Department of Physiology I, University of Tübingen, Gmelinstr. 5, 72076 Tübingen, Germany.
J Membr Biol. 2012 Mar;245(3):157-63. doi: 10.1007/s00232-012-9424-8. Epub 2012 Mar 11.
Janus-activated kinase-2 (JAK2) participates in the regulation of the Na⁺-coupled glucose transporter SGLT1 and the Na⁺-coupled amino acid transporter SLC6A19. Concentrative cellular creatine uptake is similarly accomplished by Na⁺-coupled transport. The carrier involved is SLC6A8 (CreaT). The present study thus explored whether JAK2 regulates the activity of SLC6A8. To this end, cRNA encoding SLC6A8 was injected into Xenopus oocytes with or without cRNA encoding wild-type JAK2, constitutively active (V617F)JAK2 or inactive (K882E)JAK2. Electrogenic creatine transport was determined in those oocytes by dual-electrode voltage-clamp experiments. In oocytes injected with cRNA encoding SLC6A8 but not in oocytes injected with water or with cRNA encoding JAK2 alone, addition of 1 mM creatine to the extracellular bath generated an inward current (I (crea)). In SLC6A8 expressing oocytes I (crea) was significantly decreased by coexpression of JAK2 or (V617F)JAK2 but not by coexpression of (K882E)JAK2. According to kinetic analysis, coexpression of JAK2 decreased the maximal transport rate without significantly modifying the affinity of the carrier. In oocytes expressing SLC6A8 and (V617F)JAK2 I (crea) was gradually increased by the JAK2 inhibitor AG490 (40 μM). In SLC6A8 and JAK2 coexpressing oocytes the decline of I (crea) following disruption of carrier insertion with brefeldin A (5 μM) was similar in the absence and presence of JAK2. In conclusion, JAK2 is a novel regulator of the creatine transporter SLC6A8, which downregulates the carrier, presumably by interference with carrier protein insertion into the cell membrane.
Janus 激活激酶-2（JAK2）参与调节 Na⁺-偶联葡萄糖转运体 SGLT1 和 Na⁺-偶联氨基酸转运体 SLC6A19。细胞内浓缩性肌酸摄取也是通过 Na⁺-偶联转运来完成的。所涉及的载体是 SLC6A8（CreaT）。因此，本研究探讨了 JAK2 是否调节 SLC6A8 的活性。为此，将编码 SLC6A8 的 cRNA 与编码野生型 JAK2、组成性激活（V617F）JAK2 或无活性（K882E）JAK2 的 cRNA 一起注入非洲爪蟾卵母细胞。通过双电极电压钳实验在这些卵母细胞中测定电活性肌酸转运。在注射编码 SLC6A8 的 cRNA 的卵母细胞中，但在注射水或单独注射 JAK2 的 cRNA 的卵母细胞中，向细胞外浴中添加 1 mM 肌酸会产生内向电流（I（crea））。在表达 SLC6A8 的卵母细胞中，I（crea）通过共表达 JAK2 或（V617F）JAK2 显著降低，但通过共表达（K882E）JAK2 则不降低。根据动力学分析，JAK2 的共表达降低了载体的最大转运速率，而对载体的亲和力没有显著影响。在表达 SLC6A8 和（V617F）JAK2 的卵母细胞中，JAK2 抑制剂 AG490（40 μM）逐渐增加 I（crea）。在 SLC6A8 和 JAK2 共表达的卵母细胞中，在用布雷非德菌素 A（5 μM）破坏载体插入后，I（crea）的下降在没有 JAK2 和存在 JAK2 的情况下相似。总之，JAK2 是肌酸转运体 SLC6A8 的新型调节剂，通过干扰载体蛋白插入细胞膜下调载体，可能下调载体。
