Phosphatidylinositol (4,5) bisphosphate controls T cell activation by regulating T cell rigidity and organization

Here we investigate the role of Phosphatidylinositol (4,5) bisphosphate (PIP ₂) in the physiological activation of primary murine T cells by antigen presenting cells (APC) by addressing two principal challenges in PIP ₂ biology. First, PIP ₂ is a regulator of cytoskeletal dynamics and a substrate for second messenger generation. The relative importance of these two processes needs to be determined. Second, PIP ₂ is turned over by multiple biosynthetic and metabolizing enzymes. The joint effect of these enzymes on PIP ₂ distributions needs to be determined with resolution in time and space. We found that T cells express four isoforms of the principal PIP ₂-generating enzyme phosphatidylinositol 4-phosphate 5-kinase (PIP5K) with distinct spatial and temporal characteristics. In the context of a larger systems analysis of T cell signaling, these data identify the T cell/APC interface and the T cell distal pole as sites of differential PIP ₂ turnover. Overexpression of different PIP5K isoforms, as corroborated by knock down and PIP ₂ blockade, yielded an increase in PIP ₂ levels combined with isoform-specific changes in the spatiotemporal distributions of accessible PIP ₂. It rigidified the T cell, likely by impairing the inactivation of Ezrin Moesin Radixin, delayed and diminished the clustering of the T cell receptor at the cellular interface, reduced the efficiency of T cell proximal signaling and IL-2 secretion. These effects were consistently more severe for distal PIP5K isoforms. Thus spatially constrained cytoskeletal roles of PIP ₂ in the control of T cell rigidity and spatiotemporal organization dominate the effects of PIP ₂ on T cell activation.