IDENTIFICATION OF A NOVEL INTERLEUKIN-15 (IL-15) TRANSCRIPT ISOFORM GENERATED BY ALTERNATIVE SPLICING IN HUMAN SMALL-CELL LUNG-CANCER CELL-LINES

IL-15 is a cytokine promoting growth and differentiation of T, B add N K lymphocytes. By RT-PCR analysis, using primers allowing amplificatio n of the entire IL-15 mRNA coding region, 9/11 small cell lung cancer (SCLC) cell lines displayed detectable IL-15 gene expression, In addit ion to the expected band sizing 524 bp, a larger band was also observe d, Cloning and sequence analysis of the larger cDNA from two SCLC cell lines revealed a size of 643 bp due to the presence of additional 119 bp within the previously reported IL-15 cDNA sequence, The 119 bp seq uence matched with an IL-15 genomic sequence downstream the IL-15 seco nd coding exon and may represent a previously unreported alternative e xon (exon A), The SCLC-associated IL-15 mRNA isoform has a shorter ope n reading frame (ORF) due to stop codons in exon A, followed by a new AUG codon, The predicted IL-15 precursor protein displays a shorter si gnal peptide but shares the same aminoacidic composition of mature IL- 15 protein, A possible functional role of IL-15, different from 'IL-2- like' activity, in human tumours, is suggested.