Characterization of CD44 splicing patterns in normal keratinocytes, dysplastic and squamous carcinoma cell lines

The CD44 glycoprotein is spliced from a complex gene of 10 constitutive and 10 variant exons. In this study, CD44 splicing patterns and intron 9 reten tion were investigated by exon-specific RT-PCR for variant exons v1-v10 and intron 9 in normal, immortalized, dysplastic and malignant keratinocytes. Expression of product was determined immunohistochemically for some of the exons. Normal keratinocytes showed one major transcript including exons v2- v10 and 3 minor transcripts. No lines showed a normal CD44 splicing pattern but rather a variety of truncated transcripts of contiguous variant exons which overall correlated with expression. Squamous cell carcinoma (SCC)-4 a nd SCC-9 lines showed relatively normal transcripts although protein was ex pressed only by SCC-9. SCC-12B2, SCC-15, SCC-25 and SCC-27 showed a series of shorter overlapping transcripts, with loss of exons v8-v10 in the major transcripts. Intron B was not retained in normal keratinocytes or cell line s. Despite the fact that keratinocytes constitutively express all variant e xons, splicing patterns are distinctly abnormal and merit investigation as potential markers for epidermal and oral squamous malignancy.