Elevated level of nuclear protein kinase C in multidrug-resistant MCF-7 human breast carcinoma cells.
Previous studies have demonstrated elevated levels of protein kinase C (PKC) activity in multidrug-resistant human breast carcinoma MCF-7/ADR cells compared to control drug-sensitive MCF-7/WT cells (R.L. Fine, J. Patel, and B.A. Chabner, Proc. Natl. Acad. Sci. USA, 85:582-586, 1988). In our present studies, immunohistochemical localization analysis using a polyclonal PKC antibody recognizing the alpha, beta, and gamma subtypes of PKC demonstrates that immunoreactivity is enhanced in MCF-7/ADR cells, with pronounced staining noted in the nuclear region. Other studies with purified nuclei isolated from MCF-7/ADR cells also show a marked increase in the intensity of immunostaining for PKC when compared to nuclei prepared from control MCF-7/WT cells. Western blot analysis of proteins extracted from purified nuclear preparations further establishes an increase in PKC enzyme protein associated with the nuclear fraction of MCF-7/ADR cells. Subcellular fractionation studies also indicate that MCF-7/ADR cells have 4-8 times higher nuclear PKC activity compared to that of control MCF-7/WT cells. MCF-7/ADR cells also possess 3-5-fold elevated cytosolic PKC activity, while a less than 2-fold increase is found in PKC activity associated with the plasma membrane fraction of MCF-7/ADR cells. Examination of these extracts with PKC isotype-specific antisera, as well as by DEAE-cellulose chromatography, reveals that nuclei prepared from MCF-7/ADR cells contain markedly elevated amounts of a slightly altered form of PKC alpha. These results suggest that elevated levels of a modified form of PKC alpha at the nucleus may play a role in modulating nuclear events to promote the development of multidrug resistance in MCF-7 cells.
Lee
S A
SA
Laboratory of Cellular Oncology, National Cancer Institute, NIH, Bethesda, Maryland 20892.
Karaszkiewicz
J W
JW
Anderson
W B
WB
D000595:Amino Acid Sequence; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000201:enzymology* / Q000473:pathology; D002467:Cell Nucleus / Q000201:enzymology*; D002848:Chromatography, DEAE-Cellulose; D004317:Doxorubicin / Q000494:pharmacology; D004351:Drug Resistance; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D011493:Protein Kinase C / Q000032:analysis*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D004317:Doxorubicin; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate