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Published on: September 28, 2018
Cell surface interactome analysis identifies TSPAN4 as a negative regulator of PD-L1 in melanoma
Guus A Franken1, Andrea Abel Gutierrez1, Imke van Rossum1
1Department of Medical BioSciences, Radboud Institute for Medical Innovation, Radboud University Medical Center, Nijmegen, The Netherlands.
Abstract:
PD-L1 is a key immune checkpoint ligand that suppresses antitumor immunity by engaging PD-1 on T cells. While therapeutic blockade of PD-L1/PD-1 interactions has shown clinical benefit, many patients fail to respond, indicating modulation by other factors. Here, we identified a novel regulatory axis in which the membrane-organizing protein tetraspanin-4 (TSPAN4) modulates PD-L1 in melanoma cells. Using cell surface proximity biotinylation coupled with mass spectrometry, we discovered that TSPAN4 physically associates with PD-L1, with both proteins colocalizing on migrasomes and retraction fibers. Mechanistically, we show that TSPAN4 negatively regulates PD-L1 protein levels by enhancing its degradation and restricting its lateral mobility at the plasma membrane. Loss of TSPAN4 stabilized PD-L1, promoted its interaction with CMTM6, and increased PD-L1 surface availability for PD-1 binding. Functionally, TSPAN4 knockdown in melanoma cells led to more efficient immune checkpoint blockade through PD-1 on T cells. This study identifies TSPAN4 as a negative regulator of PD-L1 at the cell surface of melanoma cells suggesting that targeting TSPAN4 may offer a new therapeutic strategy to enhance immune checkpoint blockade in melanoma and other cancers.
Insights
Tetraspanin-4 (TSPAN4) reduces levels of PD-L1, a protein that hinders anti-cancer immune responses. Targeting TSPAN4 could improve melanoma treatments by increasing PD-L1 availability for immune checkpoint blockade.
Area of Science:
- Immunology
- Cancer Biology
- Cell Biology
Background:
- Programmed death-ligand 1 (PD-L1) is crucial in immune checkpoints, suppressing anti-tumor immunity via PD-1 interaction.
- Despite therapeutic benefits of PD-L1/PD-1 blockade, patient response rates are limited, suggesting involvement of other regulatory factors.
Purpose of the Study:
- To investigate the role of tetraspanin-4 (TSPAN4) in regulating PD-L1 expression and function in melanoma cells.
- To identify novel mechanisms controlling PD-L1 surface availability and its impact on anti-tumor immunity.
Main Methods:
- Cell surface proximity biotinylation and mass spectrometry to identify protein interactions.
- Analysis of TSPAN4 and PD-L1 colocalization on cellular structures like migrasomes and retraction fibers.
- Assessment of PD-L1 protein levels, degradation, lateral mobility, and interaction with CMTM6 following TSPAN4 modulation.
Main Results:
- TSPAN4 physically associates with PD-L1, colocalizing on migrasomes and retraction fibers.
- TSPAN4 negatively regulates PD-L1 protein levels by promoting its degradation and restricting its plasma membrane mobility.
- TSPAN4 knockdown stabilizes PD-L1, enhances its interaction with CMTM6, and increases surface PD-L1 availability for PD-1 binding.
Conclusions:
- TSPAN4 acts as a negative regulator of PD-L1 at the melanoma cell surface.
- Targeting TSPAN4 presents a potential therapeutic strategy to enhance the efficacy of immune checkpoint blockade in melanoma and other cancers.
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