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 major determinants mediating drug resistance in acute lymphoblastic leukemias (ALL) unresponsive to chemotherapy, are still unclear. For example, it is still unknown whether selection or induction processes are responsible for drug resistance here or whether protein kinase C (PKC) isozymes contribute to the resistant phenotype. Therefore, inducibility of resistance factors or PKC isozymes genes was examined in CCRF-CEM cells treated with diverse anticancer drugs--adriamycin, camptothecin, etoposide or vincristine--at sublethal concentrations for 24 h. MDR1, MRP1, LRP and PKC isozyme alpha, beta(1), beta(2), epsilon, iota, eta, theta, zeta gene expression was determined by cDNA-PCR. We found significant dose-dependent, mostly combined, induction of the MDR1, MRP1 and LRP genes. Significantly enhanced gene expression of the majority of PKC isozyme genes was found after treatment with camptothecin. PKCzeta was upregulated throughout by each anticancer drug applied in this setting. A series of selected CCRF-CEM-derived multidrug resistance (MDR) sublines also showed enhanced expression of the PKC isozymes compared to the parental cell line. MDR1 and PKCeta gene expression levels were correlated highly significantly. Blasts from two patients with ALL during the first week of monotherapy with steroids revealed combined induction of the MDR1, multidrug resistance-associated protein 1 (MRP1), lung cancer resistance-related protein (LRP) and most PKC isozymes, predominantly PKCzeta. Another patient with T-ALL, who failed to respond to four months of intensive chemotherapy, showed an enhanced MRP1 gene expression combined with markedly overexpression of PKCeta and PKCtheta. Furthermore, the camptothecin and etoposide-mediated induction of resistance factors in the CCRF-CEM cell line could be suppressed by staurosporine, a rather unspecific inhibitor of protein kinases. However, selective inhibitors of PKC isozymes (bisindolylmaleimide GO 6850, indolocarbazole GO 6976) produced no significant effects here. Therefore, the PKC isozymes eta, theta and zeta are of interest as potential targets to overcome drug resistance in ALL.
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PMID:Anticancer drug-mediated induction of multidrug resistance-associated genes and protein kinase C isozymes in the T-lymphoblastoid cell line CCRF-CEM and in blasts from patients with acute lymphoblastic leukemias. 1150 23

Properties of inwardly rectifying K+ channels in small-cell lung cancer (SCLC) cells have not been clarified in detail. Here, we found inwardly rectifying K+ channels in a human SCLC cell line (RERF-LC-MA), which expresses no multidrug resistance-associated protein 1 (MRP1) and multidrug resistance P-glycoprotein (MDR1). Extracellular Ba2+ and Cs+ inhibited inwardly rectifying K+ currents of RERF-LC-MA cells in a concentration-dependent manner, but tetraethylammonium ion and glibenclamide were ineffective. Okadaic acid, an inhibitor of phosphatases 1 and 2A, and phorbol-12,13-dibutyrate, an activator of protein kinase C, significantly decreased the inwardly rectifying K+ current. Lowering the intracellular pH but not the extracellular pH decreased the K+ current. Reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting analysis showed that RERF-LC-MA cells express Kir2.1 mRNA and protein. The inwardly rectifying K+ current is suggested to be generated by Kir2.1 protein in the human small-cell lung cancer cell, and that the K+ channel is negatively regulated by protein kinase C and the intracellular acidic pH.
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PMID:Molecular and pharmacological properties of inwardly rectifying K+ channels of human lung cancer cells. 1182 Oct 18

The purpose of this investigation was to evaluate the expression profile of proteins involved in children with newly diagnosed acute lymphoblastic leukemia (ALL) children who are developing relapses. For this reason, the expressions of 10 proteins including proto-oncogene and tumor suppressor gene products, proliferative factors and resistance parameters in 104 initial cases of childhood ALL were analyzed and the proteins correlated with ALL patients who experienced relapses. Applying immunocytochemical assays, we found that 4 out of the 10 parameters revealed a relationship to developing relapses (Fisher's exact tests). These were the oncogene product Fos (p=0.002), the drug resistance proteins glutathione S-transferase (p=0.008) and P-glycoprotein (P-pg/MDR1) (p=0.07) and protein kinase C (p=0.01). By means of hierarchical cluster analysis, we were able to show that the patients could be separated according to their protein expression profile into clusters consisting of patients whose ALL relapsed later and of patients who did not show relapses in the future.
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PMID:Protein expression profile of newly diagnosed acute lymphoblastic leukemia in children developing relapses. 1216 56

