title: Mouse system-N amino acid transporter, mNAT3, expressed in hepatocytes and regulated by insulin-activated and phosphoinositide 3-kinase-dependent signalling.
abstract: Amino acid transporters are essential for normal cell function and physiology. In the present study, we report the identification and functional and regulatory characterization of a mouse system-N amino acid transporter, mNAT3. Expression of mNAT3 in Xenopus oocytes revealed that the strongest transport activities were preferred for L-alanine. In addition, mNAT3 is an Na(+)- and pH-dependent low-affinity transporter and it partially tolerates substitution of Na(+) by Li(+). mNAT3 has been found to be expressed predominantly in the liver, where it is localized to the plasma membrane of hepatocytes, with the strongest expression in those cells adjacent to the central vein, decreasing gradually towards the portal tract. Treatment of mouse hepatocyte-like H2.35 cells with insulin led to a significant increase in the expression of mNAT3, and this stimulation was associated closely with an increase in the uptake of L-alanine. Interestingly, this insulin-induced stimulatory effect on mNAT3 expression was attenuated by the phosphoinositide 3-kinase inhibitor LY294002, but not by the mitogen-activated protein kinase inhibitor PD98059, although both kinases were fully activated by insulin. The results suggest that insulin-mediated regulation of mNAT3 is likely to be mediated through a phosphoinositide 3-kinase-dependent signalling pathway. The unique expression pattern and insulin-mediated regulatory properties of mNAT3 suggest that this transporter may play an important role in liver physiology.
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
authors.forename: Sumin
authors.initials: S
authors.lastname: Gu
authors.forename: Paul
authors.initials: P
authors.lastname: Langlais
authors.forename: Feng
authors.initials: F
authors.lastname: Liu
authors.forename: Jean X
authors.initials: JX
authors.lastname: Jiang
mesh_terms: D026905:Amino Acid Transport Systems / Q000235:genetics / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D022781:Hepatocytes / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000187:drug effects; D014982:Xenopus laevis
chemical_list: D026905:Amino Acid Transport Systems; D000596:Amino Acids; D017931:DNA Primers; D018076:DNA, Complementary; D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases