scholarly journals Altered activity of the system A amino acid transporter in microvillous membrane vesicles from placentas of macrosomic babies born to diabetic women.

1994 ◽  
Vol 94 (2) ◽  
pp. 689-695 ◽  
Author(s):  
A G Kuruvilla ◽  
S W D'Souza ◽  
J D Glazier ◽  
D Mahendran ◽  
M J Maresh ◽  
...  
Keyword(s):  
Amino Acid ◽  
Membrane Vesicles ◽  
Amino Acid Transporter ◽  
System A ◽  
Acid Transporter ◽  
Microvillous Membrane Vesicles

scholarly journals B0AT1 amino acid transporter complexed with SARS-CoV-2 receptor ACE2 forms a heterodimer functional unit: in situ conformation using radiation inactivation analysis

Function ◽  
2021 ◽  
Author(s):  
Bruce R Stevens ◽  
J Clive Ellory ◽  
Robert L Preston
Keyword(s):  
Amino Acid ◽  
Membrane Trafficking ◽  
Functional Unit ◽  
Membrane Vesicles ◽  
High Energy ◽  
Amino Acid Transporter ◽  
Neutral Amino Acid ◽  
Transport Activity ◽  
Acid Transporter

Abstract The SARS-CoV-2 receptor, Angiotensin Converting Enzyme-2 (ACE2), is expressed at levels of greatest magnitude in the small intestine as compared to all other human tissues. Enterocyte ACE2 is co-expressed as the apical membrane trafficking partner obligatory for expression and activity of the B0AT1 sodium-dependent neutral amino acid transporter. These components are assembled as an [ACE2: B0AT1]2 dimer-of-heterodimers quaternary complex that putatively steers SARS-CoV-2 tropism in the gastrointestinal (GI) tract. GI clinical symptomology is reported in about half of COVID-19 patients, and can be accompanied by gut shedding of virion particles. We hypothesized that within this 4-mer structural complex, each [ACE2: B0AT1] heterodimer pair constitutes a physiological “functional unit.” This was confirmed experimentally by employing purified lyophilized enterocyte brush border membrane vesicles that were exposed to increasing doses of high-energy electron radiation from a 16 MeV linear accelerator. Based on established target theory, the results indicated the presence of Na+-dependent neutral amino acid influx transport activity functional unit with target size mw = 183.7 ± 16.8 kDa in situ in intact apical membranes. Each thermodynamically stabilized [ACE2: B0AT1] heterodimer functional unit manifests the transport activity within the whole ∼345 kDa [ACE2: B0AT1]2 dimer-of-heterodimers quaternary structural complex. The results are consistent with our prior molecular docking modeling and gut-lung axis approaches to understanding COVID-19. These findings advance the understanding of the physiology of B0AT1 interaction with ACE2 in the gut, and thereby potentially contribute to translational developments designed to treat or mitigate COVID-19 variant outbreaks and/or GI symptom persistence in long-haul Post-Acute Sequelae of SARS-CoV-2 (PASC).

scholarly journals Characterization of the amino acid response element within the human sodium-coupled neutral amino acid transporter 2 (SNAT2) System A transporter gene

2006 ◽  
Vol 395 (3) ◽  
pp. 517-527 ◽  
Author(s):  
Stela S. Palii ◽  
Michelle M. Thiaville ◽  
Yuan-Xiang Pan ◽  
Can Zhong ◽  
Michael S. Kilberg
Keyword(s):  
Amino Acid ◽  
Rna Polymerase Ii ◽  
Mammalian Cells ◽  
Amino Acid Transporter ◽  
Neutral Amino Acid ◽  
System A ◽  
Neutral Amino Acid Transporter ◽  
Acid Transporter ◽  
Amino Acid Response

The neutral amino acid transport activity, System A, is enhanced by amino acid limitation of mammalian cells. Of the three gene products that encode System A activity, the one that exhibits this regulation is SNAT2 (sodium-coupled neutral amino acid transporter 2). Fibroblasts that are deficient in the amino acid response pathway exhibited little or no induction of SNAT2 mRNA. Synthesis of SNAT2 mRNA increased within 1–2 h after amino acid removal from HepG2 human hepatoma cells. The amino acid responsive SNAT2 genomic element that mediates the regulation has been localized to the first intron. Increased binding of selected members of the ATF (activating transcription factor) and C/EBP (CCAAT/enhancer-binding protein) families to the intronic enhancer was established both in vitro and in vivo. In contrast, there was no significant association of these factors with the SNAT2 promoter. Expression of exogenous individual ATF and C/EBP proteins documented that specific family members are associated with either activation or repression of SNAT2 transcription. Chromatin immunoprecipitation analysis established in vivo that amino acid deprivation led to increased RNA polymerase II recruitment to the SNAT2 promoter.

