A novel function of DPP9 in DNA damage repair via BRCA2 regulation

by Maria Silva Garcia
Doctoral thesis
Date of Examination:2018-11-26
Date of issue:2019-01-25
Advisor:Dr. Ruth Geiss-Friedlander
Referee:Dr. Ruth Geiss-Friedlander
Referee:Prof. Dr. Ivo Feussner
Referee:Prof. Dr. Blanche Schwappach
Referee:Prof. Dr. Henning Urlaub
Referee:Prof. Dr. Matthias Dobbelstein
Referee:Prof. Dr. Michael Thumm
Persistent Address: http://dx.doi.org/10.53846/goediss-7253

 

 

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Abstract

English

Eukaryotic cells are constantly exposed to exogenous and endogenous agents that induce mutational stresses in their genome, which can lead to genetic lesions, such as chromosome loss, translocations or deletions. The most harmful type of DNA damage is the double-strand breaks (DSBs). Efficient repair of DNA DSBs is an essential process for maintaining genome integrity and defects in the repair of such breaks are a major cause for tumorigenesis. The dipeptidyl peptidase 9 (DPP9) protein has been associated in the last years with several cancers. Disruption of DPP9 basal levels is a common feature in tumor and inflamed cells, however, little is known about the role of DPP9 during cancer development. Here we present a new function of DPP9, which involves the enzymatic activity of DPP9 in the regulation of the DNA damage repair. Firstly, we found that DPP9 binds to chromatin and this increases upon DSBs induction. Moreover, the localization of DPP9 in the chromatin was found in close proximity to the DSBs sites where the repair machinery is recruited. In addition, we found that DPP9 senses DNA damage and deficiency of DPP9 in cells results in poor survival. Here, we identified a new interacting partner of DPP9, the Breast Cancer type 2 protein (BRCA2), a key player in the repair of DSBs. We found DPP9 and BRCA2 are in close proximity and that this interaction increases after DNA damage induction. We also showed that the enzymatic activity of DPP9 regulates BRCA2 protein turnover, stabilizing the protein in cells lacking DPP9 activity. In addition, we applied microscopy analysis to follow the localization and the interactome of BRCA2, which was disrupted upon DPP9 silencing. Consequently, the function of BRCA2 was affected as seen in the lower loading of RAD51 to the ssDNA, which is an essential process to complete the repair. Taken together, our results found a new role of DPP9 in DNA damage repair, by controlling the stability, localization and the interactome of BRCA2 protein. Moreover, we proved that defects in DPP9 can lead to deficient DNA damage repair and reduce cell survival, which open a possible explanation for the reported connection of DPP9 in cancer development.
Keywords: DPP9; BRCA2; DNA damage; Peptidase; Dipeptidase; cancer; HR repair
 
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