Shite S, Seguchi T, Shimada T, Ono M, Kuwano M
Department of Biochemistry, Oita Medical School, Japan.
Eur J Biochem. 1990 Jul 31;191(2):491-7. doi: 10.1111/j.1432-1033.1990.tb19148.x.
The low-density lipoprotein (LDL) receptor of molecular mass 155 kDa was expressed on the cell surface of cultured mouse macrophage J774 cells. The conversion rate of precursor to mature form of LDL receptor in J774 cells was comparable to that in mouse fibroblast L cells. The half-life of the LDL receptor of J774 cells was about 2 h, that of L cells was about 11 h. The rapid degradation of LDL receptor was not significantly inhibited by the lysosomotropic agents, chloroquine and NH4Cl, nor by the thiol-protease inhibitors leupeptin and E-64. By contrast, incubation at 18 degrees C retarded the degradation of LDL receptor. Treatment of J774 cells with brefeldin A, an inhibitor of membrane transport between the endoplasmic reticulum and the Golgi apparatus, inhibited the rapid turnover of the LDL receptor. Even after a 9-h chase in the presence of brefeldin A, LDL receptor 5-10 kDa smaller than the normal mature form was found to be stable. Rapid turnover of the LDL receptor in the macrophages appeared to occur after exit from the Golgi apparatus, possibly during transport of the LDL receptor to the plasma membrane.
分子量为155 kDa的低密度脂蛋白（LDL）受体在培养的小鼠巨噬细胞J774细胞的细胞表面表达。J774细胞中LDL受体前体向成熟形式的转化率与小鼠成纤维细胞L细胞中的转化率相当。J774细胞LDL受体的半衰期约为2小时，L细胞的半衰期约为11小时。溶酶体促渗剂氯喹和NH4Cl以及巯基蛋白酶抑制剂亮抑酶肽和E-64均未显著抑制LDL受体的快速降解。相比之下，在18℃孵育可延缓LDL受体的降解。用布雷菲德菌素A（一种内质网与高尔基体之间膜转运的抑制剂）处理J774细胞，可抑制LDL受体的快速周转。即使在布雷菲德菌素A存在的情况下进行9小时的追踪后，仍发现比正常成熟形式小5-10 kDa的LDL受体是稳定的。巨噬细胞中LDL受体的快速周转似乎发生在从高尔基体排出之后，可能在LDL受体向质膜转运的过程中。
