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Advances in Brief |
Service de Génétique [K. L., C. K., G. M. L., B. B-d. P.], Service de Dermatologie [M-F. A.], and Département de Médecine [A. S.], Institut Gustave Roussy, 94800 Villejuif, Cedex; Service de Génétique Oncologique [D. S-L.] and Service dOphtalmologie [L. D.], Institut Curie, 75248 Paris Cedex 5; Institut Curie, Centre National de la Recherche Scientifique, Cedex [A. E.]; and Unité Inserm, 91034 Evry Cedex [F. D.], France
| ABSTRACT |
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| Introduction |
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The Ras-RAF-MAP kinase pathway is a membrane-to-nucleus signaling cascade of molecules involved in the regulation of cell proliferation in response to extracellular mitogenic signals (reviewed in Ref. 16
). In melanocytes (pigment-producing cells), the binding of
-melanocyte stimulating-hormone and other
-melanocyte stimulating-hormone-related proopiomelanocortin-derived peptides to the melanocortin-1 receptor, induces proliferation and melanogenesis in response to ultraviolet (UV) A/B radiation via the activation of two specific kinases, BRAF and ERK (17)
. Different observations suggest that this pathway plays a major role in the development of melanoma. In mice, aberrant activation of this pathway appears to be necessary for the development of melanoma (18)
. Indeed, in a doxycline-inducible V12GH-RAS mouse melanoma model, null for the tumor suppressor gene CDKN2A, i.e. both p16INK4A- and p19ARF-deficient, the genesis and maintenance of melanoma are strictly dependent on the expression of V12GH-RAS. In humans, mutations of the genes involved in this MAP kinase pathway are detected in melanomas. RAS mutations are found in
25% of primary melanomas and 50% of congenital melanocytic nevi (19)
. Recently, BRAF somatic missense mutations were shown to occur in 66% of malignant melanoma (20
, 21)
. All of the mutations are within the kinase domain, with a hotspot single substitution V599E in exon 15 detected in 80% of nevi (22)
and primary melanoma (22)
, and in 60% of melanoma cell lines (20)
. Functionally, mutated V599EBRAF proteins display elevated kinase activity and transform NIH3T3 cells (20)
. All together, these data indicate that BRAF activation is an early and critical step in the initiation of melanocytic neoplasia. We hypothesized that BRAF could be a melanoma susceptibility gene.
To date, four oncogenes have been demonstrated to be susceptibility genes for familial cancers: CDK4 in melanoma, RET in multiple endocrine neoplasia type 2, MET in papillary renal cell carcinoma, and KIT in familial gastrointestinal stromal tumors. As the somatic BRAF mutations, including V599E, result in 50-fold lower transforming activity than V12GHRAS in the NIH3T3 cell line, it is conceivable that BRAF germline mutations could predispose to melanoma. Thus, we also postulated that BRAF germline mutations could be responsible for dysplastic nevi considered as a precancerous phenotype by analogy with C-cell hyperplasia seen in RET oncogene carriers before the occurrence of medullary thyroid carcinoma.
To evaluate the BRAF gene as a candidate in melanoma predisposition, we screened the entire BRAF coding region (exons 118) for germline mutations in 80 independent melanoma families or patients by sequencing analysis or dHPLC analysis. Patients tested were either index cases in melanoma-prone families or multiple melanoma patients. The inclusion criteria were cutaneous melanoma-prone families including families with DNS, patients with multiple cutaneous primary melanoma without a familial history, families with cutaneous melanoma and NSTs, and uveal melanoma-prone families (Table 1)
. The rationale for inclusion of these last two categories was, respectively: (a) BRAF proteins are expressed at high levels in adult mouse neural tissues (23)
and 11% of human glioma cell lines present V599E, the hotspot mutation (20)
; and (b) transgenic mice overexpressing H-RAS developed cutaneous but also ocular tumors spontaneously (24)
, yet no uveal susceptibility gene has been identified to date. Moreover, uveal and skin melanocytes have the same embryonic origin (the neural crest), and cells originating from this lineage are known to express BRAF (16
, 17)
.
