Downregulation of mdr-1 expression by 8-Cl-cAMP in multidrug resistant MCF-7 human breast cancer cells.
8-Cl-cAMP, a site-selective analogue of cAMP, decreased mdr-1 expression in multidrug-resistant human breast cancer cells. A sixfold reduction of mdr-1 mRNA expression by 8-Cl-cAMP began within 8 h of treatment and was associated with a decrease in the synthesis of P-glycoprotein and with an increase in vinblastine accumulation. A reduction in mdr-1 expression after 8-Cl-cAMP treatment was also observed in multidrug-resistant human ovarian cancer cell lines. 8-Cl-cAMP is known to change the ratio between the two regulatory subunits, RI and RII, of protein kinase A (PKA). We observed that RI alpha decreased within 24 h of 8-Cl-cAMP treatment, that RII beta increased after as few as 3 h of treatment, and that PKA catalytic activity remained unchanged during 48 h of 8-Cl-cAMP treatment. The results are consistent with the hypothesis that mdr-1 expression is regulated in part by changes in PKA isoenzyme levels. Although 8-Cl-cAMP has been used to differentiate cells in other model systems, the only differentiating effect that could be detected after 8-Cl-cAMP treatment in the MCF-7TH cells was an increase in cytokeratin expression. Evidence that the reduction of mdr-1 mRNA occurred at the level of gene transcription was obtained by measuring chloramphenicol acetyltransferase (CAT) mRNA in MCF-7TH cells transfected with an mdr-1 promoter-CAT construct prior to 8-Cl-cAMP treatment. Thus, 8-Cl-cAMP is able to downregulate mdr-1 expression and suggests a new approach to reversal of drug resistance in human breast cancer.
Scala
S
S
Medicine Branch, National Cancer Institute, Bethesda, Maryland 20892, USA.
Budillon
A
A
Zhan
Z
Z
Cho-Chung
Y S
YS
Jefferson
J
J
Tsokos
M
M
Bates
S E
SE
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis* / Q000235:genetics; D000230:Adenocarcinoma / Q000473:pathology*; D001483:Base Sequence; D001943:Breast Neoplasms / Q000473:pathology*; D002454:Cell Differentiation; D000242:Cyclic AMP / Q000502:physiology*; D054757:Cyclic AMP-Dependent Protein Kinase RIIbeta Subunit; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D018432:Drug Resistance, Multiple / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D017930:Genes, Reporter; D006801:Humans; D007527:Isoenzymes / Q000502:physiology; D007633:Keratins / Q000096:biosynthesis; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D014407:Tumor Cells, Cultured / Q000187:drug effects; D014747:Vinblastine / Q000378:metabolism
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D054757:Cyclic AMP-Dependent Protein Kinase RIIbeta Subunit; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; D007527:Isoenzymes; D009363:Neoplasm Proteins; C517834:PRKAR1A protein, human; C517837:PRKAR2B protein, human; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D011993:Recombinant Fusion Proteins; D015124:8-Bromo Cyclic Adenosine Monophosphate; D014747:Vinblastine; D007633:Keratins; C044258:8-chloro-cyclic adenosine monophosphate; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases