Overexpression and mutations of p53 in metastatic malignant melanomas

Immunohistologic Evaluation of Putatively Mutant p53 Protein in Cutaneous Melanocytic Neoplasms

Mutations in the p53 tumor suppressor gene, located at chromosomal locus 17pI3, are the most commonly seen genetic alterations found in human malignancies. Their role in the pathogenesis of malignant melanoma is thought to be limited, although variable results have been reported in reference to immunoreactivity for putatively mutant p53 protein (mp53) in melanocytic lesions in general. In that light, the authors undertook an immunohistologic evaluation of 256 well-characterized tumors in that category, including common nevi (CN; n=73); Spitz nevi (SN; n=40); nodular melanomas (NMMs; n=32), superficial spreading melanomas (SMMs; n=65); lentigo maligna melanomas (LMMs; n=23); and melanomas arising in preexisting nevi (MANs; n=23). One hundred cells were counted manually in randomly selected high-power microscopic fields, in regard to nuclear labeling for mp53. Results were recorded semiquantitatively, as negative, positive (1-4% of tumor cells); and positive (>5% of tumor cells). No examples of CN or SN demonstrated any immunoreactivity whatever for mp53, whereas 105 of 143 melanomas (73%) did so. However, an mp53 index of >50% was seen in only 29% of the latter lesions. NMMs were most often mp53-positive and showed the highest numerical level of nuclear labeling, followed in respective order by SMMs, and LMMs/MANs. These results suggest that negative mp53-immunostaining cannot be equated with the diagnostic interpretation of a benign melanocytic neoplasm, because 27% of melanomas also failed to label for that determinant. However, the presence of mp53-immunolabeling in a melanocytic proliferation-even if at low levels-should conversely prompt careful consideration of melanoma as the favored diagnosis in the confined setting of morphologically difficult cases, inasmuch as no example of CN or SN in this series had that characteristic.

Resveratrol induces apoptosis by directly targeting Ras-GTPase-activating protein SH3 domain-binding protein 1

Resveratrol (trans-3,5,4'-truhydroxystilbene) possesses a strong anticancer activity exhibited as the induction of apoptosis through p53 activation. However, the molecular mechanism and direct target(s) of resveratrol-induced p53 activation remain elusive. Here, the Ras-GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) was identified as a potential target of resveratrol, and in vitro binding assay results using resveratrol-conjugated Sepharose 4B beads confirmed their direct binding. Depletion of G3BP1 significantly diminishes resveratrol-induced p53 expression and apoptosis. We also found that G3BP1 negatively regulates p53 expression by interacting with ubiquitin-specific protease 10 (USP10), a deubiquitinating enzyme of p53. Disruption of the interaction of p53 with USP10 by G3BP1 interference leads to the suppression of p53 deubiquitination. Resveratrol, on the other hand, directly binds to G3BP1 and prevents the G3BP1/USP10 interaction, resulting in enhanced USP10-mediated deubiquitination of p53, and consequently increased p53 expression. These findings disclose a novel mechanism of resveratrol-induced p53 activation and resveratrol-induced apoptosis by direct targeting of G3BP1.

EZH2-dependent suppression of a cellular senescence phenotype in melanoma cells by inhibition of p21/CDKN1A expression

Polycomb group (PcG) proteins such as Enhancer of zeste homolog 2 (EZH2) are epigenetic transcriptional repressors that function through recognition and modification of histone methylation and chromatin structure. Targets of PcG include cell cycle regulatory proteins which govern cell cycle progression and cellular senescence. Senescence is a characteristic of melanocytic nevi, benign melanocytic proliferations that can be precursors of malignant melanoma. In this study, we report that EZH2, which we find absent in melanocytic nevi but expressed in many or most metastatic melanoma cells, functionally suppresses the senescent state in human melanoma cells. EZH2 depletion in melanoma cells inhibits cell proliferation, restores features of a cellular senescence phenotype, and inhibits growth of melanoma xenografts in vivo. p21/CDKN1A is activated upon EZH2 knockdown in a p53-independent manner and contributes substantially to cell cycle arrest and induction of a senescence phenotype. EZH2 depletion removes histone deacetylase 1 (HDAC1) from the CDKN1A transcriptional start site and downstream region, enhancing histone 3 acetylation globally and at CDKN1A. This results in recruitment of RNA polymerase II, leading to p21/CDKN1A activation. Depletion of EZH2 synergistically activates p21/CDKN1A expression in combination with the HDAC inhibitor trichostatin A. Since melanomas often retain wild-type p53 function activating p21, our findings describe a novel mechanism whereby EZH2 activation during tumor progression represses p21, leading to suppression of cellular senescence and enhanced tumorigenicity.

p53 prevents progression of nevi to melanoma predominantly through cell cycle regulation

p53 is the central member of a critical tumor suppressor pathway in virtually all tumor types, where it is silenced mainly by missense mutations. In melanoma, p53 predominantly remains wild type, thus its role has been neglected. To study the effect of p53 on melanocyte function and melanomagenesis, we crossed the ‘high-p53’Mdm4+/− mouse to the well-established TP-ras0/+ murine melanoma progression model. After treatment with the carcinogen dimethylbenzanthracene (DMBA), TP-ras0/+ mice on the Mdm4+/− background developed fewer tumors with a delay in the age of onset of melanomas compared to TP-ras0/+ mice. Furthermore, we observed a dramatic decrease in tumor growth, lack of metastasis with increased survival of TP-ras0/+: Mdm4+/− mice. Thus, p53 effectively prevented the conversion of small benign tumors to malignant and metastatic melanoma. p53 activation in cultured primary melanocyte and melanoma cell lines using Nutlin-3, a specific Mdm2 antagonist, supported these findings. Moreover, global gene expression and network analysis of Nutlin-3-treated primary human melanocytes indicated that cell cycle regulation through the p21WAF1/CIP1 signaling network may be the key anti-melanomagenic activity of p53.

Prognostic significance of Sox4 expression in human cutaneous melanoma and its role in cell migration and invasion

The Sox4 transcription factor is involved in various cellular processes, such as embryonic development and differentiation. Deregulated expression of Sox4 in several human cancers has been reported to date, but its role in melanoma is unknown. We explored the role of Sox4 in melanoma pathogenesis in vivo and in vitro. Using tissue microarray, we evaluated Sox4 expression in 180 melanocytic lesions and investigated its role in melanoma cell migration and invasion. Sox4 expression was remarkably reduced in metastatic melanoma compared with dysplastic nevi (P < 0.05) and primary melanoma (P < 0.01). This reduction was correlated with a poorer disease-specific survival of melanoma patients (P = 0.039). Multivariate Cox regression analysis revealed that reduced Sox4 expression is an independent prognostic factor (P = 0.049). Knockdown of Sox4 enhanced melanoma cell invasion, migration, and stress fiber formation. The increased migration and invasion on Sox4 knockdown depends on the presence of nuclear factor (NF)-κB p50 and is abrogated when p50 is knocked down. We further observed inhibition of NF-κB p50 transcription by Sox4, in addition to a reverse pattern of expression of Sox4 and NF-κB p50 in different stages of melanocytic lesions. Our results suggest that Sox4 regulates melanoma cell migration and invasion in an NF-κB p50-dependent manner and may serve as a prognostic marker and potential therapeutic target for human melanoma.

