Human tumor spontaneous metastasis in immunosuppressed newborn rats. I. Characterization of the bioassay

Cancer Cell Biomechanical Properties Accompany Tspan8-Dependent Cutaneous Melanoma Invasion

The intrinsic biomechanical properties of cancer cells remain poorly understood. To decipher whether cell stiffness modulation could increase melanoma cells' invasive capacity, we performed both in vitro and in vivo experiments exploring cell stiffness by atomic force microscopy (AFM). We correlated stiffness properties with cell morphology adaptation and the molecular mechanisms underlying epithelial-to-mesenchymal (EMT)-like phenotype switching. We found that melanoma cell stiffness reduction was systematically associated with the acquisition of invasive properties in cutaneous melanoma cell lines, human skin reconstructs, and Medaka fish developing spontaneous MAP-kinase-induced melanomas. We observed a systematic correlation of stiffness modulation with cell morphological changes towards mesenchymal characteristic gains. We accordingly found that inducing melanoma EMT switching by overexpressing the ZEB1 transcription factor, a major regulator of melanoma cell plasticity, was sufficient to decrease cell stiffness and transcriptionally induce tetraspanin-8-mediated dermal invasion. Moreover, ZEB1 expression correlated with Tspan8 expression in patient melanoma lesions. Our data suggest that intrinsic cell stiffness could be a highly relevant marker for human cutaneous melanoma development.

Sinonasal malignant melanoma with diffuse carcinomatosis: initial PET/CT staging and follow-up CT/MR imaging

Mucosal malignant melanoma of the head and neck is a rare but aggressive type of melanoma with poor clinical prognosis and outcome. Its nonspecific symptomatology frequently leads to its delayed diagnosis until advanced stages of the disease. The author presents a case of primary sinonasal amelanotic melanoma with preoperative F-18 FDG PET/CT showing diffuse bone metastasis only two months after the onset of epistaxis and nasal congestion, and subsequent postsurgical CT/MR showing diffuse soft tissue tumor dissemination and malignant pleural effusion.

Matrilysin 1 influences colon carcinoma cell migration by cleavage of the laminin-5 beta3 chain

Matrilysin 1 [matrix metalloproteinase 7 (MMP7)] is one of the most important metalloproteinases expressed in human tissues. This enzyme is generally not expressed by normal differentiated epithelial colon cells, but has been shown to be up-regulated in human colon adenomas and adenocarcinomas. Little is known about the role of MMP7 in cell invasion and its involvement in proteolytic processes. By searching the ligands of MMP7 in the colonic carcinoma cells HT29, we identified laminin-5/laminin-332 (LN5) as a specific target for MMP7 enzymatic activity. LN5, composed of alpha3, beta3, and gamma2 chains, is an important component of epithelial basement membranes where it induces firm adhesion and hemidesmosome formation. In this study, we show that LN5 and MMP7 are coexpressed in HT29 cells as well as in HT29 xenograft tumors and human colorectal adenocarcinomas. We provide evidence that human LN5 is a ligand for MMP7 and that a specific cleavage occurs in its beta3 chain, giving rise to a carboxyl-terminal beta3 chain fragment of 90 kDa. We have identified the MMP7 cleavage site at position Ala(515)-Ile(516) in the beta3 chain. Videomicroscopic analysis of HT29 cells plated on LN5 substrates reveals that the MMP7-processed LN5 significantly enhances cell motility. Moreover, the delayed migration of HT29 cells obtained after specific inhibition of MMP7 reinforces the hypothesis supporting its involvement in cell migration. Altogether, our results show that MMP7 is likely to play a crucial role in the regulation of carcinoma cell migration by targeting specific proteolytic processing of the LN5 beta3 chain.

