Treatment Of Melanoma Cells Research Articles

Transfection of melanoma cells with antisensePAX3oligonucleotides additively complements cisplatin-induced cytotoxicity

Advanced melanoma is difficult to treat, in part because of greater resistance to therapy compared with other cancer types. The mechanisms underlying this resistance are not well-understood. One factor that is reported to be involved in melanoma cell survival is PAX3, a transcription factor normally expressed during embryonic development, and which is critically required for development of neural crest-derivatives, including skin melanocytes. PAX3 expression is deregulated in primary melanomas and most melanoma cell lines. Here we have investigated whether targeting PAX3 expression in melanoma cell lines together with chemotherapeutic treatment increases susceptibility to therapeutic cell death. Using PAX3-specific antisense oligodeoxynucleotides (PAX3-AS) to treat melanoma cell lines in vitro, we showed dose-dependent reduction of proliferation of melanoma cells, and induction of apoptosis compared with control treatments. Induction of apoptosis was accompanied by the induction of active caspase-3 in UACC62 and M14 cells, and p53 protein in UACC62 cells. Treatment of melanoma cells with cisplatin induces DNA damage and cytotoxicity, which is thought to be via p53-dependent and -independent mechanisms. Treatment of either p53 mutant (M14) or wild-type (UACC62) melanoma cells with cisplatin, and varying doses of PAX3-AS, resulted in percentages of cells undergoing apoptosis equivalent to the sum of the individual treatments, irrespective of mutation status [e.g., UACC62, 43.8% (1 micromol/L PAX3-AS), 30.1% (20 micromol/L cisplatin), 69.6% (PAX3-AS + cisplatin); M14, 12.6% (1 micromol/L PAX3-AS), 41.5% (40 micromol/L cisplatin), 50.2% (PAX3-AS + cisplatin)]. These data suggest that treatment of melanoma cells with PAX3-AS complements cytotoxicity induced by cisplatin.

Eugenol Causes Melanoma Growth Suppression through Inhibition of E2F1 Transcriptional Activity

Metastatic malignant melanoma is an extremely aggressive cancer, with no currently viable therapy. 4-Allyl-2-methoxyphenol (eugenol) was tested for its ability to inhibit proliferation of melanoma cells. Eugenol but not its isomer, isoeugenol (2-methoxy-4-propenylphenol), was found to be a potent inhibitor of melanoma cell proliferation. In a B16 xenograft study, eugenol treatment produced a significant tumor growth delay (p = 0.0057), an almost 40% decrease in tumor size, and a 19% increase in the median time to end point. More significantly, 50% of the animals in the control group died from metastatic growth, whereas none in the treatment group showed any signs of invasion or metastasis. Eugenol was well tolerated as determined by measurement of bodyweights. Examination of the mechanism of the antiproliferative action of eugenol in the human malignant melanoma cell line, WM1205Lu, showed that it arrests cells in the S phase of the cell cycle. Flow cytometry coupled with biochemical analyses demonstrated that eugenol induced apoptosis. cDNA array analysis showed that eugenol caused deregulation of the E2F family of transcription factors. Transient transfection assays and electrophoretic mobility shift assays showed that eugenol inhibits the transcriptional activity of E2F1. Overexpression of E2F1 restored about 75% of proliferation ability in cultures. These results indicate that deregulation of E2F1 may be a key factor in eugenol-mediated melanoma growth inhibition both in vitro and in vivo. Since the E2F transcription factors provide growth impetus for the continuous proliferation of melanoma cells, these results suggest that eugenol could be developed as an E2F-targeted agent for melanoma treatment.

