Induction of the common fragile site FRA3B does not affect FHIT expression
1Department of Internal Medicine, Cancer Research, University of Essen Medical School and West German Cancer Center, Hufeland-Strasse 55, D-45122 Essen, Germany.
Abstract:
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.
Insights
Fragile site induction does not directly affect FHIT gene expression. This study found that FRA3B induction did not alter FHIT transcription or translation, challenging previous hypotheses on cancer-associated rearrangements.
Area of Science:
- Genetics
- Molecular Biology
- Cancer Research
Background:
- The FHIT gene, located at the common fragile site FRA3B, is frequently altered in human cancers.
- Its role as a tumor suppressor gene is debated due to conflicting functional study results.
- Previous theories suggested FHIT alterations arise from FRA3B induction by DNA replication interference.
Purpose of the Study:
- To investigate the direct impact of common fragile site (FRA3B) induction on FHIT gene expression.
- To determine if FRA3B induction influences FHIT transcription and translation.
- To clarify the relationship between fragile sites and FHIT alterations in cancer development.
Main Methods:
- Induction of common fragile sites using aphidicolin treatment.
- Cytogenetic scoring to assess fragile site induction.
- Analysis of FHIT gene transcription via RT-PCR and RNase protection assays.
- Assessment of FHIT protein levels using Western blotting.
Main Results:
- FRA3B induction did not alter FHIT gene transcription.
- No aberrant FHIT transcripts lacking exons were detected post-induction.
- FHIT protein levels remained unchanged after fragile site induction.
- Elevated p53 protein levels were observed following fragile site induction.
Conclusions:
- FRA3B induction does not directly impact FHIT transcription or translation.
- The study provides evidence against a direct mechanism linking FRA3B induction to FHIT gene alterations.
- Findings suggest that other mechanisms may be responsible for FHIT alterations observed in cancers associated with fragile sites.