Similar nucleotide excision repair capacity in melanocytes and melanoma cells

Sunlight UV exposure produces DNA photoproducts in skin that are repaired solely by nucleotide excision repair in humans. A significant fraction of melanomas are thought to result from UV-induced DNA damage that escapes repair; however, little evidence is available about the functional capacity of normal human melanocytes, malignant melanoma cells, and metastatic melanoma cells to repair UV-induced photoproducts in DNA. In this study, we measured nucleotide excision repair in both normal melanocytes and a panel of melanoma cell lines. Our results show that in 11 of 12 melanoma cell lines tested, UV photoproduct repair occurred as efficiently as in primary melanocytes. Importantly, repair capacity was not affected by mutation in the N-RAS or B-RAF oncogenes, nor was a difference observed between a highly metastatic melanoma cell line (A375SM) or its parental line (A375P). Lastly, we found that although p53 status contributed to photoproduct removal efficiency, its role did not seem to be mediated by enhanced expression or activity of DNA binding protein DDB2. We concluded that melanoma cells retain capacity for nucleotide excision repair, the loss of which probably does not commonly contribute to melanoma progression.

The role of BRAF mutation and p53 inactivation during transformation of a subpopulation of primary human melanocytes

Melanocytic nevi frequently harbor oncogenic BRAF mutations, but only a minority progress to melanoma. In human melanocytes, persistent BRAF(V600E) expression triggers oncogene-induced senescence, which implies that bypass of oncogene-induced senescence is necessary for malignant transformation of melanocytes. We show that a subpopulation of primary human melanocytes with persistent expression of BRAF(V600E) do not enter oncogene-induced senescence, but instead survive despite heightened MAPK activity. Disruption of the p53 pathway using short-hairpin RNA initiated rapid growth of these V600E(+) melanocytes in vitro. The resultant V600E(+)/p53(sh) melanocytes grew anchorage-independently in soft agar, formed pigmented lesions reminiscent of in situ melanoma in artificial skin reconstructs, and were weakly tumorigenic in vivo. Array comparative genomic hybridization analysis demonstrated that the transformed melanocytes acquired a substantial deletion in chromosome 13, which encodes the Rb1 tumor suppressor gene. Gene expression profiling study of nevi and melanomas showed that p53 target genes were differentially expressed in melanomas compared with nevi, suggesting a dysfunctional p53 pathway in melanoma in vivo. In summary, these data demonstrate that a subpopulation of melanocytes possesses the ability to survive BRAF(V600E)-induced senescence, and suggest that p53 inactivation may promote malignant transformation of these cells.

The genome and epigenome of malignant melanoma

Malignant melanoma originates in melanocytes, the pigment-producing cells of the skin and eye, and is one of the most deadly human cancers with no effective cure for metastatic disease. Like many other cancers, melanoma has both environmental and genetic components. For more than 20 years, the melanoma genome has been subject to extensive scrutiny, which has led to the identification of several genes that contribute to melanoma genesis and progression. Three molecular pathways have been found to be nearly invariably dysregulated in melanocytic tumors, including the RAS-RAF-MEK-ERK pathway (through mutation of BRAF, NRAS or KIT), the p16 INK4A-CDK4-RB pathway (through mutation of INK4A or CDK4) and the ARF-p53 pathway (through mutation of ARF or TP53). Less frequently targeted pathways include the PI3K-AKT pathway (through mutation of NRAS, PTEN or PIK3CA) and the canonical Wnt signaling pathway (through mutation of CTNNB1 or APC). Beyond the specific and well-characterized genetic events leading to activation of proto-oncogenes or inactivation of tumor suppressor genes in these pathways, systematic high-resolution genomic analysis of melanoma specimens has revealed recurrent DNA copy number aberrations as well as perturbations of DNA methylation patterns. Melanoma provides one of the best examples of how genomic analysis can lead to a better understanding of tumor biology. We review current knowledge of the genes involved in the development of melanoma and the molecular pathways in which these genes operate.

The role of p53 in pigmentation, tanning and melanoma

p53 has a central role in skin pigmentation and may impact on melanoma at all stages, however, as it's mutation frequency in melanoma is low, it's role has been somewhat under-appreciated. During normal skin function, p53 in the keratinocyte is a transducer of the skin tanning signal and an essential component of what is effectively a keratinocyte-melanocyte signaling cycle that regulates skin pigmentation. It is clear that this cycle functions optimally in skin of dark pigmentation. When melanin biosynthesis is genetically disrupted in skin of white complexion, we propose that this cycle operates as a promoter of melanocyte proliferation. The cell autonomous function of p53 in melanocytes is not well described, however, the balance of the evidence suggests that p53 is an effective tumor suppressor and the myriad of mechanisms by which the p53 pathway may be dysregulated in tumors attests to it importance as a tumor suppressor. In this review, we outline the known mechanisms that impair p53 itself and its immediate regulators or target genes during melanomagenesis. Due to the importance of this pathway, it is clear that p53 disruptions may relate directly to a patient's prognosis. This pathway will continue to be a focus of investigation, particularly with respect to targeted experimental chemotherapeutics.

Mechanism of UV-related carcinogenesis and its contribution to nevi/melanoma

Melanoma consists 4-5 % of all skin cancers, but it contributes to 71-80 % of skin cancers deaths. UV light affects cell and tissue homeostasis due to its damaging effects on DNA integrity and modification of expression of a plethora of genes. DNA repair systems protect cells from UV-induced lesions. Several animal models of melanoma have been developed (Xiphophorus, Opossum Monodelphis domestica, mouse models and human skin engrafts into other animals). This review discusses possible links between UV and genes significantly related to melanoma but does not discuss melanoma genetics. These include oncogenes, tumor suppressor genes, genes related to melanocyte-keratinocyte and melanocyte-matrix interaction, growth factors and their receptors, CRH, ACTH, α-MSH, glucocorticoids, ID1, NF-kappaB and vitamin D3.

