title: Role of HSP90 in mediating cross-talk between the estrogen receptor and the Ah receptor signal transduction pathways.
abstract: Tetrachlorodibenzo-p-dioxin (TCDD)-mediated gene transactivation via the Ah receptor (AhR) has been shown to be dependent upon estrogen receptor (ER) expression in human breast cancer cells. We have investigated the 90-kDa heat shock protein (HSP90) as a mediator of cross-talk between the AhR and the ER signal transduction pathways. The effect of HSP90 overexpression on receptor activity was determined by transient transfection assays using a HSP90 expression vector. Ligand-inducible gene expression was inhibited when the HSP90 expression vector was cotransfected with a TCDD-responsive reporter plasmid. However, overexpression of HSP90 did not block induction of an estrogen-responsive reporter plasmid. To determine whether ER facilitates AhR signaling through its ability to squelch HSP90, two vectors expressing protein products that bind HSP90 were transfected into MDA-MB-231 cells. Introduction of (i) He11, an ER deletion mutant that does not bind DNA, and (ii) the ligand-binding domain of human AhR, both led to increased basal and TCDD-inducible CYP1A1 expression. Finally, the subcellular distribution of HSP90 was investigated in human breast cancer cell lines. These studies showed HSP90 to be primarily cytoplasmic in ER-positive cell lines, whereas in matched ER-negative cell lines HSP90 was distributed equally between the cytoplasm and nucleus. Taken together, these results demonstrate that HSP90 can regulate AhR activity in vivo, and that Ah-responsiveness is dependent upon cellular ER content through a mechanism that involves HSP90.
authors.affiliation: McGill Centre for Translational Research in Cancer, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec, Canada.
authors.forename: J A
authors.initials: JA
authors.lastname: Caruso
authors.forename: D W
authors.initials: DW
authors.lastname: Laird
authors.forename: G
authors.initials: G
authors.lastname: Batist
mesh_terms: D001943:Breast Neoplasms; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D020239:Receptor Cross-Talk; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism*; D015398:Signal Transduction; D013347:Subcellular Fractions; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D018841:HSP90 Heat-Shock Proteins; D018336:Receptors, Aryl Hydrocarbon; D011960:Receptors, Estrogen