CD48 antigen
membrane raft
The oxygen-substituted palmitic acid analogue, 13-oxypalmitic acid, inhibits Lck localization to lipid rafts and T cell signaling.
Palmitoylation of cysteines 3 and 5 is necessary for targeting Lck to lipid rafts and is needed for Lck function in T cell receptor (TCR) signaling. Point mutations of cysteines 3 and 5 result in a form of Lck that fails to associate with the plasma membrane, which limits the usefulness of this genetic approach to address the role of palmitoylation in the distribution of Lck within the plasma membrane. To circumvent this problem, we sought to identify a palmitic acid analogue that would enable plasma membrane association of Lck, but not facilitate its localization within lipid rafts. Here we examined the effects of the heteroatom-substituted analogue of palmitic acid, 13-oxypalmitic acid (13-OP), on Lck subcellular localization and function. 13-OP is similar in chain length to palmitic acid, but possesses reduced hydrophobicity. We found that treatment of cells with 13-OP inhibited incorporation of omega-[(125)I]iodopalmitate into Lck. 13-OP inhibited localization of Lck to lipid rafts without altering its membrane localization. Consistent with the dissociation of Lck from rafts, treatment with 13-OP abolished Lck association with the GPI-anchored protein, CD48, but not the transmembrane glycoprotein CD4. Jurkat T cells treated with 13-OP showed marked reduction in tyrosine phosphorylation and activation of mitogen-activated protein kinase upon TCR stimulation. In conclusion, the less hydrophobic analogue of palmitate, 13-OP, alters the normal acylation of Lck that provides Lck with the necessary hydrophobicity and tight packing order required for inclusion in lipid rafts.