Co-ordinate loss of protein kinase C and multidrug resistance gene expression in revertant MCF-7/Adr breast carcinoma cells.
The aim of this study was to investigate the link between protein kinase C (PKC) and multidrug resistance (mdr) phenotype. The expression of both was studied in doxorubicin-resistant MCF-7/Adr cells as they reverted to the wild-type phenotype when cultured in the absence of drug. The following parameters were measured in cells 4, 10, 15, 20 and 24 weeks after removal of doxorubicin; (1) sensitivity of the cells towards doxorubicin; (2) levels of P-glycoprotein (P-gp) and MDR1 mRNA; (3) levels and cellular localization of PKC isoenzyme proteins alpha, theta and epsilon; and (4) gene copy number of PKC-alpha and MDR1 genes. Cells lost their resistance gradually with time, so that by week 24 they had almost completely regained the drug sensitivity seen in wild-type MCF-7 cells. P-gp levels measured by Western blot mirrored the change in doxorubicin sensitivity. By week 20, P-gp had decreased to 18% of P-gp protein levels at the outset, and P-gp was not detectable at week 24. Similarly, MDR1 mRNA levels had disappeared by week 24. MCF-7/Adr cells expressed more PKCs-alpha and -theta than wild-type cells and possessed a different cellular localization of PKC-epsilon. The expression and distribution pattern of these PKCs did not change for up to 20 weeks, but reverted back to that seen in wild-type cells by week 24. MDR1 gene amplification remained unchanged until week 20, but then was lost precipitously between weeks 20 and 24. The PKC-alpha gene was not amplified in MCF-7/Adr cells. The results suggest that MCF-7/Adr cells lose MDR1 gene expression and PKC activity in a co-ordinate fashion, consistent with the existence of a mechanistic link between MDR1 and certain PKC isoenzymes.
Budworth
J
J
Medical Research Council Toxicology Unit, University of Leicester, UK.
Gant
T W
TW
Gescher
A
A
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis / Q000235:genetics; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers / Q000737:chemistry; D004317:Doxorubicin / Q000494:pharmacology*; D018432:Drug Resistance, Multiple / Q000235:genetics*; D005260:Female; D005784:Gene Amplification; D015972:Gene Expression Regulation, Neoplastic; D019450:Genes, MDR / Q000235:genetics*; D006801:Humans; D007527:Isoenzymes / Q000096:biosynthesis; D016133:Polymerase Chain Reaction; D011493:Protein Kinase C / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D017931:DNA Primers; D007527:Isoenzymes; D012333:RNA, Messenger; D004317:Doxorubicin; D011493:Protein Kinase C