Selective increase in specific alternative splice variants of tyrosinase in murine melanomas: A projected basis for immunotherapy

Abstract

Melanomas tend to become less pigmented in the course of malignant progression. Thus, as proliferation increases, the tumors are decreasingly characterized by the tissue-specific phenotype of normally differentiated melanocytes. To learn whether the decline in melanization is associated with a shift from constitutive to alternative splicing of some pigment gene pre-mRNAs, melanomas were collected from Tyr-SV40E transgenic mice of the standard C57BL͞6 strain. The mRNAs of the tyrosinase gene, which has a key role in melanogenesis, were analyzed by quantitative reverse transcriptase-PCR in 34 samples from 16 cutaneous tumors and 9 metastases. The cutaneous tumors included some cases with distinct melanotic and amelanotic zones, which were separately analyzed. All tyrosinase transcripts found in the melanomas were also found in normal skin melanocytes. However, the ⌬1b and ⌬1d alternatively spliced transcripts, due to deletions within the first exon, were specifically augmented in most of the tumors over their very low levels in skin; the exceptions were some all-amelanotic tumors in which no tyrosinase transcripts were detected. The level of ⌬1b rose as high as 11.3% of total tyrosinase mRNAs as compared with 0.6% in skin; ⌬1d reached 4.0% as compared with 0.8% in skin. Expression of these splice variants was highest in the melanotic components of zonal primary tumors, relatively lower in their amelanotic components, and still lower in all-amelanotic primary tumors and amelanotic metastases. The increase in ⌬1b and ⌬1d transcripts may be predicted to increase the levels of unusual peptides, which could have antigenic potential in the tumors, especially in the relatively early phases of malignancy. Analyses of the alternative transcripts of other pigment genes may identify additional candidate antigens, ultimately enabling melanoma cells in all phases of the disease to be represented as a basis for immune intervention.

New insights into the active site structure and catalytic mechanism of tyrosinase and its related proteins

“…It is composed of five exons and four introns (Kwon, 1993; Murisier and Beermann, 2006). The post‐transcriptional processing of the mRNA generates several alternatively spliced products (Le Fur et al., 1997; Porter and Mintz, 1991; Shibahara et al., 1988), but only one of the translated products expresses tyrosinase activity (Muller et al., 1988; Ruppert et al., 1988). The mouse Tyrp1 gene, located on chromosome 4 [chromosome 9 for human TYRP1 (Abbott et al., 1991)], has eight exons, of which the first one is non‐coding (Bell et al., 1995; Jackson et al., 1991).…”

Translation of a Retained Intron in Tyrosinase-related Protein (TRP) 2 mRNA Generates a New Cytotoxic T Lymphocyte (CTL)-defined and Shared Human Melanoma Antigen Not Expressed in Normal Cells of the Melanocytic Lineage

“…Indeed, epitopes encoded in alternative ORFs ( 29 ), within introns ( 10 , 16 ), under the putative control of a cryptic promoter ( 30 ), or governed by a variant of conventional translation mechanisms ( 31 ) have been described. It has also been proposed that the increased expression in splice variants of pigment genes that occurs in melanoma compared with normal melanocytes may contribute to the pool of melanoma-specific antigenic peptides ( 32 ).…”

Transgenic Mouse Models for Tumors of Melanocytes and Retinal Pigment Epithelium

“…The level of the Alb alternative transcript rose as high as 11.3% of total tyrosinase mRNAs, in contrast to skin (0.6%). Such alternative transcripts might lead to unusual peptides, which could have antigenic potential in melanotic tumors (Lefur et al, 1997a). A similar experiment was performed in c2J albino mice, where an alternative splice donor site in exon 1 is affected by the mutation, thus leading to a different distribution of alternatively spliced tyrosinase transcripts (Lefur et al, 1996(Lefur et al, , 1997b.…”