Analysis ofras mutations in human melanocytic lesions: activation of theras gene seems to be associated with the nodular type of human malignant melanoma

Abstract

We have analyzed the Ha-ras, Ki-ras and N-ras gene for point mutations at codons 12, 13 and 61 via restriction fragment length polymorphism/polymerase chain reaction analysis and subsequent direct sequencing in non-cultured fresh-frozen tissues of 16 superficial spreading melanomas (SSM), 13 nodular malignant melanomas (NMM), 2 lentigo malignant melanomas (LMM), 1 dysplastic nevus, 1 congenital nevus and 5 normal nevi from 38 patients. Mutations were found in 4 melanoma samples, all belonging to the nodular malignant type. Three of them were mutated in N-ras and one in the Ha-ras gene. Mutation in N-ras was also detected in the congenital nevus. All mutations were exclusively located at the first two base pairs of codon 61. No Ki-ras mutation was detected in any lesion. No mutation could be found in SSM and LMM in addition to dysplastic and normal nevi. The frequency of ras mutation in NMM was 31%, whereas in SSM it was 0%. Our study suggests (a) an association between ras mutations (mainly N-ras) and the NMM as a subgroup of human melanoma; (b) that activation of Ki-ras is not involved in the pathogenesis of melanoma. The role of UV radiation in point mutations of ras genes in human melanoma is discussed.

Malignant melanoma: genetics and therapeutics in the genomic era

“…N-RAS is the most frequent RAS family member targeted in the melanocyte lineage, with activating mutations in as many as 56% of congenital nevi (Papp et al 1999), 33% of primary and 26% of metastatic melanoma samples (Demunter et al 2001). Activating N-RAS mutations have been correlated with nodular lesions and sun exposure (Jafari et al 1995;van Elsas et al 1996). Interestingly, N-RAS mutations are rarely found in dysplastic nevi (Albino et al 1989;Jafari et al 1995;Papp et al 1999), which may imply their distinct evolutionary path to melanoma.…”

“…Activating N-RAS mutations have been correlated with nodular lesions and sun exposure (Jafari et al 1995;van Elsas et al 1996). Interestingly, N-RAS mutations are rarely found in dysplastic nevi (Albino et al 1989;Jafari et al 1995;Papp et al 1999), which may imply their distinct evolutionary path to melanoma. H-RAS activation has occasionally been detected in melanoma, albeit more commonly associated with Spitz nevi, based on amplification of its genomic locus on 11p and oncogenic point mutations (Bastian et al 2000).…”

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

“…Additional mutations were in codon 465 (exon 11). There is an inverse correlation between the occurrence of mutations in the BRAF gene and in the ras oncogene, which is activated in approximately 10-30% of human melanomas (Albino et al, 1989;Van't Veer et al, 1989;Jafari et al, 1995;Omholt et al, 2002). This suggests that the two proteins are in the same pathway of melanomagenesis.…”

Modeling malignant melanoma in mice: pathogenesis and maintenance

“…In the case of RAS, activation can be mediated indirectly through di erent RTKs, such as EGFR, or through activating oncogenic mutations. Activating mutations in N-and H-RAS has been observed in close to 30% of a subset of melanoma, the nodular amelanotic type (Jafari et al, 1995). Although germline heterozygous mutations of PTEN do not confer a melanoma phenotype, they do lead to a cancer-prone state in the mouse (DiCristofano et al, 1998;Stambolic et al, 1998;Podsypanina et al, 1999).…”

“…With this hypothesis in mind, we speculated that the addition of oncogenic stimuli in an INK4a null setting may promote the transformation of these murine dermal melanocytes. The candidate oncogenic lesion considered early in the course of these studies was oncogenic RAS, based upon several lines of experimental evidence suggesting potent cooperative interaction between activated H-RAS V12G and INK4a/ARF de®ciency in cultured ®broblasts (Serrano et al, 1997), and the presence of activating N-and H-RAS mutations in human nodular melanoma (Jafari et al, 1995).…”