Modulation of Vitamin D‐induced growth inhibition in melanoma cell lines: implications for an important function of vitamin D receptor (VDR) and 1,25‐dihydroxyvitamin D3‐24‐hydroxylase (24‐OHase) expression, histonedeacetylation, and calpain activity

Increasing evidence indicates an important role of the skin vitamin D system for tumorigenesis and progression of malignant melanoma. We have now characterized the vitamin D system in melanoma cell lines, detecting strong RNA expression of vitamin D receptor (VDR), 25‐hydroxyvitamin D‐1α‐hydroxylase (1αOHase), vitamin D‐25‐hydroxylase (25OHase) and 1,25‐dihydroxyvitamin D‐24‐hydroxylase (24OHase) in various melanoma cell lines (MEWO, SKMEL28, BU47HOM) using real time PCR (LightCycler) and specific hybridisation probes. We then have analyzed effects of 1,25‐dihydroxyvitamin D3 and analogs (EB 1089, MC 1288) on proliferation and apoptosis as well as on expression of VDR, 1αOHase), 25OHase, and 24OHase in various melanoma cell lines (BUHOM, MEWO, SKMEL)in vitro. Using a tetrazolium salt (WST‐1) based colorimetric assay, we detected dose‐dependent inhibition of cell growth (up to 40%) induced by calcitriol or its analogs. Treatment of melanoma cells with calcitriol resulted in decreased immunoreactivity of proliferation markers including Ki‐67 and PCNA. Flow cytometry experiments (bcl‐2, bcl‐xl, bcl‐xs, bcl‐x, bax, CD95) and analysis of annexin Pi expression revealed no induction of apoptosis by calcitriol (10−7 M) or its analogs, while increased levels of bcl‐2 protein were detected. Additionally, we show modulation of vitamin D‐induced inhibition of cell proliferation by calpain inhibitors I and II (Calbiochem) as well as by inhibitors of histonedeacetylation (sodium butyrate, trichostatin A). In conclusion our findings indicate that (i) vitamin D analogs suppress proliferation but do not induce apoptosis in melanoma cell lines, (ii) induction of VDR and 24‐OHase expression as well as histonedeacetylation and calpain activity modulate vitamin D‐induced growth inhibition, (iii) new calcitriol analogs exerting less systemic side effects may be interesting candidates for the treatment of metastasizing malignant melanoma.

Protease-Activated Receptors (PAR1 and PAR2) Contribute to Tumor Cell Motility and Metastasis

The effects of the pleiotropic serine protease thrombin on tumor cells are commonly thought to be mediated by the thrombin receptor protease-activated receptor 1 (PAR1). We demonstrate here that PAR1 activation has a role in experimental metastasis using the anti-PAR1 antibodies ATAP2 and WEDE15, which block PAR1 cleavage and activation. Thrombin also stimulates chemokinesis of human melanoma cells toward fibroblast conditioned media and soluble matrix proteins. Thrombin-enhanced migration is abolished by anti-PAR1 antibodies, demonstrating that PAR1 cleavage and activation are required. The PAR1-specific agonist peptide TFLLRNPNDK, however, does not stimulate migration, indicating that PAR1 activation is not sufficient. In contrast, a combination of TFLLRNPNDK and the PAR2 agonist peptide SLIGRL mimics the thrombin effect on migration, whereas PAR2 agonist alone has no effect. Agonist peptides for the thrombin receptors PAR3 and PAR4 used alone or with PAR1 agonist also have no effect. Similarly, activation of PAR1 and PAR2 also enhances chemokinesis of prostate cancer cells. Desensitization with PAR2 agonist abolishes thrombin-enhanced cell motility, demonstrating that thrombin acts through PAR2. PAR2 is cleaved by proteases with trypsin-like specificity but not by thrombin. Thrombin enhances migration in the presence of a cleavage-blocking anti-PAR2 antibody, suggesting that thrombin activates PAR2 indirectly and independent of receptor cleavage. Treatment of melanoma cells with trypsin or PAR2 agonist peptide enhances experimental metastasis. Together, these data confirm a role for PAR1 in migration and metastasis and demonstrate an unexpected role for PAR2 in thrombin-dependent tumor cell migration and in metastasis.

