A Catalytically Inactive Protein Kinase C alpha Mutation Drives Chordoid Glioma by Pathway Rewiring

Abstract

Chordoid glioma (ChG) is a rare, low-grade brain tumor characterized by a novel recurrent point mutation, D463H, in the kinase domain of protein kinase C alpha (PKCα). The mutation is invariably an Asp to His substitution, suggesting it endows a unique function beyond catalytic inactivation associated with other cancer-associated PKCα mutations. Here we use in vitro and in cellulo activity assays to show that PKCα _D463H is catalytically inactive, functions as a dominant-negative mutant to suppress endogenous PKC and uniquely rewires the cellular interactome. Specifically, phosphoproteomic, proximity labeling, and co-immunoprecipitation mass-spectrometry data from cells overexpressing PKCα _D463H identify altered phosphorylation of substrates and binding to multiple proteins involved in cell-cell junctions compared to WT enzyme. Lastly, single nuclei RNAseq reveals that ChG derives from specialized tanycytes. Our data suggest that this disease-defining, fully penetrant mutation promotes neomorphic non-catalytic scaffolding to impair cell junction function.