The role of cell cycle regulatory proteins in the pathogenesis of melanoma

The transformation of melanocytes to melanoma cells is characterised by abnormal proliferation resulting from alterations in cell cycle regulatory mechanisms. This occurs through alterations in the two major cell cycle regulatory pathways, the retinoblastoma (Rb) and p53 tumour suppressor pathways. This review summarises the current knowledge of alterations in these two pathways at G1/S transition and specifically the role of the key cell cycle regulatory proteins pRb, p16INK4a (p16), cyclin D1, p27Kip1 (p27), p53 and p21Waf1/Cip1 (p21) in the pathogenesis of melanoma. It also considers their prognostic significance. Current data indicate that alterations of cyclin kinase inhibitor (cdki) levels are implicated in the pathogenesis of melanoma and may be useful prognostic markers. However, large validation studies linked to comprehensive clinical follow up data are necessary to clarify the prognostic significance of cell cycle regulatory proteins in individual patients.

Cellular UV damage responses--functions of tumor suppressor p53

DNA damage, provoked by ultraviolet (UV) radiation, evokes a cellular damage response composed of activation of stress signaling and DNA checkpoint functions. These are translated to responses of replicative arrest, damage repair, and apoptosis aimed at cellular recovery from the damage. p53 tumor suppressor is a central stress response protein, activated by multiple endogenous and environmental insults, including UV radiation. The significance of p53 in the DNA damage responses has frequently been reviewed in the context of ionizing radiation or other double strand break (DSB)-inducing agents. Despite partly similar patterns, the molecular events following UV radiation are, however, distinct from the responses induced by DSBs and are profoundly coupled with transcriptional stress. These are illustrated, e.g., by the UV damage-specific translocations of Mdm2, promyelocytic leukemia protein, and nucleophosmin and their interactions with p53. In this review, we discuss UV damage-provoked cellular responses and the functions of p53 in damage recovery and cell death.

Comprehensive analysis of the p53 status in mucosal and cutaneous melanomas

The abrogation of the function of the "gatekeeper of the genome", p53, is the most prevalent molecular alteration in solid human tumors. Regarding melanomas the involvement of p53 alterations is discussed controversially to date. In order to evaluate the status of p53 in detail, primary tumors and metastases of 63 sporadic cutaneous (CM) and mucosal (MuM) melanomas were examined by immunohistochemistry and sequence analysis of the entire coding region of the p53 transcript, i.e., exons 2 to 11. In addition, loss of heterozygosity (LOH) and loss of allele-specific transcription (LOT) were determined. Accumulation of the p53 protein occurred in most of the CM and MuM specimens (71% and 58%, respectively). In contrast, protein stabilizing p53 mutations were observed in 14% of the CM and no mutation was found in MuM specimens. Two of the aberrations located outside the core domain. LOH was detected in 22% CM and 58% MuM, and LOT in 25% of the CM specimens. The genotype distribution at the polymorphic p53 codon 72 in melanoma patients differed significantly from control subjects. The calculation of odds ratios (OR) and 95% confidence intervals (CI) indicated an increased risk for developing cutaneous melanomas in individuals carrying the Pro-coding allele. Altogether, aberrant p53 expression appears to be a common event in both CM and MuM.

Mutation and homozygous deletion analyses of genes that control the G1/S transition of the cell cycle in skin melanoma: p53, p21, p16 and p15

INTRODUCTION

The role of genes involved in the control of progression from the G1 to the S phase of the cell cycle in melanoma tumors is not fully known.

MATERIAL AND METHODS

The aims of our study were to analyse alterations in p53, p21, p16 and p15 genes in melanoma tumors and melanoma cell lines by single strand conformational polymorphism (SSCP), and to detect homozygous deletions. We analysed the DNA from 39 patients with primary and metastatic melanomas, and from 9 melanoma cell lines.

RESULTS

The SSCP technique showed heterozygous defects in the p53 gene in 8 of 39 (20.5%) melanoma tumors: three point mutations in intron sequences (introns 1 and 2) and exon 10, and three new polymorphisms located in introns 1 and 2 (C to T transition at position 11701 in intron 1; C insertion at position 11818 in intron 2; and C insertion at position 11875 in intron 2). One melanoma tumor exhibited two heterozygous alterations in the p16 exon 1 (stop codon and missense mutation). No defects were found in the remaining genes. Homozygous deletions were more frequent in melanoma cell lines than in melanoma tumors in p21, p16 and p15 (22.2%, 44.4%, and 44.4% versus 7.7%, 2.5%, and 5.1% respectively). TP53 did not show homozygous deletions.

CONCLUSIONS

Our results suggest that these genes are involved in melanoma tumorigenesis; but perhaps not in the major targets. Other suppressor genes that may be informative of the mechanism of tumorigenesis in skin melanomas need to be studied.

Mutation analysis of genes that control the G1/S cell cycle in melanoma: TP53, CDKN1A, CDKN2A, and CDKN2B

Background

The role of genes involved in the control of progression from the G1 to the S phase of the cell cycle in melanoma tumors in not fully known. The aim of our study was to analyse mutations in TP53, CDKN1A, CDKN2A, and CDKN2B genes in melanoma tumors and melanoma cell lines

Methods

We analysed 39 primary and metastatic melanomas and 9 melanoma cell lines by single-stranded conformational polymorphism (SSCP).

Results

The single-stranded technique showed heterozygous defects in the TP53 gene in 8 of 39 (20.5%) melanoma tumors: three new single point mutations in intronic sequences (introns 1 and 2) and exon 10, and three new single nucleotide polymorphisms located in introns 1 and 2 (C to T transition at position 11701 in intron 1; C insertion at position 11818 in intron 2; and C insertion at position 11875 in intron 2). One melanoma tumor exhibited two heterozygous alterations in the CDKN2A exon 1 one of which was novel (stop codon, and missense mutation). No defects were found in the remaining genes.

Conclusion

These results suggest that these genes are involved in melanoma tumorigenesis, although they may be not the major targets. Other suppressor genes that may be informative of the mechanism of tumorigenesis in skin melanomas should be studied.

hMLH1 and hMSH2 gene mutations are present in radial growth-phase cutaneous malignant melanoma cell lines and can be induced further by ultraviolet-B irradiation

Microsatellite instability and reduced expression of mismatch repair proteins were reported in melanomas. However, little is known about mutational changes of the mismatch repair genes in radial growth-phase melanoma especially following UVB irradiation. To investigate these changes, an in vitro system consisting of radial growth-phase Wistar melanoma cell lines (WM35, WM3211 and WM1650) was established. The cells were UVB irradiated (10 mJ/cm(2)), and evaluated for mutational changes of exon regions 13,16 and 19 (hMLH1) and 6,7 and 12 (hMLH2) of these genes before and after irradiation. The genomic DNAs were PCR amplified and the products were directly sequenced. Transition (C-->T, G-->A, T-->C) and transversion (G-->, A-->T) mutations were found in exons 6,16 and 19. Some were present in both the sham-irradiated and UV-irradiated cells but others were only detected after UVB irradiation. hMLH1 and hMLH2 gene mutations occur early in melanoma tumorigenesis. The ability of UVB irradiation to induce additional mutations in these repair genes suggests its possible role in melanoma pathogenesis. Further investigation will be needed to determine whether mutations such as these contribute to the development of microsatellite instability in melanoma.

