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)

The multidrug-resistance (MDR)-reversing ability of the catamphiphilic drugs could be mediated through their interaction with the membrane phospholipids. This could lead directly (through changes in membrane permeability and fluidity) and/or indirectly (through inhibition of P-glycoprotein phosphorylation via inhibition of the phosphatidylserine-dependent protein kinase C or changes in the conformation and functioning of the membrane-integrated proteins via changes in the structure organization of the surrounding membrane bilayer) to the reversal of MDR. Using differential scanning calorimetry and NMR techniques and artificial membranes composed of phosphatidylcholine or phosphatidylserines we found a significant correlation between the MDR-reversing activity of the drugs in doxorubicin-resistant human breast carcinoma MCF-7/DOX and murine leukaemia P388/DOX tumour cells (data taken from the literature) and their ability to interact with phosphatidylserines. Trans- and cis-flupentixol were found to interact most strongly with both the phospholipids, followed by trifluoperazine, chlorpromazine, triflupromazine, flunarizine, imipramine, quinacrine and lidocaine. Differences in the interaction of trans- and cis-flupentixol with the phospholipids studied are suggested to be responsible for their different MDR-reversing ability. Verapamil showed moderate membrane activity, assuming that the membrane interactions are not the only reason for its high MDR-reversing ability. Amiodarone showed very strong interactions with phosphatidylserines and is recommended for further MDR-reversal studies.
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PMID:Membrane interactions of some catamphiphilic drugs and relation to their multidrug-resistance-reversing ability. 854 89

Synthesis of the biologically active oestrogen, oestradiol, within breast tumours makes an important contribution to the high concentrations of oestrogens which are present in malignant breast tissues. In breast tumours, oestrone is preferentially converted to oestradiol by the Type I oestradiol 17 beta-hydroxysteroid dehydrogenase (E2DH). Several growth factors, such as insulin-like growth factor Type I, and cytokines, such as Tumour Necrosis Factor alpha (TNF alpha), have been shown to stimulate E2DH activity in MCF-7 breast cancer cells. As little is known about the regulation of Type I E2DH expression and activity in other breast cancer cell lines, the expression and activity of this enzyme was examined in other oestrogen receptor positive and also oestrogen receptor negative breast cancer cell lines. As it is possible that E2DH activity may be limited by co-factor availability, the effects of exogenous co-factors on enzyme activity in these cell lines was also investigated. For T47D and BT20 breast cancer cells, the addition of exogenous co-factors was found to enhance enzyme activity. TNF alpha, in addition to stimulating E2DH activity in MCF-7 cells, also increased activity in T47D and MDA-MB-231 cells, although to a lesser extent than in MCF-7 cells. An investigation of signalling pathways involved in the regulation of E2DH activity revealed that stimulation of both the protein kinase C (PKC) and PKA pathways may be involved in regulation of E2DH activity. As several growth factors and cytokines have now been found to be involved in regulating E2DH activity, the role that macrophages and lymphocytes have in supplying these factors and the mechanism by which these factors may stimulate tumour growth, is also reviewed.
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PMID:The role and proposed mechanism by which oestradiol 17 beta-hydroxysteroid dehydrogenase regulates breast tumour oestrogen concentrations. 854 83

The MCF-7 doxorubicin-resistant cell line MCF-7/Dox has been used extensively for studies of the multidrug resistance phenomenon. Using fluorescence-activated cell sorting (FACS), these cells were separated into two populations on the basis of rhodamine 123 (R123) accumulation. We designated these as low P-glycoprotein (LP-gp) and high P-gp (HP-gp) cells on the basis of their P-gp content. Using the reverse transcriptase polymerase chain reaction technique controlled by homologous internal standards, we analysed levels of MDR1 and MDR2 mRNA in each cell type. LP-gp and HP-gp cells had MDR1 mRNA levels of 2.17 +/- 0.17 and 6.65 +/- 2.29 amol ng-1 total RNA respectively, compared with 0.00088 +/- 0.00005 amol ng-1 in wild-type MCF-7 cells (MCF-7/WT). MCF-7/WT cells additionally contained 0.023 +/- 0.016 amol ng-1 of MDR2 mRNA, which was unchanged in LP-gp cells, but lower than in HP-gp cells, which contained 0.42 +/- 0.08 amol ng-1. Both LP-gp and HP-gp cells contained increased copies of the MDR1 gene. However, the degree of gene amplification did not correlate with the changes in MDR1 mRNA levels, indicating further regulatory levels of gene expression. The level of P-gp detected by MRK 16 correlated with R123 accumulation. HP-gp cells expressed a 10-fold higher level of P-gp1 than LP-gp cells. However, there was only a 3-fold increase in MDR1 mRNA level in HP-gp cells compared with LP-gp cells. These data suggest that some regulation of P-gp1 expression also occurred at the post-translational level. Phosphorylation of P-gp by protein kinase C (PKC)-alpha is necessary for its activity. Our analysis of PKC-alpha, 0 and epsilon isozyme levels, and subcellular distribution, shows a co-regulation of expression with P-gp, suggesting a necessary role for PKC in P-gp regulation.
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PMID:Regulation of P-glycoprotein 1 and 2 gene expression and protein activity in two MCF-7/Dox cell line subclones. 856 35

