A function for tyrosine phosphorylation of type 1 inositol 1,4,5-trisphosphate receptor in lymphocyte activation

Sustained elevation of intracellular calcium by Ca(2+) release–activated Ca(2+) channels is required for lymphocyte activation. Sustained Ca(2+) entry requires endoplasmic reticulum (ER) Ca(2+) depletion and prolonged activation of inositol 1,4,5-trisphosphate receptor (IP(3)R)/Ca(2+) release channels. However, a major isoform in lymphocyte ER, IP3R1, is inhibited by elevated levels of cytosolic Ca(2+), and the mechanism that enables the prolonged activation of IP(3)R1 required for lymphocyte activation is unclear. We show that IP(3)R1 binds to the scaffolding protein linker of activated T cells and colocalizes with the T cell receptor during activation, resulting in persistent phosphorylation of IP(3)R1 at Tyr353. This phosphorylation increases the sensitivity of the channel to activation by IP(3) and renders the channel less sensitive to Ca(2+)-induced inactivation. Expression of a mutant IP3R1-Y353F channel in lymphocytes causes defective Ca(2+) signaling and decreased nuclear factor of activated T cells activation. Thus, tyrosine phosphorylation of IP3R1-Y353 may have an important function in maintaining elevated cytosolic Ca(2+) levels during lymphocyte activation.