phosphothreonine and Liver-Neoplasms

Topics: Arginine; Carcinoma, Hepatocellular; Cell Line, Tumor; Cell Nucleus; Down-Regulation; Gene Expression Regulation, Neoplastic; Gene Silencing; Hep G2 Cells; Humans; Liver Neoplasms; Methylation; Models, Biological; Myosin-Light-Chain Phosphatase; Oligonucleotide Array Sequence Analysis; Phosphorylation; Phosphothreonine; Protein Binding; Protein Interaction Mapping; Protein-Arginine N-Methyltransferases; rho-Associated Kinases; Substrate Specificity

Dietary fructose is primarily metabolized in the liver. Here we demonstrate that, compared with normal hepatocytes, hepatocellular carcinoma (HCC) cells markedly reduce the rate of fructose metabolism and the level of reactive oxygen species, as a result of a c-Myc-dependent and heterogeneous nuclear ribonucleoprotein (hnRNP) H1- and H2-mediated switch from expression of the high-activity fructokinase (KHK)-C to the low-activity KHK-A isoform. Importantly, KHK-A acts as a protein kinase, phosphorylating and activating phosphoribosyl pyrophosphate synthetase 1 (PRPS1) to promote pentose phosphate pathway-dependent de novo nucleic acid synthesis and HCC formation. Furthermore, c-Myc, hnRNPH1/2 and KHK-A expression levels and PRPS1 Thr225 phosphorylation levels correlate with each other in HCC specimens and are associated with poor prognosis for HCC. These findings reveal a pivotal mechanism underlying the distinct fructose metabolism between HCC cells and normal hepatocytes and highlight the instrumental role of KHK-A protein kinase activity in promoting de novo nucleic acid synthesis and HCC development.

Topics: Carcinogenesis; Carcinoma, Hepatocellular; Fructokinases; Heterogeneous-Nuclear Ribonucleoprotein Group F-H; Humans; Liver Neoplasms; Nucleic Acids; Phosphorylation; Phosphothreonine; Proto-Oncogene Proteins c-myc; Reactive Oxygen Species; Ribose-Phosphate Pyrophosphokinase; RNA Splicing

There is controversy regarding whether fructose in liquid beverages constitutes another dietary ingredient of high caloric density or introduces qualitative changes in energy metabolism that further facilitate the appearance of metabolic diseases. Central to this issue is the elucidation of the molecular mechanism responsible for the metabolic alterations induced by fructose ingestion. Fructose administration (10% wt/vol) in the drinking water of Sprague-Dawley male rats for 14 days induced hyperleptinemia and hepatic leptin resistance. This was caused by impairment of the leptin-signal transduction mediated by both janus-activated kinase-2 and the mitogen-activated protein kinase pathway. The subsequent increase in activity in the liver of the unphosphorylated and active form of the forkhead box O1 nuclear factor, which transrepresses peroxisome proliferator-activated receptor alpha activity, and a lack of activation of the adenosine monophosphate-activated protein kinase, led to hypertriglyceridemia and hepatic steatosis. These alterations are attributable to two key events: (1) an increase in the amount of suppressor of cytokine signaling-3 protein, which blocks the phosphorylation and activation of janus-activated kinase-2 and Tyr(985) on the long form of the leptin receptor; and (2) a common deficit of phosphorylation in serine/threonine residues of key proteins in leptin-signal transduction pathways. The latter is probably produced by the early activation of protein phosphatase 2A, and further sustained by the accumulation in liver tissue of ceramide, an activator of protein phosphatase 2A, due to incomplete oxidation of fatty acids.. Our data indicate that fructose ingestion as a liquid solution induces qualitative changes in liver metabolism that lead to metabolic diseases.

Topics: Adenine Phosphoribosyltransferase; Adiponectin; Animals; Carcinoma, Hepatocellular; Cell Line, Tumor; Enzyme Activation; Fructose; Glucose; Leptin; Liver; Liver Neoplasms; Male; Phosphoproteins; Phosphoserine; Phosphothreonine; Polymerase Chain Reaction; Rats; Rats, Sprague-Dawley; Signal Transduction; Suppressor of Cytokine Signaling 3 Protein; Suppressor of Cytokine Signaling Proteins

beta-Glucuronidases purified from human hepatoma and from normal liver could serve as a substrate for a cAMP-dependent protein kinase. The rate of phosphorylation reaction of the hepatoma beta-glucuronidase was rapid, whereas that of the normal liver beta-glucuronidase was slow and much lower. Stoichiometry of phosphorylation was 4.3 and 0.46 mol of phosphate/mol of the beta-glucuronidase from the hepatoma and normal liver, respectively. Tryptic peptide mapping of 32P-labeled beta-glucuronidase from hepatoma identified two distinct phosphopeptides (X and Y). The peptide from hepatoma hydrolase was phosphorylated predominantly at the X, while the peptide Y was the major phosphopeptide in the hydrolase of normal liver. Analysis of phosphoamino acids revealed two sites, phosphoserine and phosphothreonine. beta-Glucuronidase from hepatoma consisted of a major subunit with molecular mass of 64,000 (64 kDa) and a minor subunit with 76 kDa, whereas the hydrolase from normal liver had almost exclusively 64 kDa subunit. 32P-labeled beta-glucuronidase indicated that the 64 kDa subunit was phosphorylated both in hepatoma and normal liver beta-glucuronidases.

Topics: Amino Acids; Carcinoma, Hepatocellular; Cyclic AMP; Glucuronidase; Humans; Immunodiffusion; Kinetics; Liver; Liver Neoplasms; Molecular Weight; Peptide Fragments; Phosphates; Phosphorylation; Phosphoserine; Phosphothreonine; Protein Kinases; Trypsin

Protein kinase activity has been found in hepatitis B virions (Dane particles) purified from the plasma of hepatitis B surface antigen carriers [Albin, C., and Robinson, W.S. (1980) J. Virol. 34, 297-302]. Dane particles were purified from the pooled, HBeAg-positive plasma. When this preparation was incubated with [gamma 32P]ATP in the presence of 10mM MnCl2 and 0.5% NP-40 for 15 seconds at 30 degrees C, several phosphorylated polypeptides of 20,000, 42,000, 48,000, 50,000 and 56,000 daltons were detected in sodium dodecyl sulfate-polyacrylamide gels. When the Dane particles were incubated with [gamma 32P]ATP, 10 mM MnCl2, and 0.5% NP-40 in the presence of human hepatoma cell (J-5) particulate fraction at 30 degrees C, 15 seconds, the 42,000, 48,000 and 50,000 daltons phosphorylated polypeptides were not found. When human peripheral blood lymphocytes particulate fraction was incubated with Dane particles under the same conditions, no change of Dane particle phosphorylated polypeptides was detected. Previous publications [Albin, C., and Robinson, W.S. (1980) J. Virol. 34, 297-302; Gerlich, W.H. et al. (1982) J. Virol. 42, 761-766] showed that when hepatitis B core particles purified from hepatoma tissues contained protein kinase activity, only phosphorylated polypeptide was 20,000 daltons. Our data suggested that when Dane particles were put in an environment of hepatoma cells (or tissues), the protein kinase could only phosphorylate selected polypeptides in these particles.

Topics: Carcinoma, Hepatocellular; Cell Line; Fibroblasts; Hepatitis B virus; Humans; Liver Neoplasms; Lymphocytes; Peptides; Phosphoproteins; Phosphorylation; Phosphoserine; Phosphothreonine; Protein Kinases; Subcellular Fractions; Viral Proteins; Virion