López-Barradas Adriana, González-Cid Tania, Vázquez Norma, Gavi-Maza Marisol, Reyes-Camacho Adriana, Velázquez-Villegas Laura A, Ramírez Victoria, Zandi-Nejad Kambiz, Mount David B, Torres Nimbe, Tovar Armando R, Romero Michael F, Gamba Gerardo, Plata Consuelo
Department of Physiology of Nutrition, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico.
Department of Nephrology & Mineral Metabolism, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico.
Am J Physiol Cell Physiol. 2016 Nov 1;311(5):C720-C734. doi: 10.1152/ajpcell.00104.2015. Epub 2016 Aug 3.
SMCTs move several important fuel molecules that are involved in lipid, carbohydrate, and amino acid metabolism, but their regulation has been poorly studied. Insulin controls the translocation of several solutes that are involved in energetic cellular metabolism, including glucose. We studied the effect of insulin on the function of human SMCT1 expressed in Xenopus oocytes. The addition of insulin reduced α-keto-isocaproate (KIC)-dependent Na uptake by 29%. Consistent with this result, the coinjection of SMCT1 with SGK1 cRNA decreased the KIC-dependent Na uptake by 34%. The reduction of SMCT1 activity by SGK1 depends on its kinase activity, and it was observed that the coinjection of SMCT1 with S442D-SGK1 (a constitutively active mutant) decreased the KIC-dependent Na uptake by 50%. In contrast, an SMCT1 coinjection with K127M-SGK1 (an inactive mutant) had no effect on the KIC-dependent Na uptake. The decreasing SMCT1 function by insulin or SGK1 was corroborated by measuring [1-C]acetate uptake and the electric currents of SMCT1-injected oocytes. Previously, we found that SMCT2/Slc5a12-mRNA, but not SMCT1/Slc5a8-mRNA, is present in zebrafish pancreas (by in situ hybridization); however, SLC5a8 gene silencing was associated with the development of human pancreatic cancer. We confirmed that the mRNA and protein of both transporters were present in rat pancreas using RT-PCR with specific primers, Western blot analysis, and immunohistochemistry. Additionally, significant propionate-dependent Na uptake occurred in pancreatic islets and was reduced by insulin treatment. Our data indicate that human SMCT1 is regulated by insulin and SGK1 and that both SMCTs are present in the mammalian pancreas.
钠-单羧酸转运体（SMCTs）转运几种参与脂质、碳水化合物和氨基酸代谢的重要燃料分子，但其调节机制尚未得到充分研究。胰岛素控制着几种参与细胞能量代谢的溶质的转运，包括葡萄糖。我们研究了胰岛素对非洲爪蟾卵母细胞中表达的人SMCT1功能的影响。添加胰岛素使α-酮异己酸（KIC）依赖性钠摄取减少了29%。与此结果一致，将SMCT1与血清糖皮质激素调节激酶1（SGK1）的互补RNA（cRNA）共注射使KIC依赖性钠摄取减少了34%。SGK1对SMCT1活性的降低依赖于其激酶活性，并且观察到将SMCT1与S442D-SGK1（一种组成型活性突变体）共注射使KIC依赖性钠摄取减少了50%。相反，将SMCT1与K127M-SGK1（一种无活性突变体）共注射对KIC依赖性钠摄取没有影响。通过测量[1-C]乙酸摄取和注射了SMCT1的卵母细胞的电流，证实了胰岛素或SGK1使SMCT1功能降低。此前，我们发现斑马鱼胰腺中存在SMCT2/Slc5a12的信使核糖核酸（mRNA），但不存在SMCT1/Slc5a8的mRNA（通过原位杂交）；然而，溶质载体家族5成员8（SLC5a8）基因沉默与人类胰腺癌的发生有关。我们使用特异性引物进行逆转录聚合酶链反应（RT-PCR）、蛋白质免疫印迹分析和免疫组织化学，证实了两种转运体的mRNA和蛋白质都存在于大鼠胰腺中。此外，胰岛中发生了显著的丙酸盐依赖性钠摄取，并且胰岛素处理使其减少。我们的数据表明，人SMCT1受胰岛素和SGK1调节，并且两种SMCTs都存在于哺乳动物胰腺中。
