Altered expression of CD44 isoforms in squamous-cell carcinomas and cell lines derived from them.

CD44 is a transmembrane glycoprotein that binds hyaluronan, extracellular matrix proteins and growth factors. Multiple isoforms of CD44 are generated by alternative splicing of 10 separate exons (V1-V10). Expression of the variable exons has been correlated with tumour progression and metastasis in a range of cell types. However, multiple CD44 isoforms are expressed by normal stratified squamous epithelia, such as the epidermis and the lining of the oral cavity. The purpose of our study 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 lost most frequently, but otherwise there was no consistent pattern as to which exons (V4/5, 6, 8) were missing. We also studied CD44 expression in a range of SCC lines, using Western blotting and semi-quantitative RT-PCR. All lines showed reduced expression of the terminal differentiation marker involucrin. Two lines showed selective loss of the largest 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.