You G, Lee W S, Barros E J, Kanai Y, Huo T L, Khawaja S, Wells R G, Nigam S K, Hediger M A
Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
J Biol Chem. 1995 Dec 8;270(49):29365-71. doi: 10.1074/jbc.270.49.29365.
Two distinct Na(+)-coupled glucose transporters (SGLTs) with either a high or a low affinity for glucose were shown to provide reabsorption of filtered glucose in the kidney. We have previously reported the characteristics of the high affinity Na+/glucose cotransporter SGLT1 from rabbit, rat, and human kidney and the low affinity Na+/glucose cotransporter SGLT2 from human kidney. Because the molecular identity of SGLT2 as the kidney cortical low affinity Na+/glucose cotransporter has been recently challenged based on studies of the porcine low affinity Na+/glucoe cotransporter SAAT-pSGLT2 (Mackenzie, B., Panayotova-Heiermann, M., Loo, D. D. F., Lever, J.E., and Wright, E. M. (1994) J. Biol. Chem. 269, 22488-22491), we have reevaluated the properties of SGLT2 in greater detail. We furthermore report new data on the regulation of SGLT1 and SGLT2 during kidney development. To analyze and compare SGLT1 and SGLT2 in adult and embryonic kidney, we have cloned and characterized SGLT2 from rat kidney and determined its tissue distribution based on Northern analysis and in situ hybridization. When expressed in Xenopus oocytes, rat SGLT2 stimulated transport of alpha-methyl-D-glucopyranoside (2 mM) in oocytes up to 4.5-fold over controls with an apparent Km of 3.0 mM. The transport properties (i.e. a Na+ to glucose coupling of 1:1 and lack of galactose transport) generally matched those of the kidney cortical low affinity system. We show that expression of rat SGLT2 mRNA is kidney specific and that it is strongly and exclusively expressed in proximal tubule S1 segments. Hybrid-depletion studies were performed to conclusively determine whether SGLT2 corresponds to the kidney cortical low affinity system. Injection of rat kidney superficial cortex mRNA into oocytes stimulated the uptake of alpha-methyl-D-glucopyranoside (2 mM) 2-3-fold. We show that hybrid depletion of this kidney RNA using an SGLT2 antisense oligonucleotide completely suppresses the uptake. These data strongly indicate that SGLT2 is the major kidney cortical low affinity glucose transporter. We therefore propose that SAAT-pSGLT2 be renamed SGLT3. Experiments addressing the expression of SGLT1 and SGLT2 mRNAs in embryonic rat kidneys reveal that the two Na+/glucose cotransporters are developmentally regulated and that there may be a different splice variant for SGLT2 in embryonic kidney compared to the adult.
两种对葡萄糖具有高亲和力或低亲和力的不同钠偶联葡萄糖转运体（SGLTs）被证明可在肾脏中重吸收滤过的葡萄糖。我们之前已经报道了来自兔、大鼠和人肾脏的高亲和力钠/葡萄糖共转运体SGLT1以及来自人肾脏的低亲和力钠/葡萄糖共转运体SGLT2的特性。由于基于对猪低亲和力钠/葡萄糖共转运体SAAT-pSGLT2的研究（麦肯齐，B.，帕纳约托娃-海尔曼，M.，卢，D.D.F.，利弗，J.E.，以及赖特，E.M.（1994年）《生物化学杂志》269卷，22488 - 22491页），SGLT2作为肾皮质低亲和力钠/葡萄糖共转运体的分子身份最近受到了挑战，我们对SGLT2的特性进行了更详细的重新评估。我们还报告了关于肾脏发育过程中SGLT1和SGLT2调节的新数据。为了分析和比较成年和胚胎肾脏中的SGLT1和SGLT2，我们克隆并鉴定了大鼠肾脏中的SGLT2，并基于Northern分析和原位杂交确定了其组织分布。当在非洲爪蟾卵母细胞中表达时，大鼠SGLT2刺激卵母细胞中α-甲基-D-吡喃葡萄糖苷（2 mM）的转运，比对照高出4.5倍，表观Km为3.0 mM。其转运特性（即钠与葡萄糖的1:1偶联以及缺乏半乳糖转运）通常与肾皮质低亲和力系统的特性相符。我们表明大鼠SGLT2 mRNA的表达具有肾脏特异性，并且它在近端小管S1节段中强烈且专一性表达。进行了杂交缺失研究以最终确定SGLT2是否对应于肾皮质低亲和力系统。将大鼠肾脏浅表皮质mRNA注射到卵母细胞中刺激了α-甲基-D-吡喃葡萄糖苷（2 mM）的摄取2 - 3倍。我们表明使用SGLT2反义寡核苷酸对这种肾脏RNA进行杂交缺失完全抑制了摄取。这些数据有力地表明SGLT2是主要的肾皮质低亲和力葡萄糖转运体。因此，我们建议将SAAT-pSGLT2重新命名为SGLT3。关于SGLT1和SGLT2 mRNA在胚胎大鼠肾脏中表达的实验表明，这两种钠/葡萄糖共转运体在发育过程中受到调节，并且与成年肾脏相比，胚胎肾脏中的SGLT2可能存在不同的剪接变体。
