The phosphatidylinositol-transfer protein Nir3 promotes PI(4,5)P 2 replenishment in response to TCR signaling during T cell development and survival.

Hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP 2 ) by phospholipase C-γ (PLCγ1) represents a critical step in T cell antigen receptor (TCR) signaling and subsequent thymocyte and T cell responses. PIP 2 replenishment following its depletion in the plasma membrane (PM) is dependent on delivery of its precursor phosphatidylinositol (PI) from the endoplasmic reticulum (ER) to the PM. We show that a PI transfer protein (PITP), Nir3 (Pitpnm2), promotes PIP 2 replenishment following TCR stimulation and is important for T cell development. In Nir3 -/- T lineage cells, the PIP 2 replenishment following TCR stimulation is slower. Nir3 deficiency attenuates calcium mobilization in double-positive (DP) thymocytes in response to weak TCR stimulation. This impaired TCR signaling leads to attenuated thymocyte development at TCRβ selection and positive selection as well as diminished mature T cell fitness in Nir3 -/- mice. This study highlights the importance of PIP 2 replenishment mediated by PITPs at ER-PM junctions during TCR signaling.