tumor cells, fibroblasts, and endothelial cells. POSTN acted as an anti-adhesive molecule counteracting the adhesive functions of FN1 and COL-I. Further, cellular FN and POSTN were specifically overexpressed in the newly forming/formed tumor blood vessels. Transforming growth factor-beta receptors and the metastasis-related matrix proteins, POSTN and FN1, in particular, may thus provide attractive targets for development of new therapies against disseminated melanoma, breast cancer, and possibly other tumors, by affecting key processes of metastasis: tumor/stromal cell migration, growth, and angiogenesis.

[Dysplastic melanocytic nevus]

The dysplastic melanocytic nevus remains an issue of controversy despite extensive investigations. On clinical grounds the term atypical melanocytic nevus should be used, while dysplastic melanocytic nevus describes histological characteristics. The association with melanoma is complex. With the clinical picture, dermatoscopy and molecular biological or genetic examinations one can often not distinguish a histological dysplastic nevus from a melanoma. In patients with large amounts of melanocytic nevi it is important to assess the total melanoma risk, the need for patient surveillance and motivate the patient for self-examination. In high-risk patients the amount of benign melanocytic nevi is increased and many clinically atypical and microscopically dysplastic nevi can be found. The relatives of these patients should also be examined. Because of the rising incidence of melanoma and the lack of therapeutic options in disseminated disease, the surveillance of high risk patients, the early detection of melanoma and excision play a key role in patient management.

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.

Surface-associated activation of plasminogen on gram-positive bacteria. Effect of plasmin on the adherence of Staphylococcus aureus

In this article we review a novel type of plasminogen activation on staphylococcal and streptococcal cells. The activation mechanism implies a specific binding of glu-plasminogen to bacterial surface via the lysine-binding sites of plasminogen. Association of plasminogen with bacterial surfaces greatly enhances the t-PA mediated activation which takes place only poorly in solution. The end product, surface-associated plasmin, is enzymatically active, protected against high molecular weight plasmin inhibitors and capable of converting itself from glu-plasmin to the lys-form. The modification is associated with an increased affinity of the bound lys-plasmin towards the binding molecules on bacterial surface. This novel way of retaining plasmin on the surface may be important for the bacteria to invade and penetrate surrounding tissues. Our data on the effect of plasmin on staphylococcal adherence indicate that plasmin is not very effective in cleaning bacteria from surfaces coated with extracellular matrix components, fibronectin and fibrinogen.

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.

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.

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.

MMP-21 is upregulated at early stages of melanoma progression but disappears with more aggressive phenotype

The expression of matrix metalloproteinases (MMPs) is frequently altered during malignant transformation. We examined the profile of three recently cloned MMPs, MMP-21, MMP-26, and MMP-28, in melanomas in vivo and in culture. Immunohistochemistry for MMPs-21, -26, -28, and -13 in melanoma specimens (27 nonmetastatic, 26 with nodal micrometastases, and 10 in situ melanomas) from 63 patients was performed. MMP-21 was expressed in melanoma cells in 29/53 cases, being more frequent in melanoma samples without micrometastases. Six out of ten in situ melanomas were positive, while five nevus samples were negative. MMP-26 and -28 were not generally expressed in melanoma cells. MMP-13 was detected in melanoma cells in 36/53 samples. MMP-21 was not found in sentinel nodes with metastases, while MMP-13 was seen in all of them. MMP-21 messenger RNA was variably expressed in all five melanoma cell lines investigated using reverse transcriptase-polymerase chain reaction. Our results suggest that expression of MMP-21 may serve as a marker of malignant transformation of melanocytes and does not associate with the presence of micrometastases.

