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// Daniela Schulz 1 , Irene Stancev 1 , Antonio Sorrentino 2 , Ayse-Nur Menevse 2 , Philipp Beckhove 2 , Gero Brockhoff 3 , Matthias Gunther Hautmann 4 , Torsten Erich Reichert 1 , Richard Josef Bauer 1, 5 and Tobias Ettl 1 1 Department of Oral and Maxillofacial Surgery, University Hospital Regensburg, Regensburg, Germany 2 Regensburg Center for Interventional Immunology, University Regensburg and Department of Hematology-Oncology, Internal Medicine III, University Hospital Regensburg, Regensburg, Germany 3 Department of Gynecology and Obstetrics, University Medical Center Regensburg, Regensburg, Germany 4 Department of Radiotherapy, University of Regensburg, Regensburg, Germany 5 Center for Medical Biotechnology, Department of Oral and Maxillofacial Surgery, University Hospital Regensburg, Regensburg, Germany Correspondence to: Richard Josef Bauer, email: richard.bauer@ukr.de Keywords: PD-L1; immune checkpoint; head and neck cancer; irradiation; GSK-3beta Received: November 15, 2018 Accepted: December 13, 2018 Published: January 15, 2019 ABSTRACT 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. |
