Abnormalities of the transforming growth factor-beta pathway in ocular melanoma.

The majority of ocular melanomas occur in the meal tract. Chemotherapy is generally ineffective and large tumours requiring enucleation have a greater than 50% mortality at 5 years. Monosomy for chromosome 3 is common in uveal melanoma and it is known that there is loss of responsiveness to transforming growth factor beta (TGF beta) in melanoma cell lines. Since the gene for TGF beta receptor II (TGF beta R2) is located on chromosome 3p22, this study investigates the possibility that the TGF beta pathway, and TGF beta R2 in particular, might be involved in the pathogenesis of this rare eye tumour. To this end, the expression of molecules in the pathway has been examined by immunocytochemistry (TGF beta, TGF beta R2, SMAD2, SMAD3, SMAD4 and p27), backed up by a cell culture assay of TGF beta -mediated growth suppression, RT-PCR for SMAD4, and loss of heterozygosity (LOH) on 3p22. There was LOH at 3p22 in 6/19 tumours and loss of TGF beta R2 expression in 10/27 tumours. Immunohistochemistry for SMADs 2, 3, and 4 showed potential loss of signal transduction in 14/27 tumours. The results indicate abnormality of the TGF beta pathway in 61% of rumours for which unequivocal results were obtained and suggest that abrogation of control of melanocyte growth by the TGF beta pathway may be important in the formation of meal melanoma. Copyright (C) 2000 John Wiley & Sons, Ltd.