Integrin affinity modulation and lung cancer

Abstract

Lung cancer accounts for the most deaths due to cancer in the United Kingdom and yet has historically been one of the most ignored of neoplastic diseases. The work presented in this thesis explores the fundamental processes that govern cell behaviour in the context of lung cancer and contributes to a deeper understanding of this behaviour at a molecular level. The work covers three main areas, centred upon the molecular regulation of integrins, proteins that are the key communicators between a cell and its local environment and which provide powerful signals governing cellular behaviour, including motility, cell survival and proliferation.Recent work has shown that the transmembrane protein CD98 is able to influence the affinity with which ß1 integrins bind to extracellular ligands. The first part of this thesis presents confocal microscopy and co-immunoprecipitation experiments that confirm the physical juxtaposition of the two proteins within the cell membrane, suggesting a direct link between the two, rather than an extensive signalling cascade. It also demonstrated that cross-linking CD98 stimulates both phosphoinositide 3- kinase intracellular signalling and increased ß1 integrin-dependent cellular adhesion. Because of the role of CD98 in integrin affinity modulation, the immunohistochemical expression of CD98 and its ligand, galectin-3, was studied in a variety of human lung diseases including lung cancers. The major finding of this work was a striking distinction between high expression of galectin-3 in non-small cell lung cancer and low expression in small cell lung cancer. This may have significant implications for the differing clinical behaviours of these two groups of cancers. The final section of this thesis returns to describe experiments aimed at defining the molecular regulators of integrin affinity more clearly. A genetic screen of a cDNA library was undertaken to identify candidate genes coding for proteins able to rescue integrins from the low affinity state induced by the small signalling protein H-Ras. This identified a candidate cDNA 480, recognised to be part of a novel gene Nessie, coding for a large protein with multiple transmembrane domains. Both 480 and Nessie appear to have the ability to rescue integrin affinity from H-Ras suppression.This thesis thus moves from the basic molecular science of integrin function to the cellular behaviour of lung cancer cells, both in vitro and in vivo, and back again. The understanding of cellular behaviour is central not just to lung cancer, but to all cancers and it is only through furthering this understanding that significant advances will be made in treating these diseases.