Effects of protein kinase C modulators on multidrug resistance in human glioma cells.
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.
Matsumoto
T
T
Department of Neurosurgery, Hyogo College of Medicine, Japan.
Tani
E
E
Yamaura
I
I
Miyaji
K
K
Kaba
K
K
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D015536:Down-Regulation; D018432:Drug Resistance, Multiple; D005910:Glioma / Q000188:drug therapy / Q000201:enzymology*; D006801:Humans; D015151:Immunoblotting; D007527:Isoenzymes / Q000378:metabolism; D009281:Naphthalenes; D010766:Phosphorylation; D011083:Polycyclic Compounds / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D014750:Vincristine / Q000378:metabolism*
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D007527:Isoenzymes; D009281:Naphthalenes; D011083:Polycyclic Compounds; C061465:calphostin complex; D014750:Vincristine; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate