title: Ca2+ regulates T-cell receptor activation by modulating the charge property of lipids.
abstract: Ionic protein-lipid interactions are critical for the structure and function of membrane receptors, ion channels, integrins and many other proteins. However, the regulatory mechanism of these interactions is largely unknown. Here we show that Ca(2+) can bind directly to anionic phospholipids and thus modulate membrane protein function. The activation of T-cell antigen receptor-CD3 complex (TCR), a key membrane receptor for adaptive immunity, is regulated by ionic interactions between positively charged CD3ε/ζ cytoplasmic domains (CD3(CD)) and negatively charged phospholipids in the plasma membrane. Crucial tyrosines are buried in the membrane and are largely protected from phosphorylation in resting T cells. It is not clear how CD3(CD) dissociates from the membrane in antigen-stimulated T cells. The antigen engagement of even a single TCR triggers a Ca(2+) influx and TCR-proximal Ca(2+) concentration is higher than the average cytosolic Ca(2+) concentration. Our biochemical, live-cell fluorescence resonance energy transfer and NMR experiments showed that an increase in Ca(2+) concentration induced the dissociation of CD3(CD) from the membrane and the solvent exposure of tyrosine residues. As a consequence, CD3 tyrosine phosphorylation was significantly enhanced by Ca(2+) influx. Moreover, when compared with wild-type cells, Ca(2+) channel-deficient T cells had substantially lower levels of CD3 phosphorylation after stimulation. The effect of Ca(2+) on facilitating CD3 phosphorylation is primarily due to the charge of this ion, as demonstrated by the fact that replacing Ca(2+) with the non-physiological ion Sr(2+) resulted in the same feedback effect. Finally, (31)P NMR spectroscopy showed that Ca(2+) bound to the phosphate group in anionic phospholipids at physiological concentrations, thus neutralizing the negative charge of phospholipids. Rather than initiating CD3 phosphorylation, this regulatory pathway of Ca(2+) has a positive feedback effect on amplifying and sustaining CD3 phosphorylation and should enhance T-cell sensitivity to foreign antigens. Our study thus provides a new regulatory mechanism of Ca(2+) to T-cell activation involving direct lipid manipulation.
authors.affiliation: State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Xiaoshan
authors.initials: X
authors.lastname: Shi
authors.forename: Yunchen
authors.initials: Y
authors.lastname: Bi
authors.forename: Wei
authors.initials: W
authors.lastname: Yang
authors.forename: Xingdong
authors.initials: X
authors.lastname: Guo
authors.forename: Yan
authors.initials: Y
authors.lastname: Jiang
authors.forename: Chanjuan
authors.initials: C
authors.lastname: Wan
authors.forename: Lunyi
authors.initials: L
authors.lastname: Li
authors.forename: Yibing
authors.initials: Y
authors.lastname: Bai
authors.forename: Jun
authors.initials: J
authors.lastname: Guo
authors.forename: Yujuan
authors.initials: Y
authors.lastname: Wang
authors.forename: Xiangjun
authors.initials: X
authors.lastname: Chen
authors.forename: Bo
authors.initials: B
authors.lastname: Wu
authors.forename: Hongbin
authors.initials: H
authors.lastname: Sun
authors.forename: Wanli
authors.initials: W
authors.lastname: Liu
authors.forename: Junfeng
authors.initials: J
authors.lastname: Wang
authors.forename: Chenqi
authors.initials: C
authors.lastname: Xu
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D025461:Feedback, Physiological / Q000187:drug effects; D006801:Humans; D019169:Jurkat Cells; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008213:Lymphocyte Activation / Q000187:drug effects; D051379:Mice; D010743:Phospholipids / Q000737:chemistry* / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D012997:Solvents / Q000737:chemistry / Q000378:metabolism; D055672:Static Electricity; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
chemical_list: D008051:Lipid Bilayers; D010743:Phospholipids; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D012997:Solvents; D014443:Tyrosine; D002118:Calcium