Center for Integrated Medical Research, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan.
J Biol Chem. 2011 Dec 16;286(50):43154-63. doi: 10.1074/jbc.M111.275586. Epub 2011 Oct 20.
Ectodomain shedding is a posttranslational modification mechanism, which liberates extracellular domains of membrane proteins through juxtamembrane processing executed mainly by the ADAM (a disintegrin and metalloprotease) family of metalloproteases. Shedding is a unique and effective mechanism for inducing multifaceted effects through the soluble extracellular domains released and/or the remaining membrane-bound portions; however, the physiological functions of shedding are not yet fully understood. In this study, we performed unbiased proteomic screening for shedding targets in a lipopolysaccharide (LPS)-stimulated macrophage cell line to elucidate a new immunological function of shedding. We identified VIP36 (36-kDa vesicular integral membrane protein), a lectin domain-containing transmembrane protein postulated as a cargo receptor for Golgi-to-endoplasmic reticulum transport, as a new target for shedding and found that the shedding of VIP36 occurs mainly on the cell surface. In addition, we demonstrate that the amount of VIP36 precisely regulates phagocytosis in macrophages and that the shedding of VIP36 is required for this regulation. These results substantially expand our knowledge of the immunological and cell biological functions of both the shedding process and VIP36 itself.
细胞外结构域脱落是一种翻译后修饰机制，通过主要由 ADAM（解整合素和金属蛋白酶）家族金属蛋白酶执行的跨膜加工，释放膜蛋白的细胞外结构域。脱落是通过释放可溶性细胞外结构域和/或剩余的膜结合部分来诱导多方面影响的独特而有效的机制；然而，脱落的生理功能尚未完全理解。在这项研究中，我们对脂多糖 (LPS) 刺激的巨噬细胞系中的脱落靶标进行了无偏蛋白质组学筛选，以阐明脱落的新免疫学功能。我们确定了 VIP36（36 kDa 囊泡整合膜蛋白），一种假定作为高尔基体到内质网运输货物受体的富含凝集素结构域的跨膜蛋白，作为脱落的新靶标，并发现 VIP36 的脱落主要发生在细胞表面。此外，我们证明 VIP36 的数量精确调节巨噬细胞中的吞噬作用，并且 VIP36 的脱落对于这种调节是必需的。这些结果大大扩展了我们对脱落过程和 VIP36 本身的免疫学和细胞生物学功能的认识。
