Particle–Based Modulation, Signaling Properties and Function of GPR133 (ADGRD1) in Glioblastoma Cells
Final Report Abstract
The overall aim of this project was to elucidate the signaling and activation mechanisms of the adhesion GPCR GPR133. The receptor is necessary for growth of glioblastoma (GBM) and is de novo expressed in GBM relative to normal brain tissue. Activation of GPR133 typically results in increased cytosolic cAMP levels. Dissociation of autoproteolytically generated N-terminal and C-terminal fragments (NTF and CTF) of GPR133 at the plasma membrane promotes receptor activation and increases signaling. Towards elucidating the mechanisms of activation of GPR133, the project initially focused on understanding the particle-based modulation of GPR133, the identification of cAMP effectors associated with GPR133 signaling in GBM cells and the effect of GPR133 modulation on GBM tumor biology. While studying the particle-based modulation of GPR133 by antibody-conjugated beads, we also tested antibodies against the N-terminus of GPR133 in the absence of beads and found that they had effects on receptor signaling. This was especially interesting, since the modulation of GPR133 function by antibodies, and other biologics as well, could be used as molecular tools in the study of receptor activation. Biologics could further be used as therapeutic platforms in the context of GBM and possibly other malignancies, where GPR133 plays important roles. Therefore, this project began to focus on the mechanism by which antibodies, targeting the NTF of GPR133, activate the receptor. Treatment of HEK293T cells overexpressing GPR133 with such antibodies increased cAMP levels in a concentrationdependent manner. Analysis of cell culture supernatants following antibody treatment revealed antibody complexes with the autoproteolytically cleaved NTF of GPR133. Cells expressing a cleavage-deficient mutant GPR133 (H543R) did not respond to antibody stimulation, suggesting that the effect is cleavage-dependent. Moreover, the antibody-mediated stimulation of wild-type GPR133, but not the cleavage-deficient H543R mutant, was reproducible in patient-derived GBM cells. In summary, these findings provide a paradigm for modulation of GPR133 function with biologics and support the hypothesis that NTF-CTF dissociation promotes receptor activation and signaling. Biologics, which could be engineered based on these findings, would serve as molecular tools towards elucidating mechanisms of receptor activation or they could be used for therapeutic approaches in disease contexts, such as GBM.
Publications
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(2020) Expression profiling of the adhesion G protein-coupled receptor GPR133 (ADGRD1) in glioma subtypes. Neuro-oncology advances 2, vdaa053
Frenster, J. D., Kader, M., Kamen, S., Sun, J., Chiriboga, L., Serrano, J., Bready, D., Golub, D., Ravn-Boess, N., Stephan, G., Chi, A. S., Kurz, S. C., Jain, R., Park, C. Y., Fenyo, D., Liebscher, I., Schöneberg, T., Wiggin, G., Newman, R., Barnes, M., Dickson, J. K., MacNeil, D. J., Huang, X., Shohdy, N., Snuderl, M., Zagzag, D., and Placantonakis, D. G.
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(2021) Adhesion G proteincoupled receptors in glioblastoma. Neuro-oncology advances 3, vdab046
Stephan, G., Ravn-Boess, N., and Placantonakis, D. G.
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(2021) Functional impact of intramolecular cleavage and dissociation of adhesion G protein-coupled receptor GPR133 (ADGRD1) on canonical signaling. The Journal of biological chemistry, 100798
Frenster, J. D., Stephan, G., Ravn-Boess, N., Bready, D., Wilcox, J., Kieslich, B., Wilde, C., Sträter, N., Wiggin, G. R., Liebscher, I., Schöneberg, T., and Placantonakis, D. G.
