Nanoscale engagement of programmed death ligand 1 (PD-L1) in membrane lipid raft domains of cancer cells

Authors:

Simone Civita, Martina Ruglioni, Matteo Mariangeli, Serena Barachini, Tiziano Salvadori, Sofia Cristiani, Vittoria Carnicelli, Iacopo Petrini, Irene Nepita, Marco Castello, Alberto Diaspro, Stefano Fogli, Paolo Bianchini, Barbara Storti, Ranieri Bizzarri, Romano Danesi

Keywords:

confined diffusion; lipid rafts; PD-L1; STED; STORM

Abstract:

Several tumors have evolved the ability to evade the immune system by expressing programmed death ligand 1 (PD-L1; also known as programmed cell death 1 ligand 1) on the membrane of neoplastic cells. PD-L1 binds the receptor programmed cell death protein 1 (PD-1) on T cells, deactivating the immune response. Accordingly, PD-L1 has recently become a crucial target for cancer therapy. Yet, the molecular organization of PD-L1 on the membrane is still rather obscure. Here, we investigated the plasma membrane organization of PD-L1 by a multiscale fluorescence imaging toolbox reaching the nanoscale by super-resolution microscopy. Our results indicate that a major fraction of PD-L1 is largely engaged in membrane nanodomains of 25 nm mean radius, which in turn organize in an irregular mesoscopic lattice with mean interdomain distance of about 180 nm. The significant colocalization of PD-L1 with lipid raft markers, which we assessed from 200 to 250 nm down to < 10 nm, supports a raft-driven organization of PD-L1, which may follow its extended palmitoylation upon expression. This pattern was also demonstrated in living cells by visualizing PD-L1 diffusion at different spatial scales. The raft-orchestrated multiscale PD-L1 organization on the cell membrane may afford novel targets for improved immuno-oncology strategies.

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