Decoding and functional characterization of the tonic B cell Antigen receptor signaling Network in human B cells
Final Report Abstract
The binding of antigen to the B cell antigen receptor (BCR) mediates signals that lead to the activation and differentiation of B-cells, which ultimately establishes adaptive humoral immunity through the production of antibodies. However, even in the absence of antigen, weak BCR signals are transduced that are necessary for B cell survival and some aggressive forms of B cell tumors, such as Burkitt's lymphoma (BL) or diffuse large B cell lymphoma (DLBCL), exploit dysregulation of such tonic BCR signals for their survival. Hence, a detailed understanding of tonic BCR signaling is necessary to decipher the molecular details that control B cell homeostasis and cause B cell lymphoma. In this project, we have identified important aspects of tonic BCR signaling in a physiological and pathological context by combining mass spectrometry, genetic and imaging techniques and have characterized their molecular details. By combining CRISPR/Cas9-based screens with the inhibition of BCR effectors, we were able to identify genes whose inactivation is either synergistic with certain inhibitors or those that confer resistance. Using this approach, we were able to show that certain selective autophagy processes counteract BTK-mediated survival signaling in the DLBCLs studied. BTK inhibition leads to the degradation of vesicle-associated BCR signalosomes (My T-BCR), thereby interrupting NFκB-mediated survival signaling. Our data thus mechanistically explain the good response of these lymphomas to BTK inhibition. In order to study tonic BCR signaling pathways in the physiological state, we established a B cell model that allows doxycycline-dependent switching from a proliferating to a quiescent state. In this way, we have characterized the survival-relevant effect of certain effectors of the tonic BCR pathway. Among other things, we were able to show that actinin-4 (ACTN4) is required to control the lateral mobility of BCR complexes in quiescent B cells. ACTN4 is localized in the cortical region of B cells where it stabilizes the F-actin cytoskeleton. In the absence of ACTN4, lateral BCR mobility is significantly increased, thereby reducing the efficiency of tonic BCR survival signaling. Accordingly, inactivation of ACTN4 leads to increased apoptosis in our B cell model and in purified primary human B cells. Collectively, in this research project we were able to identify essential processes of tonic BCR signaling and decipher certain processes at the molecular level. Our data thus support the understanding of tonic BCR signaling and thus the establishment of new and more specific treatments for aggressive B-cell lymphomas.
Publications
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Exceptional Response to BTK Inhibitors in Aggressive Lymphomas Linked to Chronic Selective Autophagy. Blood, 142(Supplement 1), 850-850.
Phelan, James D.; Scheich, Sebastian; Choi, Jaewoo; Wright, George; Häupl, Björn; Young, Ryan M.; Rieke, Sara; Pape, Martine; Ji, Yanlong; Urlaub, Henning; Doebele, Carmen; Zindel, Alena; Wotapek, Tanja; Kasbekar, Monica; Huang, Da Wei; Coulibaly, Zana; Morris, Vivian M.; Yu, Xin; Xu, Weihong ... & Oellerich, Thomas
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SH2 domain-containing inositol 5-phosphatases support the survival of Burkitt lymphoma cells by promoting energy metabolism. Haematologica, 0-0.
Mayr, Florian; Kruse, Vanessa; Fuhrmann, Dominik C.; Wolf, Sebastian; Löber, Jens; Alsouri, Saed; Paglilla, Nadia; Lee, Kwang; Chapuy, Björn; Brüne, Bernhard; Zenz, Thorsten; Häupl, Björn; Oellerich, Thomas & Engelke, Michael
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Actinin‐4 controls survival signaling in B cells by limiting the lateral mobility of B‐cell antigen receptors. European Journal of Immunology, 54(3).
Alsouri, Saed; Ambrose, Ashley; Mougios, Nikolaos; Paglilla, Nadia; Mayr, Florian; Choi, Kate; Loeber, Jens; Chapuy, Björn; Haeupl, Björn; Opazo, Felipe; Oellerich, Thomas; Gold, Michael & Engelke, Michael
