Novel insights into the role of BAFFR and CVID-associated BAFFR variants

Abstract: Binding of the pro-survival factor BAFF to its receptor BAFFR activates a variety of different cellular functions through different downstream signaling pathways, including NF-кB2 and PI3K/AKT. By stimulating protein synthesis, energy metabolism and nutrient transport across the plasma membrane, these functions support the survival of B cells. In humans, complete BAFFR deficiency therefore results in a developmental block at the stage of transitional B cells resulting in a strong reduction of mature B cell numbers, severe hypogammaglobulinemia and impaired immune responses. In addition to BAFFR deficiency, variants resulting in missense mutations have been found in patients suffering from common variable immunodeficiency. Since little is known about their impact on BAFFR function, I established an experimental model that allowed to study if these variants impaired BAFF binding to BAFFR, receptor oligomerization, interactions with CD79B, activation of NF-kB2, AKT and ERK1/2, as well as BAFF-induced shedding of the BAFFR ectodomain. To this end, six different CVID-associated BAFFR variants (P21R, A52T, G64V, DUP92-95, H159Y, and P21R-H159Y) were expressed in the Burkitt’s lymphoma cell line DG-75. The experiments revealed that binding of BAFF to BAFFR was affected by P21R and A52T, while spontaneous oligomerization of BAFFR was disturbed by P21R, A52T, G64V and P146S. BAFF-dependent activation of NF-κB2 was reduced by P21R and P146S, whereas interactions between BAFFR and the B cell antigen receptor component CD79B as well as AKT phosphorylation were impaired by P21R, A52T, G64V, and DUP92-95. In addition, P21R, G64V, and DUP92-95 interfered with phosphorylation of ERK1/2 and BAFF-induced shedding of the BAFFR ectodomain was only impaired by P21R.
BAFFR activates the PI3K and it has been suggested that it requires the interaction with proteins of the BCR complex and signalosome (CD79A, SYK and CD19). Here, we show that the BCR-associated kinase LYN is the main initiator of the PI3K downstream BAFFR, as BAFF binding induces LYN activation while loss of LYN expression or inhibition of its enzymatic activity prevented AKT phosphorylation.
Binding of BAFF to BAFFR changes BAFFR conformation and induces intracellular signaling as well as shedding of the receptor ectodomain by ADAM10 and ADAM17.
Since we found by proteomic analysis association between various peptidyl-prolyl cis-trans isomerases (PPIs) and BAFFR, we mutated two highly evolutionary conserved proline residues (P73 and P75) in the extracellular domain close to the cell surface that could potentially serve as substrates for the PPIs. As a control, we also mutated one proline residue (P82) within the transmembrane domain that would be inaccessible to the PPIs or the protease activity of ADAMs. Our results reveal that either by mutating the PPIs substrate or by directly blocking the PPIs activity, we were able to increase BAFF-induced BAFFR processing. These findings indicate that the PPIs keep BAFFR in a conformation that is resistant to ADAM10 and ADAM17 mediated processing.
Thus, the DG-75 model system proved to be useful to examine the impacts of natural variants on the function of BAFFR. It can now be used to study if other variants change the biological activity of BAFFR and such variants may contribute to agammaglobulinemia

Object Details

• Location: Deutsche Nationalbibliothek Frankfurt am Main
• Extent: Online-Ressource
• Language: Englisch
• Notes: Universität Freiburg, Dissertation, 2022

Classification and Topics

• Keyword: Signaltransduktion ; B-Lymphozyt

Contributors, Places and Time

• Event: Veröffentlichung
• (where): Freiburg
• (who): Universität
• (when): 2022
• Creator: Block Saldana, Violeta Valeria
• Contributor: Eibel, Hermann ; Warnatz, Klaus ; Minguet, Susana ; Klinik für Rheumatologie und Klinische Immunologie. Freiburg im Breisgau ; Albert-Ludwigs-Universität Freiburg. Fakultät für Biologie

Further information

• DOI: 10.6094/UNIFR/229050
• URN: urn:nbn:de:bsz:25-freidok-2290504
• Rights: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Last update: 14.08.2025, 10:52 AM CEST