Joseph, Megan Daisy;
(2025)
Illuminating the role of the protein tyrosine phosphatase PTPN22 in actin remodelling by super-resolution microscopy: insights into T cell synapse formation.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
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.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Illuminating the role of the protein tyrosine phosphatase PTPN22 in actin remodelling by super-resolution microscopy: insights into T cell synapse formation |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | 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. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10203183 |
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