Subcellular compartmentalization of signal elements and their re-distribution in resting and activated B cells

by Carolina Alexandra Martinez Grijalva
Doctoral thesis
Date of Examination:2023-12-13
Date of issue:2024-09-19
Advisor:Prof. Dr. Jürgen Wienands
Referee:Prof. Dr. Thomas Meyer
Referee:Prof. Dr. Ralph Kehlenbach
Referee:Prof. Dr. Lutz Walter
Referee:Prof. Dr. Holger Reichardt
Referee:Prof. Dr. Ralf Dressel
Persistent Address: http://dx.doi.org/10.53846/goediss-10751

 

 

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Abstract

English

BCR activation triggers a complex network of pathways and cascades, shaping the fate of B cells. This process is influenced by co-receptors as well as co-stimulatory molecules, among others. Dysregulation in this process can lead to immune disorders or B cell malignancies, emphasizing the need to understand this phenomenon. Prior research has mainly focused on individual components of BCR activation, leaving much unexplored. Translocatome studies as innovative techniques based on an unbiased and exploratory approach involving triple SILAC mass spectrometry and LGC offer new insights into regulatory mechanisms and enable a more comprehensive analysis. The primary goal of the thesis was to identify novel B cell signaling elements, particularly those with nuclear re-distribution, as they can reprogram B cells' final differentiation. The SILAC mass spectrometry data revealed three candidates, BASP1, DOCK2, and ELMO1 since they exhibited nuclear re-distribution upon BCR and/or CD40 activation. However, technical issues prevented the study of BASP1, it remains a promising candidate meriting further research. For DOCK2 and ELMO1, the research took a different path. DOCK2, a protein expressed in lymphocytes, was identified as a potential new nuclear player, especially when its partner ELMO1 was also found in the nucleus. Although their known roles relate to actin cytoskeletal reorganization, their nuclear roles were less clear. Depleting DOCK2 from Ramos B cells and the accumulating evidence from literature and studies on human patients with DOCK2 deficiency confirmed its importance in B cell activation and survival. Moreover, evidenced the importance of DOCK2 in regulating nuclear events. The investigation focused on BCR and CD40 activation, where the primary downstream events are SMH and CSR, processes carried out by AID. CSR was affected in a human patient diagnosed with DOCK2 deficiency, raising questions about the role of DOCK2 in this dysregulation. Despite structural similarities to karyopherins/importins proteins and the hypothesis that DOCK2 might be a nuclear transporter, AID's nuclear entrance was unaffected by DOCK2 depletion. Nevertheless, an interaction among AID, ELMO1, and DOCK2 was demonstrated, and the SuperDIVAC reported evidence a dysregulation in SMH in DOCK2 absence. These results together revealed a link between AID function and DOCK2:ELMO1 complex.
Keywords: B cell; translocatome; DOCK2; ELMO1 AID