Cell adhesion: implication in tumor progression.

Changes in the adhesive properties of neoplastic cells, as well as intracellular signaling mediated by cell surface adhesion molecules, play essential roles in the development and progression of cancer. In this review, we summarize the recent progress in understanding the biology of cell adhesion molecules (CAMs) as well as their clinical significance as prognostic biomarkers or as potential therapeutic targets in a variety of malignancies.

Transcriptional regulation of KiSS-1 gene expression in metastatic melanoma by specificity protein-1 and its coactivator DRIP-130.

Loss of the metastasis suppressor gene, KiSS-1 has been strongly correlated to the progression of metastases in numerous types of cancers. The mechanism through which KiSS-1 is lost during metastasis, however, is still not completely known. Previous studies have shown that genetic material on human chromosome 6q16.3-q23 is essential for KiSS-1 expression in normal tissues. Additionally, microcell-mediated transfer of this chromosome in cancerous tissue results in rescued expression of KiSS-1 and reduced metastatic phenotype. Here, we show that loss of Sp1-coactivator protein DRIP-130, which is encoded by human chromosome 6q16.3-q23, results in reduced KiSS-1 promoter activation in highly malignant melanoma cells. Co-expression of Sp1 and DRIP-130 not only rescues KiSS-1 expression, but also induces an inhibition of the invasive and migratory behavior in highly metastatic melanoma cells, similar to the overexpression of KiSS-1 metastasis suppressor gene in those cells. Furthermore, we demonstrate that KiSS-1 expression is regulated by Sp1 elements within the first 100-bp region of the KiSS-1 promoter and that targeted deletion of a single GC-rich region spanning -93 to -58 interrupts Sp1- and DRIP-130-modulated transcriptional control of KiSS-1 expression. Our results thus suggest that DRIP-130 is a key regulator in KiSS-1 transactivation in normal tissue, and that the loss of DRIP-130 expression, as a result of the gross loss of human chromosome 6q16.3-q23, provokes increased tumor metastasis.

Loss of AP-2alpha results in deregulation of E-cadherin and MMP-9 and an increase in tumorigenicity of colon cancer cells in vivo.

Activator protein-2 (AP-2) is a transcription factor that regulates proliferation and differentiation in mammalian cells and has been implicated in the acquisition of the metastatic phenotype in several types of cancer. Herein, we examine the role of AP-2alpha in colon cancer progression. We provide evidence for the lack of AP-2alpha expression in the late stages of colon cancer cells. Re-expression of the AP-2alpha gene in the AP-2alpha-negative SW480 colon cancer cells suppressed their tumorigenicity following orthotopic injection into the cecal wall of nude mice. The inhibition of tumor growth could be attributed to the increased expression of E-cadherin and decreased expression and activity of matrix-metalloproteinase-9 (MMP-9) in the transfected cells, as well as a substantial loss of their in vitro invasive properties. Conversely, targeting constitutive expression of AP-2alpha in AP-2-positive KM12C colon cancer cells with small interfering RNA resulted in an increase in their invasive potential, downregulation of E-cadherin and increased expression of MMP-9. In SW480 cells, re-expression of AP-2alpha resulted in a fourfold increase in the activity of E-cadherin promoter, and a 5-14-fold decrease in the activity of MMP-9 promoter, indicating transcriptional regulation of these genes by AP-2alpha. Chromatin immunoprecipitation assay showed that re-expressed AP-2alpha directly binds to the promoter of E-cadherin, where it has been previously reported to act as a transcriptional activator. Furthermore, chromatin immunoprecipitation assay revealed AP-2alpha binding to the MMP-9 promoter, which ensued by decreased binding of transcription factor Sp-1 and changes in the recruitment of transcription factors to a distal AP-1 element, thus, contributing to the overall downregulation of MMP-9 promoter activity. Collectively, our data provide evidence that AP-2alpha acts as a tumor suppressor gene in colon cancer..

Phase II trial of imatinib mesylate in patients with metastatic melanoma.