Early vitronectin receptor downregulation in a melanoma cell line during all-trans retinoic acid-induced apoptosis.

Recent evidence assigns the vitronectin receptors (VnRs) an important role in regulating tumour cell invasion and dissemination. In vivo and in vitro studies document that all trans-retinoid acids (ATRAs) inhibit growth-inducing apoptosis in melanomas. We have analysed the effects of ATRA treatment on melanoma cell adhesion and motility. Human M14 melanoma cells were treated with 10 micromol L-1 ATRA for different times and stained with rhodamine-phalloidin to analyse the effect of treatment on cytoskeleton organization. Cell adhesion and cell migration assays were performed to analyse the role of VnRs in the ATRA-induced early stages of apoptosis. VnR expression was evaluated by Western blot, immunoprecipitation and immunocytochemistry assays. First, using an annexin V assay, we found that apoptosis was triggered by 48 h with 10 micromol L-1 ATRA exposure. At this time point, decrease in the F-actin polymerization as well as inhibition of cell adhesive ability to vitronectin (Vn) was exerted by ATRA treatment. In the presence of serum, exposure to 10 micromol L-1 ATRA for 48 h produced a dramatic inhibition of the cell adhesion ability that was comparable with that exerted by untreated cells preincubated with anti-alpha(v)beta(3) or anti-alpha(v)beta(5) VnR monoclonal antibodies. Functionally, the treatment of melanoma cells with 10 micromol L-1 ATRA for 48 h causes an inhibition of directional cell migration towards Vn-coated filters. Therefore, we analysed the effect of ATRA on the VnR expression. Both alpha(v)beta(3) and alpha(v)beta(5) VnR levels were reduced upon exposure to 10 micromol L-1 ATRA for 48 h as shown by Western blot, immunoprecipitation and immunocytochemistry assays. Altogether, our data indicate that treatment of M14 melanoma cells with ATRA downregulates VnR expression and that this reduction is closely correlated with the ATRA-dependent inhibition of actin-fibre organization, cell adhesion and migration. Although the mechanism by which ATRA regulates the expression of VnR in M14 melanoma cells needs further elucidation, this system may represent a model for understanding the molecular basis of ATRA therapy in melanoma.

Mda-7 (IL-24) Mediates selective apoptosis in human melanoma cells by inducing the coordinated overexpression of the GADD family of genes by means of p38 MAPK.

Subtraction hybridization identified melanoma differentiation-associated gene-7 (mda-7) as a gene induced during terminal differentiation in human melanoma cells. On the basis of structure, chromosomal localization and cytokine-like properties, mda-7 is classified as IL-24. Administration of mda-7/IL-24 by means of a replication-incompetent adenovirus (Ad.mda-7) induces apoptosis selectively in diverse human cancer cells without inducing harmful effects in normal fibroblast or epithelial cells. The present studies investigated the mechanism underlying this differential apoptotic effect. Infection of melanoma cells, but not normal immortal melanocytes, with Ad.mda-7 induced a time- and dose-dependent increase in expression, mRNA and protein, of a family of growth arrest and DNA damage (GADD)-inducible genes, which correlated with induction of apoptosis. Among the members of the GADD family of genes, GADD153, GADD45 alpha, and GADD34 displayed marked, and GADD45 gamma showed minimal induction. Treatment of melanoma cells with SB203580, a selective inhibitor of the p38 mitogen-activated protein kinase (MAPK) pathway, effectively inhibited Ad.mda-7-induced apoptosis. Additional support for an involvement of the p38 MAPK pathway in Ad.mda-7-mediated apoptosis was documented by using an adenovirus expressing a dominant negative mutant of p38 MAPK. Infection with Ad.mda-7 increased the phosphorylation of p38 MAPK and heat shock protein 27 in melanoma cells but not in normal immortal melanocytes. In addition, SB203580 effectively inhibited Ad.mda-7-mediated induction of the GADD family of genes in a time- and dose-dependent manner, and it effectively blocked Ad.mda-7-mediated down-regulation of the antiapoptotic protein BCL-2. Inhibition of GADD genes by an antisense approach either alone or in combination also effectively blocked Ad.mda-7-induced apoptosis in melanoma cells. These results support the hypothesis that Ad.mda-7 mediates induction of the GADD family of genes by means of the p38 MAPK pathway, thereby resulting in the selective induction of apoptosis in human melanoma cells.