scholarly journals SNAT4 isoform of system A amino acid transporter is expressed in human placenta

2006 ◽  
Vol 290 (1) ◽  
pp. C305-C312 ◽  
Author(s):  
M. Desforges ◽  
H. A. Lacey ◽  
J. D. Glazier ◽  
S. L. Greenwood ◽  
K. J. Mynett ◽  
...  
Keyword(s):  
Amino Acid ◽  
Protein Expression ◽  
Western Blot ◽  
Human Placenta ◽  
Blot Analysis ◽  
First Trimester ◽  
Amino Acid Transporter ◽  
Full Term ◽  
System A ◽  
Acid Transporter

The system A amino acid transporter is encoded by three members of the Slc38 gene family, giving rise to three subtypes: Na+-coupled neutral amino acid transporter (SNAT)1, SNAT2, and SNAT4. SNAT2 is expressed ubiquitously in mammalian tissues; SNAT1 is predominantly expressed in heart, brain, and placenta; and SNAT4 is reported to be expressed solely by the liver. In the placenta, system A has an essential role in the supply of neutral amino acids needed for fetal growth. In the present study, we examined expression and localization of SNAT1, SNAT2, and SNAT4 in human placenta during gestation. Real-time quantitative PCR was used to examine steady-state levels of system A subtype mRNA in early (6–10 wk) and late (10–13 wk) first-trimester and full-term (38–40 wk) placentas. We detected mRNA for all three isoforms from early gestation onward. There were no differences in SNAT1 and SNAT2 mRNA expression with gestation. However, SNAT4 mRNA expression was significantly higher early in the first trimester compared with the full-term placenta ( P < 0.01). We next investigated SNAT4 protein expression in human placenta. In contrast to the observation for gene expression, Western blot analysis revealed that SNAT4 protein expression was significantly higher at term compared with the first trimester ( P < 0.05). Immunohistochemistry and Western blot analysis showed that SNAT4 is localized to the microvillous and basal plasma membranes of the syncytiotrophoblast, suggesting a role for this isoform of system A in amino acid transport across the placenta. This study therefore provides the first evidence of SNAT4 mRNA and protein expression in the human placenta, both at the first trimester and at full term.

Transforming growth factor-β1 stimulates vascular smooth muscle cell l-proline transport by inducing system A amino acid transporter 2 (SAT2) gene expression

2001 ◽  
Vol 360 (2) ◽  
pp. 507-512 ◽  
Author(s):  
Diana ENSENAT ◽  
Saamir HASSAN ◽  
Sylvia V. REYNA ◽  
Andrew I. SCHAFER ◽  
William DURANTE
Keyword(s):  
Amino Acid ◽  
Collagen Synthesis ◽  
Transforming Growth Factor ◽  
Transforming Growth Factor Β1 ◽  
Amino Acid Transporter ◽  
Proline Transport ◽  
System A ◽  
Vascular Smcs ◽  
Acid Transporter ◽  
Tgf Β1

Transforming growth factor-β1 (TGF-β1) 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-β1 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 α-(methylamino)isobutyric acid, and exhibited trans-inhibition. Treatment of SMCs with TGF-β1 stimulated l-proline transport in a concentration- and time-dependent manner. The TGF-β1-mediated l-proline uptake was inhibited by cycloheximide or actinomycin D. Kinetic studies indicated that TGF-β1-induced l-proline transport was mediated by an increase in transport capacity independent of any changes in the affinity for l-proline. TGF-β1 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-β1-treated SMCs. These results demonstrate that l-proline transport by vascular SMCs is mediated predominantly by the SAT and that TGF-β1 stimulates SMC l-proline uptake by inducing the expression of the SAT2 gene. The ability of TGF-β1 to induce SAT2 expression may function to provide SMCs with the necessary levels of l-proline required for collagen synthesis and cell growth.

Sign in / Sign up

Export Citation Format

Share Document