Metastatic melanoma cells express a number of protein tyrosine kinases (PTKs) that are considered to be targets for imatinib. We conducted a phase II trial of imatinib in patients with metastatic melanoma expressing at least one of these PTKs. Twenty-one patients whose tumours expressed at least one PTK (c-kit, platelet-derived growth factor receptors, c-abl, or abl-related gene) were treated with 400 mg of imatinib twice daily. One patient with metastatic acral lentiginous melanoma, containing the highest c-kit expression among all patients, had dramatic improvement on positron emission tomographic scan at 6 weeks and had a partial response lasting 12.8 months. The responder had a substantial increase in tumour and endothelial cell apoptosis at 2 weeks of treatment. Imatinib was fairly well tolerated: no patient required treatment discontinuation because of toxicity. Fatigue and oedema were the only grade 3 or 4 toxicities that occurred in more than 10% of the patients. Imatinib at the studied dose had minimal clinical efficacy as a single-agent therapy for metastatic melanoma. However, based on the characteristics of the responding tumour in our study, clinical activity of imatinib, specifically in patients with melanoma with certain c-kit aberrations, should be examined.

Phorbol diester-induced macrophage differentiation of leukemic blasts from patients with human myelogenous leukemia.

Phorbol esters, including 12-O-tetradecanoylphorbol 13-acetate (TPA), induce terminal macrophagelike differentiation of cells from human acute myelogenous leukemia lines. We report that myelogenous leukemia cells obtained from patients undergo macrophagelike differentiation after exposure to TPA. The myeloid leukemic cell cultured with TPA became adherent to charged surfaces with long filamentous pseudopodia; developed positive staining for alpha-napthyl acetate esterase, increased lysozyme secretion, reduced nitroblue tetrazolium, and acquired the ability to phagocytose candida. Cells from patients with lymphocytic leukemia did not become macrophagelike when cultured with TPA.

The spectrum of molecular alterations in the evolution of chronic myelocytic leukemia.

DNA from 135 patients with chronic myelogenous leukemia (CML) at various clinical stages and Philadelphia (Ph1) chromosome positive acute lymphoblastic leukemia was investigated for alterations in a variety of proto-oncogenes which have been implicated in the evolution of CML from its chronic phase to blast crisis. The most common genetic change found in the evolution of typical Ph1 chromosome positive CML to blast crisis was an alteration of the p53 gene involving either a rearrangement, a deletion, or a point mutation in the coding sequence of the gene. Alterations of the p53 gene were found in the myeloid and the rare megakaryocytic variant of blast crisis but were absent in the lymphoid leukemic transformants. Gross structural alterations were seen in 11 of 54 (20%) of myeloid or unknown phenotypes of blast crisis and in only 1 of 44 chronic phase cases. Eight examples of mutations in the open reading frame of the p53 gene at codons 49, 53, 60, 140, 202, 204, 238, and 239 were observed in blast crisis patients. Mutations in the N-RAS gene were rare in typical blast crisis (2 of 27 cases) but were found in megakaryocytic and Ph1 negative myeloid blast crisis. We concluded that heterogeneous alterations in the p53 gene and occasionally in the N-RAS genes accompany the evolution of chronic phase CML to blast crisis.

Transcription factor AP-2alpha is preferentially cleaved by caspase 6 and degraded by proteasome during tumor necrosis factor alpha-induced apoptosis in breast cancer cells.

Several reports have linked activating protein 2alpha (AP-2alpha) to apoptosis, leading us to hypothesize that AP-2alpha is a substrate for caspases. We tested this hypothesis by examining the effects of tumor necrosis factor alpha (TNF-alpha) on the expression of AP-2 in breast cancer cells. Here, we provide evidence that TNF-alpha downregulates AP-2alpha and AP-2gamma expression posttranscriptionally during TNF-alpha-induced apoptosis. Both a general caspase antagonist (zVADfmk) and a caspase 6-preferred antagonist (zVEIDfmk) inhibited TNF-alpha-induced apoptosis and AP-2alpha downregulation. In vivo tests showed that AP-2alpha was cleaved by caspases ahead of the DNA fragmentation phase of apoptosis. Recombinant caspase 6 cleaved AP-2alpha preferentially, although caspases 1 and 3 also cleaved it, albeit at 50-fold or higher concentrations. Activated caspase 6 was detected in TNF-alpha-treated cells, thus confirming its involvement in AP-2alpha cleavage. All three caspases cleaved AP-2alpha at asp(19) of the sequence asp-arg-his-asp (DRHD(19)). Mutating D(19) to A(19) abrogated AP-2alpha cleavage by all three caspases. TNF-alpha-induced cleavage of AP-2alpha in vivo led to AP-2alpha degradation and loss of DNA-binding activity, both of which were prevented by pretreatment with zVEIDfmk. AP-2alpha degradation but not cleavage was inhibited in vivo by PS-431 (a proteasome antagonist), suggesting that AP-2alpha is degraded subsequent to cleavage by caspase 6 or caspase 6-like enzymes. Cells transfected with green fluorescent protein-tagged mutant AP-2alpha are resistant to TNF-alpha-induced apoptosis, further demonstrating the link between caspase-mediated cleavage of AP-2alpha and apoptosis. This is the first report to demonstrate that degradation of AP-2alpha is a critical event in TNF-alpha-induced apoptosis. Since the DRHD sequence in vertebrate AP-2 is widely conserved, its cleavage by caspases may represent an important mechanism for regulating cell survival, proliferation, differentiation, and apoptosis.