Overexpression of laminin alpha1 chain in colonic cancer cells induces an increase in tumor growth

Laminins represent a growing family of glycoproteins constituting the basement membrane. They are known to direct many biological processes. With respect to carcinogenesis, laminins play an important role in cell adhesion, mitogenesis, differentiation and even metastasis. To further study the biological significance of laminin-1 (composed of alpha1, beta1 and gamma1 chains) in intestinal cell differentiation or tumorigenesis, an alpha1-laminin expression vector was introduced into the HT29 colonic cancer cells, in which laminin alpha1 chain is not expressed. Upon transfection of the alpha1 chain, the alpha1beta1gamma1 trimer was found secreted in the media along with free alpha1 chain as assessed by immunoprecipitation. The presence of the laminin alpha1 chain did not significantly modify the levels of the other laminin chains nor the integrins expressed by the HT29 cells. In spite of similar growth properties with the control cells in vitro (plastic dish, soft agar), the laminin alpha1 transfectants showed a significantly increased tumor growth when injected in nude mice. Histologic and immunohistochemic examination of the laminin alpha1-expressing tumors points to an increased recruitment of the host stromal and vascular cells, without modification in the differentiation profile and invasion potential. In parallel, a clear accumulation of laminin-10 (alpha5beta1gamma1) at the carcinoma/stromal interface and a segregation of the integrin beta4 subunit at the basal pole of the cancer cells occurred, compared to control tumors. Overall, our observations emphasize the importance of laminin-1 as a chemoattractant of both stromal and vascular cells and in epithelial/stromal cell interactions for the organization of the basement membrane and segregation of integrins leading to an epithelial cell growth signal. Such a sequence of events is reminiscent of what occurs during development.

Expression and activation of pro-gelatinase A by human melanoma cell lines with different tumorigenic potential

The production of various proteolytic enzymes by tumor cells facilitate the invasion of solid tumors into surrounding tissues. We examined three cell lines (M1Dor, M4Be and M3Da) derived from malignant melanoma which exhibited different abilities to grow in nude mice following subcutaneous grafting. By in vitro invasion assay using Boyden-chambers technique, we found that none of those cell lines were able to invade the Matrigel. Several studies have substantiated the role of matrix metalloproteinases (MMP), mainly gelatinases MMP-9 and MMP-2, in melanoma cell invasion. Each cell line constitutively produced MMP-2 (but not MMP-9) in its latent form only, with stronger production for the most tumorigenic cell line in vivo (M3Da). Integrity of the MMP-2 activation process was studied since MMP-2 was also recovered as zymogen at the cell plasma membrane. All cell lines secreted TIMP-1 and TIMP-2 in a constitutive manner and again, but TIMP-2 production as well as MT1-MMP expression were found inversely related to their tumorigenic potential. Plating cells onto type I or type IV collagen did not trigger pro-MMP-2 activation; on the contrary, conversion of pro-MMP-2 to its active form could be evidenced when melanoma cell lines were seeded in a three dimensional type I collagen lattice.

Site-specific epithelial-mesenchymal interactions in digestive neuroendocrine tumors. An experimental in vivo and in vitro study

Little is known about the functional interactions between digestive neuroendocrine tumor cells and their stromal microenvironment. The focus of our study is whether mesenchymal cells modulate peptide expression, cell proliferation, and invasiveness in digestive neuroendocrine tumor cells. We designed an experimental in vivo and in vitro study using the mouse enteroendocrine cell line STC-1. In vivo, STC-1 cells were injected subcutaneously in 18 immunosuppressed newborn rats. At day 21, all animals presented poorly differentiated neuroendocrine tumors with lung metastases. Subcutaneous tumors were usually limited by a capsule containing basement membrane components and myofibroblasts that presented a low mitotic index. Lung tumors were devoid of capsule and poor in myofibroblasts, and their mitotic index was high. The profile of peptide expression in STC-1 tumors was different from that of cultured STC-1 cells. In vitro, STC-1 cells were cultured with fibroblasts of different origins, including dermis, lung, digestive tract, and liver. Based on their origin, myofibroblasts differentially modulated hormone synthesis, proliferation, spreading, and adhesion of STC-1 cells. In conclusion, our results show that site-specific functional interactions between mesenchymal and neuroendocrine cells may contribute to modulating the behavior of digestive neuroendocrine tumors, depending on their growth site.

