Rearrangement of the Human mel Gene, the rab 8 Homologue, in Human Malignant Melanomas

Abstract

The human MEL gene was originally isolated following transfection into NIH3T3 mouse fibroblast cells of DNA from a human melanoma cell line NKI4. MEL was mapped to chromosome 19 (pl3.2), a region in which a number of translocation breakpoints occur. We have sequenced MEL cDNA clones and shown significant homology to the RAS-related YPT1 proteins and more specifically, identity with the recently described canine RAB 8. The original transfectant from which MEL was isolated appeared to comprise of complex rearrangements involving human sequences mapping on chromosome 8. Furthermore, most of the MEL sequences, apart from the putative first extron, were absent. The presence of the human MEL sequences may be fortuitous in this transfectant and the transforming gene has yet to be isolated. However, 12 melanoma cell lines and 20 fresh melanoma tumours were screened for MEL gene rearrangements and. DNA from a single patient with a tumour metastasis from the intestinal tract was found to have rearranged MEL sequences. DNA from this tumour was positive in NIH3T3 focus formation assays, producing anchorage independent foci with human repetitive sequences present. One of these transformants was tested and found to be tumorigenic in nude mice. These transformants showed no evidence of human H, K or N RAS or MEL activation. Six additional metastases from this patient lacked this rearrangement, suggesting that the gene rearrangement observed may be associated with late events in the evolution of the tumour metastasis.