Membrane raft-dependent regulation of phospholipase C gamma-1 activation in T lymphocytes

Numerous signaling molecules associate with lipid rafts, either constitutiv ely or after engagement of surface receptors. One such molecule, phospholip ase C gamma -1 (PLC gamma1), translocates from the cytosol to lipid rafts d uring T-cell receptor (TCR) signaling. To investigate the role played by li pid rafts in the activation of this molecule in T cells, an influenza virus hemagglutinin A (HA)-tagged PLC gamma1 was ectopically expressed in Jurkat T cells and targeted to these microdomains by the addition of a dual-acyla tion signal. Raft-targeted PLC gamma1 was constitutively tyrosine phosphory lated and induced constitutive NF-AT-dependent transcription and interleuki n-2 secretion in Jurkat cells. Tyrosine phosphorylation of raft-targeted PL C gamma1 did not require Zap-70 or the interaction with the adapters Lat an d Slp-76, molecules that are necessary for TCR signaling. In contrast, the Src family kinase Lek was required. Coexpression in HEK 293T cells of PLC g amma1-HA with Lek or the Tec family kinase Rlk resulted in preferential pho sphorylation of raft-targeted PLC gamma1 over wild-type PLC gamma1. These d ata show that localization of PLC gamma1 in lipid rafts is sufficient for i ts activation and demonstrate a role for lipid rafts as microdomains that d ynamically segregate and integrate PLC gamma1 with other signaling componen ts.