PD-L1 is an immune checkpoint ligand widely expressed on epithelial cells and is often used as a mechanism for tumor cells to evade immune killing. In order for PD-L1 to bind to its receptor on immune cells to trigger these immune inhibitory functions, it is necessary for the protein to efficiently traffic to the plasma membrane. Although PD-L1 transcriptional activation as well as protein stability and degradation have been extensively studied, not much is known about the protein’s intracellular localization and trafficking.
We use immunofluorescence and biochemical methods previously established in the lab to characterize PD-L1 intracellular trafficking kinetics, any changes associated with oncogene signaling as well as PD-L1-intrinsic mutations. We find that Akt signaling specifically regulates plasma membrane localization of PD-L1, and have identified several cytoplasmic domain mutations of PD-L1 that affect its intracellular trafficking. These mutants also display an altered glycosylation pattern, previously shown to affect PD-L1 function.
Current work focuses on identifying the molecular players involved in regulation of PD-L1 recycling to the plasma membrane as well as functional assays tying the identified perturbations of PD-L1 trafficking to its immune inhibitory function.
PD-L1 is also known to have cell-intrinsic functions with studies showing it regulates cancer cell proliferation, resistance to chemotherapy as well as interferon induced cytotoxicity. Apart from studying the localization of PD-L1 within the cells, our work also focuses on understanding how various PD-L1 mutants as well as antibody treatments affect these cell intrinsic functions. We find that the clinically used anti-PD-L1 antibody, Durvalumab, results in a loss of function of PD-L1 leading to reduced ESCRT function and reduced cell migration. Interestingly, this effect is only observed in EGFR mutant cancer cell context.
The lab is currently working on identifying the mechanism through which PD-L1 accomplishes these far reaching effects.