Evidence for involvement of Wnt signaling pathway in IB-MECA mediated suppression of melanoma cells.

The A3 adenosine receptor, A3AR, belongs to the family of Gi proteins, which upon induction, suppresses the formation of cAMP and its downstream effectors. Recent studies have indicated that activation of A3AR by its agonist, IB-MECA, results in growth inhibition of malignant cells. Here we demonstrate the ability of IB-MECA to decrease the levels of protein kinase A, a downstream effector of cAMP, and protein kinase B/Akt in melanoma cells. Examination of glycogen synthase kinase 3beta, GSK-3beta, whose phosphorylation is controlled by protein kinase A and B, showed a substantial decrease in the levels of its phosphorylated form and an increase in total GSK-3beta levels in IB-MECA treated melanoma cells. This observation suggests that the treatment of cells with IB-MECA augments the activity of GSK-3beta in the cells. Evaluation of beta-catenin, a key component of Wnt signaling pathway which, upon phosphorylation by GSK-3beta rapidly ubiquitinates, showed a substantial decrease in its level after IB-MECA treatment. Accordingly, the level of beta-catenin responsive cell growth regulatory genes including c-myc and cyclin D1 was severely declined upon treatment of the cells with IB-MECA. These observations which link cAMP to the Wnt signaling pathway provide mechanistic evidence for the involvement of Wnt pathway via its key elements GSK-3beta and beta-catenin in the anti-tumor activity of A3AR agonists.

Regulation of constitutive and induced NF-kappaB activation in malignant melanoma cells by capsaicin modulates interleukin-8 production and cell proliferation.

In the present study, we demonstrate that upregulation of interleukin-1beta(IL-1beta)-mediated and tumor necrosis factor-alpha (TNF-alpha)-mediated IL-8 expression in human malignant melanoma cells is modulated by the activation of nuclear factor-kappaB (NF-kappaB). Addition of capsaicin (8-methyl-N-vanillyl-6-nonenamide), a known inhibitor of NF-kappaB, resulted in the inhibition of constitutive as well as IL-1beta-induced and TNF-alpha-induced IL-8 expression in melanoma cells. The inhibition of IL-8 expression was dependent on the concentration of capsaicin and duration of treatment. Further, electrophoretic mobility shift assay (EMSA) of nuclear extracts from melanoma cells showed a constitutive activation of NF-kappaB and activated protein 1 (AP-1), which was upregulated following treatment with IL-1beta. Treatment of melanoma cells with capsaicin inhibited activation of constitutive and IL-1beta-induced NF-kappaB, but not AP-1, leading to inhibition of IL-8 expression. Further, downregulation of IL-8 expression in capsaicin-treated melanoma cells resulted in inhibition of in vitro cell proliferation. These results demonstrate that constitutive and induced NF-kappaB activation regulates IL-8 expression in melanoma cells. Downregulation of constitutive and induced NF-kappaB activation in malignant melanoma cells leads to inhibition of IL-8 production and in vitro cell proliferation.

