Co-ordinate loss of protein kinase C and multidrug resistance gene expression in revertant MCF-7/Adr breast carcinoma cells

• Published in: British journal of cancer Vol. 75; no. 9; pp. 1330 - 1335
• Main Authors: BUDWORTH, J, GANT, T. W, GESCHER, A
• Format: Journal Article
• Language: English
• Published: Basingstoke Nature Publishing Group 01.05.1997
• Subjects: Antineoplastic agents; ATP Binding Cassette Transporter, Subfamily B, Member 1 - biosynthesis; ATP Binding Cassette Transporter, Subfamily B, Member 1 - genetics; Biological and medical sciences; Breast Neoplasms - drug therapy; Breast Neoplasms - genetics; Breast Neoplasms - metabolism; DNA Primers - chemistry; Doxorubicin - pharmacology; Drug Resistance, Multiple - genetics; Female; Gene Amplification; Gene Expression Regulation, Neoplastic; General aspects; Genes, MDR - genetics; Humans; Isoenzymes - biosynthesis; Medical sciences; Pharmacology. Drug treatments; Polymerase Chain Reaction; Protein Kinase C - biosynthesis; Protein Kinase C - genetics; RNA, Messenger - metabolism; Tumor Cells, Cultured; Adenocarcinoma; Antineoplastic agent; Human; Protein kinase C; Enzyme; Transferases; Cytotoxicity; Malignant tumor; Gene expression; Doxorubicin; In vitro; Mammary gland diseases; Antibiotic; Gene; Multiple resistance; Established cell line; Anthracyclins; Mammary gland; Negative therapeutic reaction
• ISSN: 0007-0920; 1532-1827
• DOI: 10.1038/bjc.1997.225

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.