Selective regulation of p38beta signalling by integrin-linked kinase mediates bladder cancer cell migration

Abstract

Integrin linked kinase (ILK) is an essential transducer of integrin and growth factor signals, and its protein levels and activity are often elevated in solid tumours. ILK physically links integrins and receptor tyrosine kinases to the actin cytoskeleton, and genetic or pharmacologic inhibition of ILK activity blocks cell migration, making it an attractive target for development of anti-cancer therapeutics. Many of the functions of ILK rely on its protein adaptor role to regulate various oncogenic signals. In this study I found a striking positive correlation between levels of ILK and the p38beta isoform in bladder cancer tissues and cells. I show that ILK and p38beta promote migration of bladder cancer cells, and demonstrate selective formation of a cytoplasmic complex with ILK in these cells, which acts to stabilize p38beta protein levels. Interestingly, the ILK/p38beta complex appears to act downstream of Rac1, and regulates phosphorylation of the heat shock protein Hsp27, which has been associated with actin remodeling, cell migration and metastasis. Our data identify a novel ILK-p38beta signalling axis that regulates motility in bladder cancer cells, with potential for therapeutic targeting. Chapter 1 of this thesis details the clinical development and progression of bladder carcinoma together with the current experimental models available in our lab to study the advanced stage of this disease. In this chapter there is a particular focus on dysregulation of ILK signalling in various human cancers. The role of p38 MAPK signalling in human cancer and discussion of studies linking these two kinases is also introduced in this chapter. Chapter 2 describes general experimental methods; specialized methods are provided in the relevant chapters. Chapter 3 presents and discusses the expression pattern of ILK in tissue microarray of human bladder cancer samples and a panel of bladder cancer cell lines. Chapter 4, using specific siRNA, investigates the role of ILK in TSU-Pr1, the highly migratory bladder cancer cell line in vitro. In chapter 5, I demonstrate that the predominant p38 isoform p38betaplays an important role in bladder cancer cell migration. These findings, together with previous studies, show that ILK acts upstream of p38beta to control cell migration via regulation of cytoskeleton remodeling. Based on the results described in chapters 3-5, chapter 6 focuses on defining the mechanism by which ILK mediates p38beta expression and signalling during bladder cancer cell migration. Finally, general conclusions and future directions are discussed in chapter 7.