title: Ligand-independent activation of the arylhydrocarbon receptor by ETK (Bmx) tyrosine kinase helps MCF10AT1 breast cancer cells to survive in an apoptosis-inducing environment.
abstract: It has been reported that the arylhydrocarbon receptor (AHR) is overexpressed in certain types of breast tumors. However, so far no concrete evidence has been provided yet as to why and how the overexpressed AHR in those cancer cells is functionally activated without exogenous ligands. Here we show that the AHR was functionally activated when estrogen receptor-negative, AHR overexpressing MCF10AT1 human breast cancer cells (designated P20E) were subjected to serum starvation. Transfection of cells with ETK-KQ, a plasmid for kinase-dead epithelial and endothelial tyrosine kinase (ETK), attenuated this AHR activation. Artificial over-expression of ETK in P20E cells through transfection with wild-type ETK plasmid (ETK-wt) caused up-regulation of cytochrome P4501a1 (CYP1A1; a marker of functional activation of AHR). Furthermore, ablation of ETK expression by a specific antisense oligonucleotide or AG879, a specific inhibitor of ETK kinase suppressed activation of AHR induced by omeprazole, a strong ligand-independent activator of AHR. Activation of ETK in those cells conferred them resistance to UVB- as well as doxorubicin-induced apoptosis, both of which were reversed by ETK-KQ. Together, these findings support our conclusion that ETK is the tyrosine kinase responsible for the functional activation of the AHR in these mammary epithelial cells.
authors.affiliation: Department of Environmental Toxicology, University of California Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Fujisawa
authors.forename: Wen
authors.initials: W
authors.lastname: Li
authors.forename: Dalei
authors.initials: D
authors.lastname: Wu
authors.forename: Patrick
authors.initials: P
authors.lastname: Wong
authors.forename: Christoph
authors.initials: C
authors.lastname: Vogel
authors.forename: Bin
authors.initials: B
authors.lastname: Dong
authors.forename: Hsing-Jien
authors.initials: HJ
authors.lastname: Kung
authors.forename: Fumio
authors.initials: F
authors.lastname: Matsumura
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects; D001943:Breast Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D000903:Antibiotics, Antineoplastic; D018336:Receptors, Aryl Hydrocarbon; D004317:Doxorubicin; D019363:Cytochrome P-450 CYP1A1; C492367:BMX protein, human; D011505:Protein-Tyrosine Kinases