Preferential histiotypic expression of CD44-isoforms in human lung cancer

The CD44 transmembrane glycoprotein is expressed in most adult tissues and in the majority of neoplasias. Due to alternative splicing, this cell adhesion molecule exists in multiple isoforms some of which have been associated with specific types of tumours as well as with increased tumour metastasis. In this study, we have looked at the level and type of CD44 expression in lung cancer which represents a histologically heterogenous form of cancer composed of small cell lung carcinoma (SCLC) and non-small cell lung carcinoma (NSCLC), the latter subgroup comprising adenocarcinoma (ADC), bronchio-alveolar carcinoma (BAC), large cell carcinoma (LCC), and squamous cell carcinoma (SCC). We analysed 20 lung cancer cell lines and 64 primary tumours by RT-PCR and immunohistochemical detection of the CD44 standard and variant protein isoforms. Our results suggest that (i) CD44 is expressed in all histologically distinct subsets of lung cancer with a tendency SCC > BAC > ADC > LCC > SCLC, (ii) expression of the CD44 isoforms v5, v7, v8, and, most notably that of CD44 exon v6, strongly correlates with tumours of squamous cell and bronchio-alveolar carcinoma origin, tumours which commonly exhibit a comparatively low metastasizing potential, and (iii) the expression of CD44 isoforms is independent from the tumour size and lymph node status at surgery, the proliferative status of the tumour cell population (Ki67 antigen expression) and the histopathological grading (G1 to G3). Only non-differentiated tumours (G4), which were restricted to SCLC and LCC samples revealed markedly reduced CD44 standard and isoform antigen. In conclusion, our data point to a clear histiotype-related pattern of CD44 variant expression preferentially that of CD44v6 in SCC and BAC.