Genomic alterations in spontaneous and carcinogen-induced murine melanoma cell lines

We have conducted an analysis of genetic alterations in spontaneous murine melanoma cell line B16F0 and its two metastatic clones, B16F1 and B16F10 and the carcinogen-induced murine melanoma cell lines CM519, CM3205, and K1735. We found that unlike human melanomas, the murine melanoma cell lines did not have activating mutations in the Braf oncogene at exon 11 or 15. However, there were distinct patterns of alterations in the ras, Ink4a/Arf, and p53 genes in the two melanoma groups. In the spontaneous B16 melanoma cell lines, expression of p16Ink4a and p19Arf tumor suppressor proteins was lost as a consequence of a large deletion spanning Ink4a/Arf exons 1alpha, 1beta, and 2. In contrast, the carcinogen-induced melanoma cell lines expressed p16Ink4a but had inactivating mutations in either p19Arf (K1735) or p53 (CM519 and CM3205). Inactivation of p19Arf or p53 in carcinogen-induced melanomas was accompanied by constitutive activation of mitogen-activated protein kinases (MAPKs) and/or mutation-associated activation of N-ras. These results indicate that genetic alterations in p16Ink4a/p19Arf, p53 and ras-MAPK pathways can cooperate in the development of murine melanoma.

Allelic imbalance of 12q22-23 associated with APAF-1 locus correlates with poor disease outcome in cutaneous melanoma

Cutaneous melanoma is a highly aggressive tumor that is relatively resistant to chemotherapy and radiotherapy. This resistance may be in part due to inhibition of apoptosis. Apoptotic protease activating factor-1(APAF-1), a candidate tumor suppressor gene, mediates p53-induced apoptosis, and its loss promotes oncogenic transformation. To determine whether loss of the APAF-1 locus influences tumor progression, we assessed loss of heterozygosity microsatellites on the APAF-1 locus (12q22-23) in 62 primary and 112 metastatic melanomas. We discovered that frequency of allelic imbalance was significantly higher in metastatic tumors (n = 36 of 98; 37%) than in primary melanomas (n = 10 of 54; 19%; P = 0.02). In metastatic melanomas, APAF-1 loss significantly correlated with a worse prognosis (P < 0.05) in the patients, and its loss during melanoma tumor progression suggests that APAF-1 is a tumor suppressor gene. Furthermore, loss of heterozygosity was frequent in the 12q22-23 chromosome region centromeric to the APAF-1 locus suggesting that other tumor-related genes may be present in the 12q22-23 region. In summary, the study demonstrates that allelic imbalance in the 12q22-23 region is a genomic surrogate of poor disease outcome for cutaneous melanoma patients.

The TP53 Tumor Suppressor Gene and Melanoma Tumorigenesis: Is There a Relationship?

Mutations in the TP53 gene are found in about 11% of melanomas. Although nearly 600 papers have been published with varying degrees of consensus, there does not appear to be any comparable analysis that facilitates more than a glimpse into the role of p53 in melanomagenesis. This article reviews p53 alterations (at the gene and protein levels) in melanocytic skin lesions and discusses the following points: (i) p53 alterations commence as early as at the stage of benign and dysplastic nevi; (ii) these alterations are frequent in melanomas, and gradually increase with their progression; (iii) there is no concordance between the frequent p53 protein expression and the rarity of both TP53 gene mutations in melanomas, and (iv) the entire p53 pathway is a more critical determinant of the fate of the melanocytic skin lesions than the status of the p53 protein or the gene itself.

Inhibition of c-Myc oncoprotein limits the growth of human melanoma cells by inducing cellular crisis

Here, we show that inhibition of c-Myc causes a proliferative arrest of M14 melanoma cells through cellular crisis, evident by the increase in size, multiple nuclei, vacuolated cytoplasm, induction of senescence-associated beta-galactosidase activity and massive apoptosis. The c-Myc-induced crisis is associated with decreased human telomerase reverse transcriptase expression, telomerase activity, progressive telomere shortening, glutathione (GSH), depletion and, increased production of reactive oxygen species. Treatment of control cells with L-buthionine sulfoximine decreases GSH to levels of c-Myc low expressing cells, but it does not modify the growth kinetic of the cells. Surprisingly, when GSH is increased in the c-Myc low expressing cells by treatment with N-acetyl-L-cysteine, cells escape crisis. To test the hypothesis that both oxidative stress and telomerase dysfunction are involved in the c-Myc-dependent crisis, we directly inhibited telomerase function and glutathione levels. Inactivation of telomerase, by expression of a catalytically inactive, dominant negative form of reverse transcriptase, reduces cellular lifespan by inducing telomere shortening. Treatment of cells with L-buthionine sulfoximine decreases GSH content and accelerates cell crisis. Analysis of telomere status demonstrated that oxidative stress affects c-Myc-induced crisis by increasing telomere dysfunction. Our results demonstrate that inhibition of c-Myc oncoprotein induces cellular crisis through cooperation between telomerase dysfunction and oxidative stress.

Human melanoma: drug resistance

Advanced malignant melanoma has a poor prognosis since chemotherapy is mostly ineffective because, in part, of the intrinsic and/or extrinsic resistance of melanoma cells to systemic treatment with antineoplastic agents. The reasons for the chemoresistant phenotype are currently unknown. The relevance of well-analyzed drug resistance mechanisms in melanoma such as intracellular and extracellular transport, drug resistance by induction of certain enzyme systems, and altered drug-target interaction is reviewed. It has been shown that most anticancer drugs kill susceptible cells through induction of apoptosis. Therefore, the significance of apoptotic deficiency caused by alteration in the apoptotic pathway is discussed in relation to specific molecules and apoptotic mechanisms like death-receptors, the Bcl-2 family, and the Hsp family of proteins. The complexity of the molecular variants involved in signal transduction along apoptotic pathways suggests that the cell may possess a variety of possibilities for regulating apoptosis and generating apoptosis deficiency. Thus apoptosis and apoptosis deficiency should be analyzed to understand the mechanisms of melanoma resistance.

p53 alone or in combination with antisense cyclin D1 induces apoptosis and reduces tumor size in human melanoma

