The phosphatidylinositol-transfer protein Nir3 modulates T cell development and function

Abstract

Abstract Before emerging as functional T lymphocytes, thymocytes transit through multiple selection stages during which T cell antigen receptor (TCR) signaling controls the survival and subsequent maturation. Hydrolysis of phosphatidylinositol 4,5-biphosphate (PIP2) by phospholipase C-γ (PLCγ1) represents a critical step in T cell receptor (TCR) signaling which leads to calcium increases as well as PKC and Ras activation, events that contribute to T cell activation. PIP2 in the plasma membrane (PM) is depleted rapidly upon TCR stimulation and the replenishment of PIP2 levels is dependent on delivery of its precursor phosphatidylinositol (PI) from the endoplasmic reticulum (ER) to the PM. It was not clear how the delivery of PI from ER is regulated in thymocytes and T cells or how the process impacts T cell development and function. Here, we show that a membrane-associated PI transfer protein, Nir3 (Pitpnm2), promotes PIP2 replenishment following TCR stimulation and is important for T cell development. The high expression level of the Nir3 gene in thymocytes suggests its role in thymocyte selection. In Nir3 deficient thymocytes, the replenishment of PIP2 following TCR stimulation is significantly slower. Moreover, Nir3 deficiency attenuates calcium mobilization in DP thymocytes in response to weak TCR stimulation. The impaired TCR signaling led to impaired thymocyte development at the beta-selection and positive selection stages in Nir3 deficient mice. These findings reveal the role of Nir3 in TCR signaling and thymocyte development. This study highlights the importance of PIP2 replenishment and the role of Nir3 in PI transfer through regulated ER-PM interactions during TCR signaling. This work was supported by in part by the Howard Hughes Medical Institute, the National Institutes of Health (NIH), NIAID R37 AI114575, and DRC Center Grant P30 DK063720 (UCSF Parnassus Flow Cytometry Core, UCSF Diabetes Center).