N-RAS MUTATIONS AND SUSCEPTIBILITY TO LYMPHOKINE-ACTIVATED KILLER (LAK) CELLS IN HUMAN-MELANOMA

RAS oncogene expression has been reported to affect several biological features of rodent tumour cells, including lysability by activated na tural killer cells. In order to examine whether expression of mutated RAS genes in human melanoma cells alters their susceptibility to lysis by LAK cells, seven melanoma lines were assessed for the presence of Ki- and NRAS genes bearing all possible mutations at codons 12,13 and 61. A panel of 21 clones deriving from the metastic lesion Me665/2, wh ich had a Gln --> Arg substitution at codon 61 of NRAS (N-RAS/61+), we re also examined. Melanoma cells and clones were used as targets of al logeneic LAK in a 4-h Cr-51-release assay. LAK showed a higher lysis o n melanoma lines and clones harbouring a mutated RAS compared with cou nterparts bearing no RAS mutations. In addition, LAK-mediated lysis dr astically decreased on Me665/2 sublines progressively selected by expo sure to LAK. This loss was paralleled by a reduction or even disappear ance of N-RAS/61+ mRNA signal in Me665/2 sublines. To evaluate whether N-RAS could directly modulate LAK susceptibility to lysis, N-RAS/61gene was transfected in two N-RAS wild type (N-RAS/61-) 665/2 melanoma clones by a cosmid vector. In contrast to the high lysability of mela noma cells constitutively expressing the mutationally active N-RAS onc ogene, N-RAS/61+ transfectants did not show a consistent high lysabili ty by LAK, compared with some control pSV2neo transfectants. Taken tog ether, these results indicate that expression of a mutated RAS gene ca n be considered as a factor, although not the only one, that character izes human melanoma cells with high susceptibility to lysis and may th us affect their response to therapeutic lymphocytes.