Phorbol ester effect on differentiation of human myeloid leukemia cell lines blocked at different stages of maturation.

The control of differentiation by tumor-promoting phorbol diesters including 12-O-tetradecanoylphorbol-13-acetate (TPA) was investigated using cells from human myeloid leukemia lines and sublines that were blocked at different stages of maturation. The myeloid leukemia cells that were blocked at the myeloblast-promyelocyte stage of maturation (KG-1, HL-60, and ML-3) had a prominent response when cultured with TPA. The cells became adherent, developed pseudopodia, displayed macrophage characteristics by light microscopy, developed nonspecific acid esterase activity, phagocytized yeast, slightly reduced nitro blue tetrazolium, displayed Fc-immunoglobulin G receptors, and killed bacteria. Lysozyme secretion and enzyme activity for beta-glucuronidase and acid phosphatase increased 2- to 20-fold concomitant with macrophage differentiation. The myeloid leukemia cells that were blocked at the undifferentiated myeloid blast stage of maturation (KG-1a and K562) were completely resistant to TPA-induced macrophage differentiation. We examined ten macrophage functions in the myeloid cell lines and sublines after exposure to phorbol diesters. The leukemic lines blocked at the myeloblast-promyelocyte stage of maturation expressed almost all the macrophage-specific functions. Phorbol diesters probably induced differentiation through a common cellular mechanism because the macrophage-differentiated events could not be dissociated. In sharp contrast, the early myeloid blast cells (KG-1a and K562) were incapable of acquiring any of the macrophage-specific functions after exposure to phorbol diesters. The KG-1a variant, in particular, should provide a good model to help elucidate the regulatory mechanism controlling the expression of macrophage functions during exposure to phorbol diesters.

Association in the expression of Kirsten-ras oncogene and the major histocompatibility complex class I antigens in fibrosarcoma tumor cell variants exhibiting different metastatic capabilities.

The metastatic properties of the methylcholanthrene-induced T-10 sarcoma tumor variants which originated in C3H x C57Bl/6 F1 mice are correlated with the relative expression of class I major histocompatibility complex antigens. Both the nonmetastatic and the highly metastatic clones were found to lack the H-2K region-controlled H-2Kb and H-2Kk antigens. However, the nonmetastatic clones express only the H-2Db molecule whereas the metastatic clones express both the H-2Db and the H-2Dk molecules. Transfection of the highly metastatic lines with cloned H-2K genes (Kb, Kk) reduced their tumorigenicity and abolished the formation of metastasis in syngeneic mice, while the transfection of the nonmetastatic lines with cloned H-2Dk genes resulted in shifting the cells to the metastatic phenotype. The present study is aimed to investigate the expression of protooncogenes in the T-10 fibrosarcoma lines that exhibit distinct metastatic properties in correlation with the expressed H-2 antigens. The major oncogene which showed differential expression in the T-10 clones is Ki-ras. The amounts of specific Ki-ras messenger RNA and the Ki-ras Mr 21,000 protein are expressed in elevated levels in the H-2Dk-negative nonmetastatic clones in comparison with a low level of expression in the H-2Dk-positive highly metastatic clones. Expression of H-2K antigens following transfection with cloned H-2K genes had no effect on the expressed Ki-ras oncogene in the T-10 clones. However, transfection of the nonmetastatic cells with the cloned H-2Dk gene resulted in shifting of the cells to a highly metastatic phenotype and in reduction of the expressed c-Ki-ras oncogene.

