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Selection and characterization of Fc?RI phospho-ITAM specific antibodies.

ABSTRACT: Post-translational modifications, such as the phosphorylation of tyrosines, are often the initiation step for intracellular signaling cascades. Pan-reactive antibodies against modified amino acids (e.g., anti-phosphotyrosine), which are often used to assay these changes, require isolation of the specific protein prior to analysis and do not identify the specific residue that has been modified (in the case that multiple amino acids have been modified). Phosphorylation state-specific antibodies (PSSAs) developed to recognize post-translational modifications within a specific amino acid sequence can be used to study the timeline of modifications during a signal cascade. We used the Fc?RI receptor as a model system to develop and characterize high-affinity PSSAs using phage and yeast display technologies. We selected three ?-subunit antibodies that recognized: 1) phosphorylation of tyrosines Y218 or Y224; 2) phosphorylation of the Y228 tyrosine; and 3) phosphorylation of all three tyrosines. We used these antibodies to study the receptor activation timeline of Fc?R1 in rat basophilic leukemia cells (RBL-2H3) upon stimulation with DNP24-BSA. We also selected an antibody recognizing the N-terminal phosphorylation site of the ?-subunit (Y65) of the receptor and applied this antibody to evaluate receptor activation. Recognition patterns of these antibodies show different timelines for phosphorylation of tyrosines in both ? and ? subunits. Our methodology provides a strategy to select antibodies specific to post-translational modifications and provides new reagents to study mast cell activation by the high-affinity IgE receptor, Fc?RI.

SUBMITTER: Velappan N

PROVIDER: S-EPMC6748597 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Selection and characterization of FcεRI phospho-ITAM specific antibodies.

Velappan Nileena N Mahajan Avanika A Naranjo Leslie L Velappan Priyanka P Andrews Nasim N Tiee Nicholas N Chakraborti Subhendu S Hemez Colin C Gaiotto Tiziano T Wilson Bridget B Bradbury Andrew A

mAbs 20190716 7

Post-translational modifications, such as the phosphorylation of tyrosines, are often the initiation step for intracellular signaling cascades. Pan-reactive antibodies against modified amino acids (e.g., anti-phosphotyrosine), which are often used to assay these changes, require isolation of the specific protein prior to analysis and do not identify the specific residue that has been modified (in the case that multiple amino acids have been modified). Phosphorylation state-specific antibodies (P ...[more]

PMID: 31311408

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Project description:Rationale: The overwhelming majority of radioimmunoconjugates are produced via random conjugation methods predicated on attaching bifunctional chelators to the lysines of antibodies. However, this approach inevitably produces poorly defined and heterogeneous immunoconjugates because antibodies have several lysines distributed throughout their structure. To circumvent this issue, we have previously developed a chemoenzymatic bioconjugation strategy that site-specifically appends cargoes to the biantennary heavy chain glycans attached to CH2 domains of the immunoglobulin's Fc region. In the study at hand, we explore the effects of this approach to site-specific bioconjugation on the Fc receptor binding and in vivo behavior of radioimmunoconjugates. Methods: We synthesized three desferrioxamine (DFO)-labeled immunoconjugates based on the HER2-targeting antibody pertuzumab: one using random bioconjugation methods (DFO-nsspertuzumab) and two using variants of our chemoenzymatic protocol (DFO-sspertuzumab-EndoS and DFO-sspertuzumab-?Gal). Subsequently, we characterized these constructs and evaluated their ability to bind HER2, human Fc?RI (huFc?RI), and mouse Fc?RI (muFc?RI). After radiolabeling the immunoconjugates with zirconium-89, we conducted PET imaging and biodistribution studies in two different mouse models of HER2-expressing breast cancer. Results: MALDI-ToF and SDS-PAGE analysis confirmed the site-specific nature of the bioconjugation, and flow cytometry and surface plasmon resonance (SPR) revealed that all three immunoconjugates bind HER2 as effectively as native pertuzumab. Critically, however, SPR experiments also illuminated that DFO-sspertuzumab-EndoS possesses an attenuated binding affinity for huFc?RI (17.4 ± 0.3 nM) compared to native pertuzumab (4.7 ± 0.2 nM), DFO-nsspertuzumab (4.1 ± 0.1 nM), and DFO-sspertuzumab-?Gal (4.7 ± 0.2 nM). ImmunoPET and biodistribution experiments in athymic nude mice bearing HER2-expressing BT474 human breast cancer xenografts yielded no significant differences in the in vivo behavior of the radioimmunoconjugates. Yet experiments in tumor-bearing humanized NSG mice revealed that 89Zr-DFO-sspertuzumab-EndoS produces higher activity concentrations in the tumor (111.8 ± 39.9 %ID/g) and lower activity concentrations in the liver and spleen (4.7 ± 0.8 %ID/g and 13.1 ± 4.0 %ID/g, respectively) than its non-site-specifically labeled cousin, a phenomenon we believe stems from the altered binding of the former to huFc?RI. Conclusion: These data underscore that this approach to site-specific bioconjugation not only produces more homogeneous and well-defined radioimmunoconjugates than traditional methods but may also improve their in vivo performance in mouse models by reducing binding to Fc?RI.

Dataset Information

Selection and characterization of Fc?RI phospho-ITAM specific antibodies.

Publications

Selection and characterization of FcεRI phospho-ITAM specific antibodies.

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