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| Materials and Methods |
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The 80 melanoma families or sporadic cases were (Table 1)
: (a) 23 cutaneous melanoma-prone families (>3 melanoma cases) including 13 melanoma-prone families with DNS; (b) 12 cutaneous melanoma-prone families (2 melanoma cases including a multiple case); (c) 16 patients with multiple cutaneous primary melanoma (patients who developed at least 3 primary melanomas); (d) 11 cutaneous melanoma-prone families with joint proneness to melanoma and NSTs; and (e) 18 uveal melanoma families (2 uveal melanoma cases or uveal and cutaneous melanoma cases or multiple uveal melanoma cases). For all of the subjects, the search for CDKN2A/p16INK4A/p14ARF and CDK4 germline mutations was negative. All of the melanoma cases were confirmed by pathological reports. Written informed consent was obtained for all of the subjects before participation in the study under a protocol approved by the internal as well as an external Institutional Review Board (Hospital Necker, Paris, France).
Controls were constituted of lymphoblastoid DNA samples from 91 breast and/or ovarian cancer patients free of melanoma. These DNA samples were considered as waste and used anonymously.
Mutation Analysis of the BRAF Gene
DNA Samples and PCR.
Genomic DNA was extracted from peripheral blood lymphocytes, using the QIAamp DNA blood mini kit (Qiagen, Chatsworth, CA) according to the manufacturers instructions. The coding exons and intron-exon junctions of the BRAF gene were screened for mutations by direct sequencing of exons 11 and 15, and by dHPLC followed by sequencing of abnormal profiles for the 16 other exons. PCR primers were designed to amplify each exon including at least 50100 bp of flanking intronic sequences and primers were chosen with the assistance of the computer program Oligo Version 4.0. Primer sequences and the size of the PCR products for the different BRAF exons are described in Table 2
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Sequencing Analysis.
To screen BRAF exons 11 and 15 for germline mutations, PCR products were bidirectionally sequenced with the Big Dye Terminator sequencing kit, using the same primers as those used for PCR. PCR products were purified by solid-phase extraction through Sephacryl S400-HR (Pharmacia) and subsequently analyzed using an ABI 377 sequencer (Perkin-Elmer, Applied Biosystem).
dHPLC Analysis.
Screening for germline mutations in exons 118 excluding exons 11 and 15 was performed by dHPLC analysis, an automated method for heteroduplex detection. To obtain the heteroduplex, the PCR products were heat-denatured at 95°C for 5 min followed by gradual cooling from 95°C down to 25°C (0.1°C/s) to allow reannealing. Analyses were carried out on an automated dHPLC (Wave; Transgenomic) instrument. The PCR products were eluted from the column using an acetonitrile gradient in a 0.1 M triethylamine acetate buffer (pH 7.0), at the constant flow rate of 1.5 ml/min. Samples displaying abnormal profiles were subsequently sequenced with the Big Dye Terminator sequencing kit, as described previously. This method allows heterozygote patients to be detected but cannot discriminate wild-type/wild-type and mutant/mutant homozygotes.
Statistical Analysis.
The
2 test was used to compare the frequency of heterozygotes for each BRAF variant between melanoma cases and control groups.
| Results and Discussion |
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BRAF somatic missense mutations in melanoma and nevi were detected in exons 11 and 15 within the kinase domain of the BRAF gene (CR3 domain; Fig. 1
). The most frequent mutations involved either codon 599 with a mutational hotspot, V599E, located in exon 15 within the kinase activation loop or codons 463 (G463E and G463V) and 465 (G465A, G465E, and G465V) that participate in the G-loop and codon 438 (K438Q) located in exon 11 (20
, 21) . We first sequenced BRAF exons 11 and 15 for each index case in the 80 melanoma-prone families or individuals selected. No mutation was detected in BRAF exon 15 in these patients. In BRAF exon 11, we detected a silent germline single-base substitution G1299A that did not change amino acids at position 443 (R443R), in 1 patient. This variant was not detected in the other 2 melanoma patients in these 3 melanoma kindred cases. No germline mutations were detected in this study at the molecular hotspots described in nevi, primary melanoma, and melanoma cell lines (20, 21, 22)
.
