Malignant melanoma in transgenic mice.

Abstract

Ocular and cutaneous melanomas arose in new inbred lines of transgenic mice having an integrated recombinant gene comprised of the tyrosinase promoter, expressed in pigment cells, and the simian virus 40 early-region transforming sequences. The tumors were hypomelanotic and were histopathologically similar to corresponding human melanomas. Eye melanomas often originated at a young age, chiefly from the retinal pigment epithelium, also from the choroid, and rarely from the ciliary body. The eye tumors grew aggressively, were highly invasive, and metastasized to local and distant sites. The earliest formation of these tumors was associated with higher copy numbers of the transgene; mice of different single-copy lines varied greatly in age of onset and frequency of eye tumors. Coat pigmentation was reduced in almost all lines, to various extents. Primary skin melanomas arose later and less frequently than eye melanomas. Hence they were at early stages and of unknown long-range incidence in this investigation, in which autopsies covered the first half-year of life. For both ocular and cutaneous melanomas, the transgenic mice offer numerous possibilities for experimental study of mechanisms underlying formation and spread of melanomas.Melanomas have a propensity for metastasis (1) We were interested in producing mice with a heritable change, on a uniform genetic background, that would lead consistently to malignant melanomas. We report here the regular occurrence and metastasis of melanomas in inbredstrain transgenic mice with an integrated fusion gene containing the simian virus 40 (SV40) early region under the control of the tyrosinase promoter expressed in pigment cells. This paper deals chiefly with melanomas originating in the eyes and to a lesser extent in the skin, at the age range studied thus far. In the accompanying paper (5), other tumors associated with melanosis occurring in the same animals are described. MATERIALS AND METHODSConstruction and Preparation of Tyr-SV40E. The SV40 early region, including the coding sequences of the transforming large tumor (T) and small tumor (t) antigens (6) and extending from the Avr II (nucleotide 5187) to the BamHI (nucleotide 2533) restriction site, was excised from p6-1AL (a gift from James Alwine, University of Pennsylvania). An Avr II/Bgl II/Sma I adaptor was ligated to the Avr II site, and the fragment was cleaved with Bgl II. Two and one-halfkilobases of 5' flanking sequence of the mouse tyrosinase gene was derived from AgTYR101 (a gift from Siegfried Ruppert; ref. 7) and was used as a promoter. This fragment was bounded by an EcoRI site and a Sau3A site 65 base pairs downstream of the major transcription start site (7, 8) and 15 base pairs upstream of the initiation codon. The tyrosinase promoter was ligated, in the vector pBS, to the Bgl II/BamHI fragment of SV40 early region to generate Tyr-SV40E (Fig. 1). The EcoRI/BamHI fragment containing the mouse tyrosinase promoter and the coding regions of SV40 early genes was separated from vector DNA by gel el...

Malignant melanoma: genetics and therapeutics in the genomic era

“…Moreover, HMD2 amplification (encodes human ortholog of MDM2) occurs in only 3%-5% of human melanomas (Muthusamy et al 2006), raising questions as to the pathogenetic relevance of the p53 pathway in melanoma. On the other hand, support for a role for p53 has been suggested by Mintz and colleagues, who showed that SV40 T antigen (which inactivates both RB and p53) generates a highly penetrant and aggressive melanoma phenotype (Bradl et al 1991). More direct evidence for a role of p53 in melanoma suppression derived from Tyr-RAS + ; Trp53 +/− mutant mice.…”

Vasculogenic Mimicry and Tumor Angiogenesis

“…22 Few animals develop these tumors spontaneously, and the transgenic models of pigmented intraocular tumors [23][24][25][26] are complicated by histological features that indicate retinal pigment epithelial differentiation (uveal melanomas develop from melanocytes of the iris, ciliary body or choroid and not from the retinal pigment epithelium; retinal pigment epithelial neoplasms are rarely encountered in humans 27 ). Following the precedent of studying the histogenesis of primary cutaneous melanoma in animals following the application of 7,12-dimethylbenz[a]anthracene (DMBA), 28 -30 Folberg et al 22,31 attempted to induce primary uveal melanocytic lesions by the repeated application of this carcinogen to the rabbit sclera.…”

Transgenic mouse model for skin malignant melanoma

“…By using a recombinant gene comprised of the tyrosinase promoter and the simian virus 40 transforming segment, Bradl et al (1991) established transgenic mouse lines in which primary skin melanomas arose later and less frequently than ocular melanomas. By introducing the ret recombinant oncogene (Takahashi et al, 1985) fused to the mouse MT promoter-enhancer, we previously produced MT/ ret transgenic mouse lines with a mixed strain background (C57BL/6xBALB/c) (Iwamoto et al, 1991).…”