Genomic Medicine Institute, Lerner Research Institute of Cleveland Clinic, Cleveland, OH, USA.
Blood. 2011 Sep 22;118(12):3384-91. doi: 10.1182/blood-2011-05-352815. Epub 2011 Jul 27.
The type 1-transmembrane protein LMAN1 (ERGIC-53) forms a complex with the soluble protein MCFD2 and cycles between the endoplasmic reticulum (ER) and the ER-Golgi intermediate compartment (ERGIC). Mutations in either LMAN1 or MCFD2 cause the combined deficiency of factor V (FV) and factor VIII (FVIII; F5F8D), suggesting an ER-to-Golgi cargo receptor function for the LMAN1-MCFD2 complex. Here we report the analysis of LMAN1-deficient mice. Levels of plasma FV and FVIII, and platelet FV, are all reduced to ∼ 50% of wild-type in Lman1(-/-) mice, compared with the 5%-30% levels typically observed in human F5F8D patients. Despite previous reports identifying cathepsin C, cathepsin Z, and α1-antitrypsin as additional potential cargoes for LMAN1, no differences were observed between wild-type and Lman1(-/-) mice in the levels of cathepsin C and cathepsin Z in liver lysates or α1-antitrypsin levels in plasma. LMAN1 deficiency had no apparent effect on COPII-coated vesicle formation in an in vitro assay. However, the ER in Lman1(-/-) hepatocytes is slightly distended, with significant accumulation of α1-antitrypsin and GRP78. An unexpected, partially penetrant, perinatal lethality was observed for Lman1(-/-) mice, dependent on the specific inbred strain genetic background, suggesting a potential role for other, as yet unidentified LMAN1-dependent cargo proteins.
跨膜蛋白 1 型 LMAN1（ERGIC-53）与可溶性蛋白 MCFD2 形成复合物，并在内质网（ER）和 ER-Golgi 中间隔室（ERGIC）之间循环。LMAN1 或 MCFD2 中的突变导致因子 V（FV）和因子 VIII（FVIII；F5F8D）的联合缺乏，这表明 LMAN1-MCFD2 复合物具有 ER 到高尔基体货物受体的功能。在这里，我们报告了 LMAN1 缺陷型小鼠的分析。与人类 F5F8D 患者通常观察到的 5％-30％水平相比，Lman1（-/-）小鼠的血浆 FV 和 FVIII 以及血小板 FV 水平均降低至野生型的约 50％。尽管之前的报道确定组织蛋白酶 C、组织蛋白酶 Z 和 α1-抗胰蛋白酶是 LMAN1 的其他潜在货物，但在野生型和 Lman1（-/-）小鼠的肝裂解物中的组织蛋白酶 C 和组织蛋白酶 Z 水平或血浆中的 α1-抗胰蛋白酶水平方面未观察到差异。在体外测定中，LMAN1 缺陷对 COPII 包被囊泡的形成没有明显影响。然而，Lman1（-/-）肝细胞中的 ER 略有扩张，α1-抗胰蛋白酶和 GRP78 大量积累。出乎意料的是，观察到 Lman1（-/-）小鼠的部分穿透性围产期致死性，这取决于特定的近交系遗传背景，这表明其他尚未确定的 LMAN1 依赖性货物蛋白可能具有潜在作用。