Loss of epithelial differentiation markers and acquisition of vimentin expression after xenograft with laminin-1 enhance migratory and invasive abilities of human colon cancer cells LoVo C5

Clone C5 of the human colon adenocarcinoma LoVo cell line was subcutaneously injected with or without exogenous laminin-1 (EHS laminin) into immunosuppressed newborn rats. Cultures were initiated from lung metastases obtained with or without laminin-1 and gave rise to the C5 sublines LM and M4, respectively. The LM subline was mainly composed of spreading cells whereas most C5 and M4 cells remained round and aggregated. The mesenchymal marker vimentin was expressed by very rare C5 and M4 cells (< 1%), and by many LM cells (about 35%). On the opposite, the epithelial markers villin and dipeptidylpeptidase IV were well expressed by C5 cells but not by LM cells. In in vitro migration and invasion assays, LM cells migrated and invaded basement membrane extract twice as much as the parental C5 clone and the M4 subline, probably in association with vimentin-expressing cells, because invasion of basement membrane extract Matrigel by LM cells gave rise to 100% vimentin-positive cells (sublines LM 22, LM 23 and LM 24). When subcutaneously injected, C5 cells induced tumors limited by an interrupted but well organized basement membrane, whereas LM cells induced tumor masses, occasionally limited by a very irregular basement membrane, as observed when C5 cells were injected with laminin-1. Gelatin zymographic analysis clearly showed an increased expression of matrix metalloproteinase-2 by LM cells. Our results suggest a specific role of laminin-1 on the in vivo proliferation of highly invasive vimentin-expressing colon carcinoma cells. This proliferation may result from the initial interaction of C5 cells with large amounts of laminin-1, leading to a selection of vimentin-expressing cells during the metastatic cascade.

The gangliosides as a possible molecular coupling factor between the proportion of radiosensitive cells in vitro and the metastatic potential in vivo within a human melanoma cell line

With an experimental model of spontaneous lung metastases in immunosuppressed newborn rats, seven clones and variants with different metastatic potential and gangliosides expression were derived from a single parental human melanoma cell line M4Be. The cellular radiosensitivity of M4Be and its seven sublines was estimated using an in vitro colony assay. The total amount of gangliosides in M4Be and its seven sublines was determined by cell extraction and thin-layer chromatography, while the expression of GD3 gangliosides was estimated by flow cytometry with a monoclonal antibody. The radiation-cell survival curves of most clones and variants derived from M4Be showed a zero dose extrapolation clearly lower than 100%, suggesting that two populations of cells of very different radiosensitivity coexist within each of these clones and variants. Although the proportion of radiosensitive cells could be estimated from the shape of the survival curve, its radiosensitivity is too high to be properly evaluated by the colony assay. The eight survival curves differ essentially in the proportion of radiosensitive cells--which varied from 0% to 40% among M4Be and its seven sublines--whereas the cellular radiosensitivity of the radioresistant population was similar among them. The metastatic potential in vivo of M4Be and its seven sublines was not significantly related to the cellular radiosensitivity of their corresponding radioresistant population, but significantly increased with the fraction of radiosensitive cells. This relationship is valid only when the highly metastatic cells are cultured for no more than five passages in vitro as the fraction of radiosensitive cells is rapidly lost during subcultures. The relationship remains valid in vivo as metastatic melanoma-bearing newborn rats whole body irradiated with 20 cGy show no lung metastasis compared with controls. The radiosensitive cell fraction is inversely correlated with both the total ganglioside content (r = 0.84, P < 0.02) and the number of cells positively labelled with the monoclonal antibody directed to GD3 (r = 0.92, P < 0.001). The incubation of a radiosensitive clone with the exogenous bovine brain ganglioside GM1 significantly increases the proportion of radioresistant cells and suppresses its metastatic potential, while the inhibition of the endogenous gangliosides synthesis in the radioresistant cell line M4Be increases the proportion of radiosensitive cells. This study provides a possible explanation for the correlation between the metastatic potential and the proportion of radiosensitive cells within the seven sublines derived from a single parental human melanoma cell line.

