CD44 comprises a family of membrane adhesion molecules encoded by a single gene and diversified by alternative splicing and extensive posttranslational modifications. Alterations of CD44 expression patterns are linked to tumour invasion and formation of metastases. However, CD44 expression and its relation to the biological properties of tumours vary depending on the tumour type and origin. In transitional cell carcinoma of the urinary bladder, low CD44 expression is linked to enhanced tumour aggressiveness. We studied CD44 expression in two urothelial cancer cell lines, HT1197 and 5637. CD44s and a v6 variable exon-containing splice variants were detected in both cell lines by reverse transcription-PCR and by commercially available monoclonal antibodies. In both cell lines, Western blot analysis detected immunoreactive proteins with approximate sizes 70–85 kD, 95–110 kD, and 120–140 kD with CD44v6 antibody and weak bands with size 70–98 kD with CD44s antibody. At the cellular level, the pattern of CD44 immunoreactivity correlated with a lower level of cell differentiation and a higher degree of cell proliferation. In HT1197 cells, the CD44v6 was detected predominantly in small proliferating cells and in large multinuclear atypical cells. CD44s and CD44v6 displayed low immunoreactivity in HT1197 cells with a higher degree of epithelial differentiation. The 5637 cells expressed CD44v6 strongly and CD44s weakly. We conclude that CD44v6 expression correlates with a higher proliferative activity and with a stem cell-like phenotype in both cell lines and with cellular atypia in HT1197 cells.

CD44 forms a family of cell surface adhesion glycoproteins involved in the regulation of organ differentiation and the maintenance of tissue integrity (Borland et al., 1998; Sneath and Mangham, 1998; Goodison et al., 1999). These proteins are also engaged in tissue repair and immune reactions (Seth et al., 1991; Kaya et al., 1997). The CD44 protein molecules ranging in size from 38 kD to approximately 250 kD originate from a single gene residing on human chromosome 11 (11p13)(Screaton et al., 1992). Alternative splicing and subsequent extensive posttranslational modifications including glycosylation, phosphorylation and enzymatic cleavage result in a spectrum of proteins that differ in size as well as in composition of functional domains (Screaton et al., 1992; Kajita et al., 2001). Alterations in the CD44 expression pattern have been shown to be linked to neoplastic transformation of various cell types and may be closely related to invasive growth and formation of metastases of several tumour types (Gotley et al., 1996; Goodison and Tarin, 1998; Lipponen et al., 1998; Saegusa et al., 1999; Mikami et al., 2000; Nguyen et al., 2000; Khoursheed et al., 2002). The profile of CD44 isoforms is variable in tumours of identical histologic type, depending especially on the degree of differentiation and cytologic atypia of the tumour cells. The CD44 profile is also closely related to the malignant features of tumours (Hong et al., 1995; Sugino et al., 1996; Lipponen et al., 1998; Nguyen et al., 2000; Wong et al., 2003). The CD44 gene spans almost 92 kb and contains at least 20 exons. CD44 variants contain five constant