Increased PD-L1 expression in radioresistant HNSCC cell lines after irradiation affects cell proliferation due to inactivation of GSK-3beta
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Daniela Schulz1, Irene Stancev1, Antonio Sorrentino2, Ayse-Nur Menevse2, Philipp Beckhove2, Gero Brockhoff3, Matthias Günther Hautmann4, Torsten Erich Reichert1, Richard Josef Bauer1,5 and Tobias Ettl1
1Department of Oral and Maxillofacial Surgery, University Hospital Regensburg, Regensburg, Germany
2Regensburg Center for Interventional Immunology, University Regensburg and Department of Hematology-Oncology, Internal Medicine III, University Hospital Regensburg, Regensburg, Germany
3Department of Gynecology and Obstetrics, University Medical Center Regensburg, Regensburg, Germany
4Department of Radiotherapy, University of Regensburg, Regensburg, Germany
5Center for Medical Biotechnology, Department of Oral and Maxillofacial Surgery, University Hospital Regensburg, Regensburg, Germany
Richard Josef Bauer, email: [email protected]
Keywords: PD-L1; immune checkpoint; head and neck cancer; irradiation; GSK-3beta
Received: November 15, 2018 Accepted: December 13, 2018 Published: January 15, 2019
At present, targeting PD-1/PD-L1 axis for immune checkpoint inhibition has improved treatment of various tumor entities, including head and neck squamous cell carcinoma (HNSCC). However, one part of the patient cohort still shows little improvement or even hyperprogression. We established three radioresistant (RR) and three radiosensitive (RS) HNSCC cell lines. RR cells showed prolonged survival as well as delayed and diminished apoptosis after irradiation with vimentin expression but no E-cadherin expression, whereas RS cell lines died early and exhibited early apoptosis after irradiation and high vimentin expression. Here, we present results demonstrating differential basal PD-L1 gene and protein expression in RR and RS HNSCC cell lines. Moreover, we observed a radiation dose dependent increase of total PD-L1 protein expression in RR cell lines up to 96h after irradiation compared to non-irradiated (non-IRR) cells. We found a significant GSK-3beta phosphorylation, resulting in an inactivation, after irradiation of RR cell lines. Co-immunoprecipitation experiments revealed decreased interaction of GSK-3beta with PD-L1 in non-IRR compared to irradiated (IRR) RR cells leading to PD-L1 stabilization in RR cells. PD-L1 knockdown in RR cells showed a strong decrease in cell survival. In summary, our results suggest an irradiation dependent increase in basal PD-L1 expression in RR HNSCC cell lines via GSK-3beta inactivation.
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