Role of Zyxin in Differential Cell Spreading and Proliferation of Melanoma Cells and Melanocytes

Cell spreading, proliferation, and survival are modulated by focal adhesions linking extracellular matrix proteins, integrins, and the cytoskeleton. Zyxin is a focal-adhesion-associated phosphoprotein with one domain involved in the control of actin assembly and three protein-protein adapter domains implicated in the regulation of cell growth and differentiation. We characterized zyxin expression in normal human melanocytes and six melanoma cell lines in relation to cell spreading, growth, and differentiation using Western immunoblotting techniques, image analysis, flow cytometry, and confocal microscopy. We found that zyxin, focal adhesion kinase, and paxillin were significantly upregulated in melanoma cells compared to melanocytes. Zyxin expression directly related to cell spreading and proliferation and inversely related to differentiation, whereas focal adhesion kinase correlated only to cell spreading and paxillin did not significantly correlate with any of the parameters. Treatment of melanoma cells with 12-O-tetradecanoylphorbol-13-acetate downregulated zyxin expression, inhibited cell spreading and proliferation, and promoted differentiation. In contrast, 12-O-tetradecanoylphorbol-13-acetate, a mitogen for melanocytes, induced upregulation of zyxin expression in melanocytes. These findings are consistent with a role of zyxin in modulation of cell spreading, proliferation, and differentiation. Therapies directed at the downregulation of this focal adhesion phosphoprotein in melanoma cells implicate a new approach for controlling melanoma cell growth.

Myc down-regulation induces apoptosis in M14 melanoma cells by increasing p27(kip1) levels.

In recent years, increasing evidence indicated the importance of a deregulated c-myc gene in the melanoma pathogenesis. We have previously demonstrated that treatment of melanoma cells with c-myc antisense oligodeoxynucleotides can inhibit cell proliferation and activate apoptosis. To gain insight into the mechanisms activated by Myc down-regulation, we have now developed an experimental model that allows modulating Myc protein expression in melanoma cells. This was achieved by originating stable melanoma cell clones expressing ecdysone-inducible c-myc antisense RNA. We show that the induction of c-myc antisense RNA in M14 melanoma cells leads to an inhibition of cell proliferation characterized by accumulation of cells in the G(1) phase of the cell cycle (up to 80%) and activation of apoptosis (50%). These data are associated with an increase of p27(kip1) levels and a significant reduction of the cdk2-associated kinase activity. In addition, we show that an ectopic overexpression of p27(kip1) in this experimental model can enhance the apoptotic rate. Our results indicate that down-regulation of Myc protein induces a G(1) arrest and activates apoptosis by increasing p27(kip1) content in melanoma cells, that are known to be defective for the p16-cyclinD/cdk4-pRb G(1) checkpoint. This is particularly relevant for identifying new therapeutic strategies based on the re-establishment of the apoptotic pathways in cancer cells.

Macrophage infiltration correlates with tumor stage and angiogenesis in human malignant melanoma: Possible involvement of TNFα and IL-1α

We examined whether macrophage infiltration is associated with angiogenesis in cutaneous melanoma. The numbers of macrophages and microvessels increased significantly with increasing depth of tumor and with tumor angiogenesis. Macrophage infiltration thus appeared to provide a useful diagnostic marker for the progression of cutaneous melanoma. We further examined whether human melanoma cells produce angiogenic factors in response to macrophage-derived cytokines, tumor necrosis factor alpha (TNFα) and interleukin-1 alpha (IL-1α). Treatment of melanoma cells with TNFα and IL-1α in vitro enhanced the production of interleukin-8 (IL-8) and vascular endothelial growth factor (VEGF), and of basic fibroblast growth factor (bFGF) to a lesser degree, in human melanoma cells. Lipopolysaccharide (LPS)-activated human monocytes enhanced production of IL-8, VEGF, TNF α, as well as IL-1α, but not bFGF. Co-culture of human monocytes and human melanoma cells was also found to significantly enhance production of IL-8 and VEGF in the absence and presence of LPS, compared with either monocytes or melanoma cells alone. The production of IL-8 and VEGF from co-cultured melanoma cells and LPS-activated monocytes was blocked when anti-TNF-α antibody or anti-IL-1α antibody was co-administrated. This is direct evidence that production of the potent angiogenic factors IL-8 and VEGF from melanoma cells is up-regulated through TNFα and/or IL-1α secreted by activated monocytes/macrophages, influencing both tumor growth and angiogenesis in melanomas. Int. J. Cancer 85:182–188, 2000. ©2000 Wiley-Liss, Inc.

