Modulation in vitro of H-ras oncogene expression by trans-splicing

In man, activated N-, K- and H-ras oncogenes have been found in around 30% of the solid tumours tested, An exon known as IDX, which has been described previously and is located between exon 3 and exon 4A of the c-H-ras pre-mR NA, allows an alternative splicing process that results in the synthesis of the mRNA of a putative protein named p19, It has been suggested that this alternative pathway is less tumorigenic than that which results in the acti vation of p21, We have used the mammalian trans-splicing mechanism as a too l with which to modulate this particular pre-mRNA processing to produce mRN A similar to that of mature p19 RNA. The E4A exon of the activated H-vas ge ne was found to be a good target for external trans-splicing. We reprogramm ed the rat carnitine octanoyltransferase exon 2 to specifically invade the terminal region of H-ras. Assays performed with this reprogrammed trans-exo n showed that the trans-splicing product was obtained in competition with c is-splicing of the D intron of the H-ras gene, and was associated with conc omitant downmodulation of D intron cis-splicing. We also found that the exo n 4A of the human c-H-ras gene underwent successive trans-splicing rounds w ith an external exon.