Tamoxifen resistance by a conformational arrest of the estrogen receptor alpha after PKA activation in breast cancer.
Using a novel approach that detects changes in the conformation of ERalpha, we studied the efficacy of anti-estrogens to inactivate ERalpha under different experimental conditions. We show that phosphorylation of serine-305 in the hinge region of ERalpha by protein kinase A (PKA) induced resistance to tamoxifen. Tamoxifen bound but then failed to induce the inactive conformation, invoking ERalpha-dependent transactivation instead. PKA activity thus induces a switch from antagonistic to agonistic effects of tamoxifen on ERalpha. In clinical samples, we found that downregulation of a negative regulator of PKA, PKA-RIalpha, was associated with tamoxifen resistance prior to treatment. Activation of PKA by downregulation of PKA-RIalpha converts tamoxifen from an ERalpha inhibitor into a growth stimulator, without any effect on ICI 182780 (Fulvestrant).
Michalides
Rob
R
Department of Tumor Biology, The Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands.
Griekspoor
Alexander
A
Balkenende
Astrid
A
Verwoerd
Desiree
D
Janssen
Lennert
L
Jalink
Kees
K
Floore
Arno
A
Velds
Arno
A
van't Veer
Laura
L
Neefjes
Jacques
J
D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D001665:Binding Sites; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000201:enzymology / Q000473:pathology*; D002455:Cell Division; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology; D047628:Estrogen Receptor alpha; D005260:Female; D031541:Fluorescence Resonance Energy Transfer; D000077267:Fulvestrant; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D018613:Microscopy, Confocal; D008954:Models, Biological; D009693:Nucleic Acid Hybridization; D020411:Oligonucleotide Array Sequence Analysis; D010766:Phosphorylation; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D011960:Receptors, Estrogen / Q000737:chemistry* / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D013629:Tamoxifen / Q000494:pharmacology*; D013997:Time Factors; D015533:Transcriptional Activation; D014162:Transfection
D018931:Antineoplastic Agents, Hormonal; D004791:Enzyme Inhibitors; D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D011960:Receptors, Estrogen; D013629:Tamoxifen; D000077267:Fulvestrant; D012694:Serine; D004958:Estradiol; D008156:Luciferases; D017868:Cyclic AMP-Dependent Protein Kinases