Melanoma incidence is growing at a faster rate than any other human malignancy. Wild-type (wt) p53 is important in both G(1) and G(2) cell cycle arrest, and cyclin D1 (CD1) is necessary for G(1)-->S progression in melanoma cells. We reported that an adenoviral vector containing wt p53 significantly reduced [(3)H]thymidine uptake in melanoma cells containing mutant but not wt p53. Subsequently we showed that CD1 decreased melanoma proliferation and increased apoptosis. We now extend these findings by evaluating the effect on preformed melanomas of (1) intratumoral therapy with wt p53 alone, (2) wt p53 in combination with antisense (AS) CD1, both short (< or =14 days) and longer term, and (3) doubling the dose or repeat doses of wt p53 or AS CD1. Two melanoma cells lines that metastasize in SCID mice (451 and 1205) were used, one containing a p53 mutation (451) and the other a normal p53 gene sequence (1205). Compared to injection with a control adenoviral vector containing beta-galactosidase (LacZ), intratumoral injection of wt p53 slowed the growth of tumors formed from 451 cells. Using 5 x 10(8) plaque forming units as our standard intratumoral dose, neither doubling the dose of LacZ, p53 or AS CD1, nor repeat doses of the vectors, was as effective as combined therapy with wt p53+AS CD1, which resulted in the shrinkage of all tumors treated and 4/7 (57%) tumors vanished. No tumors treated with wt p53 or AS CD1 alone vanished. Wt p53+AS CD1 treatment resulted in significantly more cells undergoing apoptosis compared to either therapy alone. In summary, combining the separately effective treatment vectors p53 and AS CD1 led to an enhanced growth-suppressive and apoptotic effect, supporting a role for combination gene therapy to treat human malignant melanoma.

Dolastatin-10 in metastatic melanoma: a phase II and pharmokinetic trial of the California Cancer Consortium

Dolastatin-10 is a novel pentapeptide agent originally isolated from the marine mollusk Dolabella auricularia with a mechanism of antitumor activity that involves the inhibition of microtubule assembly. We performed a Phase II trial of Dolastatin-10, 400 microg/m2 in patients with advanced melanoma who had received no prior chemotherapy. Dolastatin-10 pharmokinetics were evaluated in a subset of patients following courses 1 and 2. Twelve patients were treated with a median of 2 cycles of Dolastatin-10, and no patient experienced an objective response. The only grade >2 toxicities were grade 3 neutropenia uncomplicated by infection, occurring in 4 patients following the first treatment cycle. The total systemic clearance and volume of distribution at steady-state were 2.61 +/- 1.9 L/h/m2 and 28.4 +/- 13 L/m2, respectively. Due to prolonged terminal elimination. Dolastatin-10 plasma concentrations of greater than 1 nM were sustained for 24 h in all patients studied. Dolastatin-10 is unlikely to have substantial activity in the treatment of melanoma.

The protein phosphatase 2A subunit Bgamma gene is identified to be differentially expressed in malignant melanomas by subtractive suppression hybridization

Several genes implicated in the development of various malignancies appear to be of minor relevance in melanoma. We therefore aimed to find a tumour suppressor candidate involved in this malignancy by comparing gene expression in uncultured primary melanoma specimens with those in acquired melanocytic naevi, from which quite often melanomas are known to arise. Applying the subtractive suppression hybridization technique, we generated a subtracted library of candidate genes downregulated in melanoma. Among the cDNA fragments identical to known genes, this library included a cDNA fragment 630 bp in length that is identical to the gene for the human protein phosphatase 2A (PP2A) regulatory subunit B (B56) gamma isoform (PP2A-Bgamma, PPP2R5C). On further evaluation of 15 primary melanoma and 16 acquired melanocytic naevus tissue specimens from independent patients using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis, expression of this gene was found to be suppressed in melanomas compared with naevi; the difference was statistically significant. As PP2A is known to be a major cellular serine-threonine phosphatase, and has been implicated not only in the regulation of cell growth and division but also in the control of gene transcription and growth factor signal transduction, alterations in the pattern of the regulatory subunits may affect substrate specificity and subcellular localization of the PP2A holoenzyme in melanoma cells.

Malignant melanoma

CONTEXT

The rapidly developing fields of melanoma research are revolutionizing the current concepts on melanoma etiology and pathogenesis and are introducing newer diagnostic techniques and potential therapeutic approaches.

OBJECTIVES

To present the most current concepts on the etiology and pathogenesis of melanoma and to introduce the recent diagnostic techniques and the potential therapeutic approaches.

METHODS

Data sources were reports on melanoma published in the English language literature and observations made using specimens available at Harvard University, Johns Hopkins Medical Center, Albany Medical College, Loyola University Medical Center, and University of Tennessee Health Science Center.

RESULTS

Studies on melanoma containing chromosomal or genetic evaluation were selected for further analysis. Current clinical and pathologic categories with the reported genetic abnormalities were related to the latest information on pigment biology. The data extracted were used to develop a conceptual framework on the pathogenesis of melanoma; the generated model was then evaluated and used to suggest potential therapeutic approaches.

CONCLUSIONS

(1) Melanoma is not genetically homogeneous, and the existing differences between the pathologic categories, particularly in areas such as type of growth phase (radial vs vertical growth), total vertical dimension, ulceration of primary tumor, and metastatic process, have profound prognostic and therapeutic implications. (2) Chromosomal aberrations and gene mutations are found in sporadic and familial melanomas; among the most important are those affecting the 9p21, which contains the p16 locus, a site known to be critical for normal progression of the cell cycle. Aberrant p16 expression is associated with more aggressive behavior. (3) Melanoma cells possess a remarkable repertoire of biosynthetic capacities represented by the production of hormones, growth factors, and their receptors that may sustain and accelerate tumor development and progression. For example, expression of the tumoral products alpha-melanocyte-stimulating hormone and adrenocorticotropic hormone is regulated in vitro by ultraviolet light, a known carcinogen. (4) Melanomas differ from other tumors in their intrinsic capability to express melanogenic enzymes with the corresponding structural proteins to actually synthesize melanin. Melanogenesis-related proteins are rapidly entering the clinical arena, being used not only as diagnostic markers, but also as potential targets for melanoma therapy.

Drug-resistance in human melanoma

Advanced malignant melanoma has a poor prognosis since chemotherapy is mostly ineffective due in part to the intrinsic and/or extrinsic resistance of melanoma cells to systemic treatment with anti-neoplastic agents. The reasons for the chemoresistant phenotype are unknown. The relevance of well-analyzed drug-resistance mechanisms, e.g., intracellular/extracellular transport and induction of certain enzyme systems, is reviewed. Most anti-cancer drugs kill susceptible cells through induction of apoptosis. Therefore, it appears that differences in the apoptotic pathways which lead to apoptotic deficiency may account for the ability of some tumor cells to resist drug therapy. Human melanomas, which are characteristically drug-resistant, are more likely to have altered apoptotic pathways and fewer pro-apoptotic molecules. Tumor cells with these characteristics are seldom sensitive to drugs. The complexity of the molecular variants involved in signal transduction along apoptotic pathways suggests that the cell may have a variety of possibilities for regulating apoptosis and generating apoptotic deficiency. Thus, apoptosis and apoptotic deficiency should be analyzed to better clarify the mechanisms of melanoma resistance.

