To assess whether RAS oncogenes may affect the expression of cytokines in tumor cells, the presence of interleukins (IL) 1α, 1β, 4, 6, 7, and 8, tumor necrosis factor (TNF) α and interferon γ mRNA has been analyzed by reverse transcriptase-polymerase chain reaction in 19 melanoma clones derived from the metastatic cell line 665/2 and previously characterized for RAS mutation and expression. Five of these clones and the parental cell line showed a mutation at codon 61 of N-RAS that resulted in Gln→ Arg substitution (N-RAS/61+), while in the remaining 14, only the wild-type allele for N-RAS was present (N-RAS/61-). With the exception of interferon γ and IL-4, all the cytokines tested were expressed by the parental 665/2 cell line, whereas IL-1α, IL-6, and TNF-α were coordinately transcribed only in the subset of the clones bearing the mutated N-RAS gene. The other cytokine genes studied (IL-1β, IL-4, IL-7, and IL-8) displayed a variable degree of expression, and such an heterogeneity was not correlated to the N-RAS phenotype of the clones. The association between N-RAS oncogene and IL-1α, IL-6, and TNF-α expression was also found in a 665/2 subline (665/2/5) in which loss of mutated N-RAS genes simultaneously occurred with the loss of Il-1α, IL-6, and TNF-α expression. Direct evidence that N-RAS oncogene could influence the pattern of cytokine expression was provided by the coordinate induction of IL-1α, IL-6, and TNF-α messenger RNA achieved in N-RAS/61+ transfectants of the N-RAS wild-type melanoma clone 2/21. Furthermore, IL-1α, IL-6, and TNF-α could be detected by enzyme-linked immunosorbent assay in the culture medium obtained from N-RAS/61+ melanoma clones as well as from positive transfectants, indicating that lymphokine mRNA expression triggered by the activated N-RAS oncogene lead to a secreted protein. In an N-RAS/61+ melanoma clone, by adding specific antibodies against each cytokine, it was found that soluble IL-1α exerted a positive control on IL-6 mRNA and a negative one on its own expression. In addition, IL-1α and IL-6 were negatively regulated by soluble IL-6 and TNF-α.