We examined the inducibility of drug resistance (MDR1, MRP1, LRP) and protein kinase C (PKC) isozyme (alpha, epsilon, eta, theta, tau, zeta) corresponding genes in A2780 ovarian cancer cells after a 24-hour treatment with adriamycin (ADR), camptothecin (CAM), etoposide (ETO) or vincristine (VCR). Sublethal concentrations of drugs were used to exclude short-term effects caused by selection. Cell cycle analysis was performed to identify possible correlation between resistance factors, PKC isozymes and proliferation. We found a mostly combined induction of MDR1, LRP, PKC tau and PKC zeta by CAM, ETO and VCR. PKC alpha, epsilon, eta and theta gene expression altered variably. Cell cycle analysis showed that A2780 cells responded with a marked G2/M arrest after a 24-hour treatment with CAM, ETO and VCR but an association between the induction of PKC isozymes corresponding genes and proliferation was not seen. Our analysis points to a possible link between atypical PKC tau/PKC zeta and MDR1/LRP in cytostatic stress response of cancer cells.
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PMID:Induction of drug resistance and protein kinase C genes in A2780 ovarian cancer cells after incubation with antineoplastic agents at sublethal concentrations. 1255 62

Protein kinase C (PKC) comprises a family of isozymes (alpha, betaI, betaII, gamma, delta, epsilon, theta, eta, lambda/iota [mouse/human], and zeta) which are involved in signal transduction from membrane receptors to the nucleus. Activation of PKC by phorbol esters promotes tumor formation, and from that it was concluded that inhibitors of PKC might prevent carcinogenesis or inhibit tumor proliferation. However, the situation is more complicated because the exact function of the different PKC isozymes is not known at present. They have been shown to be involved in synaptic transmissions, the activation of ion fluxes, secretion, cell cycle control, differentiation, proliferation, tumorigenesis, metastasis and apoptosis. Modulators such as bryostatin-1, phospholipid analogues, PKC-activating adriamycin derivatives, CGP41251, UCN-01, and antisense oligonucleotides directed against PKCalpha, have shown antitumor activity in cancer patients. PKC inhibitors are not specific to PKC, but also interact with other signaling molecules, which may contribute to the antitumor effects. Modulators of PKC have also been shown to influence non-MDR1-mediated and MDR1-mediated antitumor drug resistance. This review is focussed on the role of PKC isozymes in human cell proliferation, apoptosis and antitumor drug resistance, and on the use of PKC modulators as antitumor agents.
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PMID:Protein kinase C isozymes as potential targets for anticancer therapy. 1503 65

Ubiquitination plays a crucial role in regulating protein turnover. Here we show that ubiquitination regulates the stability of the MDR1 gene product, P-glycoprotein, thereby affecting the functions of this membrane transporter that mediates multidrug resistance. We found that P-glycoprotein was constitutively ubiquitinated in drug-resistant cancer cells. Transfection of multidrug-resistant cells with wild-type ubiquitin or treatment with an N-glycosylation inhibitor increased the ubiquitination of P-glycoprotein and increased P-glycoprotein degradation. Carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG-132), a proteasome inhibitor, induced accumulation of ubiquitinated P-glycoprotein, suggesting the involvement of the proteasome in the turnover of the transporter. Treatment of multidrug-resistant cells with 12-O-tetradecanoylphorbol-13-acetate, a phorbol ester that increases the phosphorylation of P-glycoprotein through activation of protein kinase C, or substituting phosphorylation sites of P-glycoprotein by nonphosphorylatable residues did not affect the ubiquitination of the transporter. Enhanced ubiquitination of P-glycoprotein resulted in a decrease of the function of the transporter, as demonstrated by increased intracellular drug accumulation and increased cellular sensitivity to drugs transported by P-glycoprotein. Our results indicate that the stability and function of P-glycoprotein can be regulated by the ubiquitin-proteasome pathway and suggest that modulating the ubiquitination of P-glycoprotein might be a novel approach to the reversal of drug resistance.
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PMID:Regulation of the stability of P-glycoprotein by ubiquitination. 1532 30

The protein kinase C (PKC) family consists of serine/threonine protein kinases that play important roles in signal transduction, cell proliferation, and tumor formation. Recent studies found that PKCs are commonly overexpressed in human tumors, including soft tissue sarcoma (STS). Overexpression of PKCs contributes to invasion and migration of tumor cells and induction of angiogenesis. PKC can also phosphorylate the multidrug resistance (MDR) gene-encoded P-glycoprotein and induce MDR phenotype. Our previous studies showed that mutation of p53 enhanced STS metastasis and mediated the MDR phenotype. Restoring wild type (WT) p53 in STS cells containing mutant p53 sensitized the cells to chemotherapy. In the present study, we found that PKCalpha protein expression is inhibited by WT p53 partly due to reduced PKCalpha mRNA expression in STS cells, but p53 does not affect PKCalpha mRNA stability. Deletion and mutation analysis of the PKCalpha promoter fused to the luciferase reporter gene identified a Sp1 binding site (-244/-234) in the PKCalpha promoter that is required for p53-mediated inhibition of PKCalpha promoter activity. More importantly, PKCalpha phosphorylates and activates MDR1 P-glycoprotein, whereas inhibition of PKCalpha by p53 leads to decreased MDR1 phosphorylation in STS cells, which sensitizes STS cells to chemotherapeutic agents. These data indicate that WT p53 may resensitize STS to chemotherapeutic agents by reducing MDR1 phosphorylation via transcriptional repression of PKCalpha expression. Thus, molecular-based therapies targeting mutant p53 and PKCalpha may be an effective new strategy to improve chemotherapeutic efficacy in STS.
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PMID:Transcriptional repression of protein kinase Calpha via Sp1 by wild type p53 is involved in inhibition of multidrug resistance 1 P-glycoprotein phosphorylation. 1556 62

