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The role of PTPRF and PTPRK in regulating cell adhesion https://doi.org/10.17863/CAM.120837 Lai, Tiffany 0000000324510892 Sharpe, Hayley Receptor-type protein tyrosine phosphatases (RPTPs) are critical regulators of cell signalling and communication, controlling cellular phospho-tyrosine (pTyr) levels and playing essential roles in tissue morphogenesis. Plasma membrane RPTPs are well positioned to sense external environmental cues, such as cell-cell contact, and transmit signals via their intracellular domains (ICDs). Among these, Protein tyrosine phosphatase receptor type K (PTPRK), and Protein tyrosine phosphatase receptor type F (PTPRF) have emerged as important players in cytoskeletal dynamics and cell-cell interactions. However, their precise molecular functions, particularly the contribution of their inactive D2 pseudophosphatase domains, remain unclear. We previously demonstrated that PTPRK promotes cell-cell adhesion by selectively dephosphorylating several junction regulators, including Afadin, which is recruited via its D2 domain. Using biochemical approaches, I investigated the specificity of this interaction and found that the same region of Afadin had previously been shown to interact with αE-catenin, a junctional plaque component. Both Afadin and αE-catenin are actin-binding proteins that are essential for cytoskeletal organisation and adherens junction regulation. We found that PTPRK competes with αE-catenin for Afadin binding when αE-catenin is under tension and in an open conformation, implicating PTPRK in mechano-regulated processes. To explore the molecular function of PTPRF, I used unbiased proteomics, structural modelling, biochemical reconstitution, and confocal imaging. This work aimed to uncover how PTPRF contributes to physiological processes such as cell migration. Mass spectrometry analysis and phosphatase activity assays identified PTPRF to dephosphorylate key cell adhesion proteins, including p120-catenin, Paxillin and Caveolin-1, in epithelial cells. In line with this, PTPRF knock out (KO) cells exhibit impaired migration, supporting a role for PTPRF in regulating focal adhesions. In silico structural studies revealed that MTSS1 and Liprin-α1 bind to the PTPRF-D2 domain in a mutually exclusive manner, suggesting a regulatory mechanism controlled by the relative stoichiometry of these interactors. Collectively this work substantially advances prior findings by demonstrating how PTPs achieve substrate and interactor specificity. These processes are subject to redox control, adding further complexity to PTPRK and PTPRF functions. By generating an interactome, this study elucidates the function of PTPRF, revealing highly context-specific utilisation of PTPRF in cell adhesion regulation. University of Cambridge 2025-03-31 Thesis Doctoral Doctor of Philosophy (PhD) eng BBSRC and Trinity College, Cambridge https://www.repository.cam.ac.uk/handle/1810/388537 embargo 2026-08-22 https://www.repository.cam.ac.uk/bitstreams/f70311fa-fe30-4500-bd0f-bc10fa546a5f/download d550396fc2a25f36a4cd89c79baf4841 https://www.repository.cam.ac.uk/bitstreams/b70c581e-0a72-45fd-bea7-242e3b67d56f/download 87eda9de84448d1f82354d60eee3eb5f http://purl.org/NET/rdflicense/allrightsreserved phosphatases