ALTERED EXPRESSION OF CD44 ISOFORMS IN SQUAMOUS-CELL CARCINOMAS AND CELL-LINES DERIVED FROM THEM

CD44 is a transmembrane glycoprotein that binds hyaluronan, extracellu lar matrix proteins and growth factors. Multiple isoforms of CD44 ave generated by alternative splicing of 10 separate exons (VI-V10). Expre ssion of the variable exons has been correlated with tumour progressio n and metastasis in a range of cell types. However, multiple CD44 isof orms are expressed by normal stratified squamous epithelia, such as th e epidermis and the lining of the oral cavity. The purpose of our stud y was to examine CD44 expression in squamous-cell carcinomas (SCC). By immunofluorescence we found reduced expression of one or more of the variant exons in a series of 13 oral SCC, with loss being most common in poorly differentiated tumours. Of the exons we examined, V3 was los t most frequently, but otherwise there was no consistent pattern as to which exons (V4/5, 6, 8) were missing. We also studied CD44 expressio n in a range of SCC lines, using Western blotting and semi-quantitativ e RT-PCR. All lines showed reduced expression of the terminal differen tiation marker involucrin. Two lines showed selective loss of the larg est forms of CD44 and one failed to express any of the variant exons. These cell lines, therefore, provide a useful experimental model with which to study the biological significance of exon loss in SCC. (C) 19 96 Wiley-Liss, Inc.