CD44 EXPRESSION PATTERNS IN BREAST AND COLON TUMORS - A PCR-BASED STUDY OF SPLICE VARIANTS

CD44 cell-surface receptor expresses multiple isoforms, some of which are believed to play a role in tumor growth and metastasis. The CD44 g ene is composed of 19 exons, of which 9 (exons 6 to 14) are alternativ ely spliced to form inclusions in the intervening membrane proximal re gion. Sequences present in the shortest metastatic variant cloned from a rat metastatic cell line have been shown to correspond to human exo ns 10 and 11, also called exons vb and v7. Using RT-PCR, we have addre ssed in detail the CD44 isoforms produced in human breast and colon tu mors. We analyzed 53 breast-tumor- and 58 colon-tumor-related samples as well as I benign mastopathy, I normal breast, 4 non-invaded lymph n odes and 8 normal colon tissues. All tumors analyzed expressed the hem opoietic CD44 (CD44H) isoform (no alternatively spliced exons added), whereas 81% expressed the CD44E form (addition exons IZ, 13 and 14). F urthermore, 85% of tumors presented complex patterns of expression, wi th an average number of 5 to 6 bands detected. In view of their implic ation in the metastatic process, we investigated in greater detail the isoforms containing exons IO and I I (v6 and v7). Exon IO was more fr equently expressed than exon 11, 80% and 57% of the samples respective ly. The great majority of cases showed ladder-like patterns starting f rom the shortest forms (exons 5-10 or 5-10-11) and larger-molecular-we ight bands corresponding predominantly to sequential inclusions of exo ns from 3' to 5'. Exon-10 and exon-11 variants were also found in one benign mastopathy. The majority of normal tissues (I breast and 6/8 co lon) expressed only the CD44H isoform. These data indicate that expres sion of metastatic variants is common in human breast and colon tumors and can occur early during cancer progression, as testified by their presence in a benign breast tumor. While expression of exon-10 variant s were correlated with presence of distal metastases in colon tumors, exon-ll variants were not (metastatic events were too rare in our brea st-tumor series to reach significance). This suggest that exon 10 may correspond to the minimal sequences required to favor metastatic event s. (C) 1995 Wiley-Liss, Inc.