The serine/threonine kinases SGK1, 3 and PKB stimulate the amino acid transporter ASCT2

The human Na+-dependent neutral amino acid transporter type 2 (hASCT2/SLC1A5) plays an important role in the transport of neutral amino acids in epithelial cells. The serine and threonine kinases SGK1 3 and protein kinase B have been implicated in the regulation of several members of the SLC1 transporter family by enhancing their plasma moembrane abundance. The present study explored whether those kinases modulate hASCT2. In Xenopus oocytes heterologously expressing hASCT2, coexpression of constitutively active (S422D)SGK1, (S419D)SGK3 or (PKB)-P-T308DS473D upregulated the transporter activity. The stimulation requires the catalytical activity of the kinases since the inactive mutant, (K127N)SGK1. (K191N)SGK3, and (PKB)-P-1308VS473A failed to modulate the transporter. According to kinetic analysis and chemiluminescence assays. SGK1 and SGK3 modulate hASCT2 by enhancing the transporter abundance in the plasma membrane. As SGKL 3 and PKB are activated by insulin and IGF1. The described mechanisms presumably participate in the hormonal stimulation of cellular amino acid uptake. (c) 2005 Elsevier Inc. All rights reserved.