A ‘sweet spot’ for complement receptor CD46 activity via direct regulation of glycolytic vs. moonlighting functions of GAPDH

Abstract

Abstract Autocrine engagement of the complement receptor CD46, driven by T cell receptor (TCR) activation on human CD4+ T cells, is critical for human Th1 induction: Processing of the intracellular CD46 domains by γ-secretase and their nuclear translocation mediates the expression of nutrient transporters GLUT1 and LAT1, increases glycolysis and oxidative phosphorylation, and enables metabolic reprogramming required for cell growth, expansion and effector function. How, at the molecular level, CYT-1 enables this fundamental cellular adaptation remains unknown. To probe for CYT-1 interacting proteins we generated antibodies against cleaved CYT-1 and performed co-immunoprecipitation experiments. Unexpectedly, mass spectrometry revealed association of CYT-1 with several glycolytic enzymes, including glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Although ELISA and MST-based experiments confirmed a strong, dose-dependent CYT-1/GAPDH interaction, glycolytic activity was hardly affected by CYT-1. Rather, CYT-1 modulated the activity of a key ‘moonlighting function’ of GAPDH, namely the posttranscriptional regulation of mRNA stability/translation: CYT-1 binding fostered desoligomerization of glycolytically active GAPDH tetramers to monomers with altered mRNA binding abilities – particularly for mRNAs encoding metabolic enzymes. These data identify CD46 as a ‘shape-shifter’ of GAPDH activity, critically balancing its canonical (glycolysis) versus non-canonical (posttranscriptional regulation) activity – further substantiating the notion that autocrine complement is a critical regulator of normal cell physiology.