Downregulation of the type 1 insulin-like growth factor receptor in mouse melanoma cells is associated with enhanced radiosensitivity and impaired activation of Atm kinase

The type 1 insulin-like growth factor receptor (IGF1R) is required for growth, tumorigenicity and protection from apoptosis. IGF1R overexpression is associated with radioresistance in breast cancer. We used antisense (AS) RNA to downregulate IGF1R expression in mouse melanoma cells. Cells expressing AS-IGF1R transcripts were more radiosensitive in vitro and in vivo than controls. Also they showed reduced radiation-induced p53 accumulation and p53 serine 18 phosphorylation, and radioresistant DNA synthesis. These changes were reminiscent of the cellular phenotype of the human genetic disorder ataxia-telangiectasia (A-T), caused by mutations in the ATM gene. Cellular Atm protein levels were lower in AS-IGF1R-transfected cells than in control cells, although there was no difference in Atm expression at the transcriptional level. AS-IGF1R cells had detectable basal Atm kinase activity, but failed to induce kinase activity after irradiation. This suggests that IGF1R signalling can modulate the function of Atm, and supports the concept of targeted IGF1R downregulation as a potential treatment for malignant melanoma and other radioresistant tumours.

Second malignancies in melanoma patients in Thuringia

OBJECTIVE

The incidence of melanoma is increasing. Melanoma patients are at risk for the development of second neoplasias. Data for the new German Bundesländer are not available, but would be suitable to define frequency, site and type of secondary malignancies and conclusions for follow-up of melanoma patients.

DESIGN

Retrospective study at the Melanoma Outpatient Clinic of the Department of Dermatology and Allergology at the University of Jena (Germany) for patients seen between June 1966 and June 1999. To investigate the impact of second malignancies on survival a case-comparison study of mortality was performed. The log-rank test and chi2-test were used to investigate statistical significance. There were 554 patients with malignant melanoma, 237 male and 317 female, with an age at time of diagnosis between 17.0 and 90.1 years (mean 53.7 years). The mean follow-up was 5.6 years.

RESULTS

Sixty-one patients (11.0%) developed a second tumour. The total number of tumours was 83. Forty-five patients developed one, 16 developed > or = 2 second tumours. Basal cell carcinoma (BBC) was the most frequent neoplasia (17 patients, 22 tumours; mean age 64.9 years). A second melanoma was found in 15 patients, while two developed a third melanoma. The mean tumour thickness was 0.81 mm (in second or third melanomas) compared with 1.92 mm of primary melanomas. Seven female patients developed breast cancer (eight cancers; mean age 57.3 years). The other second tumours included skin cancer (eight), gastrointestinal tract tumours (four), genital cancers (19), brain tumours (two), lung cancer (two) and other tumours (six). The difference in survival of patients with second tumours was not statistically significant from age-, sex- and melanoma thickness-matched controls.

CONCLUSIONS

Second malignancies were seen in 11.0% of melanoma patients. Most important are second skin tumours such as second melanomas and BCC, recommending follow-up by the dermatologist. In a group of patients with regular follow-up examinations, no negative impact of second tumours (BCC, melanoma, breast cancer) on overall survival could be detected.

Analysis of G(1)/S checkpoint regulators in metastatic melanoma

We have analyzed the expression of the CDKN1A (p21(CIP1)), CDKN1B (p27(Kip1)), TP53, RB1 and MDM2 proteins and tumor cell proliferation by immunohistochemical staining in 59 cases of metastatic melanoma. The genomic status of the CDKN2A (INK4-ARF, p16/p14(ARF)), CDKN2B (p15) and CDKN2C (p18) genes was determined by PCR-SSCP (single-strand conformation polymorphism) in 46 of these cases. These results were correlated with various clinico-pathological parameters, including the outcome of combined chemoimmunotherapy. We found positive correlations between the expression of CDKN1A and MDM2 (r = 0.5063, P = 0.001), between the expression of CDKN1B and RB1 (r = 0.5026, P = 0.001), and between RB1 expression and tumor cell proliferation (0.5564, P<0.001). Two mutations in the CDKN2A (p16) gene were detected, including a novel base change AAC-->ATC (Asn to Ile) at codon 71, that also changes the codon 85 of the alternative reading frame gene p14(ARF) from CAA to CAT (Gln to His). Homozygous deletion at exon 2 of the CDKN2A (INK4-ARF) gene was detected in six cases. In seven cases, the 540C-->G polymorphism in the 3'UTR of the CDKN2A (p16) gene was found in linkage disequilibrium with the 74C-->A polymorphism in intron 1 of the CDKN2B gene (P < 0.0001). These cases had significantly lower expression of the TP53 protein (P = 0.0032). Both 540C-->G and 580C-->T polymorphisms in the 3'UTR of the CDKN2A (p16) gene were associated with significantly shorter progression time from primary to metastatic disease (P = 0.0071). We conclude, that although none of the analyzed cell cycle regulators could be singled out as a major prognostic factor, G(1)/S checkpoint abnormalities remain one of the most significant factors in the development of malignant melanoma.

Cell cycle and melanoma--two different tumours from the same cell type

Melanoma of the uvea of the eye and melanoma of the skin share a common cell of origin, but differ substantially in their behaviour and response to chemotherapy. There is increasing evidence that this is related to differences in their molecular phenotype, particularly in relation to the expression of cell cycle-associated proteins. Since many cytotoxic agents act by damaging DNA, resistance is often associated with intact mechanisms which allow the neoplastic cells to arrest their growth while DNA is repaired, or to resist apoptosis in response to detection of DNA damage. p53 is important to these processes, but mutation appears to be a less common event in uveal melanoma than in skin melanoma, probably due to the lack of UV exposure in the uvea. There are also differences in proliferation-associated proteins such as c-myc and cyclin D1. Overexpression of the former molecule is associated with a poor prognosis in skin melanoma, but is associated with a good prognosis in uveal melanoma, although there is considerable genetic heterogeneity within each type. While prognostic studies may therefore be of little relevance to individual patients, they continue to inform our understanding of tumour biology.

