Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two independent approaches were employed to explore the potential role of endogenous glucosylceramide or a closely related glucosphingolipid in mediating the cellular proliferation of Madin-Darby canine kidney cells. First, cultured cells were depleted of glucosphingolipids by exposure to a glucosylceramide synthase inhibitor, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol. This agent markedly inhibited cell growth and DNA synthesis in a time- and concentration-dependent manner. Second, cells were grown in the presence of conduritol B epoxide, an inhibitor of glucosylceramide beta-D-glucosidase. Exposure of cells to this inhibitor resulted in the time-dependent accumulation of glucosylceramide with a corresponding increase in cellular proliferation. Alterations in protein kinase C activity were evaluated as a potential mechanism for these effects on growth. Both membrane- and cytosol-associated protein kinase C (PKC) activity declined under conditions of glucosylceramide synthase inhibition and increased under conditions of beta-glucosidase inhibition. The changes in PKC activity were evident after DEAE-cellulose purification. Diacylglycerol levels increased in response to both glucosylceramide synthase and beta-glucosidase inhibition. Ceramide and sphingosine levels changed only in the presence of D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, increasing due to lack of conversion to glucosylceramide. However, the elevation in endogenous sphingosine was probably insufficient to account for the decrease in PKC, considering the high level of diacylglycerol in the cells. These data demonstrate an association between glucosylceramide levels, PKC activity, and cell growth.
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PMID:Modulation of renal epithelial cell growth by glucosylceramide. Association with protein kinase C, sphingosine, and diacylglycerol. 174 91

A proposed weak point in cancer cells is their need to synthesize novel or rare glucosphingolipids. It is further proposed that cancer patients be treated with a drug that slows the synthesis of glucosylceramide, the precursor of a large family of glucosphingolipids. Experimental data are furnished for chemotherapeutic and biochemical effects of PDMP, an analog of glucosylceramide and its precursor, ceramide. Promising results were obtained in the treatment of mice carrying Ehrlich ascites carcinoma cells and rats carrying C6 glioma cells. PDMP was found to be oxidized by cytochrome P-450, but this process could be blocked in vivo with piperonyl butoxide or cimetidine. A high level of blood glucose was found to elevate the size of rat kidneys and their content of UDP-glucose and its product, glucosylceramide. The excessive growth could be blocked by PDMP, which competes with UDP-glc for binding to glucosylceramide synthase. It is suggested that cancer patients be maintained at a low glucose level in order to slow the synthesis of glucosylceramide by tumor cells. Metabolic changes produced by PDMP in cultured cells, besides a rapid deletion of glucosphingolipids, were accumulation of the precursors (ceramide and sphingosine), loss of protein kinase C, and accumulation of diacylglycerol. It is suggested that many of the cellular changes produced by PDMP, such as loss of cell binding, are owing to existence of glucosylceramide-based "islands" floating in the outer cell surface; the islands may contain growth factor receptors and adhesion factors. An inhibitor that blocks sphingolipid synthesis, such as cycloserine, may prove to be a useful adjuvant for therapy with PDMP.
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PMID:Rationales for cancer chemotherapy with PDMP, a specific inhibitor of glucosylceramide synthase. 808 32

Interaction between sphingomyelin metabolism and cyclic nucleotide synthesis in rat pinealocytes was investigated by determining the effect of ceramide on adrenergic-stimulated cAMP and cGMP accumulation. Although C2-, C6-, and C8-ceramide had no effect on basal, isoproterenol-, or norepinephrine-stimulated cAMP and cGMP accumulation, they inhibited the potentiation caused by depolarising concentrations of K+ or BayK 8644. Similar inhibition was observed when ceramide metabolism was inhibited by a glucosylceramide synthase inhibitor. In contrast, the potentiation of cAMP and cGMP accumulation caused by other intracellular Ca(2+)-elevating agents such as ionomycin or thapsigargin or by an activator of protein kinase C was not affected by ceramide. Taken together, our results suggest that ceramide selectively inhibits cyclic nucleotide synthesis when the nucleotide synthesis is potentiated by an increase in intracellular Ca2+ through L-type Ca2+ channels and that the sphingomyelin cycle probably plays an important role in the regulation of these channels.
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PMID:Ceramide selectively inhibits calcium-mediated potentiation of beta-adrenergic-stimulated cyclic nucleotide accumulation in rat pinealocytes. 951 88

