ANTISENSE NUCLEIC-ACIDS TARGETED TO THE THYMIDYLATE SYNTHASE (TS) MESSENGER-RNA TRANSLATION START SITE STIMULATE TS GENE-TRANSCRIPTION

Thymidylate synthase (TS) is a key enzyme in the synthesis of DNA and a target for cancer chemotherapeutic agents. Antisense TS nucleic acid s may be useful in enhancing anticancer drug effectiveness. MCF-7 and HeLa cells were transfected with vectors expressing antisense TS RNA o r with antisense oligodeoxynucleotides (AS-ODNs) to different TS mRNA regions. Antisense RNAs were targeted to 30 bases of the TS mRNA inclu ding part of the stem loop at the translation start site and to 30 bas es spanning the exon1/exon2 boundary. AS-ODNs were targeted to the tra nslation start site and the translation stop site. Antisense nucleic a cids complementary to the translation start site (and not the exon1/ex on2 boundary or translation stop site) significantly enhanced constitu tive TS gene transcription. Therefore, TS mRNA sequences appear to be involved in a novel pathway controlling TS gene transcription. Induced transcription could hinder antisense-based attempts to inhibit TS and must be considered when designing such strategies. (C) 1998 Academic Press.