Gangliosides protect human melanoma cells from ionizing radiation-induced clonogenic cell death

With an experimental model of spontaneous lung metastases of melanoma developed in this laboratory, a range of sublines (variants and clones) with different metastatic potential and ganglioside expression was established from a single human melanoma cell line M4Be. Using an in vitro clonogenic assay and provided that cells were cultured for no more than five passages, variations in cellular radioresistance of M4Be and seven sublines derived from M4Be were detected. This study shows a positive correlation between the cell intrinsic radioresistance of M4Be and its seven sublines and their total ganglioside content. More precisely, the proportion of radioresistant cells in M4Be and the seven sublines correlated with the number of cells determined by flow cytometry that were positively labelled with a monoclonal antibody directed to GD3 disialoganglioside. Blocking the cellular biosynthesis of gangliosides with the inhibitor Fumonisin B1 or cleaving with Vibrio cholerae neuraminidase the cell surface ganglioside-bound sialic acid in a radioresistant poorly metastatic subline increased its radiosensitivity in vitro. In contrast, enrichment of a radiosensitive metastatic subline with exogenous bovine brain GM1 increased its radioresistance in vitro. These results suggest that, in the radiation dose range important for radioprotection (0-1 Gy), membrane gangliosides radioprotect human melanoma cells in vitro.

Deficiency of ganglioside biosynthesis in metastatic human melanoma cells: relevance of CMP-NeuAc:LacCer alpha 2-3 sialyltransferase (GM3 synthase)

The glycosphingolipid patterns were analyzed on two clones derived from a human melanoma cell line and selected for their respectively high and low metastatic ability in immunosuppressed newborn rats. Conversely to the weakly metastatic cells which exhibited a pattern similar to that of the parental cell line, highly metastatic human melanoma cells appeared to be deficient in ganglioside biosynthesis. An accumulation of lactosylceramide was found in the latter cells, with low amounts of GM3 as the only ganglioside detected and a fourfold decreased activity of GM3 synthase (EC 2.4.99.9). After subcutaneous injection of metastatic cells in newborn rats, the cells proliferating in the tumor induced at the injection site re-expressed the four common gangliosides of melanoma: GM3, GM2, GD3 and GD2, whereas the cells growing in the lungs as metastatic nodules were deficient in ganglioside synthesis and showed an accumulation of lactosylceramide. Taken together, our results suggest that the human melanoma cells which are able to escape from the primary tumor and invade the lungs have an impaired ganglioside biosynthesis with a deficient GM3 synthase.

Correlation between the radiosensitivity in vitro of clones and variants derived from a human melanoma cell line and their spontaneous metastatic potential in vivo

With an experimental model of spontaneous lung metastases of human melanoma in immunosuppressed newborn rats, a large panel of clones and variants with different metastatic potential were derived from a single human melanoma parental cell line (M4Be). Seven clones and variants from M4Be were selected, respectively, for their low (parental, clone 1), intermediate (clones 2 and 3, subvariant 1-) and high (variant 1, subvariant 1+, clone 4) metastatic potential. This paper investigates the relationship between the in vivo metastatic potential of the eight cell lines and their sensitivity to ionizing radiation in vitro (range 0.05-7 Gy). The radiosensitivity was estimated from the mean inactivation dose, a parameter equal to the area under the survival curve plotted in linear coordinates. Examination of the eight survival curves, obtained with cells cultured for no more than five passages after defrost, shows that clone 1, subvariant 1- and the M4be parental line are the most radioresistant cells, clone 4 and subvariant 1+ are the most radiosensitive cells, while clones 2 and 3 and variant 1 showed an intermediate response to radiation. The metastatic potential in vivo of the parental line and the seven sublines is significantly correlated to their radiosensitivity in vitro: the higher the metastatic potential, the higher the radiosensitivity.