Wild-type p53 gene transfer inhibits invasion and reduces matrix metalloproteinase-2 levels in p53-mutated human melanoma cells

The tumor suppressor gene p53 has inhibitory effects on cell growth and angiogenesis and induces apoptosis when overexpressed in melanoma and in a variety of tumor cells by adenovirus-mediated gene transfer. The invasive ability of tumor cells, facilitating local infiltration and metastasis, is related to matrix metalloproteinase levels. In melanoma, matrix metalloproteinase-2 and matrix metalloproteinase-9 have a prominent role in this process. The aim of this study was to evaluate whether wild-type p53 overexpression, obtained by a recombinant adenovirus vector (AdCMV.p53), affects cell invasiveness through modulation of matrix metalloproteinase-2 and matrix metalloproteinase-9. Two human melanoma cell lines were used in this study: the SK-MEL-110, carrying a mutated p53 gene, and the SK-MEL-147, carrying the wild-type p53 gene. SK-MEL-110 cells infected with AdCMV.p53 exhibited decreased invasion capability from day 1 after infection, compared with cells not infected or infected with the control vector AdCMV.Null. This reduced invasiveness was associated with decreased matrix metalloproteinase-2 levels in conditioned media whereas no changes were detected in matrix metalloproteinase-9 secreted levels. No modulation in matrix metalloproteinase-2 mRNA levels was detectable, however, after wild-type p53 gene transfer. Furthermore, protein expression of secreted tissue inhibitor of metalloproteinase-2 was not altered by AdCMV.p53 treatment. In contrast, in SK-MEL-147 cells, AdCMV.p53 did not affect cell invasiveness and levels of secreted matrix metalloproteinase-2. Gene transfer of wild-type p53 inhibited proliferation of both cell lines, showing that also SK-MEL-147 cells respond to wild-type p53 overexpression. This novel mechanism of action of wild-type p53 gene transfer may contribute to its antitumor effect by downregulating cell invasion and matrix metalloproteinase-2 secreted levels in mutated p53 human melanoma cell lines.

p53-dependent apoptosis in melanoma cells after treatment with camptothecin

Cutaneous malignant melanoma is a life-threatening cancer with poor prognosis due to a high metastasis potential. The main obstacle in treatment of metastatic melanoma is the resistance to chemotherapy. Recent studies indicated that apoptosis is a common mechanism of action for various cytotoxic agents. As p53 plays an important part in apoptosis, we investigated the role of p53 in chemosensitivity of melanoma cells. Previously, we found that melanoma cell lines containing wild-type p53 have significantly higher response rates to chemotherapy than cell lines with a mutant p53 gene. To confirm the role of p53 in melanoma chemosensitivity further, we transfected an expression vector, pED1, which carries a mutant p53 gene, into a wild-type p53 melanoma cell line, MMAN. We examined the effect of mutant p53 on camptothecin-induced apoptosis and the expression of genes which are known to be involved in apoptosis or drug resistance, such as bcl-2, bax, bak, p21waf1, and P-glycoprotein. Our results indicate that overexpression of the mutant p53 increased the growth rate of MMAN cells, reduced the sensitivity to camptothecin, and lowered drug-induced apoptosis by 2-3-fold. Flow cytometry indicated that the camptothecin-induced apoptosis is not associated with G1 arrest. Furthermore, camptothecin treatment reduced bcl-2 and P-glycoprotein expression in wild-type p53 MMAN cells, but not cells overexpressing mutant p53. These results demonstrate that p53 mutational status is a determinant of melanoma chemosensitivity. p53 may downregulate bcl-2 and P-glycoprotein to induce apoptosis in melanoma cells after chemotherapy.

Lack of p73 mutations and late occurrence of p73 allelic deletions in melanoma tissues and cell lines

A novel gene, termed p73 with significant homology to p53, has been identified at 1p36, a chromosomal region which is frequently deleted in malignant melanoma. To determine whether p73 is involved in melanoma development we analyzed 8 benign melanocytic nevi, 17 primary melanomas, 34 melanoma metastases and 9 melanoma cell lines for p73 alterations. Allelic loss at the p73 locus was observed in 2 of 10 cases (20%) and occurred only in metastatic tumors. Mutation analysis of the DNA-binding domain of p73 revealed no somatic mutations in the tumor specimens and melanoma cell lines analyzed, whereas the p53 gene was mutated in 5 of 9 melanoma cell lines. Expression analysis of p73 using semiquantitative RT-PCR demonstrated that p73 is not expressed or at exceedingly low levels in benign melanocytic nevi, primary melanomas and lymph node metastases, but at various levels in melanoma cell lines. Our data indicate that p73 does not play a role as a tumor suppressor in melanoma development.

Apoptosis in neuroendocrine tumours

Acquired resistance to apoptosis in neuroendocrine tumours (NETs) may promote clonal expansion and enhance the likelihood that subsequent mutations lead to growth or persistence of the neoplastic clone. Recent studies have demonstrated that deregulation of programmed cell death may be a critical component in multistep tumourigenesis of NETs and that the frequent expression of the Bcl-2 oncoprotein in these tumours may contribute to their pathogenesis. The genetic complementation of simultaneously deregulated Bcl-2 and c-Myc may be implicated in the multistep tumourigenesis of human NETs. Furthermore, because the efficacy of cytotoxic chemotherapy relies on its ability to induce programmed cell death, resistance to apoptosis typically correlates with chemoresistance, a phenomenon that is typical in NETs. Consideration of how oncogenes affect rates of cell death, in addition to augmenting growth, has already provided valuable insights into the biology of cancer. Understanding the molecular and cellular features of this process may enable the development and application of more effective and potentially curative treatment strategies in which the induction of programmed cell death is an integral component.

p53 mutations in human cutaneous melanoma correlate with sun exposure but are not always involved in melanomagenesis

In melanoma, the relationship between sun exposure and the origin of mutations in either the N-ras oncogene or the p53 tumour-suppressor gene is not as clear as in other types of skin cancer. We have previously shown that mutations in the N-ras gene occur more frequently in melanomas originating from sun-exposed body sites, indicating that these mutations are UV induced. To investigate whether sun exposure also affects p53 in melanoma, we analysed 81 melanoma specimens for mutations in the p53 gene. The mutation frequency is higher than thus far reported: 17 specimens (21%) harbour one or more p53 mutations. Strikingly, 17 out of 22 mutations in p53 are of the C:G to TA or CC:GG to TT:AA transitional type, strongly suggesting an aetiology involving UV exposure. Interestingly, the p53 mutation frequency in metastases was much lower than in primary tumours. In the case of metastases, a role for sun exposure was indicated by the finding that the mutations are present exclusively in skin metastases and not in internal metastases. Together with a relatively frequent occurrence of silent third-base pair mutations in primary melanomas, this indicates that the p53 mutations, at least in these tumours, have not contributed to melanomagenesis and may have originated after establishment of the primary tumour.

