Megan D. Joseph

Protein tyrosine phosphatase nonreceptor type 22 (PTPN22) is a key negative regulator of T cell activation, acting with C-terminal Src kinase (Csk) to suppress early T cell receptor (TCR) signaling and maintain immune tolerance. Given that the autoimmune disease–associated R620W variant alters T cell responses, we investigated the effects of PTPN22 on T cell activation. We identified a role for PTPN22 in modulating cytoskeletal dynamics at the immunological synapse in Jurkat cells through its interaction with proline-serine-threonine phosphatase–interacting protein 1 (PSTPIP1), a cytoskeletal adaptor protein that recruits actin nucleation–promoting factors, including WASp, to the TCR. PTPN22 deficiency or inhibition disrupted Arp2/3-dependent actin remodeling, leading to excessive central F-actin foci, PSTPIP1 mislocalization, and enhanced Ca ²⁺ signaling, especially under low-affinity stimulation of the TCR. Super-resolution DNA-PAINT analysis revealed that loss of PTPN22 promoted aberrant PSTPIP1-TCR nanoscale colocalization and increased TCR clustering. These findings uncover a PTPN22-PSTPIP1 signaling axis that is critical for regulating cytoskeletal remodeling and receptor organization, providing insights into T cell hyperactivation that may be relevant to autoimmune disease.

Pancreatic ductal adenocarcinoma (PDAC) continues to show no improvement in survival rates. One aspect of PDAC is elevated ATP levels, pointing to the purinergic axis as a potential attractive therapeutic target. Mediated in part by highly druggable extracellular proteins, this axis plays essential roles in fibrosis, inflammation response, and immune function. Analyzing the main members of the PDAC extracellular purinome using publicly available databases discerned which members may impact patient survival. P2RY2 presents as the purinergic gene with the strongest association with hypoxia, the highest cancer cell-specific expression, and the strongest impact on overall survival. Invasion assays using a 3D spheroid model revealed P2Y₂ to be critical in facilitating invasion driven by extracellular ATP. Using genetic modification and pharmacological strategies, we demonstrate mechanistically that this ATP-driven invasion requires direct protein-protein interactions between P2Y₂ and αV integrins. DNA-PAINT super-resolution fluorescence microscopy reveals that P2Y₂ regulates the amount and distribution of integrin αV in the plasma membrane. Moreover, receptor-integrin interactions were required for effective downstream signaling, leading to cancer cell invasion. This work elucidates a novel GPCR-integrin interaction in cancer invasion, highlighting its potential for therapeutic targeting.