Macrophage infiltration correlates with tumor stage and angiogenesis in human malignant melanoma: Possible involvement of TNFα and IL-1α

We examined whether macrophage infiltration is associated with angiogenesis in cutaneous melanoma. The numbers of macrophages and microvessels increased significantly with increasing depth of tumor and with tumor angiogenesis. Macrophage infiltration thus appeared to provide a useful diagnostic marker for the progression of cutaneous melanoma. We further examined whether human melanoma cells produce angiogenic factors in response to macrophage-derived cytokines, tumor necrosis factor alpha (TNFalpha) and interleukin-1 alpha (IL-1alpha). Treatment of melanoma cells with TNFalpha and IL-1alpha in vitro enhanced the production of interleukin-8 (IL-8) and vascular endothelial growth factor (VEGF), and of basic fibroblast growth factor (bFGF) to a lesser degree, in human melanoma cells. Lipopolysaccharide (LPS)-activated human monocytes enhanced production of IL-8, VEGF, TNF alpha, as well as IL-1alpha, but not bFGF. Co-culture of human monocytes and human melanoma cells was also found to significantly enhance production of IL-8 and VEGF in the absence and presence of LPS, compared with either monocytes or melanoma cells alone. The production of IL-8 and VEGF from co-cultured melanoma cells and LPS-activated monocytes was blocked when anti-TNF-alpha antibody or anti-IL-1alpha antibody was co-administrated. This is direct evidence that production of the potent angiogenic factors IL-8 and VEGF from melanoma cells is up-regulated through TNFalpha and/or IL-1alpha secreted by activated monocytes/macrophages, influencing both tumor growth and angiogenesis in melanomas.

Down-regulation of Tumor Necrosis Factor α Expression by Activating Transcription Factor 2 Increases UVC-induced Apoptosis of Late-stage Melanoma Cells

To identify mechanisms whereby activating transcription factor 2 (ATF2) alters the radiation resistance of human melanoma cells, we examined the possible role of ATF2 in UVC-induced apoptosis. Forced expression of full-length or truncated (Delta1-195 amino acids) forms of ATF2 in LU1205, a late-stage human melanoma cell line, elevated the levels of UVC-induced apoptosis. At the same time, either truncated or full-length forms of ATF2 reduced UVC-induced activation of the tumor necrosis factor-alpha (TNFalpha) promoter and decreased expression of TNFalpha. Forced expression of c-Jun in ATF2-expressing melanoma cells restored TNFalpha expression, suggesting that both forms of ATF2 sequestered transcription factors that positively regulate TNFalpha expression in response to UV irradiation. Antagonistic antibodies to Fas, but not to TNFR1, efficiently suppressed UVC-induced apoptosis, suggesting that the Fas pathway mediates the primary apoptotic signal in melanoma cells whereas the TNFR1 pathway elicits a survival signal. Indeed, treatment of melanoma cells with TNFalpha before UVC irradiation partially suppressed UVC-induced apoptosis, further supporting the protective role of TNFalpha in UVC-treated melanoma cells. Taken together, our findings suggest that ATF2 contributes to UVC-induced apoptosis through transcriptional silencing of TNFalpha, which balances Fas-mediated cell death in melanoma.

