Strutz-Seebohm Nathalie, Shojaiefard Manzar, Christie David, Tavare Jeremy, Seebohm Guiscard, Lang Florian
Department of Physiology I, University of Tubingen, Tubingen (Germany).
Cell Physiol Biochem. 2007;20(6):729-34. doi: 10.1159/000110433.
The Na(+),Cl(-),creatine transporter CreaT (SLC6A8) mediates concentrative cellular uptake of creatine into a wide variety of cells. Previous observations disclosed that SLC6A8 transport activity is enhanced by mammalian target of rapamycin (mTOR) at least partially through the serum and glucocorticoid inducible kinase isoforms SGK1 and SGK3. As SLC6A8 does not contain a putative SGK consensus motif, the mechanism linking SGK1 with SLC6A8 activity remained elusive. A candidate kinase is the mammalian phosphatidylinositol-3-phosphate-5-kinase PIKfyve (PIP5K3), which has previously been shown to regulate the glucose transporter GLUT4. The present experiments explored the possibility that SLC6A8 is regulated by PIKfyve. In Xenopus oocytes expressing SLC6A8 but not in water injected oocytes creatine induced a current which was significantly enhanced by coexpression of PIKfyve. The effect of PIKfyve on SLC6A8 was blunted by additional coexpression of the inactive mutant of the serum and glucocorticoid inducible kinase (K127N)SGK1. The stimulating effect of PIKfyve was abrogated by replacement of the serine in the SGK consensus sequence by alanine ((S318A)PIKfyve). Moreover, coexpression of ( S318A)PIKfyve blunted the effect of SGK1 on SLC6A8 activity. The observations suggest that SGK1 regulates the creatine transporter SLC6A8 at least partially through phosphorylation and activation of PIKfyve and subsequent formation of PI(3,5)P(2).
钠离子、氯离子、肌酸转运体CreaT（SLC6A8）介导肌酸向多种细胞的浓缩性细胞摄取。先前的观察结果表明，雷帕霉素哺乳动物靶点（mTOR）至少部分通过血清和糖皮质激素诱导激酶同工型SGK1和SGK3增强SLC6A8的转运活性。由于SLC6A8不包含假定的SGK共有基序，连接SGK1与SLC6A8活性的机制仍不清楚。一个候选激酶是哺乳动物磷脂酰肌醇-3-磷酸-5-激酶PIKfyve（PIP5K3），其先前已被证明可调节葡萄糖转运体GLUT4。本实验探讨了SLC6A8受PIKfyve调节的可能性。在表达SLC6A8的非洲爪蟾卵母细胞中，但在注射水的卵母细胞中未观察到，肌酸诱导了一种电流，该电流通过共表达PIKfyve而显著增强。血清和糖皮质激素诱导激酶（K127N）SGK1的无活性突变体的额外共表达减弱了PIKfyve对SLC6A8的作用。通过将SGK共有序列中的丝氨酸替换为丙氨酸（（S318A）PIKfyve），消除了PIKfyve的刺激作用。此外，（S318A）PIKfyve的共表达减弱了SGK1对SLC6A8活性的作用。这些观察结果表明，SGK1至少部分通过磷酸化和激活PIKfyve以及随后形成PI(3,5)P(2)来调节肌酸转运体SLC6A8。
