Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We report here on the primary structure and functional characteristics of the protein responsible for the system A amino acid transport activity that is known to be expressed in most human tissues. This transporter, designated ATA2 for amino acid transporter A2, was cloned from the human hepatoma cell line HepG2. Human ATA2 (hATA2) consists of 506 amino acids and exhibits a high degree of homology to rat ATA2. hATA2-specific mRNA is ubiquitously expressed in human tissues. When expressed in mammalian cells, hATA2 mediates Na+-dependent transport of alpha-(methylamino)isobutyric acid, a specific model substrate for system A. The transporter is specific for neutral amino acids. It is pH-sensitive and Li+-intolerant. The Na+:amino acid stoichiometry is 1:1.
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PMID:Primary structure, functional characteristics and tissue expression pattern of human ATA2, a subtype of amino acid transport system A. 1093 May 3

After amino acid deprivation, the mRNA content for both asparagine synthetase (AS) and the system A transporter ATA2 is increased. The purpose of the reported experiments was to characterize the molecular mechanism for the ATA2 gene and to contrast the ATA2 regulatory characteristics with those of AS. Amino acid limitation was initiated by incubation of HepG2 human hepatoma cells in either amino acid-free Krebs-Ringer bicarbonate buffer or culture medium lacking the single amino acid histidine. For ATA2, like AS, the elevated mRNA content was due to increased transcription. However, there were fundamental differences between the mechanisms for nutrient regulation of the AS and ATA2 genes. When cells were deprived of amino acids, there was a lag period of approximately 4 h before an increase in AS mRNA occurred, whereas the elevation of ATA2 mRNA was readily detectable at 2-4 h. Consistent with these observations, de novo protein synthesis was absolutely required for the activation of the AS gene, but the increase in ATA2 mRNA was largely independent of protein synthesis. Furthermore, in contrast to AS, transcription from the ATA2 gene was not increased by glucose deprivation. Given this lack of ATA2 transcriptional activation by glucose starvation and that the induction of the AS gene by glucose or amino acid starvation is mediated by common genomic elements, it is likely that the ATA2 gene does not contain the same genomic amino acid-responsive cis-elements as the AS gene.
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PMID:The mechanism for transcriptional activation of the human ATA2 transporter gene by amino acid deprivation is different than that for asparagine synthetase. 1236 90

Human hepatoma cells take up glutamine at rates severalfold faster than the system N-mediated transport rates observed in normal human hepatocytes. Amino acid inhibition, kinetic, Northern blotting, RT-PCR, and restriction enzyme analyses collectively identified the transporter responsible in six human hepatoma cell lines as amino acid transporter B(0) (ATB(0)), the human ortholog of rodent ASCT2. The majority of glutamine uptake in liver fibroblasts and an immortalized human liver epithelial cell line (THLE-5B) was also mediated by ATB(0). The 2.9-kb ATB(0) mRNA was equally expressed in all cell lines, whereas expression of the system A transporters ATA2 and ATA3 was variable. In contrast, the system N isoforms (SN1 and SN2) were expressed only in well-differentiated hepatomas. ATB(0) mRNA was also expressed in cirrhotic liver and adult and pediatric liver cancer biopsies but was not detectable in isolated human hepatocytes or fetal liver. Although the growth of all hepatomas was glutamine dependent, competitive inhibition of ATB(0)-mediated glutamine uptake blocked proliferation only in poorly differentiated cells lacking SN1 or SN2 expression and exhibiting low glutamine synthetase mRNA levels.
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PMID:Molecular and functional analysis of glutamine uptake in human hepatoma and liver-derived cells. 1238 19

The expression of amino acid transporter (AT) mRNAs including A system (ATA1/SNAT1/SLC38A1, ATA2/SNAT2/SLC38A2 and ATA3/SNAT3/SLC38A4), L system (LAT1/SLC7A5 and LAT2/SLC7A8), and y+ (CAT2/SLC7A2) genes, were compared among hepatocellular carcinoma (HCC) and non-cancerous liver cells. Among them the ATA1 mRNA expression was significantly elevated in all HCC cell lines (HepG2, HLF, HuH7 and JHH4) examined compared with normal liver tissue. We further discovered that the expression of ATA1 mRNA was significantly activated in HCC tissues and also elevated in pre-malignant cirrhotic livers from HCC patients, compared with normal livers from non-HCC patients. The ATA1 protein was extensively accumulated in the cytoplasm of pre-malignant liver and most HCCs, while being weak or undetectably low in normal liver tissues. SiRNA-mediated suppression of endogenous ATA1 lowered the viability of HepG2 cells. Thus, the activation of ATA1 confers growth and survival advantages in pre-malignant and malignant liver lesions.
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PMID:Activation of a system A amino acid transporter, ATA1/SLC38A1, in human hepatocellular carcinoma and preneoplastic liver tissues. 1754 7