Involvement of CD44 in matrix metalloproteinase‐2 regulation in human melanoma cells

CD44 is a family of cell-surface-adhesion proteins that are thought to play an important role in cancer invasion and metastasis. However, the specific mechanisms by which CD44 expression modulates invasion or metastasis are not well understood. In the current study, we have demonstrated that treatment of human melanoma cells with a CD44 MAb, F10-44-2, induces up-regulation of matrix metalloproteinase-2 (MMP-2) protein and mRNA. Moreover, treatment of melanoma cells with MAb F10-44-2 enhances their migration through gelatin-coated membranes and invasion through reconstituted basement membranes. Treatment of melanoma cells with several known CD44 ligands, including hyaluronate, extracellular-matrix proteins, and osteopontin, did not induce MMP-2 production. CD44 binding by F10-44-2 MAb results in induction of MMP-2 expression, which is associated with enhanced cell migration and invasion. These findings have several implications for investigations into tumor metastasis, development, and lymphocyte function. Int. J. Cancer 80:387–395, 1999. © 1999 Wiley-Liss, Inc.

Involvement of CD44 in matrix metalloproteinase-2 regulation in human melanoma cells.

CD44 is a family of cell-surface-adhesion proteins that are thought to play an important role in cancer invasion and metastasis. However, the specific mechanisms by which CD44 expression modulates invasion or metastasis are not well understood. In the current study, we have demonstrated that treatment of human melanoma cells with a CD44 MAb, F10-44-2, induces up-regulation of matrix metalloproteinase-2 (MMP-2) protein and mRNA. Moreover, treatment of melanoma cells with MAb F10-44-2 enhances their migration through gelatin-coated membranes and invasion through reconstituted basement membranes. Treatment of melanoma cells with several known CD44 ligands, including hyaluronate, extracellular-matrix proteins, and osteopontin, did not induce MMP-2 production. CD44 binding by F10-44-2 MAb results in induction of MMP-2 expression, which is associated with enhanced cell migration and invasion. These findings have several implications for investigations into tumor metastasis, development, and lymphocyte function.

Contribution of phosphatidylinositol 3-kinase to radiation resistance in human melanoma cells.

The activity of phosphatidylinositol 3-kinase (PI3K), a key component of multiple signal transduction pathways, was investigated in early- and late-stage melanoma cells that have varying degrees of radiation resistance. Analysis of PI3K biproducts (PI-3,4-P2 and PI-3,4,5-triphosphate) revealed a direct correlation between radiation resistance and levels of PI3K activity. Treating melanoma cells with wortmanin or LY294002, two different PI3K inhibitors, decreased PI3K activity and caused a dose-dependent decrease in resistance to ultraviolet radiation. Lower resistance to radiation elicited by LY294002 coincided with increased apoptosis. To further establish the role of PI3K in radiation resistance, we transfected early-stage melanoma cells with the cDNA of p85, the regulatory subunit of PI3K. Clones that constitutively overexpressed p85 exhibited a higher degree of PI-3,4-P2 synthesis and a corresponding increase in their resistance to ultraviolet radiation. The results of this study point to the role of PI3K and its biproducts in radiation resistance of human melanoma cells.

3'-Azidothymidine significantly alters glycosphingolipid synthesis in melanoma cells and decreases the shedding of gangliosides.

In this report, we establish that 3'-azido-3'-deoxythymidine (AZT) treatment of melanoma cells greatly alters the pattern of glycosphingolipid biosynthesis. In SK-MEL-30 cells, synthesis of the gangliosides GM3 and GD3 was significantly inhibited (60% and 50% of control, respectively) and the production of their precursor, lactosylceramide, was stimulated by 2.5-fold. Control experiments established that phospholipid synthesis was not affected by AZT treatment, consistent with AZT treatment only affecting lipid biosynthetic reactions that involve glycosylation. Likely as a consequence of decreased rates of ganglioside synthesis, AZT treatment of SK-MEL-30 cells also significantly suppressed the amount of gangliosides shed from the membranes of these cells. Since shedding of gangliosides has been proposed to allow melanoma cells to avoid destruction by the immune system and alterations of glycosphingolipid levels are likely important for the malignant cell phenotype, these results may have important implications regarding the potential use of AZT or related glycosylation inhibitors as cancer chemotherapeutics.

Receptor-mediated endocytosis of urokinase-type plasminogen activator is regulated by cAMP-dependent protein kinase.

