Promotion of breast cancer by beta-hexachlorocyclohexane in MCF10AT1 cells and MMTV-neu mice.
BACKGROUND
Exposure to beta-Hexachlorocyclohexane (beta-HCH), a contaminant of the hexachlorohexane pesticide lindane, has been implicated as a risk factor in the development of breast cancers in epidemiological studies. Previous studies in our laboratory have demonstrated the ability of beta-HCH to elicit its actions via a ligand-independent activation of the estrogen receptor through increased c-Neu (= erbB2 or HER-2) expression and kinase activation in both the BG-1 and MCF-7 cell lines. In addition, long term exposure (33 passages) to beta-HCH was shown to promote the selection of MCF-7 cells which exhibit a more metastatic phenotype.


METHODS
In this current study, we decided to investigate the long-term effects of beta-HCH in both the MCF10AT1 cell line which was derived from a normal epithelial cell line by stably transfecting a mutated c-Ha-ras and a MMTV-Neu mouse model for mammary cancer in vivo. MCF10AT1 cells were exposed for 20 passages with beta-HCH, 4-OH-Tamoxifen (Tam), or 17-beta-estradiol (E2) after which cells were analyzed for proliferation rates and mRNA expression by RT-PCR. In our in vivo studies, MMTV-Neu mice were injected with beta-HCH and observed for tumor formation over a 70 week period.


RESULTS
beta-HCH and Tam selected MCF10AT1 cells demonstrated increased mRNA expression of MMP-13 (collagenase-3) a marker of increased invasiveness. beta-HCH treatment was also seen to increase the expression in a number of proto-oncogenes (c-Neu, Cyclin D1, p27), cell status markers (Met-1, CK19), and the inflammatory marker NFkappaB. Previous studies, have demonstrated the role of these markers as evidence of malignant transformations, and further illustrate the ability of beta-HCH to be carcinogenic. To demonstrate beta-HCH's tumorigenic properties in an in vivo system, we used an MMTV-Neu mouse model.MMTV-Neu is a c-Neu overexpressing strain which has been shown to spontaneously develop mammary tumors at later stages of aging. In this experiment, beta-HCH exposure was shown to both accelerate the appearance (~8 weeks for median tumor-free period) and incidence (~25% increase at the end of the test period) of tumors when compared to control mice receiving only the corn-oil vehicle.


CONCLUSIONS
Based upon these results, it was concluded that beta-HCH does act as a breast cancer promoter which exerts its tumorigenic activity via increased c-Neu expression.
Wong
Patrick S
PS
Center for Health and the Environment-John Muir Institute of the Environment, Department of Environmental Toxicology, University of California, Davis, CA 95616, USA. patwong@ucdavis.edu
Matsumura
Fumio
F
D000818:Animals; D002273:Carcinogens / Q000008:administration & dosage; D045744:Cell Line, Tumor; D005260:Female; D001556:Hexachlorocyclohexane / Q000008:administration & dosage*; D006801:Humans; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced* / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics*; D051379:Mice; D008822:Mice, Transgenic; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D014162:Transfection
D002273:Carcinogens; D001556:Hexachlorocyclohexane; D018719:Erb-b2 Receptor Tyrosine Kinases; C023888:beta-hexachlorocyclohexane