Loo T W, Clarke D M
MRC Group in Membrane Biology, Department of Medicine and Department of Biochemistry, University of Toronto, Ontario M5S 1A8, Canada.
FASEB J. 1999 Oct;13(13):1724-32. doi: 10.1096/fasebj.13.13.1724.
The human multidrug resistance P-glycoprotein (P-gp) contributes to the phenomenon of multidrug resistance during cancer and AIDS chemotherapy. A potential novel strategy to circumvent the effects of P-gp during chemotherapy is to prevent maturation of P-gp during biosynthesis so that the transporter does not reach the cell surface. Here we report that immature, core-glycosylated P-gp that is prevented from reaching the cell surface by processing mutations or by proteasome inhibitors such as lactacystin or MG-132 exhibited no detectable drug-stimulated ATPase activity. Disulfide cross-linking analysis also showed that the immature P-gp did not exhibit ATP-induced conformational changes as found in the mature enzyme. In addition, the immature P-gp was more sensitive to trypsin than the mature enzyme. These results suggest that P-gp is unlikely to be functional immediately after synthesis. These differences in the structural and enzymatic properties of the mature and core-glycosylated, immature P-gp could potentially be used during chemotherapy, and should result in the search for compounds that can specifically inhibit the maturation of P-gp.
人类多药耐药性P-糖蛋白（P-gp）在癌症和艾滋病化疗过程中导致多药耐药现象。在化疗期间规避P-gp作用的一种潜在新策略是在生物合成过程中阻止P-gp成熟，以使转运蛋白无法到达细胞表面。在此我们报告，通过加工突变或蛋白酶体抑制剂（如乳胞素或MG-132）阻止其到达细胞表面的未成熟、核心糖基化的P-gp未表现出可检测到的药物刺激的ATP酶活性。二硫键交联分析还表明，未成熟的P-gp未表现出成熟酶中发现的ATP诱导的构象变化。此外，未成熟的P-gp比成熟酶对胰蛋白酶更敏感。这些结果表明，P-gp在合成后不太可能立即发挥功能。成熟的和核心糖基化的未成熟P-gp在结构和酶学性质上的这些差异可能在化疗期间被利用，并且应该促使人们寻找能够特异性抑制P-gp成熟的化合物。
