Modulation of amino acid uptake by TGF-beta in lung myofibroblasts.
Hormones such as insulin, growth factors, and cell stress stimulate system A amino acid transporter. Transforming growth factor-beta (TGF-beta) stimulates amino acid uptake thereby inducing cell proliferation, cellular hypertrophy, and matrix synthesis. Insulin appears to activate amino acid in smooth muscle cells via a phosphatidylinositol 3-kinase (PI3-kinase)-dependent pathway. We examine the effect and interaction of TGF-beta, insulin, and PI3-kinase activity on amino acid uptake in human lung myofibroblasts. TGF-beta treatment induced large increases in system A activity and a small delayed increase in the phosphorylation of protein kinase B, also termed phospho-Akt. In contrast, insulin induced small increases in system A activity and large increases in phospho-Akt levels. LY294002, a PI3-kinase inhibitor, blocked the TGF-beta-induced amino acid uptake only partially, but completely blocked TGF-beta-induced Akt phosphorylation. Moreover, the level of phospho-Smad3 was found to be high even when LY294002 blocked TGF-beta-induced phospho-Akt levels. Inhibition of PI3-kinase activity resulted in increase in Km, consistent with a major change in transporter activity without change in transporter number. The PI3-kinase inhibitor also did not change the amino acid transporter 2 (ATA2) mRNA levels. Taken together, these results suggest that TGF-beta induced Smad-3 and amino acid uptake through a PI3-kinase independent pathway.
Subramanian
Mangalalaxmy
M
Pulmonary Center, Department of Medicine, Boston University School of Medicine, Boston, Massachusetts 02118, USA. ramyats@bu.edu
Kuang
Ping-Ping
PP
Wei
Lin
L
Rishikof
David C
DC
Liu
Hanqiao
H
Goldstein
Ronald H
RH
D026924:Amino Acid Transport System A / Q000187:drug effects / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D008168:Lung / Q000166:cytology / Q000378:metabolism*; D009025:Morpholines / Q000494:pharmacology; D051058:Oncogene Protein v-akt / Q000187:drug effects / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D051900:Smad3 Protein / Q000187:drug effects / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000494:pharmacology*
D026924:Amino Acid Transport System A; D000596:Amino Acids; D002867:Chromones; D004791:Enzyme Inhibitors; D007328:Insulin; D009025:Morpholines; D051058:Oncogene Protein v-akt; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; C497790:SMAD3 protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one