The potent kinase inhibitor staurosporine and its protein kinase C (PKC)-selective analogue CGP 41251 are known to sensitise cells with the multidrug resistance (MDR) phenotype mediated by P-glycoprotein (P-gp) to cytotoxic agents. Here four PKC-selective staurosporine cogeners, CGP 41251, UCN-01, RO 31 8220 and GF 109203X, were compared with staurosporine in terms of their MDR-reversing properties and their susceptibility towards P-gp-mediated drug efflux from MCF-7/Adr cells. Staurosporine was the most potent and the bisindolylmaleimides RO 31 8220 and GF 109203X the least potent cytostatic agents. When compared with MCF-7 wild-type cells, MCF-7/Adr cells were resistant towards the growth-arresting properties of RO 31 8220 and UCN-01, with resistance ratios of 12.6 and 7.0 respectively. This resistance could be substantially reduced by inclusion of the P-gp inhibitor reserpine. The ratios for GF 109203X, staurosporine and CGP 41251 were 1.2, 2.0 and 2.9 respectively, and they were hardly affected by reserpine. These results suggest that RO 31 8220 and UCN-01 are avidly transported by P-gp but that the other compounds are not. Staurosporine and CGP 41251 at 10 and 20 nM, respectively, decreased efflux of the P-gp probe rhodamine 123 (R123) from MCF-7/Adr cells, whereas RO 31 8220 and GF 109203X at 640 nM were inactive. CGP 41251 was the most effective and GF 109203X the least effective inhibitor of equilibrium binding of [3H]vinblastine to its specific binding sites, probably P-gp, in MCF-7/Adr cells. Overall, the results imply that for this class of compound the structural properties that determine susceptibility towards P-gp-mediated substrate transport are complex. Comparison with ability to inhibit PKC suggests that the kinase inhibitors affect P-gp directly and not via inhibition of PKC. Among these compounds CGP 41251 was a very potent MDR-reversing agent with high affinity for P-gp and least affected by P-gp-mediated resistance, rendering it an attractive drug candidate for clinical development.
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PMID:Comparison of staurosporine and four analogues: their effects on growth, rhodamine 123 retention and binding to P-glycoprotein in multidrug-resistant MCF-7/Adr cells. 862 64

The possible regulation of the multidrug-resistant (MDR) phenotype and P-glycoprotein by protein kinase C (PKC) was investigated in the doxorubicin (Dox)-resistant MCF-7 cell line (MCF-7/Dox). In a clonogenic assay, cells exposed to 100 nM phorbol 12-myristate 13-acetate (PMA) for 1 hr were about 3-fold more resistant to Dox than were cells exposed to Dox alone. The PKC inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7, 30 microM) completely blocked the PMA-induced effect, but did not reverse the MDR phenotype. Complete down-regulation of PKC from MCF-7/Dox cells by 24-hr preincubation with PMA did not alter the degree of Dox resistance. Intracellular accumulation of [14C]Dox decreased from a baseline of 28 pmol/10(6) cells to 15 pmol/10(6) cells in the presence of 100 nM PMA. The reduced Dox accumulation in the presence of PMA was not blocked by pretreatment of cells with H7. Following a 24-hr pretreatment with PMA, the cells accumulated almost equal amounts of [14C]Dox in the absence or presence of PMA. Cells from PMA-treated colonies showed significantly higher levels of expression of P-glycoprotein when compared with those from control colonies. H7 did not affect the basal level of P-glycoprotein in cells from control colonies or PMA-induced overexpression of P-glycoprotein in cells from PMA-treated colonies. Upon stimulation with PMA (100 nM), PKC alpha and beta translocated to the cell membrane and nucleus and PKC delta and epsilon to the perinuclear membrane and the nucleus, respectively. H7 (30 microM) completely inhibited PMA-induced translocations of PKC delta and epsilon, whereas it only partially blocked the translocations of PKC alpha and beta. These results suggest that PMA appears to alter Dox resistance and intracellular Dox accumulation in a PKC-dependent manner and to induce increased expression of P-glycoprotein in MCF-7/Dox cells. Differential effects of H7 on the PMA-induced changes suggest that different isoforms of PKC may be involved in cell growth and drug accumulation processes as well as P-glycoprotein expression.
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PMID:Selective inhibition of the effects of phorbol ester on doxorubicin resistance and P-glycoprotein by the protein kinase C inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7) in multidrug-resistant MCF-7/Dox human breast carcinoma cells. 868 92