In this study, the effect of ceramide on GH-releasing hormone (GHRH)-stimulated cAMP accumulation and GH release in rat anterior pituitary cells was investigated. C2-, C6-, and C8-ceramide were found to enhance GHRH-stimulated cAMP accumulation. In contrast, their effects on GHRH-stimulated GH release were inhibitory. Treatment with a glucosylceramide synthase inhibitor produced a similar enhancing effect on cAMP accumulation and an inhibitory effect on GH release. To identify the pathway through which ceramide mediated its effect, it was found that ceramide inhibited GH release stimulated by KCl, BayK 8644, and a GH-releasing peptide, but not that stimulated by ionomycin or an activator of protein kinase C. Direct measurement of intracellular Ca2+ revealed that C2-ceramide inhibited GHRH- and KCl-mediated increases in intracellular Ca2+, suggesting that ceramide probably inhibits GH release through inhibition of the L-type Ca2+ channels. As for its mechanism on cAMP accumulation, the enhancing effect of ceramide on GHRH-stimulated cAMP accumulation was abolished in the presence of a phosphodiesterase inhibitor, isobutylmethylxanthine, suggesting that ceramide enhances the cAMP response through inhibition of its metabolism. Taken together, our results suggest that ceramide plays an important role in the regulation of GHRH-stimulated responses in somatotrophs. By reducing GH secretion while enhancing cAMP accumulation, ceramide may promote the synthesis and storage of GH in rat anterior pituitary cells.
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PMID:Ceramide enhances growth hormone (GH)-releasing hormone-stimulated cyclic adenosine 3',5'-monophosphate accumulation but inhibits GH release in rat anterior pituitary cells. 1057 33

Previous studies have demonstrated that the activity of GM3 synthase and GM3 content are increased during the differentiation of human promyelocytic leukemia HL-60 cells into the monocyte/macrophage lineage after phorbol 12-myristate 13-acetate (PMA) treatment. However, the molecular mechanisms involved in transcriptional activation of GM3 synthase during differentiation of PMA-induced HL-60 cells are not well understood. As evidenced by western blot analysis, PMA induced the marked activation of protein kinase C (PKC)/extracellular regulated kinases (ERKs) signal transduction pathway during the differentiation of HL-60 cells. In addition, PKC/ERKs activation induced by PMA in HL-60 cells led to the phosphorylation of cAMP-responsive element binding protein (CREB) as a transcription factor. In PMA-stimulated HL-60 cells, the PKC/ERKs-dependent CREB activation regulated expression of GM3 synthase, inducing a synthesis of ganglioside GM3 product. On the other hand, although ganglioside GM3 was shown to be able to induce the differentiation of HL-60 cells into the monocyte/macrophage lineage, effect of ganglioside GM3 on expression of CD11b as a differentiation marker in HL-60 cells has been not reported yet. Interestingly, the increased ganglioside GM3 through PKC/ERKs/CREB-dependent pathway by PMA resulted in an increase of CD11b surface antigen expression and induction of HL-60 cells adherence. Treatment with L-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), glucosylceramide synthase inhibitor, decreased induction of not only CD11b expression but also cellular adherence by reduction of PMA-induced ganglioside GM3. Furthermore, treatment of HL-60 cells with exogenous ganglioside GM3 induced CD11b expression. These results show that the enhanced expression of GM3 synthase through PKC/ERKs-dependent CREB activation by PMA is associated with the differentiation of HL-60 cells by inducing expression of CD11b known as a monocyte/macrophage differentiation maker.
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PMID:Molecular mechanism for transcriptional activation of ganglioside GM3 synthase and its function in differentiation of HL-60 cells. 1538 32

Vascular endothelial growth factor (VEGF) has been implicated in angiogenesis associated with coronary heart disease, vascular complications in diabetes, inflammatory vascular diseases, and tumor metastasis. The mechanism of VEGF-driven angiogenesis involving glycosphingolipids such as lactosylceramide (LacCer), however, is not known. To demonstrate the involvement of LacCer in VEGF-induced angiogenesis, we used small interfering RNA (siRNA)-mediated silencing of LacCer synthase expression (GalT-V) in human umbilical vein endothelial cells. This gene silencing markedly inhibited VEGF-induced platelet endothelial cell adhesion molecule-1 (PECAM-1) expression and angiogenesis. Second, we used D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP), an inhibitor of LacCer synthase and glucosylceramide synthase, that significantly mitigated VEGF-induced PECAM-1 expression and angiogenesis. Interestingly, these phenotypic changes were reversed by LacCer but not by structurally related compounds such as glucosylceramide, digalactosylceramide, and ceramide. In a human mesothelioma cell line (REN) that lacks the endogenous expression of PECAM-1, VEGF/LacCer failed to stimulate PECAM-1 expression and tube formation/angiogenesis. In REN cells expressing human PECAM-1 gene/protein, however, both VEGF and LacCer-induced PECAM-1 protein expression and tube formation/angiogenesis. In fact, VEGF-induced but not LacCer-induced angiogenesis was mitigated by SU-1498, a VEGF receptor tyrosine kinase inhibitor. Also, VEGF/LacCer-induced PECAM-1 expression and angiogenesis was mitigated by protein kinase C and phospholipase A2 inhibitors. These results indicate that LacCer generated in VEGF-treated endothelial cells may serve as an important signaling molecule for PECAM-1 expression and in angiogenesis. This finding and the reagents developed in our report may be useful as anti-angiogenic drugs for further studies in vitro and in vivo.
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PMID:Novel role of lactosylceramide in vascular endothelial growth factor-mediated angiogenesis in human endothelial cells. 1615 Oct 23

