Feng Y, Wente S R, Majerus P W
Division of Hematology and Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
Proc Natl Acad Sci U S A. 2001 Jan 30;98(3):875-9. doi: 10.1073/pnas.98.3.875. Epub 2001 Jan 16.
SopB is an inositol phosphate phosphatase that is a virulence factor in Salmonella species. We have overexpressed SopB cDNA in a tetracycline-dependent system in human embryonic 293 cells, and used this model system to directly analyze the role of SopB in altering inositol metabolite levels in vivo. Addition of tetracycline to these cells resulted in the rapid induction of SopB expression, which was coincident with perturbations in the cellular levels of multiple soluble inositol phosphates. All of the changes induced by SopB expression were reversed within 24 h on removal of tetracycline from media. Specifically, cellular inositol 1,3,4,5,6-pentakisphosphate (InsP(5)) and inositol hexakisphosphate (InsP(6)) levels were depleted within 4 to 6 h after inducing SopB expression. A transient rise in cellular inositol 1,4,5,6-tetrakisphosphate was also observed and was accompanied by increased chloride channel activity. This indicates that SopB alone is sufficient for changes in chloride channel function in cells infected with Salmonella organisms. Depletion of inositol phosphates, including InsP(5) and InsP(6) metabolites, was coincident with the accumulation of polyadenylated RNA in the nucleus. This suggested that a defect in nuclear export had occurred. Moreover, the penetrance of the export defect required localization of SopB to the nucleus. These results provide evidence that inositol phosphate productions may be required for efficient mRNA export in mammalian cells.
SopB是一种肌醇磷酸磷酸酶，是沙门氏菌属的一种毒力因子。我们在人胚胎293细胞的四环素依赖性系统中过表达了SopB cDNA，并使用该模型系统直接分析SopB在体内改变肌醇代谢物水平中的作用。向这些细胞中添加四环素导致SopB表达迅速诱导，这与多种可溶性肌醇磷酸的细胞水平扰动同时发生。在从培养基中去除四环素后24小时内，SopB表达诱导的所有变化都得到了逆转。具体而言，在诱导SopB表达后4至6小时内，细胞中的1,3,4,5,6-五磷酸肌醇（InsP(5)）和六磷酸肌醇（InsP(6)）水平降低。还观察到细胞内1,4,5,6-四磷酸肌醇短暂升高，并伴有氯离子通道活性增加。这表明仅SopB就足以使感染沙门氏菌的细胞中的氯离子通道功能发生变化。包括InsP(5)和InsP(6)代谢物在内的肌醇磷酸的消耗与细胞核中聚腺苷酸化RNA的积累同时发生。这表明发生了核输出缺陷。此外，输出缺陷的发生率要求SopB定位于细胞核。这些结果提供了证据，表明肌醇磷酸的产生可能是哺乳动物细胞中有效mRNA输出所必需的。