We investigated the effect of hypoglycemic treatment on the activation of the AP-1 transcription factors and the regulation of basic fibroblast growth factor (bFGF) gene expression in multidrug resistant human breast carcinoma MCF-7/ADR cells. Northern blot and gel mobility shift assays showed that hypoglycemic treatment induced c-jun and c-fos gene expression, AP-1 binding activity, as well as bFGF gene expression. Moreover, transfected cells expressing high levels of abnormal c-Jun protein exhibited a reduction in the bFGF protein levels compared to parental cells. A potent protein kinase C (PKC) inhibitor, H-7 (60 micrograms/ml) suppressed the stress-induced bFGF gene expression. Our study also demonstrated that H-7 did not facilitate the decay of bFGF mRNA. Thus, the suppression of bFGF gene expression by treatment with H-7 was due to the effect of the drug on the synthesis of bFGF mRNA rather than the stability of bFGF mRNA. Our data suggest that hypoglycemia-induced bFGF gene expression is mediated through the activation of PKC and the AP-1 transcription factors.
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PMID:Hypoglycemia-induced AP-1 transcription factor and basic fibroblast growth factor gene expression in multidrug resistant human breast carcinoma MCF-7/ADR cells. 870 Jan 61

Mutual interactions between 17 beta-estradiol (E2) and insulin or insulin-like growth factor-I (IGF-1) in the regulation of ornithine decarboxylase (ODC) expression were examined in estrogen-responsive MCF-7 human breast cancer cells. Whereas E2 only retarded the rapid decay of ODC activity observed upon mitogen withdrawal, both insulin and IGF-1 led to a rapid (< 4 h), net increase in ODC activity that was mediated, at least in part, through their cognate receptors. E2 synergistically potentiated the induction of ODC by IGF-1, resulting in a 170-fold elevation of enzyme activity after 48 h, as compared with 23- and 70-fold increases caused by E2 and IGF-1 alone, respectively. Cooperativity was more pronounced at suboptimal peptide concentrations due to a decrease in the half-maximal concentration of insulin or IGF-1 required for ODC induction. Phorbol-12-myristate-13-acetate (PMA) also strongly induced ODC activity in a transient manner, and additively to the effect of IGF-1. IGF-1 and PMA additively increased ODC mRNA level, whereas E2 alone had no effect on ODC mRNA abundance. IGF-1 increased the half-life of ODC activity by 60%, whereas E2 or PMA alone had no significant effect on enzyme stability. On the other hand, the simultaneous addition of IGF-1 and either E2 or PMA cooperatively reduced ODC turnover, resulting in 3.5- and 2-fold increases, respectively, in the half-life of ODC activity. Thus, ODC expression in breast cancer cells is primarily regulated by tyrosine kinase- and protein kinase C-dependent pathways, whereas estrogens increase ODC activity through a novel type of synergistic interaction with growth factors that results in a decreased rate of enzyme turnover.
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PMID:Post-translational cooperativity of ornithine decarboxylase induction by estrogens and peptide growth factors in human breast cancer cells. 873 82

