Reduced mRNA levels for the multidrug-resistance genes in cAMP-dependent protein kinase mutant cell lines

✍ Scribed by Khew-Voon Chin; Shyam S. Chauhan; Irene Abraham; Kathleen E. Sampson; Arkadiusz J. Krolczyk; Margaret Wong; Bernard Schimmer; Ira Pastan; Michael M. Gottesman

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 887 KB
• Volume: 152
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1041520112

✦ Synopsis

We have previously shown that in Chinese hamster ovary (CHO) cells, a mutant cell line with a defective regulatory subunit (RI) for the CAMP-dependent protein kinase (Abraham et al: Mol. Cell. Biol., 7:3098-3106, 19871, and a transfectant cell line expressing the same mutant kinase, showed increased sensitivity to a number of drugs that arc known to be substrates for the multidrug transporter (P-glycoprotein). In the current study we have investigated the mechanism by which CAMP-dependent protein kinase controls drug resistance. We report here that the sensitivity of the kinase defective CHO cell lines to multiple drugs results from decreased R N A levels for the multidrug-resistance gene. Similar results were obtained with mouse Y1 adrenal cells. Wild-type Y1 cells had high levels of P-glycoprotein due to expression of both t h e mdrl b and mdr2 genes, whereas the CAMP-dependent protein kinase mutant Kin 8 cells had decreased RNA levels for these genes. A Kin 8 transfectant with restored CAMP-dependent protein kinase activity recovered mdr expression, indicating a cause and effect relationship between the protein kinase mutations and mdr expression. No changes in nuclear run-off assays could be detected, suggesting a nun-transcriptional mechanism of regulation. Wild-type Y1 cells are more drug sensitive despite having higher levels of P-glycoprotein than the mutant cells. This paradoxical result may be explained by the higher rate of synthesis of steroids by the wild-type Y1 cells, which appear to be inhibitors of P-glycoprotein transport activity.