Increased cFLIP expression in thymic epithelial tumors blocks autophagy via NF-κB signalling

// Djeda Belharazem 1 , Albert Grass 1 , Cornelia Paul 1 , Mario Vitacolonna 2 , Berthold Schalke 3 , Ralf J. Rieker 4, 5 , Daniel Korner 6 , Philipp Jungebluth 6 , Katja Simon-Keller 1 , Peter Hohenberger 2 , Eric M. Roessner 2 , Karsten Wiebe 7 , Thomas Grater 8 , Thomas Kyriss 9 , German Ott 10, 11 , Peter Geserick 12 , Martin Leverkus 12, 13, * , Philipp Strobel 14 and Alexander Marx 1 1 Institute of Pathology and Medical Research Center (ZMF), University Medical Centre Mannheim, University of Heidelberg, Mannheim, Germany 2 Department of Thoracic Surgery, University Medical Centre Mannheim, University of Heidelberg, Mannheim, Germany 3 Department of Neurology, University of Regensburg, Regensburg, Germany 4 Institute of Pathology, University Hospital Heidelberg, University of Heidelberg, Heidelberg, Germany 5 Institute of Pathology, University Hospital Erlangen, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen, Germany 6 Department of Thoracic Surgery, Thorax Clinic, University of Heidelberg, Heidelberg, Germany 7 Department of Thoracic Surgery, University of Munster, Munster, Germany 8 Department of Thoracic Surgery, Clinic Lowenstein, Lowenstein, Germany 9 Department of Thoracic Surgery, Clinic Schillerhohe, Robert-Bosch-Hospital, Gerlingen, Germany 10 Department of Clinical Pathology, Robert-Bosch-Hospital, Stuttgart, Germany 11 Dr. Margarete Fischer-Bosch Institute for Clinical Pharmacology, Stuttgart, Germany 12 Department of Dermatology, Venereology, and Allergology, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany 13 Department for Dermatology and Allergology, University Hospital Aachen, RWTH Aachen, Aachen, Germany 14 Institute of Pathology, University Medical Center Gottingen, University of Gottingen, Gottingen, Germany * Deceased Correspondence to: Djeda Belharazem, email: djeda.belharazem@medma.uni-heidelberg.de Keywords: thymic tumors, cFLIP, NF-κB, senescence, autophagy Received: September 01, 2016 Accepted: December 26, 2016 Published: February 06, 2017 ABSTRACT The anti-apoptotic cellular FLICE-like inhibitory protein cFLIP plays a pivotal role in normal tissues homoeostasis and the development of many tumors, but its role in normal thymus (NT), thymomas and thymic carcinomas (TC) is largely unknown. Expression, regulation and function of cFLIP were analyzed in biopsies of NT, thymomas, thymic squamous cell carcinomas (TSCC), thymic epithelial cells (TECs) derived thereof and in the TC line 1889c by qRT-PCR, western blot, shRNA techniques, and functional assays addressing survival, senescence and autophagy. More than 90% of thymomas and TSCCs showed increased cFLIP expression compared to NT. cFLIP expression declined with age in NTs but not in thymomas. During short term culture cFLIP expression levels declined significantly slower in neoplastic than non-neoplastic primary TECs. Down-regulation of cFLIP by shRNA or NF-κB inhibition accelerated senescence and induced autophagy and cell death in neoplastic TECs. The results suggest a role of cFLIP in the involution of normal thymus and the development of thymomas and TSCC. Since increased expression of cFLIP is a known tumor escape mechanism, it may serve as tissue-based biomarker in future clinical trials, including immune checkpoint inhibitor trials in the commonly PD-L1 high thymomas and TCs.