Bouillon Marlene, El Fakhry Youssef, Girouard Julie, Khalil Hayssam, Thibodeau Jacques, Mourad Walid
Centre de Recherche en Rhumatologie et Immunologie, (CHUL), Département de Médecine, Université Laval, Quebec City, Quebec G1V 4G2, Canada.
J Biol Chem. 2003 Feb 28;278(9):7099-107. doi: 10.1074/jbc.M211566200. Epub 2002 Dec 22.
Lipid rafts are plasma membrane microdomains that are highly enriched in signaling molecules and that act as signal transduction platforms for many immune receptors. The involvement of these microdomains in HLA-DR-induced signaling is less well defined. We examined the constitutive presence of HLA-DR molecules in lipid rafts, their possible recruitment into these microdomains, and the role of these microdomains in HLA-DR-induced responses. We detected significant amounts of HLA-DR molecules in the lipid rafts of EBV(+) and EBV(-) B cell lines, monocytic cell lines, transfected HeLa cells, tonsillar B cells, and human monocytes. Localization of HLA-DR in these microdomains was unaffected by the deletion of the cytoplasmic domain of both the alpha and beta chains. Ligation of HLA-DR with a bivalent, but not a monovalent, ligand resulted in rapid tyrosine phosphorylation of many substrates, especially Lyn, and activation of ERK1/2 MAP kinase. However, the treatment failed to induce further recruitment of HLA-DR molecules into lipid rafts. The HLA-DR-induced signaling events were accompanied by the induction of cell-cell adhesion that could be inhibited by PTK and Lyn but not ERK1/2 inhibitors. Disruption of lipid rafts by methyl-beta-cyclodextrin (MbetaCD) resulted in the loss of membrane raft association with HLA-DR molecules, inhibition of HLA-DR-mediated protein tyrosine phosphorylation and cell-cell adhesion. MbetaCD did not affect the activation of ERK1/2, which was absent from lipid rafts. These results indicate that although all the HLA-DR-induced events studied are dependent on HLA-DR dimerization, some require the presence of HLA-DR molecules in lipid rafts, whereas others do not.
脂筏是质膜微结构域，高度富集信号分子，并作为许多免疫受体的信号转导平台。这些微结构域在HLA - DR诱导的信号传导中的作用尚不太明确。我们研究了脂筏中HLA - DR分子的组成性存在、它们可能被募集到这些微结构域的情况，以及这些微结构域在HLA - DR诱导的反应中的作用。我们在EBV(+)和EBV(-) B细胞系、单核细胞系、转染的HeLa细胞、扁桃体B细胞和人单核细胞的脂筏中检测到大量HLA - DR分子。HLA - DR在这些微结构域中的定位不受α链和β链胞质结构域缺失的影响。用二价而非单价配体连接HLA - DR导致许多底物快速酪氨酸磷酸化，尤其是Lyn，并激活ERK1/2丝裂原活化蛋白激酶。然而，该处理未能诱导HLA - DR分子进一步募集到脂筏中。HLA - DR诱导的信号事件伴随着细胞间黏附的诱导，这可被PTK和Lyn抑制剂而非ERK1/2抑制剂抑制。用甲基 - β - 环糊精（MβCD）破坏脂筏导致膜筏与HLA - DR分子的结合丧失，抑制HLA - DR介导的蛋白酪氨酸磷酸化和细胞间黏附。MβCD不影响脂筏中不存在的ERK1/2的激活。这些结果表明，尽管所研究的所有HLA - DR诱导的事件都依赖于HLA - DR二聚化，但有些事件需要脂筏中存在HLA - DR分子，而另一些则不需要。
