A novel modulator of cellular invasion and metastasis

Introduction: Metastasis is a vital process responsible for the majority of endocrine cancer deaths. Central to the ability of cells to move is the recruitment of actin fibres at the periphery of the cell by the cortical actin binding protein cortactin. A precise understanding of all of cortactin's mechanisms is required to address metastatic cell activity.

Materials and Methods: We used IP-MS to discover protein binding partners. We determined the interaction and co-localisation between cortactin and PBF through co-immunoprecipitation (Co-IP), immunofluorescence and Proximity Ligation Assays. Boyden chamber assays were used to quantify cell invasion. Western blotting and real-time PCR were used to study the levels of gene expression in papillary thyroid cancers (PTC).

Results: We identify the proto-oncogene PBF as a new functional binding partner of cortactin, PBF has recently been correlated with thyroid and breast cancer metastasis. Cortactin and PBF co-localised and bound preferentially at the leading edge of migrating cells. Oncogenic expression of PBF induced potent cell invasion and migration in thyroid (p = 0.01) and breast (p < 0.001) cancer cells, which was entirely abrogated by cortactin knockdown. In N = 43 matched PTC, cortactin was significantly upregulated at the mRNA (p = 0.022) and protein (p = 0.045) levels, particularly in more aggressive tumours, and significantly correlated with PBF expression. We also demonstrate the interaction between PBF and cortactin through co-IP and reveal that artificially targeting PBF to the plasma membrane results in increased cortactin binding, blocking cellular invasion.

Conclusion: Taken together, we identify a new modulator of cortactin function, and show for the first time that cortactin is over-expressed in thyroid cancer. Modulation of PBF subcellular localisation may present a novel mechanism of addressing tumour cell invasion and migration.