Mechanisms of metastasis development Breast cancer (BC) spreads to other tissues, a major cause of mortality. The identification of mechanisms that underlie such metastasis formation is a major undertaking in BC research. Fundamental Research Health © royaltystockphoto.com, Shutterstock Cancer cells form protrusions called invadopodia, which degrade the extracellular matrix to invade surrounding tissues and blood vessels during metastasis formation. Pyk2 is the non-receptor tyrosine kinase expressed in invasive cancers. This is similar to the FAK tyrosine kinase that is involved in invadopodia regulation. Despite the known correlation between Pyk2 and metastasis formation, the protein signalling mechanism that leads to invasion of BC cells into tissues has not been studied. The objective of the EU-funded BCIMPYK2 (Regulation of breast cancer invasion and metastasis by the non-receptor tyrosine kinase Pyk2) project was to investigate the role of Pyk2 in invadopodia formation as well as in regulation of invasion and metastasis in vivo. Researchers performed high-throughput protein-protein and kinase-substrate proteomic screens. Bioinformatics analysis of the results revealed cortactin as a novel substrate and interactor of Pyk2. Biochemical analysis and high-resolution 2D and 3D microscopy verified the direct interaction between Pyk2 and cortactin. Knockdown of Pyk2 in BC cells suggested that Pyk2 regulates invadopodia maturation and activation. Overall, study outcomes indicate that Pyk2 regulates cortactin recruitment and phosphorylation to promote invadopodia maturation in BC cells. Another significant achievement, the team demonstrated the overlapping and unique roles of Pyk2 and FAK kinases in invadopodia regulation. Via mouse models and gene knockdown experiments, researchers concluded that both Pyk2 and FAK regulate tumour cell invasion via different mechanisms. Pyk2 regulates invadopodia formation by recruiting Src kinase, MMP-mediated matrix degradation and actin-polymerisation dependent invasion via recruitment of cortactin. FAK regulates focal adhesion-mediated motility and consequent BC cell invasion via recruitment and activation of Src kinase and cortactin to focal adhesions. Results proved that both Pyk2 and FAK regulate BC metastasis via different mechanisms. Pyk2 regulates cell dissemination controlling invadopodia-mediated invasion and FAK mediates invasiveness controlling focal adhesion-mediated motility. The data suggest that Pyk2 and FAK might regulate the switch between fast-locomoting and slow-locomoting matrix degrading tumour cells. Keywords Metastasis, breast cancer, invadopodia, Pyk2, BCIMPYK2
