Induction of the common fragile site FRA3B does not affect FHIT expression.

A long-standing issue concerns the extent to which fragile sites predispose to cancer-associated chromosomal rearrangements. The FHIT gene at chromosome 3p14.2 spans the most common fragile site, FRA3B, in the human genome. Although the FHIT gene is altered in many human cancers, its status as a tumor suppressor gene has remained controversial, particularly since functional studies provided contradictory results. It had been suggested the FHIT alterations result from FRA3B induction promoted by the interference of carcinogens with DNA replication. Here we investigated the effect of FRA3B induction on FHIT expression. Common fragile sites were induced by treatment with aphidicolin and scored cytogenetically. FHIT transcription was analysed by RT--PCR and RNase protection analysis. Unexpectedly, FHIT transcription proceeded unchanged after fragile site induction. Aberrant FHIT transcripts lacking one or more exons were not observed. Moreover, Western blots revealed that the levels of FHIT prior to and following fragile site induction was unchanged, whereas p53 was found at elevated levels after induction. FRA3B induction thus has no direct effect on FHIT transcription and translation.