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The potential pathogenicity of each BRAF variant was assessed by studying segregation with melanoma in 11 families through sequencing analysis of all of the available family members. None of the BRAF variants cosegregated fully with melanoma in the families tested (Table 3)
. In addition, no specific BRAF variant segregated in families with patients affected by both melanoma and DNS (data not shown). Moreover, no variant was specifically associated with any clinical subgroups, i.e., CMM families, multiple primary melanoma cases, CMM and NSTs families, or uveal melanoma families. The absence of the two most frequent BRAF variants exhibiting linkage disequilibrium (G642G and IVS16 + 16G>C) in clinical subgroups 2 and 4 was probably because these groups were small, 12 and 11 patients, respectively (Table 4)
. These observations suggest that the different variants detected in 80 melanoma-prone index cases are probably not germ-line mutations conferring a high risk of developing melanoma in carriers.
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2 test was used to compare the frequency of heterozygotes for each BRAF variant between individuals from melanoma-prone families and controls. No statistically significant difference was found, suggesting that BRAF germline variants are germline polymorphisms and are not low or moderate risk melanoma susceptibility alleles. Studies based on allelic frequencies rather than heterozygote frequencies may be required to corroborate our study. In conclusion, by screening the entire BRAF gene in 80 melanoma-prone individuals, we found 13 variants within the BRAF gene, 9 intronic nucleotide substitutions and 4 silent mutations in coding regions in 80 melanoma-prone families or cases. None of these variants segregated with disease in melanoma-prone families, and the frequency of heterozygotes for these variants did not differ significantly between melanoma cases and controls suggesting that BRAF variants are polymorphisms rather than disease-causing mutations. Consequently, our data suggest that BRAF is not a melanoma susceptibility gene. However, detection of BRAF somatic mutations in nevi does suggest that the BRAF mutations occur at a very early stage in melanoma pathogenesis.
Although BRAF somatic missense mutations have been reported at a very high frequency in nevi and melanoma, and at a lower frequency in many human cancers, our study shows that the BRAF gene does not seem to play any role in melanoma susceptibility. However, our negative results may suggest that other genes in the RAS-RAF-MAP kinase pathway play a role in melanoma susceptibility and should be tested for germline mutation in melanoma-prone families.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 Supported by a Program Hospitalier de Recherche Clinique (PHRC) Regional 2001 grant (AOR 01 091). K. L. is a recipient of a postdoctoral fellowship from Institut Gustave Roussy (CRC 2001). ![]()
2 French Hereditary Melanoma Study Group members who participated in this study: Drs. P. Andry-Benzaquen, M. Baccard, B. Bachollet, N. Basset-Seguin, M. Baspeyras, P. Berthet, J-M. Bonnetblanc, P. Blanchet, F. Boitier, V. Bonadona, F. Caux, J-P. Cesarini, J. Chevrant-Breton, D. Couillet, A-M. Courouge-Dorcier, L. Demange, C. Levy, O. Dereure, M. DIncan, M. Dore, E. Esteve, M. Frenay, V. Gaillard, I. Gorin, F. Grange, B. Guillot, P. Joly, L. Laroche, C. Lasset, D. Leroux, J-M. Limacher, M. Longy, L. Lumbroso, J-L. Michel, S. Negrier, L. Ollivaud, J-C. Ortoli, P. Robin, B. Sassolas, R. Triller, F. Truchetet, P. Vabres, and L. Verne. ![]()
3 To whom requests for reprints should be addressed, at Service de Génétique, Institut Gustave Roussy, 39, Rue Camille Desmoulins, 94800 Villejuif Cedex, France. Phone: 33-1-42-11-54-90; Fax: 33-1-42-11-52-66; E-mail: bressac{at}igr.fr ![]()
4 The abbreviations used are: CMM, cutaneous malignant melanoma; ERK, extracellular signal-regulated kinase; MAP, mitogen-activated protein; dHPLC, denaturing high-performance liquid chromatography; DNS, dysplasic naevus syndrome; NST, neural system tumor. ![]()
Received 1/ 8/03. Accepted 4/23/03.
| REFERENCES |
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