Enhanced expression of Ki-67, topoisomerase IIalpha, PCNA, p53 and p21WAF1/Cip1 reflecting proliferation and repair activity in UV-irradiated melanocytic nevi

To investigate the effect of ultraviolet (UV) irradiation on the expression of cell cycle-associated proteins, melanocytic nevi from healthy volunteers were partially covered, irradiated with a defined UV dose, and excised 1 week thereafter. The irradiated and the protected parts were examined separately by conventional microscopy and immunohistochemistry using the antibodies Ki-S11 (Ki-67), Ki-S7 (topoisomerase IIalpha), PC10 (proliferating cell nuclear antigen [PCNA]), DO-7 (p53), 6B6 (p21WAF1/Cip1), and the melanocytic marker HMB-45. DNA nick-end labeling was used as a marker of apoptosis. Irradiation resulted in morphological changes and increased HMB-45 reactivity. Proliferation, as assessed by Ki-67 and topoisomerase IIalpha expression, was also clearly enhanced in the UV-exposed areas. This was confirmed by the appearance of occasional mitotic figures. PCNA expression levels markedly exceeded those of the proliferation markers and did not correlate with the latter in most cases. p21 immunolabeling indices were also consistently augmented after UV exposure; hence it is likely that growth-inhibitory mechanisms partly compensate for the proliferative impulse, and the disproportional rise in PCNA expression probably reflects DNA repair activity. Enhanced p53 immunostaining in four cases suggests that the induction of p21 after irradiation may be p53 mediated, whereas no concomitant apoptotic events were observed. We conclude that UV light can stimulate the proliferative activity of melanocytes in melanocytic nevi, but that simultaneously cell cycle inhibitors are activated to permit DNA repair.

Molecular and cellular effects of ultraviolet light-induced genotoxicity

Exposure to the solar ultraviolet spectrum that penetrates the Earth's stratosphere (UVA and UVB) causes cellular DNA damage within skin cells. This damage is elicited directly through absorption of energy (UVB), and indirectly through intermediates such as sensitizer radicals and reactive oxygen species (UVA). DNA damage is detected as strand breaks or as base lesions, the most common lesions being 8-hydroxydeoxyguanosine (8OHdG) from UVA exposure and cyclobutane pyrimidine dimers from UVB exposure. The presence of these products in the genome may cause misreading and misreplication. Cells are protected by free radical scavengers that remove potentially mutagenic radical intermediates. In addition, the glutathione-S-transferase family can catalyze the removal of epoxides and peroxides. An extensive repair capacity exists for removing (1) strand breaks, (2) small base modifications (8OHdG), and (3) bulky lesions (cyclobutane pyrimidine dimers). UV also stimulates the cell to produce early response genes that activate a cascade of signaling molecules (e.g., protein kinases) and protective enzymes (e.g., haem oxygenase). The cell cycle is restricted via p53-dependent and -independent pathways to facilitate repair processes prior to replication and division. Failure to rescue the cell from replication block will ultimately lead to cell death, and apoptosis may be induced. The implications for UV-induced genotoxicity in disease are considered.

Frequent mutations of the p53 gene in cutaneous melanoma of the nodular type

The frequency and significance of p53 alterations in cutaneous melanoma have not been completely clarified. In the present study, 31 primary melanomas of the nodular type and 15 metastases occurring between 1981 and 1983 were studied with respect to mutations in exons 7 and 8, as well as to p53 protein immunostaining using different antibodies. Altogether 13% of the primary tumors showed strong p53 staining using the DO-7 antibody. Different results were obtained with other antibodies. Seven mutations were found in primary and metastatic tumors; all of these were single base changes, most of which occurred in the core domain of the p53 protein responsible for sequence-specific DNA binding (residues 102-293). The mutations were not significantly associated with p53 staining results, and p53 alterations (mutations or marked immunopositivity) had no prognostic value. Our results indicate that point mutations in exons 7 and 8 are more frequent than previously reported in primary melanomas, and such changes may be important for the development of certain melanoma subgroups.

Prognostic implications of p53 overexpression in cutaneous melanoma from sun-exposed and nonexposed sites

BACKGROUND

There is increasing evidence that mutations in the p53 tumor suppressor gene are among the most common genetic alterations in human malignancies. Because ultraviolet light can induce specific p53 mutations and is linked to the development of skin cancers, this study was done to determine the significance of p53 protein (p53p) overexpression in melanomas originating at different cutaneous sites varying in frequency of sunlight exposure.

METHODS

Sixty-three paraffin embedded primary and metastatic melanoma biopsy specimens from 61 patients were deparaffinized and stained with the mouse monoclonal antibody DO-1 to wild-type and mutant p53p. Twenty-eight specimens were from primary tumors and 35 specimens were from lymph node, subcutaneous, or visceral metastases. The chi-square test was used to assess the significance of p53p overexpression, and the Cox proportional hazards model was used to estimate the impact of p53p overexpression on survival.

RESULTS

Of the 61 patients studied, 37 had primary cutaneous melanomas arising on chronically sun-exposed head and neck sites, 12 patients on intermittently exposed extremity sites, and 12 patients on rarely exposed trunk sites. Thirteen of the 63 primary or metastatic specimens (21%) overexpressed p53p. Overexpression of p53p was not related to patient gender or age, anatomic site of the primary tumor, Clark level, or Breslow thickness. However, those patients with p53p positive primary tumors or metastases had significantly better survival than those determined to be negative for p53p overexpression (P = 0.045). The median survival was 152.4 months for p53p positive patients versus 55.7 months for p53p negative patients. The risk ratio of dying from melanoma was 0.32 for patients with tumor specimens overexpressing p53p.

CONCLUSIONS

In this study, p53p overexpression was infrequent in paraffin embedded melanoma specimens and independent of the primary melanoma's anatomic site. Although p53p overexpression was not related to other prognostic features of primary or metastatic lesions, it was associated with a significantly improved survival in this group of melanoma patients.

Alterations and prognostic significance of p16 and p53 protein expression in subgroups of cutaneous melanoma

The role of p16 and p53 alterations in cutaneous melanoma has been recently discussed, but it remains to be clarified. In the present immunohistochemical study, the expression of p16 and p53 proteins and their possible prognostic relevance have been examined in 102 melanomas of the aggressive nodular type. Twelve percent showed a strong expression of p53 protein, and these cases were significantly more frequent in the head/neck area compared with other sites (32% vs. 6%). Expression of p16 protein was negative or weak in 9% of the cases, and this tended to be less frequent in head/neck tumors compared with the others (0% vs. 12%). Whereas p53 staining was not prognostically important, loss of p16 staining was significantly associated with markedly reduced recurrence free and patient survival in univariate analysis (product-limit method). In multivariate analysis, lack of p16 staining was significantly associated with recurrent disease (p = 0.013). Our findings indicate an important role of altered p16 protein expression in a subgroup of melanoma patients.