Ultraviolet B irradiation promotes tumorigenic and metastatic properties in primary cutaneous melanoma via induction of interleukin 8.

UV radiation has been shown to play a role in the initiation of human cutaneous melanoma, but its role in the development of malignant melanoma to the metastatic state is not very well defined. Although previous studies have concentrated on the effect of UV-B on the host immune response, the effect of UV-B on the tumor cells was not elucidated. Here we show that UV-B can induce interleukin 8 (IL-8) mRNA and protein secretion in human cutaneous melanoma with negligible expression of IL-8. UV-B-induced IL-8 was constitutively expressed 60 days after irradiation in tumors implanted in mice. Induction of IL-8 was UV-B dose dependent and blocked by cyclohexamide, indicating that de novo protein synthesis is required for its expression. The UV-irradiated cells demonstrated enhanced tumorigenicity and metastatic potential in nude mice. The increase in tumorigenicity and metastatic ability could be explained by the increase in Mr 72,000 type IV collagenase activity and angiogenesis attributed to the induction of IL-8 after irradiation. The acquisition of the metastatic phenotype induced by UV-B could not be attributed to abnormalities in the p53 or MTS-1 (p16INK4) genes. To the best of our knowledge, this is the first report to show that UV-B can increase the aggressiveness of human cutaneous melanoma for growth and metastasis.

A cysteine proteinase, which cleaves human C3, the third component of complement, is involved in tumorigenicity and metastasis of human melanoma.

The DM-4 human melanoma cell line, which is highly metastatic in nude mice, expresses a C3-cleaving activity that proteolyzes labeled as well as unlabeled human C3. This C3-cleaving activity is a cysteine proteinase characterized by a M(r) 41,000. The p41 proteinase shares antigenic determinants with murine p39 procathepsin-L and human procathepsin-L. Preincubation of DM-4 cells with anti-p39 F(ab')2 induced up to 45% decrease in their complement resistance. Pretreatment of DM-4 cells with anti-p39 Ab strongly inhibited their tumorigenicity and significantly decreased their metastatic potential in nude mice. Thus, the p41 C3-cleaving proteinase contributes to tumorigenicity and metastasis of human melanoma DM-4 cells.

Expression of MCAM/MUC18 by human melanoma cells leads to increased tumor growth and metastasis.

The cell surface adhesion molecule MCAM (MUC18) is strongly expressed by advanced primary and metastatic melanomas but is weaker and less frequent in nevus cells. Previous studies have shown that MCAM expression correlates with tumor thickness and metastatic potential of human melanoma cells in nude mice. To provide direct evidence that MCAM plays a role in tumor growth and metastasis of human melanoma, the nonmetastatic MCAM-negative primary cutaneous melanoma SB-2 cells were transfected with MCAM cDNA and analyzed subsequently for changes in their tumorigenic and metastatic potential. Enforced expression of MCAM in SB-2 cells rendered them highly tumorigenic and increased their metastatic potential in nude mice as compared with parental and control transfected cells. The transfected cells displayed increased homotypic adhesion, increased attachment to human endothelial cells, decreased ability to adhere to laminin, and increased invasiveness through Matrigel-coated filters. Anti-MCAM monoclonal antibody reversed these functions in the transfected cells but not in control cells. The above changes in function attributed to the expression of MCAM may underlie the contribution of MCAM/MUC18 to the malignant phenotype.

Procathepsin-L, a proteinase that cleaves human C3 (the third component of complement), confers high tumorigenic and metastatic properties to human melanoma cells.

We previously demonstrated that highly metastatic human melanoma cells secrete a 41 kDa proteinase that cleaves C3, the third component of complement, and shares antigenic determinants with procathepsin-L. Thus, we herein transfected the nonmetastatic DX-3 melanoma cells with the procathepsin-L cDNA. Three clones expressing and secreting high levels of procathepsin-L were selected. Conditioned medium and whole cell extracts from these clones, but not from control cells, carried a high C3-cleaving activity. The transfected clones displayed up to 60% resistance to complement-mediated lysis. Overexpression of procathepsin-L in melanoma cells increased their tumorigenicity and switched their phenotype from nonmetastatic to highly metastatic cells. This is the first report that demonstrates that enforced expression of procathepsin-L by human melanoma cells arms them with the ability to inactivate complement-mediated lysis and contributes to tumor growth and metastasis.