FGF-2 blocks TGF-beta1-mediated suppression of Bcl-2 in normal melanocytes

Normal melanocytes require growth support provided by the adjacent basement membrane. In contrast, nevus cells and melanoma cells survive in the dermis, and in vitro on a soft collagen gel. Transforming growth factor-beta1 (TGF-beta1) produced by melanocytes themselves induces apoptosis in normal melanocytes cultured on collagen gel, an effect that can be counteracted by fibroblast growth factor-2 (FGF-2). The purpose of this study was to investigate the mechanisms by which FGF-2 counteracts the apoptotic signals from TGF-beta1 in melanocytes cultured on collagen gel. We report that FGF-2 did not interfere with the signal transduction from the TGF-beta1 receptors to SMAD2/3 proteins. Instead, TGF-beta1 decreased the level of Bcl-2 in normal melanocytes cultured on collagen gel, and FGF-2 reversed the TGF-beta1-mediated reduction in the level of Bcl-2. In nevus and melanoma cells, TGF-beta1 was unable to induce a decrease in the level of Bcl-2, and treatment with FGF-2 did not cause an increase in the level of Bcl-2 in nevus or melanoma cells. In conclusion, our results suggest that a reduction in the level of the anti-apoptotic Bcl-2 is involved in the execution of apoptosis induced by TGF-beta1 in normal melanocytes cultured on collagen gel and that FGF-2 can prevent TGF-beta1 from causing this reduction.

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.

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.

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.

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.

Fibroblast growth factor-mediated stimulation of differentiating teratocarcinoma cells: evidence for paracrine growth regulation

Tera 2 human embryonal carcinoma cells proliferate rapidly in culture but are capable of differentiating into quiescent cells with neuronal features. We have characterized the effects of exogenous and endogenous fibroblast growth factors on the proliferation of differentiating Tera 2 cells. Exogenous basic fibroblast growth factor (bFGF) stimulated DNA synthesis and induced the proliferation-associated antigen Ki 67 in differentiated Tera 2 cells. Heparin-binding growth factors isolated from the undifferentiated cells excerted a similar stimulatory effect on their differentiated derivatives. The functional potential of these endogenous growth factors was further demonstrated by their ability to stimulate plasminogen activator production by capillary endothelial cells. A major part of the growth promoting activity was removed by absorption with immobilized bFGF antibodies. bFGF was also detected in Tera 2 cells by immunoblotting. The production of heparin-binding growth-promoting activity decreased during differentiation. The results demonstrate a potential role for heparin-binding growth factors in the autocrine or paracrine growth regulation of teratocarcinoma cells.

Keratinocyte growth factor is a bifunctional regulator of HPV16 DNA-immortalized cervical epithelial cells

Various factors are known to regulate cell growth and differentiation in epithelial-mesenchymal interactions. Keratinocyte growth factor (KGF), an epithelial-specific cytokine produced by dermal fibroblasts and other mesenchymal cells, appears to affect growth, migration, and differentiation in epithelial-mesenchymal interactions. We have previously shown that human embryonic skin fibroblasts induce anchorage-independent growth of HPV16 DNA-immortalized human uterine exocervical epithelial cells (HCE16/3 cell line) in cocultures of HCE16/3 cells and fibroblasts. Here we report that KGF may be a major factor influencing growth and behavior of HCE16/3 cells in the coculture system. KGF stimulated both DNA synthesis and proliferation of normal human cervical epithelial (HCE) cells and HCE16/3 cells and the increase was stronger in HCE16/3 cells than in HCE cells. SiHa cells, a cervical carcinoma cell line with integrated HPV16 DNA, did not respond to the KGF mitogen signal. KGF receptor (KGFR) studies suggested that the different responses to the KGF mitogen signal may be correlated with KGFR. In addition, KGF alone was able to induce anchorage-independent growth of HCE16/3 cells, suggesting a potential role for KGF in the transformation process of epithelial cells. However, the transcription of HPV16 early genes was suppressed by KGF in the immortalized HCE16/3 cells, and this appeared to be due to transcriptional repression rather than a posttranscriptional process according to nuclear run-on analysis. In contrast, viral gene expression was not affected by KGF in SiHa cells. Our results suggest that KGF is a bifunctional growth factor in the HPV-immortalized cells, a positive regulator of cell growth and negative regulator of HPV16 early gene expression.

