Exon 14-skipping of the adenomatous polyposis coli gene in purified epithelial cells of colonic mucosa and tumors

Adenomatous polyposis coli (APC) exon 14-skipped transcripts encode putativ e APC proteins of low molecular weight. To prove that exon 14-skipped mRNA variants do not simply represent tissue culture artifacts, expression of th ese APC transcript variants was demonstrated in native colorectal epitheliu m. Fresh surgical specimens of human colon were processed and epithelial ce lls were affinity-purified with the dynabead-immobilized monoclonal antibod y Ber-EP4. Epithelium derived cDNA was PCR-amplified in the range of linear accumulation. RT-PCR products with and without APC exon 14 were evaluated by densitometry. Analyses of normal mucosa (n=8) and matching mucosa - tumo r samples (n=4) revealed a consistent 4 to 1 ratio of APC exon 14-positive to exon 14-negative mRNA levels. We conclude, a) that APC exon 14-skipped t ranscripts are physiologically expressed in native human colon mucosa, and b) that ratios of exon 14-negative to exon 14-positive isoforms were not al tered when colorectal tumor cells were compared with matching normal mucosa (p = 0.80).