Aberrant splicing of FHIT transcripts in human gastric cancer cell lines.

Alterations of the FHIT gene occur as frequent events in several human cancers. Replacement of exogenous wild-type FHIT gene has been shown to induce suppression of tumorigenicity of human FHIT-negative cells in nude mice and aberrant FHIT transcripts have been observed in a variety of human solid tumors. In the presence study, we performed a nested reverse transcription-polymerase chain reaction (RT-PCR) analysis to identify aberrant FHIT transcripts in 6 gastric cancer cell lines. In addition to the wild-type FHIT transcript, small-sized transcripts with various number and lengths were observed in all of the cell lines examined. Sequence analysis confirmed that different types of truncated transcripts included exonic deletions, insertions of intron 5 sequences between exons, and combinations of both. Most of these transcripts lacked exon 5 in which translation initiation codon is located. Aberrant transcripts with partial exonic deletions, resulting from activation of cryptic splice sites, were also observed in 5 cell lines. Additionally, multi-step splice patterns, indicative of additional downstream processing, were observed in several cancer lines. Our results suggest that the aberrant FHIT transcripts in gastric cancer cell lines resulted from faulty splicing, including exon skipping, selection of cryptic splice site and additional downstream splice processing.

Expression of the fragile histidine triad gene in normal rat tissues and human kidney cancer cell lines.

The fragile histidine triad (FHIT) gene located in human chromosome 3p14.2 is a candidate tumor suppressor gene that has a diadenosine triphosphate (Ap3A) hydrolase activity, but its role in carcinogenesis remains uncertain. To investigate the role of FHIT in normal cells, specific polyclonal antibodies to recombinant rat FHIT protein were generated. Immunoblot analysis revealed the 17-kd FHIT protein was most abundantly expressed in kidney and liver, whereas heart, skeletal muscle, and adrenal gland expressed trace amounts. In kidney, immunohistochemical staining was strongly observed in distal convoluted tubule and collecting duct during postnatal growth period. By a nested reverse transcription-PCR analysis of FHIT from 2 human kidney cancer cell lines, four abnormal-sized FHIT transcripts, with deletion and/or insertion, were detected. These were derived from the results of exon skipping, and/or insertion of FHIT intron 5 sequence, or selection of cryptic splice site within the FHIT cDNA sequence 179-180. Taken together, our data indicate that FHIT expression is frequently altered in human kidney cancer cell lines by alternative splicing, and suggest that the FHIT protein may play a pivotal role in regulating intracellular metabolism of the distal convoluted tubule and collecting duct in maturity.