Indirect evidence has suggested that P-glycoprotein (P-gp), the multidrug transporter, is phosphorylated by protein kinase C (PKC) and that phosphorylation modulates its transport function. To address the first premise more directly, ie., that P-gp is phosphorylated by PKC, we investigated the interaction between P-gp and PKC in sensitive and multidrug resistant MCF-7 and KB human carcinoma cell lines. We found that P-gp and PKC were coimmunoprecipitated from the multidrug-resistant cell lines MCF-7/AdrR and KB-V-1, using antibodies to either protein. The association between the two proteins was enhanced by phorbol 12-myristate 13-acetate, an analogue of diacylglycerol that induces translocation of PKC to the plasma membrane. The anti-P-gp immunoprecipitates contained PKC activity as measured by direct phosphorylation reactions. The interaction of PKC with P-gp displayed isozyme specificity: PKC-alpha, -beta, gamma, -epsilon, and -phi, but not -delta, -mu, -zeta, -lambda, were found to coimmunoprecipitate with P-gp. These studies indicate that P-gp closely interacts with PKC and serves as a substrate, and that specific isozymes of this kinase may be involved in the phosphorylation of the multidrug transporter.
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PMID:Interaction of P-glycoprotein with protein kinase C in human multidrug resistant carcinoma cells. 875 35

To investigate the role of protein kinase C (PKC) in the regulation of multidrug resistance and P-glycoprotein (P-gp) phosphorylation, the natural isomer of sphingosine (SPH), D-erythro sphingosine (De SPH), and its three unnatural stereoisomers were synthesized. The SPH isomers showed similar potencies as inhibitors of in vitro PKC activity and phorbol binding, with IC50 values of approximately 50 microM in both assays. Treatment of multidrug-resistant MCF-7ADR cells with SPH stereoisomers increased vinblastine (VLB) accumulation up to 6-fold at 50 microM but did not alter VLB accumulation in drug-sensitive MCF-7 wild-type (WT) cells or accumulation of 5-fluorouracil in either cell line. Phorbol dibutyrate treatment of MCF-7ADR cells increased phosphorylation of P-gp, and this increase was inhibited by prior treatment with SPH stereoisomers. Treatment of MCF-7ADR cells with SPH stereoisomers decreased basal phosphorylation of the P-gp, suggesting inhibition of PKC-mediated phosphorylation of P-gp. Most drugs that are known to reverse multidrug resistance, including several PKC inhibitors, have been shown to directly interact with P-gp and inhibit drug binding. SPH stereoisomers did not inhibit specific binding of [3H] VLB to MCF-7ADR cell membranes or [3H]azidopine photoaffinity labeling of P-gp or alter P-gp ATPase activity. These results suggest that SPH isomers are not substrates of P-gp and suggest that modulation of VLB accumulation by SPH stereoisomers is associated with inhibition of PKC-mediated phosphorylation of P-gp.
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PMID:Effects of sphingosine stereoisomers on P-glycoprotein phosphorylation and vinblastine accumulation in multidrug-resistant MCF-7 cells. 875 33

We assessed the effect of the protein kinase C inhibitor 2,6-diamino-N-([1-(1-oxotridecyl)-2-piperidinyl]methyl)hexanami de (NPC 15437) on the action of anthracyclines, epipodophyllotoxins and vinca alkaloids in P-glycoprotein (Pgp)-expressing CH(R)C5 hamster ovary and MCF-7/Adria(R) human breast cancer cells. Flow microfluorimetry revealed that treatment of CH(R)C5 cells with 75 microM NPC 15437 for 1 h resulted in a 6- to 10-fold increase in the nuclear accumulation of daunorubicin. Colony forming assays revealed that treatment with 75 microM NPC 15437 was associated with a 4-fold decrease in the LD90 for etoposide and a 2.5-fold decrease in the LD50 for vincristine. At higher concentrations of NPC 15437, greater modulation of anthracycline accumulation was observed; but NPC 15437 itself inhibited subsequent colony formation. Similar effects on drug accumulation and cytotoxicity were observed in MCF-7/Adria(R) cells. Experiments designed to investigate the mechanism by which NPC 15437 exerts these effects revealed that treatment with the protein kinase C activator phorbol-12-myristate 12-acetate partially reversed the effect of NPC 15437, suggesting that NPC 15437 was exerting an effect through protein kinase C. Photoaffinity labeling experiments revealed that NPC 15437 also inhibited the binding of [3H]-azidopine to Pgp in isolated membrane vesicles. These results identify NPC 15437 [correction of NPC15437] as the prototype of a new class of potential Pgp modulators but indicate that the effects of this agent as a modulator are potentially limited by its cytotoxicity.
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PMID:Evaluation of 2,6-diamino-N-([1-(1-oxotridecyl)-2-piperidinyl]methyl)- hexanamide (NPC 15437), a protein kinase C inhibitor, as a modulator of P-glycoprotein-mediated resistance in vitro. 882 46


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