Selective expression of PNA-binding glycoconjugates by invasive human melanomas: a new marker of metastatic potential

Alterations of cell-surface glycoconjugates have been associated with invasiveness and metastatic capacity in a number of experimental and human tumors (bladder and colon cancer). We have recently shown that human melanoma cells from variants selected for high metastatic potential in an animal model bind the lectin peanut agglutinin (PNA), and that human melanoma cell populations enriched for PNA binding cells generated a higher frequency of metastases when xenografted into immune suppressed neonatal rats. We have therefore sought cells binding PNA in biopsied human melanocytic tumors and compared frequencies of PNA binding by cells from benign nevi, early and late primary melanomas, and metastatic melanomas. Sections of conventionally processed tissues were deparaffinised and exposed to biotinylated PNA; PNA fixation was revealed by the avidine/peroxidase/AEC technique. In 51 specimens tested, PNA appears to react electively with invasive tumors, since only one of the 7 early primary melanomas (Clark I-II) reacted while 13/23 late primary melanomas (Clark III-V), and 4/21 melanoma metastases were reactive. In addition, only 1/17 benign nevi bound PNA. In primary tumors, the reactive cells were exclusively invasive tumors cells in the dermis. PNA reactive material was observed in the cytoplasm and plasma membrane of reactive cells. Hence, alterations in composition and cellular localisation of glycoconjugates detectable by lectin histochemistry in melanoma cells may be markers of metastatic potential that may be applicable on an individual patient basis.

Expression of the galactose binding protein Mac-2 by human melanoma cell-lines

The Mac-2 protein is a lectin specific for galactose-containing glycoconjugates. Present in some normal cells, it was also associated with the metastatic potential of some carcinoma cells. We studied Mac-2 expression in three human melanoma cell lines and in five variants and clones from one of them. By using the M3/38 rat monoclonal antibody, Mac-2 was demonstrated on cell surface by flow cytometry as well as in the cytoplasm and in the nucleus by confocal microscopy. The expression of Mac-2 was not correlated with that of terminal unsialylated Gal beta 1-3 GalNac structures on metastatic melanoma cell lines. However, the presence of extracellular Mac-2 containing vesicles was observed in cell lines with metastatic potency. Western blot analysis of cell lysates, in reducing or non-reducing conditions, revealed two bands of 34-36 and 93-98 kDa apparent M(r), also found in HL60 and P388.D1 cell lines used as positive controls.

Expression of PNA-binding sites on specific glycoproteins by human melanoma cells is associated with a high metastatic potential

