Tumor progression in melanocytic lesions : biological and diagnostic implications

Abstract

Cutaneous malignant melanoma has an annual incidence of 5% in Sweden, with about 1500 cases diagnosed yearly. In routine histopathology there are diagnostic difficulties in the analysis of pigmented lesions. In spite of useful generalizations and criteria for the diagnosis of pigmented lesions, there are clinical as well as histological difficulties. To distinguish melanoma from Spitz nevi proliferation was assessed using antibodies against Ki-67 (MIB-1) and the anti-apoptotic protein BcI-2. My results clearly show that benign and dysplastic nevi in contrast to malignant lesions have a low proliferation. The majority (96%) of the mm expressed Ki-67 as well as Bcl-2, while this was only seen in 6% of the Spitz nevi.

IGF-1R is required for the establishment and maintenance of the transformed phenotype and is also important as an anti-apoptotic regulator in melanoma cells. By Western blotting and binding analysis I could confirm IGF-1R expression in 4 several melanoma cell lines. Two ways of blocking the IGF-1R function were used. For the translocation of the receptor to the cell surface N-linked glycosylation is essential. Cell growth arrest and cell death were induced by the N-linked glycosylation blocker Tunicamycin. A similar effect was obtained by the [alpha]IR-3 antibody, which blocks the binding domain of IGF-1R. These treatments resulted in apoptosis. Primary melanoma tissues and tissues from melanoma metastases, obtained from lymph nodes of patients with advanced mm, were also found to express the IGF-1R. However, none of benign nevi used for comparison stained positive. I also noted that there was an inverse correlation between the expression of IGF-1R. and the frequency of apoptotic cells, which suggest that IGF-1R. has also an anti-apoptotic effect in vivo.

Cdk inhibitors may be important in controlling cellular proliferation. To evaluate other possible mechanisms in IGF-1R. dependent control of proliferation, the influence of p27 Kip1 and its related cyclins were of interest as my analyses have revealed an inverse relation between p27 Kip1 and expression of IGF-1R. in melanoma cells. Both Tunicamycin and [alpha]IR-3 caused substantial redistribution of p27 from cyclin DI to cyclin E and cyclin A. These effects may underlie the growth-inhibitory and apoptotic; effect of inhibition of IGF-1R. in melanoma cells.

Previous clinical studies have indicated that the estrogen receptor blocker, Tamoxifen (TAM) has some favorable effects on the clinical outcome of mm. There is support from studies on breast cancer that TAM interferes with the IGF- 1 pathway by increasing the release of insulin-like growth factor binding proteins (IGFBPs). I showed that TAM induced cytotoxicity in several nun cell lines, which did not express ER. I could, however, confirm that TAM did not affect the IGFBPs. Instead, it seems that TAM inhibits autophosphorylation of the [beta]-subunit of the IGF- 1 receptor.

This may indicate the role of TAM as an inhibitor of tyrosine kinases and a potential therapeutical approach for advanced mm.