CD44 splicing pattern is associated with disease progression in pulmonary adenocarcinoma

Certain alternatively spliced exons of CD44 gene have been associated with specific functions. However, these functions may have come from inclusion of a central array of alternatively spliced exons, rather than a single one. The goals of this study were to analyze all of the variant exons included by alternative splicing, the entire population of CD44 mRNA transcripts, and the prognostic implications of CD44 mRNA and protein isoforms expressed by non-small cell lung cancer (NSCLC).

Using a polymerase chain reaction protocol with short reaction times, we amplified, sequenced and quantified CD44 mRNA transcripts from 52 samples of NSCLC to determine the splicing patterns of alternatively included exons and the proportion of each CD44 mRNA transcript. The expression of CD44 standard form and variant isoforms CD44v3 and CD44v6 were also analyzed by immunohistochemistry (IHC).

Normal lung and NSCLC expressed CD44 mRNA transcripts containing variant exons v10, v8-10, v6-10, v3-10 and v2-10. In squamous cell carcinoma, the expression rates of these mRNA transcripts were equal to or higher than those of the normal lung, and the splicing pattern was not associated with disease progression. In adenocarcinoma, the expression rates of CD44v6-10, v3-10 and v2-10 mRNA were lower than in normal lung. The down-regulation of CD44v6-10, CD44v3-10 mRNA and CD44v6 protein paralleled the progression of adenocarcinoma. Recurrence of adenocarcinoma was associated with negative expression of CD44v6-10 or CD44v3-10 mRNA, and with low-level expression of CD44v6 or CD44v3 by IHC. Negative expression of CD44v6-10 mRNA and reduced expression of CD44 v6 protein were associated with a shorter disease-free and overall survival in the univariate but not the multivariate analysis.

Our data suggest that CD44 splicing pattern is associated with disease progression in adenocarcinoma.