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Effects of protein kinase C modulators on multidrug resistance in human glioma cells
T Matsumoto1, E Tani, I Yamaura
1Department of Neurosurgery, Hyogo College of Medicine, Japan.
Abstract:
To identify the role of protein kinase C (PKC) in multidrug resistance, the effects of phorbol-12-myristate-13-acetate (PMA), a PKC activator, or calphostin C, a PKC inhibitor, on intracellular vincristine accumulation and expression of P-glycoprotein phosphorylation were studied in one multidrug-resistant and three multidrug-sensitive human glioma cell lines. Basal PKC activities and immunoreactivities of PKC-alpha and -zeta were higher in multidrug-resistant cells than in multidrug-sensitive cells. There was no significant difference in the immunoreactivity of PKC-delta between multidrug-resistant and -sensitive cells, and immunoreactive PKC-beta, -gamma, and -epsilon were not detected in either multidrug-resistant or -sensitive cells. The treatment of multidrug-resistant cells with 100 nM PMA for 2 hours resulted in the activation not of PKC-zeta but of PKC-alpha, with concomitant decrease in vincristine accumulation and increase in P-glycoprotein phosphorylation. The exposure of multidrug-resistant cells to 100 nM PMA for 24 hours induced down-regulation not of PKC-zeta but of PKC-alpha, with concurrent decrease in vincristine accumulation, and reduced but still increased P-glycoprotein phosphorylation. The treatment of multidrug-resistant cells with 100 nM calphostin C for 2 hours decreased immunoreactive PKC-zeta and not immunoreactive PKC-alpha, inducing increase in vincristine accumulation, with concomitant decrease in P-glycoprotein phosphorylation. There was no evidence of significant change in vincristine accumulation in multidrug-sensitive cells treated with PMA or calphostin C. This may suggest that at least two isozymes of PKC, PKC-alpha and -zeta, are involved in P-glycoprotein phosphorylation and that vincristine efflux function in multidrug-resistant human glioma cells is closely associated with P-glycoprotein phosphorylation and is decreased by PKC inhibitor.
Insights
Protein kinase C (PKC) plays a role in multidrug resistance in glioma cells. Inhibiting PKC increases vincristine accumulation by affecting P-glycoprotein phosphorylation.
Area of Science:
- Biochemistry
- Molecular Biology
- Oncology
Background:
- Multidrug resistance (MDR) is a major challenge in cancer chemotherapy.
- Protein kinase C (PKC) signaling pathways are implicated in MDR.
- P-glycoprotein (P-gp) is a key efflux pump contributing to MDR.
Purpose of the Study:
- To investigate the role of specific protein kinase C (PKC) isozymes in mediating multidrug resistance in human glioma cells.
- To determine the effect of PKC activation and inhibition on intracellular vincristine accumulation and P-glycoprotein phosphorylation.
Main Methods:
- Utilized human glioma cell lines (one MDR, three sensitive).
- Administered phorbol-12-myristate-13-acetate (PMA) as a PKC activator and calphostin C as a PKC inhibitor.
- Assessed intracellular vincristine accumulation and P-glycoprotein phosphorylation levels.
Main Results:
- Basal PKC-alpha and -zeta activities were higher in MDR cells.
- PMA treatment activated PKC-alpha, decreasing vincristine accumulation and increasing P-gp phosphorylation in MDR cells.
- Calphostin C treatment decreased PKC-zeta, increasing vincristine accumulation and decreasing P-gp phosphorylation in MDR cells.
- PMA and calphostin C had no significant effect on vincristine accumulation in sensitive cells.
Conclusions:
- PKC-alpha and PKC-zeta are involved in P-glycoprotein phosphorylation in multidrug-resistant human glioma cells.
- PKC-mediated P-glycoprotein phosphorylation is closely associated with vincristine efflux function.
- PKC inhibition may represent a therapeutic strategy to overcome multidrug resistance in glioma.