Spiro D J, Boll W, Kirchhausen T, Wessling-Resnick M
Program in Biological and Biomedical Sciences, Harvard Medical School, Boston, Massachusetts 02115, USA.
Mol Biol Cell. 1996 Mar;7(3):355-67. doi: 10.1091/mbc.7.3.355.
Treatment with the phosphatidylinositol 3-kinase inhibitor wortmannin promotes approximately 30% decrease in the steady-state number of cell-surface transferrin receptors. This effect is rapid and dose dependent, with maximal down-regulation elicited with 30 min of treatment and with an IC50 approximately 25 nM wortmannin. Wortmannin-treated cells display an increased endocytic rate constant for transferrin internalization and decreased exocytic rate constants for transferrin recycling. In addition to these effects in vivo, wortmannin is a potent inhibitor (IC50 approximately 15 nM) of a cell-free assay that detects the delivery of endocytosed probes into a common compartment. Inhibition of the in vitro assay involves the inactivation of a membrane-associated factor that can be recruited onto the surface of vesicles from the cytosol. Its effects on the cell-free assay suggest that wortmannin inhibits receptor sorting and/or vesicle budding required for delivery of endocytosed material to "mixing" endosomes. This idea is consistent with morphological changes induced by wortmannin, which include the formation of enlarged transferrin-containing structures and the disruption of the perinuclear endosomal compartment. However, the differential effects of wortmannin, specifically increased transferrin receptor internalization and inhibition of receptor recycling, implicate a role for phosphatidylinositol 3-kinase activity in multiple sorting events in the transferrin receptor's membrane traffic pathway.
用磷脂酰肌醇3激酶抑制剂渥曼青霉素处理可使细胞表面转铁蛋白受体的稳态数量减少约30%。这种效应迅速且呈剂量依赖性，30分钟处理可引发最大程度的下调，渥曼青霉素的半数抑制浓度（IC50）约为25 nM。经渥曼青霉素处理的细胞对转铁蛋白内化的内吞速率常数增加，而对转铁蛋白再循环的胞吐速率常数降低。除了在体内的这些效应外，渥曼青霉素还是一种有效的无细胞检测抑制剂（IC50约为15 nM），该检测可检测内吞探针向一个共同区室的递送。体外检测的抑制涉及一种膜相关因子的失活，该因子可从细胞质募集到囊泡表面。其对无细胞检测的影响表明，渥曼青霉素抑制了将内吞物质递送至“混合”内体所需的受体分选和/或囊泡出芽。这一观点与渥曼青霉素诱导的形态学变化一致，这些变化包括形成含转铁蛋白的扩大结构以及破坏核周内体区室。然而，渥曼青霉素的不同效应，特别是转铁蛋白受体内化增加和受体再循环受抑制，暗示了磷脂酰肌醇3激酶活性在转铁蛋白受体膜转运途径的多个分选事件中的作用。