Internalization of the urokinase-type plasminogen activator (uPA) requires two receptors, the uPA receptor (uPAR) and the low density lipoprotein receptor-related protein (LRP)/alpha2-macroglobulin (alpha2M) receptor. Here, we address whether protein kinases are involved in the internalization of uPA by human melanoma cells. Initially, we found that the internalization of uPA was significantly inhibited by the serine/threonine protein kinase inhibitors staurosporine, K-252a and H-89, but not by the tyrosine kinase inhibitors, genistein and lavendustin A. Internalization of uPA was also inhibited by a pseudosubstrate peptide for cAMP-dependent protein kinase (PKA), but not by a pseudosubstrate peptide for protein kinase C. We confirmed a requirement for PKA-activity and implicated a specific isoform by using an antisense oligonucleotide against the regulatory subunit RI alpha of PKA which suppresses PKA-I activity. Exposure of cells to this oligonucleotide led to a specific, dose-dependent decrease in RI alpha protein and to a significant inhibition in the rate of uPA internalization. We further demonstrate that treatment of melanoma cells with either H-89 or PKA RI alpha antisense oligonucleotides also resulted in a decreased internalization of two other ligands of LRP, activated alpha2M and lactoferrin, indicating that PKA activity is associated with LRP. Finally, we demonstrate that PKA activity is also required for the internalization of transferrin, but not for the internalization of the epidermal growth factor or adenovirus 2, suggesting that in melanoma cells, PKA activity is not generally required for clathrin-mediated endocytosis, but is rather associated with specific internalization receptors.

Treatment of melanoma cells with the synthetic retinoid CD437 induces apoptosis via activation of AP-1 in vitro, and causes growth inhibition in xenografts in vivo.

Human malignant melanoma is notoriously resistant to pharmacological modulation. We describe here for the first time that the synthetic retinoid CD437 has a strong dose-dependent antiproliferative effect on human melanoma cells (IC50: 5 x 10(-6) M) via the induction of programmed cell death, as judged by analysis of cell morphology, electron microscopical features, and DNA fragmentation. Programmed cell death was preceded by a strong activation of the AP-1 complex in CD437-treated cells as demonstrated by gel retardation and chloramphenicol transferase (CAT) assays. Northern blot analysis showed a time-dependent increase in the expression of c-fos and c-jun encoding components of AP-1, whereas bcl-2 and p53 mRNA levels remained constant. CD437 also exhibited a strong growth inhibitory effect on MeWo melanoma cells in a xenograft model. In tissue sections of CD437-treated MeWo tumors from these animals, apoptotic melanoma cells and c-fos overexpressing cells were colocalized by TdT-mediated deoxyuridine triphosphate-digoxigenin nick end labeling (TUNEL) staining and in situ hybridization. Taken together, this report identifies CD437 as a retinoid that activates and upregulates the transcription factor AP-1, leading eventually to programmed cell death of exposed human melanoma cells in vitro and in vivo. Further studies are needed to evaluate whether synthetic retinoids such as CD437 represent a new class of retinoids, which may open up new ways to a more effective therapy of malignant melanoma.

The pleiotropic effect of TPA on in vitro invasion/migration of glioma and melanoma cell lines.

The invasion/migration of two cell lines, melanoma (MEW) and glioma (BT5C), and their counterparts treated for prolonged time with TPA were studied. On Western blots both cell lines expressed alpha, beta I protein kinase C isoforms, whereas beta II and gamma were not detected. The down-regulation of alpha and beta I PKC was observed in glioma cells after long treatment with TPA, whereas the same treatment of melanoma cells did not lead to PKC downregulation. The down-regulation of PKC was accompanied by stimulation of cell migration/invasion through Transwell chambers coated with collagen IV or fibronectin. In the case of melanoma cells treated with TPA, whose PKC was not down-regulated, the inhibition of migration/invasion was observed. The invasive properties of studied cells did not correlate with any conventional PKC isoform expression.