Lectin-binding patterns of seven human melanoma clones and variants selected from the same parental cell line and differing in their spontaneous metastatic potential in an animal model were compared by flow cytometry and Scatchard analysis. Human melanoma clones and variants with high and low metastatic potential could be distinguished by their peanut agglutinin (PNA)-binding patterns, but not by their wheat germ agglutinin (WGA)-, Ulex europaeus agglutinin I (UEA I)-, and soybean agglutinin (SBA)-binding patterns. Low metastatic clones and variants proved to be made up of single poorly peanut agglutinin-binding cell population (2.20-3.52 x 10(6) sites/cell, Ka = 2.48-2.75 x 10(6) M-1). By contrast, highly metastatic variants were found to be constituted by two cellular subpopulations, exhibiting respectively a moderate 2.62-3.72 x 10(6) sites/cell) and a high peanut agglutinin staining (17.68-18.76 x 10(6) sites/cell). One highly metastatic clone was found to be homogeneously constituted by a single population of cells strongly binding this lectin (18.86 x 10(6) sites/cell) with an association constant of 4.06 +/- 10(6) M-1. Using an EPICS V cytometer, these two subpopulations were sorted from a highly metastatic variant and tested for their metastatic abilities: cells with high PNA binding generated a higher frequency of metastases than did moderately PNA-binding cells. Following treatment with Vibrio cholerae neuraminidase, all cells from all variants and clones were brightly labeled by PNA, collecting in a single peak with similar fluorescence intensities. Electrophoresis of total cellular proteins and subsequent detection with labeled PNA om Western blots show two major PNA-reactive glycoproteins with apparent molecular weights of 140 and 110 kDa (MAGP1 and MAGP2), expressed only in highly metastatic cells, but which can be strongly labeled by PNA in slightly metastatic cells following a treatment with neuraminidase. These results provide evidence that the expression of terminal galactose (beta 1-3)N-acetyl galactosamine structure, positioned on MAGP1 and MAGP2 glycoproteins, is associated with the metastatic potential of human melanoma cells.

Accumulation of heparan sulfate in the culture of human melanoma cells with different metastatic ability

Glycosaminoglycans were metabolically labeled in subconfluent cultures of highly metastatic 7Gp122 and poorly metastatic IC8 variants and of the low metastatic parental M4Be human melanoma cell line. Proteoglycans were separated by DEAE Trisacryl chromatography from the culture medium, from the heparin extract of the cell layer and from the heparin-extracted cell residue lyzed with detergents. Glycosaminoglycans were released from the proteoglycans by reductive alkaline hydrolysis and heparan sulfate (HS) was detected by deaminative cleavage with nitrous acid. Expressed on cell protein basis, the labeled HS content in the medium and in the cell layer decreased with increasing metastatic ability. The extraction of HS with heparin from the 7Gp122 cells indicated that this variant was enriched in (polypeptide bound) HS non inserted into the plasma membrane, compared with the low metastatic IC8 and M4Be cells. The HS fraction in heparin extract and in the heparin-extracted cell residue exhibited molecular mass heterogeneity on gel permeation chromatography and it contained HS fragments. Scission with nitrous acid followed by molecular sieve chromatography of the degradation products indicated that the tetra- and disaccharide repeats separated by the N-sulfated glucosamine residue were present in about equal amounts and constituted 60% of the HS chains in the IC8 and M4Be cells. HS from 7Gp122, IC8 and M4Be cells did not bind antithrombin III with high affinity but it was capable of binding bFGF in in vitro assay.

Comparative tumor morphogenesis of two human colon adenocarcinoma cell clones xenografted in the immunosuppressed newborn rat

Two clones derived from the human adenocarcinoma cell line LoVo, E2 and C5 xenografted subcutaneously to immunosuppressed newborn rats, respectively produced well-differentiated and undifferentiated tumors. The comparative morphogenesis of these tumors was performed on xenografts explanted as early as 18 h and up to 21 days after grafting by studying the progressive setting of the enterocyte differentiation marker dipeptidylpeptidase IV, the basal lamina component laminin and the alpha 6 integrin subunit. E2 xenografts which were entirely undifferentiated 18 h after grafting, presented well-polarized acini-like tumoral islets 6 h later, i.e. only 1 day after injection. Basement membranes, which were not organized at this moment, may not be necessary for morphological polarization. The chronology of function antigens polarization was characterized by formation of a basement membrane 5 days after the graft with associated basal sorting of alpha 6 integrin. The polarization of alpha 6 integrin took, however, longer to be achieved while apical addressing of dipeptidylpeptidase IV was the last to be completed. In contrast, C5 tumors never differentiated. Even 21 days after grafting alpha 6 integrin remained pericellular, dipeptidylpeptidase IV was underexpressed and laminin was found as perilobular patches. Quantitative differences in laminin or alpha 6 integrin expression could not account for the differences in the polarization process observed in the two variants.