Metabolic inhibition by inositol-tetrakisphosphate delays thymocyte β-selection and renders it Notch-dependent (HEM2P.241)

Abstract

Abstract In β-selection, surface-expression of a pre-T cell receptor (pre-TCR) induces thymocyte metabolic activation, proliferation, survival and differentiation. This pivotal αβ T cell fate-determining event requires co-stimulatory Notch signals. Here, we show that this Notch dependence is enforced through antagonistic signaling by inositol-trisphosphate 3-kinase B (Itpkb) and phosphoinositide 3-kinase (PI3K). Itpkb produces soluble inositol-tetrakisphosphate which competes with the PI3K lipid-product PIP3 for binding to the effector-kinase Akt. Itpkb-/- thymocytes are pre-TCR hyperresponsive, hyperactivate Akt, downstream mTOR and metabolism, undergo an accelerated β-selection and can develop to CD4+CD8+ cells without Notch. This is reversed by inhibition of Akt, mTOR or glucose-metabolism. Thus, Itpkb restricts pre-TCR induced metabolic activation to enforce coincidence-detection of pre-TCR expression and Notch-engagement, and to prevent premature thymocyte maturation.