Virtually 100% of melanoma cell lines harbor alterations at the DNA level withinCDKN2A, CDKN2B, or one of their downstream targets

Abstract

The cyclin‐dependent kinase inhibitor 2A (CDKN2A), or p16INK4a, gene on 9p21 is important in the genesis of both familial and sporadic melanoma. Homozygous deletions and intragenic mutations of this gene have been identified in both melanoma cell lines and uncultured tumors, although the frequency of these alterations is higher in the cell lines. A proportion of melanoma cell lines and tumors without deletion/mutation of CDKN2A have also been determined to harbor transcriptionally inactive CDKN2A alleles or carry alterations in other components of the pathway through which p16 INK4a acts on pRb to mediate cell cycle arrest. We sought to determine the frequency of these alternative events (in relationship to those that specifically inactivate CDKN2A) in a panel of 45 melanoma cell lines. Surprisingly, at the DNA level alone, 96% (43/45) of melanoma cell lines examined were found to be deleted/mutated/methylated for CDKN2A (34/45), homozygously deleted for CDKN2A's neighbor and homolog CDKN2B (6/45), and/or mutated/amplified for CDK4 (5/45). In two of these 43 cases, homozygous deletions of CDKN2A were detected along with a CDK4 mutation or amplification of the cyclin D1 (CCND1) gene. The latter discoveries were made in two of three cell lines which harbored extremely large (3–6 Mb) homozygous deletions on 9p21; all other homozygous deletions in similarly affected cell lines (N = 23) were confined to a region immediately surrounding the CDKN2A/CDKN2B loci. These results suggest that (1) only melanoma cells with alterations in this pathway can be propagated in culture, and (2) the homozygous deletions on 9p21 in the cell lines, which are also mutated/amplified for CDK4 or CCND1, could serve to target tumor suppressor genes other than CDKN2A. Genes Chromosomes Cancer 22:157–163, 1998. © 1998 Wiley‐Liss, Inc.

Human melanocyte senescence and melanoma susceptibility genes

“…The RB family proteins are transcriptional regulators, of which the best-characterized function in the inhibition of proliferation is to suppress transactivation by the E2F family of transcription factors (Figure 1). The RB pathway appears critically important in the suppression of melanoma development, since all or nearly all human melanoma lines tested show disruption of this pathway, via p16 or RB1 deficiency, CDK4 mutation or overexpression of cyclin D1 (Bartkova et al, 1996;Walker et al, 1998). ARF acts in a different pathway, namely by indirectly activating yet another key tumor-and growthsuppressor, p53.…”

Identification of candidate tumor suppressor genes inactivated by promoter methylation in melanoma

“…The CDKN2A locus accounts for susceptibility in $25% of all melanoma families (Bishop et al, 2002), whereas mutations in the CDK4 oncogene are rare (Zuo et al, 1996;Soufir et al, 1998;Molven et al, 2005). In addition to germline changes, somatic mutations of both CDKN2A and CDK4 occur during melanoma development (Castellano et al, 1997;Whiteman et al, 1997;Monzon et al, 1998;Walker et al, 1998;Auroy et al, 2001). Apart from CDK4, other oncogenes thus far identified to play a significant role in melanoma tumorigenesis encode components of the mitogen-activated protein kinase (MAPK) pathway.…”

Somatic mutation of the Peutz-Jeghers syndrome gene, LKB1/STK11, in malignant melanoma

“…The most commonly altered targets identi®ed thus far include chromosome arms 1q, 6q, 9p, 10q and 11q (Albino, 1995;Welch and Goldberg, 1997). Recently, alterations of the tumour suppressor genes p16 INK4/CDKN2 and PTEN/MMAC1 on 9p and 10q, respectively, have been demonstrated in signi®cant proportions of melanoma lesions and cell lines (Kamb et al, 1994;Bartkova et al, 1996;Castellano et al, 1997;Guldberg et al, 1997;Walker et al, 1998;Tsao et al, 1998), and the AIM1 gene has been suggested as a good candidate for the putative tumour suppressor on chromosome 6 (Ray et al, 1997).…”

“…Alternatively, they may represent molecular tumour-suppressive pathways that are abrogated only rarely in melanoma, or they may represent rarely altered components of commonly altered pathways. An example of the latter situation is the p16-cyclin D/ Cdk4-pRB pathway which is abrogated through alteration of one of its components in virtually all melanoma cell lines, yet with p16 INK4/CDKN2 being by far the most common genetic target (Bartkova et al, 1996;Walker et al, 1998).…”