Theses Doctoral

The missing link: PAG orchestrates T cell immune synapse function by binding to actin

Moore, Emily

Despite breakthroughs in research and treatment, cancer remains a leading cause of mortality in the U.S. and globally. Immunotherapy represents a promising class of cancer medications that target proteins found on the surface of T cells to alter signaling in T cell immune synapses. A key target in this field is the checkpoint protein PD-1. Although anti-PD-1 antibody therapy is very successful in some patients, in others it can fail or even result in complications like cancer hyper-progression and immune-related adverse effects. Enhancing response rates and preventing autoimmune reactions requires a deeper understanding of the PD-1 pathway to create more nuanced therapies and combination strategies.

Our 2022 review focused on promising targets within the PD-1 pathway, including the phosphatases SHP2 and PTPN2; kinases ITK, VRK2, GSK-3, and CDK4/6; as well as the signaling adaptor protein PAG. While all of these proteins are strong candidates for combination therapy, our work shown here focuses on PAG. The transmembrane adaptor Phosphoprotein Associated with Glycosphingolipid-enriched microdomains 1 (PAG) is phosphorylated in T cells following PD-1 ligation and necessary for PD-1function.

In our 2022 research, we developed an antibody that targets PAG, resulting in its mislocalization within the immune synapse and enhancing the anti-tumor immune response in a mouse tumor model. To optimally develop and implement an anti-PAG therapeutic antibody, it’s essential to consider all of PAG's functions. Beyond its role in PD-1 signaling, PAG is found in lipid rafts and acts as a scaffold, gathering various kinases and phosphatases to this vital area of intracellular signaling. PAG contains a PDZ domain, allowing it to connect lipid rafts, kinases/phosphatases, and the actin cytoskeleton. This dissertation demonstrates that PAG acts with actin to regulate T cell synapse organization and function. Mutating PAG in its PDZ domain disrupts the PAG-actin connection, which hinders synapse formation, stability, and function. To investigate the functional impact of the PDZ mutation in vivo, we used a mouse model of type IV hypersensitivity alongside an OVA-tumor mouse model.

In both instances, mice with T cells expressing PDZ-mutant PAG showed weakened immune responses, including impaired cytotoxic function. These findings underscore the significance of the PAG-actin link in eliciting effective T cell immune responses. Although many questions remain, our findings support therapeutically targeting PAG as a promising strategy for modulating immune responses and treating immune- related conditions and diseases.

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More About This Work

Academic Units
Cellular, Molecular and Biomedical Studies
Thesis Advisors
Mor, Adam
Degree
Ph.D., Columbia University
Published Here
January 29, 2025