Membrane Raft-Dependent Regulation of Phospholipase Cγ-1 Activation in T Lymphocytes

Numerous signaling molecules associate with lipid rafts, either constitutively or after engagement of surface receptors. One such molecule, phospholipase Cγ-1 (PLCγ1), translocates from the cytosol to lipid rafts during T-cell receptor (TCR) signaling. To investigate the role played by lipid rafts in the activation of this molecule in T cells, an influenza virus hemagglutinin A (HA)-tagged PLCγ1 was ectopically expressed in Jurkat T cells and targeted to these microdomains by the addition of a dual-acylation signal. Raft-targeted PLCγ1 was constitutively tyrosine phosphorylated and induced constitutive NF-AT-dependent transcription and interleukin-2 secretion in Jurkat cells. Tyrosine phosphorylation of raft-targeted PLCγ1 did not require Zap-70 or the interaction with the adapters Lat and Slp-76, molecules that are necessary for TCR signaling. In contrast, the Src family kinase Lck was required. Coexpression in HEK 293T cells of PLCγ1-HA with Lck or the Tec family kinase Rlk resulted in preferential phosphorylation of raft-targeted PLCγ1 over wild-type PLCγ1. These data show that localization of PLCγ1 in lipid rafts is sufficient for its activation and demonstrate a role for lipid rafts as microdomains that dynamically segregate and integrate PLCγ1 with other signaling components.