Transforming growth factor-beta 1 stimulates vascular smooth muscle cell L-proline transport by inducing system A amino acid transporter 2 (SAT2) gene expression.
Transforming growth factor-beta1 (TGF-beta 1) is a multifunctional cytokine that contributes to arterial remodelling by stimulating vascular smooth muscle cell (SMC) growth and collagen synthesis at sites of vascular injury. Since l-proline is essential for the synthesis of collagen, we examined whether TGF-beta 1 regulates the transcellular transport of l-proline by vascular SMCs. l-Proline uptake by vascular SMCs was primarily sodium-dependent, pH-sensitive, blocked by neutral amino acids and alpha-(methylamino)isobutyric acid, and exhibited trans-inhibition. Treatment of SMCs with TGF-beta 1 stimulated l-proline transport in a concentration- and time-dependent manner. The TGF-beta 1-mediated l-proline uptake was inhibited by cycloheximide or actinomycin D. Kinetic studies indicated that TGF-beta 1-induced l-proline transport was mediated by an increase in transport capacity independent of any changes in the affinity for l-proline. TGF-beta 1 stimulated the expression of system A amino acid transporter 2 (SAT2) mRNA in a time-dependent fashion that paralleled the increase in l-proline transport. Reverse transcriptase PCR failed to detect the presence of SAT1 or amino acid transporter 3 (ATA3) in either untreated or TGF-beta 1-treated SMCs. These results demonstrate that l-proline transport by vascular SMCs is mediated predominantly by the SAT and that TGF-beta 1 stimulates SMC l-proline uptake by inducing the expression of the SAT2 gene. The ability of TGF-beta 1 to induce SAT2 expression may function to provide SMCs with the necessary levels of l-proline required for collagen synthesis and cell growth.
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Houston VA Medical Center, Building 109, Room 130, 2002 Holcombe Blvd, Houston, TX 77030, USA.
Hassan
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Reyna
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Schafer
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Durante
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D026924:Amino Acid Transport System A / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics*; D000818:Animals; D001693:Biological Transport, Active / Q000235:genetics; D002478:Cells, Cultured; D018076:DNA, Complementary / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000502:physiology*; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D011392:Proline / Q000378:metabolism*; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013379:Substrate Specificity / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000494:pharmacology / Q000502:physiology*; D053773:Transforming Growth Factor beta1
D026924:Amino Acid Transport System A; D018076:DNA, Complementary; C412568:Slc38a2 protein, rat; C508962:Tgfb1 protein, rat; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D011392:Proline