Multidrug resistance (MDR) of neoplastic tissues is a major obstacle in cancer chemotherapy. The predominant cause of MDR is the overexpression and drug transport activity of P-glycoprotein (P-gp, a product of the MDR gene). P-gp is a member of the ATP binding cassette (ABC) transporters family, with broad substrate specificity for several substances including anticancer drugs, linear and cyclic peptides, inhibitors of HIV protease, and several other substances. The development of P-gp-mediated MDR is often associated with several changes in cell structure and metabolism of resistant cells. In the present review are discussed the relations between glucosylceramide synthase activity, Pregnane X receptor and development of P-gp mediated MDR phenotype. Attention is also focused on the changes in protein kinase systems (mitogen-activated protein kinases, protein kinase C, Akt kinase) that are associated with the development of MDR phenotype and to the possible role of these kinase cascades in modulation of P-gp expression and function. The overexpression of P-gp may be associated with changes in metabolism of sugars as well as energy production. Structural and ultrastructural characteristics of multidrug resistant cells expressing P-gp are typical for cells engaged in a metabolically demanding process of protein synthesis and transport. P-gp mediated MDR phenotype is often also associated with alterations in cytoskeletal elements, microtubule and mitochondria distribution, Golgi apparatus, chromatin texture, vacuoles and caveolae formation. The current review also aims at bringing some state-of-the-art information on interactions of P-glycoprotein with various substances. To capture and transport the numerous unrelated substances, P-gp should contain site(s) able to bind compounds with a molecular weight of several hundreds and comprising hydrophobic and/or base regions that are protonated under physiological conditions. Drug binding sites that are able to recognize substances with different chemical structures may have a complex architecture in which different parts are responsible for binding of different drugs. For P-gp substrates and inhibitors, a pharmacophore-based model has been described. The pharmacophores have to contain parts with hydrophobic and aromatic characteristics and functional groups that can act as hydrogen-bond donors and/or acceptors. Several drugs are known to be P-glycoprotein antagonizing agents. They represent a large group of structurally unrelated substances that can act via direct interaction with P-gp and inhibition of its transport activity, or via possible modulation of processes (such as phosphorylation) regulating P-gp transport activity. Effects of MDR reversal agents on the P-gp expression have also been reported. Function and expression of P-gp can be affected indirectly as well, e.g. through cyclooxygenase-2 or carbonic anhydrase-IX expression and effects.
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PMID:P-glycoprotein--implications of metabolism of neoplastic cells and cancer therapy. 1617 19

The membrane type sialidase (Neu3) has been suggested to participate in cell growth, migration and differentiation. To determine whether a Neu3 is able to modulate megakaryocytic differentiation of K562 cells, we studied the functional significance of human Neu3 induced by phorbol 12-myristate 13-acetate (PMA). Northern blot and reverse transcription-polymerase chain reaction (RT-PCR) indicated that the induction of hST3Gal V, which synthesizes ganglioside GM3 and reduction of Neu3 by PMA, are linked for the expression of differentiation marker protein, CD41b surface antigen. To elucidate the mechanism underlying the down-regulation of the CD41b surface antigen expression when Neu3 gene is expressed in PMA-treated cells, we characterized the Neu3-mediated signaling pathway. Neu3 overexpression inhibited the PMA-induced ERK1/2 and p38 MAPK phosphorylation in the K562 cells. Down-regulation of expression of CD41b surface antigen was dependent on expression of Neu3 gene. However, a Neu3 inhibitor Neu5Ac2en induced morphological changes, showing megakaryocytic differentiation of K562 cells, with expression of CD41b surface antigen, while a specific glucosylceramide synthase inhibitor PDMP inhibited megakaryocytic differentiation of K562 cells. The molecular mechanisms involved in Neu3-involved inhibition of CD41b surface antigen expression in K562 cells have been suggested: the Neu3 degrades membrane sialic acids and the resulting signaling pathway of the PKC/ERKs/p38 MAPK is down-regulated, causing a decrease in CD41b surface antigen expression and inhibition of megakaryocytic differentiation of K562 cells.
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PMID:Membrane type sialidase inhibits the megakaryocytic differentiation of human leukemia K562 cells. 1833 27