Interleukin 8 expression regulates tumorigenicity and metastasis in human bladder cancer.

Interleukin 8 (IL-8) is mitogenic and chemotactic for endothelial cells. Within a neoplasm, IL-8 is secreted by inflammatory and neoplastic cells. The highly tumorigenic and highly metastatic human transitional cell carcinoma (TCC) cell line 253J B-V overexpresses IL-8 relative to the nontumorigenic and nometastatic 253J-P cell line. To determine whether IL-8 expression regulates tumorigenicity and metastasis in human TCC, 253J B-V cells were transfected with the full-sequence antisense (AS) cDNA for IL-8, whereas 253J-P cells were transfected with the full-length IL-8 cDNA, and control cells for each were transfected with the neomycin resistance (Neo) gene. In vitro, sense-transfected 253J-P cells overexpressed IL-8-specific mRNA and protein, whereas both of these were markedly reduced in AS-IL-8-transfected 253J B-V cells relative to controls. Moreover, sense-transfected cells showed up-regulation in matrix metalloproteinase type 9 mRNA, collagenase activity, and increased invasiveness through Matrigel-coated filters, whereas these measures were lower in AS-transfected cells relative to controls. After implantation into the bladders of athymic nude mice, the sense-transfected 253J-P cells acquired increased tumorigenicity and metastasis, whereas the AS-transfected cells significantly inhibited tumorigenicity and metastases in the 253J B-V cell lines. This effect was accompanied by reduced IL-8 expression and microvessel density. These studies demonstrate that IL-8 expression enhances angiogenic activity through the induction of matrix metalloproteinase type 9 and subsequently regulates the tumorigenesis and production of spontaneous metastases of human TCC.

Targeting melanoma with NT157 by blocking Stat3 and IGF1R signaling.

It is well known that specific signal transduction inhibitors rarely suffice as anti-cancer agents. In most cases, tumors possess primary drug resistance due to their inherent heterogeneity, or acquire drug resistance due to genomic instability and acquisition of mutations. Here we expand our previous study of the novel compound, NT157, and show that it acts as a dual-targeting agent that invokes the blockage of two signal transduction pathways that are central to the development and maintenance of multiple human cancers. We show that NT157 targets not only IGF1R-IRS1/2, as previously reported, but also the Stat3 signaling pathway and demonstrates remarkable anti-cancer characteristics in A375 human melanoma cells and in a metastatic melanoma model in mice.

Mitochondrial oligomers boost glycolysis in cancer stem cells to facilitate blebbishield-mediated transformation after apoptosis.

Apoptosis culminates in secondary necrosis due to lack of ATP. Cancer stem cells form spheres after apoptosis by evoking the blebbishield emergency program. Hence, determining how blebbishields avoid secondary necrosis is crucial. Here we demonstrate that N-Myc and VEGFR2 control transformation from blebbishields, during which oligomers of K-Ras, p27, BAD, Bax, and Bak boost glycolysis to avoid secondary necrosis. Non-apoptotic cancer cells also utilize oligomers to boost glycolysis, which differentiates the glycolytic function of oligomers from their apoptotic action. Smac mimetic in combination with TNF-α or TRAIL but not in combination with FasL abrogates transformation from blebbishields by inducing secondary necrosis. Thus blebbishield-mediated transformation is dependent on glycolysis, and Smac mimetics represent potential candidates to abrogate the blebbishield emergency program.

Hypoxia-upregulated microRNA-630 targets Dicer, leading to increased tumor progression.

MicroRNAs (miRNAs) are small RNA molecules that affect cellular processes by controlling gene expression. Recent studies have shown that hypoxia downregulates Drosha and Dicer, key enzymes in miRNA biogenesis, causing a decreased pool of miRNAs in cancer and resulting in increased tumor growth and metastasis. Here we demonstrate a previously unrecognized mechanism by which hypoxia downregulates Dicer. We found that miR-630, which is upregulated under hypoxic conditions, targets and downregulates Dicer expression. In an orthotopic mouse model of ovarian cancer, delivery of miR-630 using 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) nanoliposomes resulted in increased tumor growth and metastasis, and decreased Dicer expression. Treatment with the combination of anti-miR-630 and anti-vascular endothelial growth factor antibody in mice resulted in rescue of Dicer expression and significantly decreased tumor growth and metastasis. These results indicate that targeting miR-630 is a promising approach to overcome Dicer deregulation in cancer. As demonstrated in the study, use of DOPC nanoliposomes for anti-miR delivery serves as a better alternative approach to cell line-based overexpression of sense or antisense miRNAs, while avoiding potential in vitro selection effects. Findings from this study provide a new understanding of miRNA biogenesis downregulation observed under hypoxia and suggest therapeutic avenues to target this dysregulation in cancer.

