measuring-cell-edge-protrusion-dynamics-during-spreading-using-live

Measuring Cell-Edge Protrusion Dynamics during Spreading using Live-Cell Microscopy

The development and homeostasis of multicellular organisms rely on coordinated regulation of cell migration. Cell migration is an essential event in the ...

Bar Ilan University

Bar-Ilan University

The nonreceptor tyrosine kinase Pyk2 is highly expressed in invasive breast cancer, but the mechanism by which it potentiates tumor cell invasiveness is unclear at present. Using high-throughput protein array screening and bioinformatic analysis, we identified cortactin as a novel substrate and interactor of proline-rich tyrosine kinase 2 (Pyk2). Pyk2 colocalizes with cortactin to invadopodia of invasive breast cancer cells, where it mediates epidermal growth factor-induced cortactin tyrosine phosphorylation both directly and indirectly via Src-mediated Abl-related gene (Arg) activation, leading to actin polymerization in invadopodia, extracellular matrix degradation, and tumor cell invasion. Both Pyk2 and the closely related focal adhesion kinase (FAK) regulate tumor cell invasion, albeit via distinct mechanisms. Although Pyk2 regulates tumor cell invasion by controlling invadopodium-mediated functions, FAK controls invasiveness of tumor cells by regulating focal adhesion-mediated motility. Collectively, our findings identify Pyk2 as a unique mediator of invadopodium formation and function and also provide a novel insight into the mechanisms by which Pyk2 mediates tumor cell invasion.

Pyk2 and FAK differentially regulate invadopodia formation and function in breast cancer cells.

Recent advances in proteomic screening approaches have led to the isolation of a wide variety of binding partners to interacting proteins and opened an avenue to analyze and understand signaling pathways. The study of protein-protein interactions is a key component in elucidating and understanding signaling pathways. Despite the importance of these interactions, very few studies are quantitative or report binding affinities. Here we present a simple method for examination and analysis of direct protein-protein binding interactions between two purified proteins. In the quantitative pull-down assay, one protein (the bait protein) is immobilized on beads whereas a second protein (the prey) is kept in solution. The concentration of the bait protein is kept constant, whereas the concentration of the prey protein is increased until binding saturation is achieved. After incubation, the beads are precipitated to separate unbound prey protein in solution from prey protein bound to the bait. The fraction of bound prey protein can then be loaded on a protein gel and the resulting bands can be analyzed with standard software. The quantitative pull-down assay with purified recombinant proteins provides a simple method to obtain dissociation constants ( ). These quantifications are invaluable to compare relative binding of proteins, to map binding sites, and to show that binding is direct. This assay presents a powerful method to quantitatively analyze protein-protein interactions with tools that are available in most biochemistry laboratories and does not require the use of specialized or expensive equipment.

A guide to simple, direct, and quantitative  binding assays.

Focal adhesion kinase (FAK) is well established as a regulator of cell migration, but whether and how the closely related proline-rich tyrosine kinase 2 (Pyk2) regulates fibroblast motility is still under debate. Using mouse embryonic fibroblasts (MEFs) from Pyk2 mice, we show here, for the first time, that lack of Pyk2 significantly impairs both random and directed fibroblast motility. Pyk2 MEFs show reduced cell-edge protrusion dynamics, which is dependent on both the kinase and protein-protein binding activities of Pyk2. Using bioinformatics analysis of in vitro high- throughput screens followed by text mining, we identified CrkI/II as novel substrates and interactors of Pyk2. Knockdown of CrkI/II shows altered dynamics of cell-edge protrusions, which is similar to the phenotype observed in Pyk2 MEFs. Moreover, epistasis experiments suggest that Pyk2 regulates the dynamics of cell-edge protrusions via direct and indirect interactions with Crk that enable both activation and down-regulation of Crk-mediated cytoskeletal signaling. This complex mechanism may enable fine-tuning of cell-edge protrusion dynamics and consequent cell migration on the one hand together with tight regulation of cell motility, a process that should be strictly limited to specific time and context in normal cells, on the other hand.

Article	Year
Pyk2 and FAK differentially regulate invadopodia formation and function in breast cancer cells. The Journal of cell biology\| PubMed ID: 29133485	2018
A guide to simple, direct, and quantitative binding assays. Journal of biological methods\| PubMed ID: 31453222	2017
Pyk2 regulates cell-edge protrusion dynamics by interacting with Crk. Molecular biology of the cell\| PubMed ID: 34432482	2021

Stefanie Lapetina

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