Science, Technology and Engineering

Lock Laboratory

Department of Biochemistry

Figure 2. Cartoon of a tumour cell in contact with the extracellular matrix (ECM) showing some of the signalling pathways involved in invadopodium formation and ECM degradation.

Figure 1. Confocal microscopy image of cancer cells (actin is stained orange, nucleus blue) on a film of FITC-labelled gelatin (green). Zones of proteolytically degraded gelatin appear black.Figure 3. Confocal microscopy image of a B16F10 melanoma cell in which fluorescent Tks5 (green) and Nck1 (red) can be seen to co-localize within invadopodia (yellow signal).

Cancer cell signalling pathways in invasion and metastasis

Metastasis – the dissemination of a primary tumour to another tissue – is perhaps the least understood property of cancer, although it remains the leading cause of death. A key step in metastasis is the proteolysis-dependent invasion of cancer cells through extracellular matrix (ECM) barriers such as the basement membranes that line all epithelial and endothelial tissues. In invasive breast cancer, melanoma and other tumour cells, several of the extracellular proteases that degrade the ECM are targeted to needle-like projections called invadopodia.

Invadopodia form on the ventral surface of invasive cells and can be visualized and studied by culturing cells on a fluorescently labelled ECM substrate such as FITC-gelatin; proteolysis of the substrate by active invadopodia results in the appearance of fluorescence-negative (black) zones underneath the cells (Figure 1). In addition to harbouring multiple enzymes involved in ECM degradation, invadopodia contain receptors involved in ECM adhesion and are also major centres of signal transduction, actin reorganization and membrane remodelling (Figure 2). Research into the molecular biology of invadopodia has the potential to identify molecular targets that may be useful in the treatment of cancer.

Our interest in invadopodia revolves around the Src tyrosine kinase, which can trigger invadopodia formation, and its substrates, many of which are targeted to invadopodia and contribute to their regulation. One of these molecules is the multidomain scaffold protein Tks5/Fish, which we discovered several years ago. In recent studies aimed at understanding the role of Tks5 in invadopodia we have demonstrated that phosphorylation of Tks5 by Src promotes the recruitment of the adaptor proteins, Nck1 and Nck2, which in turn link Tks5 to invadopodia actin regulation and extracellular matrix degradation (Figure 3). We are continuing to explore the biology of invadopodia and investigate the roles of Src, Tks5 and Nck in invasion using a variety of strategies.