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To investigate protein kinase C (PKC) expression and its association with multidrug resistance (MDR) in KBV200 cells.KBV200 cells were preincubated with PKC activator phorbol-12-myristate-13-acetate (PMA, 200 nmol/L) and PKC activity was assayed by measurement of peptide substrate (32)P incorporation from [gamma-(32)P]ATP, with the cells without PMA preincubation serving as the control. Western blotting was performed for assessing the expression of PKC isoform, and the cell inhibition rate was evaluated by MTT assay.PMA preincubation of the cells significantly enhanced the activity of the total PKC and the membrane fraction, but lowered the PKC activity of the cytosol fraction, as compared with the cells without PMA treatment (P0.01). PKC-alpha expression was upregulated in the membrane fraction and down-regulated in the cytosol fraction in KBV200 cells after PMA preincubation. PKCbeta expression was slightly elevated in the cytosol fraction but exhibited no obvious changes in the membrane fraction after PMA pretreatment of the cells. The values of IC(50) of vincristine and adriamycin in PMA-treated cells were increased to 2275.5 nmol/L and 233.25 nmol/L, respectively (P0.01).PMA can increase the multidrug resistance of KBV200 cells, which suggests the possible involvement of PKC in the mechanism of multidrug resistance of tumor cells.

To observe the effects of functional inhibition of p-glycoprotein on radiosensitivity of drug-resistant MCF-7/Adr tumor cells.Flow cytometry was used to examine the dynamic changes of apoptosis rate and mitochondrial membrane potential (deltapsim) in verapamil-treated and untreated MCF-7/Adr cells after the X-ray exposure.The apoptotic rate of verapamil-treated cells was 25.53%+/-2.85%, 30.43%+/-2.21%, 39.03%+/-2.60% at 6, 12, and 24 h after X-ray exposure, respectively, and was 16.13%+/-1.16%, 21.73%+/-1.31%, and 27.53%+/-2.55% for the untreated cells. The mean fluorescence intensity of verapamil-treated cells was 75.27+/-4.90, 96.47+/-5.59, 57.77+/-2.55, respectively, at the corresponding time points, in comparison with the intensity of 54.17+/-4.05, 62.30+/-5.93, and 39.53+/-2.65 for the untreated cells. The apoptosis rate and deltapsim of the treated cells were significantly higher than those in the untreated cells at each of the specified time point (P0.01), and in the former cells, the apoptosis rate reached the maximum at 24 h (F=47.870, P=0.000) and the deltapsim at 12 h after X-ray exposure (F=74.485, P=0.000).The radiosensitivity of MCF-7/Adr cells is increased after functional inhibition of p-glycoprotein, possibly in relation to the alteration of deltapsim.

To examine the changes in the function and expression of multidrug resistance gene (mdr1) and P-gly-coprotein (P-gp) in nasopharyngeal carcinoma (NPC) CNE1 cell following irradiation for determining the sequential order of radiotherapy and chemotherapy in the treatment of NPC.The expressions of mdr1 gene and its protein P-gp as well as the function of P-gp efflux were examined in CNE1 cells before and after irradiation exposure by reverse transcriptional polymerase chain reaction (RT-PCR), Western blotting and flow cytometry, respectively.Irradiation of CNE1 cells induced a long-term overexpression of mdr1 gene and P-gp and reduction in intracellular daunorubicin accumulation.Irradiation decreases the chemotherapy sensitivity of CNE1 cell, and induction chemotherapy should be therefore performed before radiotherapy in the treatment of advanced NPC.

To investigate the association of protein kinase C (PKC) isoforms and multidrug resistance (MDR) mechanism in KBV200 cells.Western blotting was utilized to examine the expression and subcellular distribution of PKC isoforms were measured in KBV200 cells with MDR and drug-sensitive KB cells, and the fluorescence intensity of PKC isoforms was detected by flow cytometry (FCM).KBV200 cells possessed higher PKC activities, with increased percentage of membrane fraction. As compared with parental KB cells, the expression of PKCalpha was significantly increased in KBV200 cells, while PKCbeta and epsilon expressions remained unchanged, and PKCgamma and zeta failed to be detected. Fluorescence intensity of PKCalpha in KBV200 cells was increased.PKC might contribute to MDR phenotype in KBV200 cells, and of the isoforms so far detected, PKCalpha might play an important role in MDR phenotype.

To investigate the relationship between protein kinase C (PKC) and multidrug resistance (MDR) in cancer cell line KBV200.MTT assay was used to evaluate the IC50 of vincristine (VCR) and adriamycin (ADR) in KB cell line and its VCR-resistant derivative KBV200 cells. PKC activities in the 2 cell lines were assayed by measuring the incorporation of (32)P from [gamma-(32)P] ATP into the peptide substrates.The IC50 values of VCR and ADR in KBV200 cells was 64.03 and 18.8 folds greater than those in KB cells. PKC activities of the membrane and cytosol fraction in KBV200 cells were increased compared with that in KB cells, with the total PKC activity 1.12-fold higher. Phorbol-12-myristate-13 -acetate increased PKC activity of the membrane fraction and IC50 values of KBV200 cells, while staurosporine worked to the opposite effects.PKC may contribute to MDR mechanism in KBV200 cells.

To investigate the expression of c-myc in drug-resistant MCF-7/Adr human breast cancer cells and the counteractive effect of c-myc antisense oligonucleotide on their drug-resistance.Flow cytometry was performed to examine c-myc expression in multi-drug resistant MCF-7/Adr cell line and its parental cell line MCF-7. The IC50 value of doxorubicin was evaluated by MTT assay.MCF-7/Adr cell line was shown to have a significantly higher expression rate of c-myc than its parent cell line MCF-7 (70.48% vs 46.02%). The IC50 value of doxorubicin was (22.00+/-1.92) micomol/L in MCF-7/Adr cells, which was significantly decreased to (9.60+/-1.04) micromol/L (P0.05) after coincubation with 4 micromol/L c-myc antisense oligonecleotide.c-myc expression is up-regulated in MCF-7/Adr cells as compared with their parent cell line MCF-7. Inhibition of c-myc expression may partially reverse the resistance of MCF-7/Adr against doxorubicin, suggesting that c-myc may be involved in the mechanism of drug-resistance of tumor cells.