title: A proposed mechanism for the protective effect of dioxin against breast cancer.
abstract: Although it is causative for many types of cancers, experimental and epidemiological evidence suggest that 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) may in fact protect against breast cancer. The mechanism(s) for this protection remain unclear. In an attempt to further elucidate this mechanism, we performed a microarray experiment to identify genes that were modulated upon dioxin treatment. We found that dioxin downregulated the messenger RNAs for the G-protein-coupled receptor, CXCR4, as well as its unique chemokine ligand, CXCL12, in MCF-7 breast cancer cells. We demonstrated that the corresponding proteins are also downregulated by dioxin. The interaction between CXCR4 and CXCL12 plays a central role in the metastasis of breast cancer, as disruption of the CXCL12/CXCR4 axis has been shown to limit the metastasis of breast cancer cells to the lung in mice. Utilizing an in vitro chemotaxis assay, we demonstrate that dioxin specifically inhibits the migration of MCF-7 cells toward CXCL12. We also show that dioxin reduces CXCR4 under hypoxia and CXCL12 under estradiol-induced conditions in MCF-7 cells. Finally, as the CXCR4/CXCL12 axis is implicated in the progression of numerous types of cancer, we identified several other cancer cell lines in which dioxin modulates CXCR4 and CXCL12 levels. We therefore propose that one mechanism whereby dioxin may protect against breast cancer is via downregulation of CXCR4 and CXCL12, thereby inhibiting progression of the disease. Further, other nontoxic ligands for the aryl hydrocarbon receptor (selective AHR modulators) may exert their protective effects by a similar mechanism.
authors.affiliation: Molecular Toxicology Interdepartmental Doctoral Program, School of Public Health, University of California Los Angeles, Los Angeles, CA 90095-1732, USA.
authors.forename: Erin L
authors.initials: EL
authors.lastname: Hsu
authors.forename: Diana
authors.initials: D
authors.lastname: Yoon
authors.forename: Hyun Ho
authors.initials: HH
authors.lastname: Choi
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
authors.forename: Robert T
authors.initials: RT
authors.lastname: Taylor
authors.forename: Natalie
authors.initials: N
authors.lastname: Chen
authors.forename: Ruixue
authors.initials: R
authors.lastname: Zhang
authors.forename: Oliver
authors.initials: O
authors.lastname: Hankinson
mesh_terms: D000444:Aldehyde Dehydrogenase / Q000235:genetics; D001943:Breast Neoplasms / Q000378:metabolism / Q000517:prevention & control*; D045744:Cell Line, Tumor; D054377:Chemokine CXCL12; D019743:Chemokines, CXC / Q000235:genetics*; D002633:Chemotaxis / Q000187:drug effects; D015536:Down-Regulation; D004785:Environmental Pollutants / Q000494:pharmacology; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D020011:Protective Agents / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D019718:Receptors, CXCR4 / Q000235:genetics*
chemical_list: C515255:CXCL12 protein, human; D054377:Chemokine CXCL12; D019743:Chemokines, CXC; D004785:Environmental Pollutants; D000072317:Polychlorinated Dibenzodioxins; D020011:Protective Agents; D012333:RNA, Messenger; D019718:Receptors, CXCR4; C030863:corneal protein 54, bovine; D000444:Aldehyde Dehydrogenase