Abnormalities in the CDKN2 (p16INK4/MTS-1) gene in human melanoma cells: relevance to tumor growth and metastasis.

The inhibitor of cyclin-dependent kinase 4, CDKN2 (also known as p16INK4 or MTS-1, multiple tumor suppressor gene 1), has been mapped to 9p21. The gene has been shown to be deleted or mutated in high frequency in human melanoma cell lines and familial melanoma patients, suggesting that it could be a melanoma suppressor gene. How these observations are related to tumorigenicity and metastasis of human melanoma is not clear however. To test the role of CDKN2 in human melanoma metastasis, 14 human melanoma cell lines with different metastatic abilities in nude mice were analysed for possible abnormalities in the CDKN2 gene. Homozygous deletions that resulted in a lack of gene expression were found in six of 14 cell lines tested. SSCP-direct sequencing revealed point mutations in three other cell lines. One cell line displayed CC to TT transitions which constitute a hallmark of ultraviolet-induced DNA damage. Overall, abnormalities in the CDKN2 gene were found in nine of 14 (64%) cell lines tested. Homozygous deletion and lack of gene expression were found in several low tumorigenic and nonmetastatic melanoma lines, whereas other metastatic cells did not exhibit abnormalities in the CDKN2 gene. These data suggest that the absence of normal CDKN2 does not confer growth advantage to melanoma cells in vivo and that the production of metastasis by human melanoma cells can occur in the absence of CDKN2 gene abnormalities.

Direct sequencing analysis of exon 1 of the c-K-ras gene shows a low frequency of mutations in human pancreatic adenocarcinomas.

We have applied direct dideoxy sequencing of DNA fragments amplified in vitro by the polymerase chain reaction to the detection of mutations in exon 1 of the c-K-ras gene in human pancreatic adenocarcinomas. Four fresh frozen primary tumors, one metastatic tumor, and twelve formalin-fixed paraffin embedded tumors were analysed. Only three cases showed a possible mutation in codon 12 in a small population of cells, in contrast to the high frequency reported for this alteration with the RNAase A protection assay and allele-specific oligoxynucleotide hybridization. No major difference in sensitivity was found between DNA sequence analysis, and the latter method. Our results suggest that if c-K-ras mutations are indeed present in pancreatic adenocarcinomas at the high frequency reported by others, they must be confined to a small fraction of the cell population to escape detection by direct sequencing. Such a phenomenon would have implications for c-K-ras mutations in the pathogenesis of pancreatic adenocarcinomas.

Dominant-negative CREB inhibits tumor growth and metastasis of human melanoma cells.

The ATF/CREB family of eukaryotic transcription factors contain the bZIP structural motif and mediate their transcriptional activities via heterodimerization with ATF and AP-1 family members. Quenching of CREB-associated proteins by a dominant-negative CREB (KCREB) that is mutated within its DNA-binding domain decreases radiation resistance of human melanoma cells. The purpose of this study was to determine the role of CREB in tumor growth and metastasis of human melanoma using KCREB. Highly metastatic MeWo human melanoma cells were transfected with the KCREB expression vector and subsequently analysed for changes in their tumorigenic and metastatic potential. Expression of KCREB in MeWo human cells decreased their tumorigenic and metastatic potential in nude mice compared with parental and control transfected cells. The KCREB-transfected cells displayed downregulation of 72 kDa collagenase type IV (MMP-2) mRNA expression and activity and decreased invasiveness through Matrigel-coated filters. Moreover, transcriptional activities mediated by the CAT gene driven by the MMP-2 promoter were decreased by 14-45-fold in KCREB-transfected cells. In addition, the cell-surface adhesion molecule MCAM/MUC18 that is involved in metastasis of human melanoma was downregulated in the KCREB-transfected cells. These data indicate that, through their transcriptional activities, CREB and its associated proteins play an important role in the acquisition of the metastatic phenotype of human melanoma cells.