Gavi-Maza, Marisol

The Na + /monocarboxylate transporters (SMCT1 and SMCT2) are expressed several organ between them intestine and kidney, suggesting that its main physiological function are the absorption of fuel molecules involved in cellular metabolism and have only one ‐COOH group in its chemical structure; (lactate, propionate). Drugs with similar chemical properties also are translocated by SMCTs (B3 vitamin, pyrazinoate). However some propionate‐derivative NSAIDs (ibuprofen) reduce the activity of mammalian SMCT1. Using 22 Na + uptake in Xenopus oocytes injected with zebrafish SMCT’s (zSMCT1, zSMCT2) or human SMCT1 cRNA, we evaluated the effect of aspirin and salicylate on the function SMCT’s. Our results indicate a 22 Na + uptake that is aspirin concentration dependent in all SMCT’s. Similar affinity by aspirin was observed between hSMCT1 (K m ~2.4mM) and zSMCT1 (K m ~2.5 mM) in contrast to a lower affinity of zSMCT2 (K m ~5mM). Also the difference of substrate affinity between zSMCT2 and hSMCT1 was evident by salicylate ( hSMCT1 K m ~4mM vs zSMCT1 K m ~30 mM). Interestingly, although zSMCT1 and hSMCT1 shares a similar affinity and transport capacity for several substrates, the salicylate transport by zSMCT1 was not detected and only reduced a small percentage propionate transport induced by zSMCT1 (~10%) in contrast of ibuprofen which drops to 80%. The clear difference of salicylate transporter between SMCT1 could be explained by changes in the structure of proteins because the amino acids sequences are approximately 50% different, so the salicylate could be candidate for studies of structural‐function between SMCT1. Grant Funding Source : CONACYT48709MJ(CP)

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 KIC-dependent 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 propionate-dependent 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.