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Identification of Novel CK2 Kinase Substrates Using a Versatile Biochemical Approach
Published on: February 21, 2019
Chemoproteomics reveals immunogenic and tumor-associated cell surface substrates of ectokinase CK2α
Corleone S Delaveris1, Sophie Kong1, Jeff Glasgow1
1Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, CA 94158, USA.
Abstract:
Foreign epitopes for immune recognition provide the basis of anticancer immunity. Due to the high concentration of extracellular adenosine triphosphate in the tumor microenvironment, we hypothesized that extracellular kinases (ectokinases) could have dysregulated activity and introduce aberrant phosphorylation sites on cell surface proteins. We engineered a cell-tethered version of the extracellular kinase CK2α, demonstrated it was active on cells under tumor-relevant conditions, and profiled its substrate scope using a chemoproteomic workflow. We then demonstrated that mice developed polyreactive antisera in response to syngeneic tumor cells that had been subjected to surface hyperphosphorylation with CK2α. Interestingly, these mice developed B cell and CD4+ T cell responses in response to these antigens but failed to develop a CD8+ T cell response. This work provides a workflow for probing the extracellular phosphoproteome and demonstrates that extracellular phosphoproteins are immunogenic even in a syngeneic system.
Insights
Extracellular kinases can modify tumor cell surfaces, creating new antigens. These novel antigens trigger immune responses, even in syngeneic systems, offering potential for cancer immunotherapy.
Area of Science:
- Biochemistry
- Immunology
- Oncology
Background:
- Anticancer immunity relies on recognizing foreign epitopes.
- The tumor microenvironment has high extracellular adenosine triphosphate, suggesting dysregulated ectokinase activity.
- Aberrant phosphorylation of cell surface proteins by ectokinases could create tumor-specific antigens.
Purpose of the Study:
- To investigate the role of extracellular kinases in generating tumor-specific antigens.
- To develop a method for probing the extracellular phosphoproteome.
- To assess the immunogenicity of extracellularly phosphorylated proteins in a syngeneic model.
Main Methods:
- Engineered a cell-tethered version of the extracellular kinase CK2α.
- Validated CK2α activity under tumor-relevant conditions.
- Utilized a chemoproteomic workflow to profile CK2α substrate scope.
- Hyperphosphorylated syngeneic tumor cells and analyzed immune responses in mice.
Main Results:
- Demonstrated CK2α activity on cell surfaces under tumor conditions.
- Identified a range of substrates for extracellular CK2α.
- Showed that hyperphosphorylated tumor cells elicited polyreactive antisera in mice.
- Observed B cell and CD4+ T cell responses, but not CD8+ T cell responses, to these novel antigens.
Conclusions:
- Extracellular phosphoproteins are immunogenic, even in syngeneic systems.
- A workflow for probing the extracellular phosphoproteome was established.
- Dysregulated ectokinase activity in tumors can generate novel antigens for immunotherapy.