Active efflux of xenobiotics is a major mechanism of cell adaptation to environmental stress. The ATP-dependent transmembrane transporter P-glycoprotein (Pgp) confers long-term cell survival in the presence of different toxins, including anticancer drugs (this concept is referred to as multidrug resistance, or MDR). The vital importance of this mechanism for cell survival dictates the reliability and promptness of its acquisition. To fulfill this requirement, the MDR1 gene that encodes Pgp in humans must be readily upregulated in cells that express low to null levels of MDR1 mRNA prior to stress. The MDR1 gene and a stable MDR phenotype can be induced after short-term exposure of cells to a variety of cues. This effect is implemented by activation of MDR1 transcription and mRNA stabilization. The MDR1 message abundance is regulated by mechanisms generally involved in stress response, namely activation of phospholipase C, protein kinase C and mitogen-activated protein kinase cascades, mobilization of intracellular Ca2+, and nuclear factor kappa B activation. Furthermore, the proximal MDR1 promoter sites critical for induction are not unique for the MDR1 gene; they are common regulatory elements in eukaryotic promoters. Moreover, MDR1 induction can result from activation of (an) intermediate gene(s) whose product(s), in turn, directly activate(s) the MDR1 promoter and/or cause(s) mRNA stabilization. Redundancy of signal transduction and transcriptional mechanisms is the basis for the virtually ubiquitous inducibility of the MDR1 gene. Thus, the complex network of MDR1 regulation ensures rapid emergence of pleiotropic resistance in cells.
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PMID:Redundancy of biological regulation as the basis of emergence of multidrug resistance. 1616 65

It is known that protein kinase C (PKC) signal transduction is enhanced in a diabetic state, and that PKC activator phorbol esters increase the gene expression of MDR1 in human tumor cells. To clarify the expression of the liver transporters under diabetic conditions and the roles of PKCalpha and the transcription factor NF-kappaB, we investigated the expression levels of Mdr1a, Mdr1b, Mdr2, Mrp2, Bcrp, Bsep, Oct1, Oat2, and Oat3 transporters, PKCalpha, IkappaB, and NF-kappaB in the liver of rats with STZ-induced hyperglycemia. A selective increase in the gene expression of Mdr1b was detected by RT-PCR. Western blotting with C219 antibody revealed an increase in P-glycoprotein. Although the mRNA level of PKCalpha was not affected, translocation of PKCalpha to the microsomal fraction was detected. NF-kappaB p65, IkappaBalpha and IkappaBbeta mRNA levels were increased as was the level of nuclear NF-kappaB p65. From these findings, it was suggested that STZ-induced hyperglycemia caused the upregulation of Mdr1b P-gp expression through the activation of PKCalpha and NF-kappaB.
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PMID:Increase in P-glycoprotein accompanied by activation of protein kinase Calpha and NF-kappaB p65 in the livers of rats with streptozotocin-induced diabetes. 1834 69

The objective of this research was to functionally characterize sodium-dependent vitamin C transporter (SVCT) in MDCK-MDR1 cells and to study the effect of substituted benzene derivatives on the intracellular accumulation of ascorbic acid (AA). Mechanism of AA uptake and transport was delineated. Uptake of [(14)C]ascorbic acid ([(14)C]AA) was studied in the absence and presence of excess unlabelled AA, anion transporter inhibitors, and a series of mono- and di-substituted benzenes. Transepithelial transport of [(14)C]AA across polarized cell membrane has been studied for the first time. Role of cellular protein kinase-mediated pathways on the regulation of AA uptake has been investigated. The cellular localizations of SVCTs were observed using confocal microscopy. Uptake of AA was found to be saturable with a K(m) of 83.2muM and V(max) of 94.2pmol/min/mg protein for SVCT1. The process was pH, sodium, temperature, and energy-dependent. It was under the regulation of cellular protein kinase C (PKC) and Ca(2+)/CaM mediated pathways. [(14)C]AA uptake was significantly inhibited in the presence of excess unlabelled AA and a series of electron-withdrawing group, i.e., halogen- and nitro-substituted benzene derivatives. AA appears to translocate across polarized cell membrane from apical to basal side (A-B) as well as basal to apical side (B-A) at a similar permeability. It appears that SVCT1 was mainly expressed on the apical side and SVCT2 may be located on both apical and basal sides. In conclusion, SVCT has been functionally characterized in MDCK-MDR1 cells. The interference of a series of electrophile-substituted benzenes on the AA uptake process may be explained by their structural similarity. SVCT may be targeted to facilitate the delivery of drugs with low bioavailability by conjugating with AA and its structural analogs. MDCK-MDR1 cell line may be utilized as an in vitro model to study the permeability of AA conjugated prodrugs.
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PMID:Activity of a sodium-dependent vitamin C transporter (SVCT) in MDCK-MDR1 cells and mechanism of ascorbate uptake. 1841 4


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