Parthasarathy Varadarajan, Martin Francine, Higginbottom Adrian, Murray Helen, Moseley Gregory W, Read Robert C, Mal Gorakh, Hulme Rachel, Monk Peter N, Partridge Lynda J
Department of Molecular Biology and Biotechnology, University of Sheffield, UK.
Immunology. 2009 Jun;127(2):237-48. doi: 10.1111/j.1365-2567.2008.02945.x.
Members of the tetraspanin superfamily of proteins are implicated in a variety of complex cell processes including cell fusion. However, the contribution of individual tetraspanins to these processes has proved difficult to define. Here we report the use of recombinant extracellular regions of tetraspanins to investigate the role of specific members of this family in the fusion of monocytes to form multinucleated giant cells (MGC). In contrast to their positive requirement in sperm-egg fusion, previous studies using antibodies and knockout mice have indicated a negative regulatory role for tetraspanins CD9 and CD81 in this process. In an in vitro model of fusion using human monocytes, we have confirmed observations that antibodies to CD9 and CD81 enhance MGC formation; however, in contrast to previous investigations, we found that all members of a panel of antibodies to CD63 inhibited fusion. Moreover, recombinant proteins corresponding to the large extracellular domains (EC2s) of CD63 and CD9 inhibited MGC formation, whereas the EC2s of CD81 and CD151 had no effect. The potent inhibition of fusion and binding of labelled CD63 EC2 to monocytes under fusogenic conditions suggest a direct interaction with a membrane component required for fusion. Our findings indicate that the tetraspanins CD9, CD63 and CD81 are all involved in MGC formation, but play distinct roles.
四跨膜蛋白超家族的成员参与多种复杂的细胞过程，包括细胞融合。然而，单个四跨膜蛋白对这些过程的贡献难以界定。在此，我们报道利用四跨膜蛋白的重组细胞外区域来研究该家族特定成员在单核细胞融合形成多核巨细胞（MGC）过程中的作用。与它们在精卵融合中的积极作用相反，先前使用抗体和基因敲除小鼠的研究表明，四跨膜蛋白CD9和CD81在此过程中起负调控作用。在使用人单核细胞的体外融合模型中，我们证实了CD9和CD81抗体可增强MGC形成的观察结果；然而，与先前的研究不同，我们发现一组针对CD63的抗体均抑制融合。此外，与CD63和CD9的大细胞外结构域（EC2）相对应的重组蛋白抑制MGC形成，而CD81和CD151的EC2则无此作用。在融合条件下，标记的CD63 EC2对融合和与单核细胞结合的有效抑制表明其与融合所需的膜成分直接相互作用。我们的研究结果表明，四跨膜蛋白CD9、CD63和CD81均参与MGC形成，但发挥不同作用。
