Molecular and functional analysis of glutamine uptake in human hepatoma and liver-derived cells

Abstract

Inflammatory mediators including chemokines play a critical role in acute pancreatitis. The precise nature of early inflammatory signals within the pancreas remains, however, unclear. We examined the ability of isolated pancreatic acini to synthesize CC chemokine monocyte chemotactic protein-1 (MCP-1) and CXC chemokine cytokine-induced neutrophil chemoattractant (CINC) and the response to the secretagogue cerulein at physiological and supraphysiological concentrations. Isolated rat pancreatic acini maintained in short-term (< or =48 h) primary culture constitutively synthesized MCP-1 and CINC. Cerulein (10(-7) M; supramaximal dose) increased production of MCP-1 but not CINC. Cerulein-induced increase in MCP-1 synthesis was accompanied by increase in nuclear factor (NF)-kappaB activation shown by EMSA. Pretreatment with NF-kappaB inhibitors N-acetylcysteine (NAC) and N-tosylphenyalanine chloromethyl ketone (TPCK) blocked cerulein-induced NF-kappaB activation and abolished cerulein's effect on MCP-1 synthesis. Pretreatment with calcium antagonist BAPTA-AM also blocked cerulein's effect on MCP-1 synthesis. These results indicate that isolated acini synthesize MCP-1 and CINC and support the idea of acinar-derived chemokines as early mediators of inflammatory response in acute pancreatitis. Although cerulein hyperstimulation increased MCP-1 synthesis by a calcium-dependent mechanism involving NF-kappaB activation, CINC synthesis was not affected. This suggests that regulation of CC and CXC chemokines within acinar cells may be quite different.

Activation of a system A amino acid transporter, ATA1/SLC38A1, in human hepatocellular carcinoma and preneoplastic liver tissues

“…Analogous to our present observations, a neural amino acid transporter, ATB 0 , has also been shown previously to be overexpressed in cirrhotic liver samples (19). It has been further reported that the activity of ATA2 (20,21) is adaptively up-regulated in response to physiological changes such as nutrient starvation.…”

“…HCC cells may thus have compensatory mechanisms for specific amino acid uptake. In fact, it is known that a neutral amino acid transporter, ATB 0 is activated in HCC cells and promotes glutamine-dependent tumor growth (19).…”

Inducible antisense RNA targeting amino acid transporter ATB0/ASCT2 elicits apoptosis in human hepatoma cells

“…Consequently, the systemic glutamine homeostatic function of the liver is subverted, resulting in significantly decreased plasma glutamine levels in patients with liver cancer (16), an event that can adversely impact glutamine-dependent cells, such as those in the immune system (1). Previous work from our laboratory (6)(7)(8)(9) showed that human hepatoma cells take up glutamine at rates 10-to 30-fold faster than normal human hepatocytes via a transporter historically termed System ASC. This high-affinity Na ϩ -dependent glutamine transport activity is not expressed in normal hepatocytes (7).…”

“…This transporter has also been identified as a cell surface receptor for mammalian retroviruses and is referred to as human ASCT2 (35). ATB 0 /ASCT2 expression was recently reported to be absent in normal human hepatocytes but present in six human hepatoma cell lines and primary liver tumors and shown to mediate the glutamine-dependent growth of rapidly growing human hepatoma cells (6). These results were confirmed by a recent query at the Cancer Genome Anatomy Project website (http://cgap.nci.nih.gov) that showed no ATB 0 / ASCT2 (accession #U53347) expression in normal human liver [0/34,164 expressed sequence tags (ESTs)] but appreciable expression in liver cancer (17/40,737 ESTs) using the Virtual Northern program.…”

Transactivating effect of complete S protein of hepatitis B virus and cloning of genes transactivated by complete S protein using suppression subtractive hybridization technique

“…When amino acid is starved, the expression of ATA2 increases, suggesting that this expression is directly related to the activity of amino acid transporter [26] . Its mRNA increases in the biopsy of hepatocirrhosis and hepatic carcinoma [27] , especially in chorion after hepatectomy, suggesting that ATA2 is closely associated with hepatic regeneration [26,28] . ATA2 is cloned in hepatic carcinoma HepG2, and increases in patients of hepatic carcinoma [29] .…”