Redefining the Facilitated Transport of Mannose in Human Cells: Absence of a Glucose-Insensitive, High-Affinity Facilitated Mannose Transport System

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• 作者：Patricio Rodr&iacute ; guez ; Coralia I. Rivas ; Alejandro Godoy ; Marcela Villanueva ; Jorge Fischbarg ; Juan Carlos Vera ; and Alejandro M. Reyes
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：January 11, 2005
• 年：2005
• 卷：44
• 期：1
• 页码：313 - 320
• 全文大小：205K
• 年卷期：v.44,no.1(January 11, 2005)
• ISSN：1520-4995

文摘

Current evidence suggests that extracellular mannose can be transported intracellularly andutilized for glycoprotein synthesis; however, the identity and the functional characteristics of the transportersof mannose are controversial. Although the glucose transporters are capable of transporting mannose, ithas been postulated that the entry of mannose in mammalian cells is mediated by a transporter that isinsensitive to glucose [Panneerselvam, K., and Freeze, H. (1996) J. Biol. Chem. 271, 9417-9421] or bya transporter induced by cell treatment with metformin [Shang, J., and Lehrman, M. A. (2004) J. Biol.Chem. 279, 9703-9712]. We performed a detailed analysis of the uptake of mannose in normal humanerythrocytes and in leukemia cell line HL-60. Short uptake assays allowed the identification of a singlefunctional activity involved in mannose uptake in both cell types, with a K_m for transport of 6 mM.Transport was inhibited in a competitive manner by classical glucose transporter substrates. Similarly,the glucose transporter inhibitors cytochalasin B, genistein, and myricetin inhibited mannose transport by100%. Using long uptake experiments, we identified a second, high-affinity component associated withthe intracellular trapping of mannose in the HL-60 cells that is not directly involved in the transport ofmannose via the glucose transporters. Thus, the transport of mannose via glucose transporters is a processwhich is kinetically and biologically separable from its intracellular trapping. A general survey of humancells revealed that mannose uptake was entirely blocked by concentrations of cytochalasin B that obliteratesthe activity of the glucose transporters. The transport and inhibition data demonstrate that extracellularmannose, whose physiological concentration is in the micromolar range, enters cells in the presence ofphysiological concentrations of glucose. Overall, our data indicate that transport through the glucosetransporter is the main mechanism by which human cells acquire mannose.