Reduced mRNA levels for the multidrug-resistance genes in cAMP-dependent protein kinase mutant cell lines.
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, 1987), and a transfectant cell line expressing the same mutant kinase, showed increased sensitivity to a number of drugs that are 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 RNA 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 the mdr1b 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 non-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.
Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
K V
KV
Chin
S S
SS
Chauhan
I
I
Abraham
K E
KE
Sampson
A J
AJ
Krolczyk
M
M
Wong
B
B
Schimmer
I
I
Pastan
M M
MM
Gottesman
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000311:Adrenal Glands / Q000737:chemistry / Q000166:cytology* / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D003078:Colchicine / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000494:pharmacology*; D003603:Cytotoxins / Q000494:pharmacology; D005260:Female; D008562:Membrane Glycoproteins / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D010053:Ovary / Q000737:chemistry / Q000166:cytology* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011233:Precipitin Tests; D011494:Protein Kinases / Q000235:genetics*; D011802:Quinidine / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D013256:Steroids / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D014700:Verapamil / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D003603:Cytotoxins; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D013256:Steroids; D014700:Verapamil; D000242:Cyclic AMP; D011494:Protein Kinases; D011802:Quinidine; D003078:Colchicine