Journal of the National Cancer Institute Advance Access originally published online on May 27, 2008
JNCI Journal of the National Cancer Institute 2008 100(11):784-795; doi:10.1093/jnci/djn157
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© The Author 2008. Published by Oxford University Press.
ARTICLES |
Frequent p16-Independent Inactivation of p14ARF in Human Melanoma
Affiliations of authors: Ronald O. Perelman Department of Dermatology, New York University School of Medicine, New York, NY (DEF, JR, WG, MK, IO, DP); Section of Epidemiology and Biostatistics, Leeds Institute of Molecular Medicine, Cancer Research UK Clinical Centre, St James's University Hospital, Beckett Street, Leeds, UK (SHR, FT, JARM, DTB, JANB); Memorial Sloan-Kettering Cancer Center, New York, NY (AH, KB); Departments of Dermatology and Pathology and Comprehensive Cancer Center, University of California San Francisco, San Francisco, CA (BCB)
Correspondence to: David Polsky, MD, PhD, Department of Dermatology, New York University School of Medicine, 550 First Ave, New York, NY 10016 (e-mail: david.polsky{at}med.nyu.edu).
Background: The tumor suppressors p14ARF (ARF) and p16INK4A (p16) are encoded by overlapping reading frames at the CDKN2A/INK4A locus on chromosome 9p21. In human melanoma, the accumulated evidence has suggested that the predominant tumor suppressor at 9p21 is p16, not ARF. However, recent observations from melanoma-prone families and murine melanoma models suggest a p16-independent tumor suppressor role for ARF. We analyzed a group of melanoma metastases and cell lines to investigate directly whether somatic alterations to the ARF gene support its role as a p16-independent tumor suppressor in human melanoma, assuming that two alterations (genetic and/or epigenetic) would be required to inactivate a gene.
Methods: We examined the p16/ARF locus in 60 melanoma metastases from 58 patients and in 9 human melanoma cell lines using multiplex ligation-dependent probe amplification and multiplex polymerase chain reaction (PCR) to detect deletions, methylation-specific PCR to detect promoter methylation, direct sequencing to detect mutations affecting ARF and p16, and, in a subset of 20 tumors, immunohistochemistry to determine the effect of these alterations on p16 protein expression. All statistical tests were two-sided.
Results: We observed two or more alterations to the ARF gene in 26/60 (43%) metastases. The p16 gene sustained two or more alterations in 13/60 (22%) metastases (P = .03). Inactivation of ARF in the presence of wild-type p16 was seen in 18/60 (30%) metastases.
Conclusion: Genetic and epigenetic analyses of the human 9p21 locus indicate that modifications of ARF occur independently of p16 inactivation in human melanoma and suggest that ARF is more frequently inactivated than p16.
| CONTEXT AND CAVEATS Prior knowledge The role of p14ARF, whose reading frame overlaps that of the tumor suppressor p16INK4A, in human melanoma was unclear. Study design Using a variety of molecular assays, the p16/ARF locus was analyzed in melanoma metastases for mutations and promoter methylation. Contribution The study provided a detailed description of genetic and epigenetic changes at the p16/ARF locus in melanoma metastases. Inactivation of the gene encoding p14ARF occurred frequently, sometimes in the absence of p16 inactivation, suggesting that alterations in p14ARF function may play a role in melanoma pathogenesis. Implications Additional work is needed to define the relative contributions of alterations in p14ARF and p16 function to melanoma pathogenesis. Limitations Lack of an adequate antibody to p14ARF prevented the authors from measuring the changes in this protein's expression that corresponded to the genetic changes observed.
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Manuscript received September 20, 2007; revised March 21, 2008; accepted April 21, 2008.
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J Natl Cancer Inst 2008 100: 757-759.
J Natl Cancer Inst 2008 100: 755.
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  G. Peters Tumor Suppression for ARFicionados: The Relative Contributions of p16INK4a and p14ARF in Melanoma J Natl Cancer Inst, June 4, 2008; 100(11): 757 - 759. [Full Text] [PDF]
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