Axl receptor tyrosine kinase expression in human lung cancer cell lines correlates with cellular adhesion

Axl is a receptor tyrosine kinase (RTK) with oncogenic potential and transf orming activity, Since Axl bears structural similarities to cell adhesion m olecules such as neural cell adhesion molecule (NCAM) (FNIII domains), it i s thought that Axl might play a role in adhesion. In this study, we have an alysed the expression of the Axl protein and its ligand, Gas6. in human lun g cancer cell lines of different histological origin. Axl expression occurr ed in approximately 60% of non-small Cell lung cancer (NSCLC) cell lines, w hich grow adherently, and in normal bronchial epithelial cells (NHBE). but not ill cell lines of small cell lung cancer origin (SCLC), which grow in s uspension. A number of SCLC sublines, which could be selected spontaneously or after oneogene transfection for adherent growth, all expressed Axl prot ein. Overexpression of Axl per se, however. did not induce ally change in t he adhesion phenotype. All Axl-expressing cell lines demonstrated a membran e-bound 140 kD form, as well as a soluble 85 kD form, detectable in superna tant, of Axl-RTK. Expression or the Axl ligand Gas6 was detected in approxi mately 80% of all cell lines investigated. We conclude from these data that loss of Axl expression is a feature or SCLC tumour cells. Axl expression a ppears to be a consequence of cellular adhesion and possibly influences dif ferentiation in human lung cancers. (C) 2001 Published by Elsevier Science Ltd. All rights reserved.