ABNORMAL RETENTION OF INTRON-9 IN CD44 GENE TRANSCRIPTS IN HUMAN GASTROINTESTINAL TUMORS

We have recently identified a new exon of the CD44 gene and demonstrat ed abnormal retention of a noncoding section, intron 9, in mRNA from b ladder carcinomas. To analyze this further, the present study examined CD44 gene expression in cell lines from 14 esophageal, 3 colonic, and 4 breast carcinomas and in fresh samples from 20 colorectal carcinoma s and corresponding normal colonic mucosa, using reverse transcriptase followed by the polymerase chain reaction (RT-PCR). This confirmed th at there was abnormal assembly of several exons of the gene in cell li nes and in tumor tissues from these organs. However, the most striking new finding was that intron 9 was present in RNA from 11 esophageal, 3 colon, and 1 breast carcinoma cell line, respectively. This was conf irmed by RNase and DNase digestion analysis. Moreover, it was detected both in nuclear and cytoplasmic mRNA fractions, indicating that abnor mal splicing of pre-mRNA occurs in cancer cells. The abnormal retentio n of intron 9 in CD44 gene transcripts was also demonstrated in tumor tissues from 16 (80%) of 20 patients with colon carcinoma, but there w as no correlation with Dukes' stage. The biological significance of th ese observations is not yet understood. However, it is clear that, as with the abnormal expression pattern of CD44 variant exons, intron 9 r etention is a good-candidate molecular diagnostic tool for colorectal carcinomas.