Bypass von mRNA-Qualitätskontrolle generiert aberrante EYA1-Isoform in tumorassoziierten Fibroblasten des Pankreas-CA

by Stefan Quickstedt
Doctoral thesis
Date of Examination:2025-03-06
Date of issue:2025-02-10
Advisor:Prof. Dr. Michael Zeisberg
Referee:Prof. Dr. Michael Zeisberg
Referee:Prof. Dr. Markus Bohnsack
Referee:Prof. Dr. mult. Thomas Meyer
Persistent Address: http://dx.doi.org/10.53846/goediss-11084

 

 

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Abstract

English

EYA1 plays a key role in the embryonic development of various organs. Further, it has a profibrotic effect, thus influencing the pathogenesis of various diseases and malignancies. Its tyrosine phosphatase activity and initiation of DNA repair mechanisms have been identified as driving factors for the profibrotic effect. Exon-array datasets have shown that EYA1 undergoes alternative splicing in different parenchymal organs, leading to the formation of various EYA1 isoforms. Alternative splicing affects the phosphatase activity of individual EYA1 isoforms and thus also their profibrotic effect. In samples from pancreatic ductal adenocarcinoma (PDAC), which is characterized by its destructive, fibrotic organ remodeling, an aberrant EYA1 splice variant called EYA1A∆e11 was identified, characterized by the loss of exon 11. For the first time, this study reports the detection of this aberrant splice variant at the protein level via western blot, both in vitro and in vivo. At the same time, a decrease in the normal variant, which predominantly appears in healthy pancreatic tissue, was observed. Additionally, EYA1A∆e11 was described as a stress-induced transcript in tumor tissue as well as isolated tumor-associated fibroblasts. Epigenetic modifications play a crucial role in gene activation and protein biosynthesis. The oxidation of 5-methylcytosine to 5-hydroxymethylcytosine (hmrC) in mRNA, catalyzed by the TET3 oxygenase, enables rapid translation of transcripts. This thesis demonstrates that cellular stress induces an increase in the expression and a simultaneous cytoplasmic shift of TET3 in PDAC, which is associated with a concomitant rise in hmrC. The detection of RNA modification was also achieved via dot blot in tumor-associated fibroblasts. This may explain the faster and enhanced expression of stress-induced transcripts such as EYA1A∆e11 and underscores the assumption that TET3 does not function as a tumor suppressor gene, as was long assumed.
Keywords: Pancreatic ductal adenocarcinoma (PDAC); EYA1; alternative splicing; RNA modification; Stress-induced transcription; TET3 dioxygenase; Hydroxymethylcytosine in mRNA (hmrC)