%0 Thesis
%9 Doctoral
%A Joseph, Megan Daisy
%B London Centre for Nanotechnology
%D 2025
%F discovery:10203183
%I UCL (University College London)
%P 263
%T Illuminating the role of the protein tyrosine phosphatase PTPN22 in actin remodelling by super-resolution microscopy: insights into T cell synapse formation
%U https://discovery.ucl.ac.uk/id/eprint/10203183/
%X Protein Tyrosine Phosphatase Non-Receptor Type 22 (PTPN22) is a protein tyrosine phosphatase  operating within the T cell signalling cascade. PTPN22 dephosphorylates key signalling proteins,  in combination with the binding partner c-SRC kinase (Csk), which leads to downregulation of T  cell activation. Associated with over 15 autoimmune diseases, PTPN22 R620W is one of the most  common autoimmune disease related mutations. Recently, studies have uncovered a novel binding  partner of PTPN22, proline-serine-threonine phosphatase interacting protein 1 (PSTPIP-1). Whilst  decades of research have focused on understanding the consequences of PTPN22 mutation in T cell  activation, the effects of the PTPN22-PSTPIP-1 interaction are poorly understood. PSTPIP-1 regulates F-actin remodelling via association with Wiskott-Aldrich syndrome protein (WASp). WASp  promotes the formation of F-actin foci following T cell receptor (TCR) microcluster formation,  amplifying downstream TCR signals. Mutations within PSTPIP-1 are associated with autoinflammatory disorders and immunodeficiencies. These mutations correlate with defects in F-actin  formation and lie within the PTPN22 binding domain, suggesting that PTPN22/PSTPIP-1 interactions regulate actin remodelling in T cells and thus T cell signalling. Using both live and fixed  multicolour 3D super-resolution imaging on a Spinning Disk Super Resolution by Optical Pixel  Reassignment (SoRa) microscope, this thesis describes a series of experiments exploiting Jurkat T  cells deficient in PTPN22 expression and expressing T cell receptors reactive to ligands of different  affinity. A key finding is that Jurkat T cells lacking PTPN22 exhibit aberrant actin remodelling  along with disrupted PSTPIP-1 and TCR clustering upon activation. The nanoscale organisation  of PSTPIP-1 and TCR clusters at different Z-planes was visualised using single molecule localization DNA-PAINT microscopy on the SoRa microscope, coupled with quantitative PAINT analysis.  These results uncover a novel pathway involving PTPN22 and PSTPIP-1 in T cell signalling, providing new insight into the molecular mechanisms that underpin susceptibility to a wide range of  autoimmune diseases.
%Z Copyright © The Author 2025.   Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/).  Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms.  Access may initially be restricted at the author’s request.