Increased proteolytic activity of the granule neurons may contribute to neuronal death in the weaver mouse cerebellum

The weaver mouse mutation is a genetic defect of unknown origin that leads to impairment of cerebellar granule neuronal migration and to neuronal cell death. We investigated laminin expression and proteolytic enzyme activity in this migration-deficient mouse mutant in vivo and in vitro to search for a molecular basis for the weaver defect. The weaver cerebellum showed a general increase in immunoreactivity for laminin, for a neurite outgrowth domain of the B2 chain of laminin, and for tissue plasminogen activator compared to the normal animals. Zymographic assays and immunocytochemistry confirmed that tissue plasminogen activator was the proteolytic enzyme synthesized in excess in the weaver mouse cerebellum in vivo. When placed in culture, the weaver granule neurons survived poorly on a laminin substratum, and failed to extend long neurites, unlike the normal cerebellar granule neurons. The cultured weaver granule neurons were proteolytically overactive and secreted excessive amounts of tissue plasminogen activator, which was likely to interfere with their neurite outgrowth potential on a laminin substratum. Indeed, the weaver granule neurons but not the normal neurons degraded laminin from their culture substratum and deposited a neurite outgrowth domain of the B2 chain of laminin onto their surfaces. Electrophysiology showed that the weaver granule neurons had poor resting membrane potentials (-38 V), whereas the normal neurons had normal resting membrane potentials of (-61 V). The resting membrane potentials of the weaver granule neurons were restored to near normal (-59 V) by a protease inhibitor, aprotinin. Aprotinin also rescued the weaver granule neurons from death on a laminin substratum and promoted their neurite outgrowth to the level of the normal animals. These results indicate that increased proteolytic activity accompanied with increased synthesis of laminin, and its B2 chain, distinguish the weaver mutation from the normal animals. These molecular changes may contribute to the impairment of granule neuronal migration and to the neuronal death, characteristic of the weaver mutation.

Vascular endothelial growth factor is induced in response to transforming growth factor-beta in fibroblastic and epithelial cells

Transforming growth factor beta (TGF-beta) is a multifunctional polypeptide that regulates the proliferation and differentiation of various cells and has an angiogenic effect in vivo, although it inhibits the growth of cultured endothelial cells. We report here that TGF-beta treatment of quiescent cultures of mouse embryo-derived AKR-2B cells, which are growth-stimulated by TGF-beta, and human lung adenocarcinoma A549 cells, which are growth-inhibited by TGF-beta, results in the induction of vascular endothelial growth factor (VEGF) mRNA and protein. Maximal VEGF mRNA levels occurred 4-8 h after stimulation with a decline to background levels in 24 h. In contrast, the related placenta growth factor mRNA was not induced by TGF-beta in these cells. No VEGF receptor mRNA was seen in AKR-2B cells. Also, TGF-beta treatment of endothelial cells, which express the FLT1 and KDR/FLK-1 receptors for VEGF, did not cause VEGF induction. Because VEGF is known to be a strong angiogenic factor for endothelial cells, the results suggest that the angiogenic effect of TGF-beta on endothelial cells in blood vessels may be mediated at least partly by a paracrine induction of VEGF in other surrounding cell types.

Increased expression of the matrix metalloproteinase 2 in differentiating Tera 2 human embryonal carcinoma cells

Secretion of proteolytic enzymes by cells has been implicated in tissue remodeling during embryonic development as well as in invasive neoplastic diseases. We studied the regulation of type-IV-collagenase activity in Tera 2 human embryonal carcinoma cells, which in the undifferentiated state proliferate rapidly and are tumorigenic. The undifferentiated cells produced relatively low levels of matrix-metalloproteinase-2 (MMP-2) activity. This activity was not markedly affected by exogenous basic fibroblast growth factor (bFGF) or 12-O-tetradecanoyl-phorbol-13-acetate (TPA), even though the plasminogen activator activity of the cells was increased by these agents. Tera 2 cells can be induced by retinoic acid to differentiate into quiescent cells, of which many express neuronal characteristics. The type-IV-collagenase activity of the cells increased markedly during the differentiation. This increase was mainly due to increased expression of MMP-2. Expression of tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2) was not markedly affected by the differentiation of Tera 2 cells. The results show that in the Tera 2 cell system, increased expression of MMP-2 is characteristic of the differentiated derivatives. This is in contrast with many other model systems, where increased type-IV-collagenase activity is associated with the malignant phenotype. This pattern of regulation may reflect the facts that Tera 2 cells resemble early embryonic cells and that their differentiation mimics related cell-differentiation processes in the developing embryo.