Aberrant FHIT transcripts in human colorectal cancers.

Abstract

The FHIT gene, located at human chromosome 3p14.2 spanning the FRA3B common fragile region, is frequently altered in several types of human cancers. To study the potential role of FHIT gene in colorectal cancer, expression of the FHIT gene were examined from 20 colorectal cancers for by reverse transcription-polymerase chain reaction (RT-PCR) and all of aberrant transcripts were cloned and sequenced. In addition, the effect of exogeneous rat FHIT overexpression on cell cycle was investigated by introducing the gene into normal rat kidney cells (NRK-52E). In RT-PCR, 7 cases of 25 patients with colorectal cancer showed 16 transcripts of abnormal sizes. Sequence analysis of the abnormal transcripts revealed these transcripts due to the deletion of multiple entire exons or part of exon sequences by errors in the splicing of pre-mRNA. The inserts of 59-bp and 138-bp sizes occurred in combination with in-frame deletions and was identified as part of the FHIT intron 5 sequence. In cell cycle analysis, over-expression of the FHIT gene in the FHIT-pTARGET-transformed NRK-52E cells did not affect cell proliferation and cell cycle distribution. Taken together, although alternative splicing of human FHIT is not directly associated with carcinogenicity, FHIT is frequently inactivated by exon skipping, intron retention, and activation of cryptic splice site within exon 6 in colorectal cancer.