Insulin and SGK1 reduce the function of Na+/monocarboxylate transporter 1 (SMCT1/SLC5A8)

Adriana López-Barradas, Tania González-Cid, Norma Vázquez, Marisol Gavi-Maza, Adriana Reyes-Camacho, Laura A. Velázquez-Villegas, Victoria Ramírez, Kambiz Zandi-Nejad, David B. Mount, Nimbe Torres, Armando R. Tovar, Michael F Romero, Gerardo Gamba, Consuelo Plata

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3 Scopus citations

Abstract

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 22Na+ uptake by 29%. Consistent with this result, the coinjection of SMCT1 with SGK1 cRNA decreased the KIC-dependent 22Na+ 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 KICdependent 22Na+ 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 [1-14C]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 propionatedependent 22Na+ 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.

Original languageEnglish (US)
Pages (from-to)C720-C734
JournalAmerican Journal of Physiology - Cell Physiology
Volume311
Issue number5
DOIs
StatePublished - 2016

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Keywords

  • Member 12 (SLC5A12)
  • Monocarboxylates
  • Na-monocarboxylate cotransporter with high affinity for MCs (SMCT1)
  • Na-monocarboxylate cotransporter with low affinity for MCs (SMCT2)
  • Serum- and glucocorticoidinducible kinase-1 (SGK1)
  • Solute carrier family 5
  • Solute carrier family 5 member 8 (SLC5A8)
  • α-keto-isocaproate

ASJC Scopus subject areas

  • Physiology
  • Cell Biology

Cite this

López-Barradas, A., González-Cid, T., Vázquez, N., Gavi-Maza, M., Reyes-Camacho, A., Velázquez-Villegas, L. A., Ramírez, V., Zandi-Nejad, K., Mount, D. B., Torres, N., Tovar, A. R., Romero, M. F., Gamba, G., & Plata, C. (2016). Insulin and SGK1 reduce the function of Na+/monocarboxylate transporter 1 (SMCT1/SLC5A8). American Journal of Physiology - Cell Physiology, 311(5), C720-C734. https://doi.org/10.1152/ajpcell.00104.2015