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Biomedical subjects

C Kent

Publications and source records attributed to C Kent.

At least 37 records · Page 2Linked to original sources
PubMed1995

Cholecystokinin stimulates the down-regulation of CTP:phosphocholine cytidylyltransferase in pancreatic acinar cells.

Stimulation of rat pancreatic acinar cells with cholecystokinin (CCK) is known to result in a significant inhibition of CTP:phosphocholine cytidylyltransferase (CT), a rate-limiting enzyme in phosphatidylcholine biosynthesis. Immunoprecipitation of CT from 32P-labeled acinar cells revealed that CCK treatment also caused a marked reduction in CT phosphate levels. The effects of CCK were maximal over 60 min and dependent on concentration, exhibiting an EC50 of 800 pM. Other calcium mobilizing secretagogues such as carbamylcholine (100 microM) and bombesin (10 nM) also reduced CT phosphate levels to 20 and 39% of control, respectively. Treatment of cells with thapsigargin and/or 12-O-tetradecanoyl-phorbol-13-acetate established that a combination of increased intracellular Ca2+ and protein kinase C activation was necessary to decrease phosphorylated CT content. Conversely, secretin (10 nM) or 8-(4-chlorophenylthio)-cAMP (100 microM) added alone had no effects. Use of the compound JMV-180 indicated CCK was acting through the low affinity state of the CCKA receptor to reduce CT phosphate levels. Further, the decrease in phosphorylated CT caused by CCK was blocked by the phosphatase inhibitors okadaic acid (3 microM) and calyculin A (100 nM). Finally, immunoblotting from whole cell lysates revealed CT was partially degraded in response to CCK, providing a novel mechanism by which the inhibition of CT enzyme activity occurs in response to the hormone. Moreover, this degradation was also blocked by a phosphatase inhibitor. These data suggest that the dephosphorylation of either CT itself or some other regulatory molecule(s) which mediates the CCK-induced protease activation may play a central role in reducing CT enzyme levels in acinar cells.

Animals↗
PubMed1995

Identification of the nuclear localization signal of rat liver CTP:phosphocholine cytidylyltransferase.

CTP:phosphocholine cytidylyltransferase (CT) is a major regulatory enzyme in phosphatidylcholine synthesis in mammalian cells. CT is found in both soluble and particulate forms, both of which are nuclear. We report here the identification of a 21-residue sequence at the amino terminus of CT, 8KVNSRKRRKEVPGPNGATEED28, which was sufficient to direct beta-galactosidase into the cell nucleus. Further deletions from either end of this sequence greatly reduced the nuclear localization of beta-galactosidase. Deletions of amino acids within the nuclear localization signal or of the entire signal disrupted CT nuclear localization, but CT was not completely excluded from the nucleus. Clones of stable transfectants of the nuclear localization signal-deficient CT expressed in Chinese hamster ovary (CHO) 58 cells, which is temperature-sensitive for growth and CT activity, were isolated and characterized. The deletion mutants were active under the same conditions as the wild-type enzyme. Despite the difference in subcellular location from wild-type CT, the nuclear localization mutants were fully able to complement the CT-deficient cell line CHO 58 for both growth and choline incorporation into phosphatidylcholine at the nonpermissive temperature. The mobility of the mutant enzymes on SDS gels was altered relative to the mobility of wild-type CT; however, the extent of phosphorylation of the mutant enzymes was decreased only slightly. Thus, the distribution of CT in both cytoplasm and nucleus, rather than exclusively nucleus, has little effect on the ability of CT to function in growing CHO cells.

Amino Acid Sequence↗
PubMed1995

Eukaryotic phospholipid biosynthesis.

The current status of the biochemistry of phospholipid biosynthesis is presented. The review focuses on the identification and characterization of molecular tools such as purified enzymes and cloned genes and cDNAs for those enzymes. The enzymes discussed are those involved in the biosynthesis of the major phospholipid classes, namely, phosphatidate, phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin, phosphatidylinositol and its phosphorylated derivatives, and cardiolipin. The review centers on the pathways in mammals and yeast. Novel genetic approaches used to delineate pathways and clone cDNAs are discussed. The regulatory roles played by some of the enzymes involved in controlling the biosynthetic pathways are presented.

Animals↗