Lymphotoxin gene expression by melanocytes and melanoma cell lines and persistence of unspliced mRNA

Human melanoma cell lines express many different cytokines [1], including lymphotoxin (LT), the production of which has been considered to be restricted to cells of the lymphocytic lineage in response to cell activation. LT expression by melanomas is constitutive and characterized by the presence of two mRNAs. In the present paper we report an analysis of the origin of the two LT-specific transcripts in four human melanoma cell lines at different stages of progression and in four melanocytic cell lines. Reverse transcription-polymerase chain reaction (RT-PCR) performed with primers lying in the first and fourth exons and hybridization with intron probes showed a spliced and a full-unspliced LT mRNA. This pattern was also displayed by one of four melanocyte cell lines. Western blot analysis indicated that LT RNA is properly translated to a 23-25 kDa protein and immunocytochemistry showed its localization within the cytoplasm and on the cell membrane.