Journal Article

Interferon regulatory factor-1 (IRF-1) exhibits tumor suppressor activities in breast cancer associated with caspase activation and induction of apoptosis

Kerrie B. Bouker, Todd C. Skaar, Rebecca B. Riggins, David S. Harburger, David R. Fernandez, Alan Zwart, Antai Wang and Robert Clarke

in Carcinogenesis

Volume 26, issue 9, pages 1527-1535
Published in print September 2005 | ISSN: 0143-3334
Published online May 2005 | e-ISSN: 1460-2180 | DOI:
Interferon regulatory factor-1 (IRF-1) exhibits tumor suppressor activities in breast cancer associated with caspase activation and induction of apoptosis

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We have directly assessed the ability of interferon regulatory factor-1 (IRF-1) to act as a tumor suppressor gene in human breast cancer cells and explored whether this suppressor function is mechanistically conferred by affecting cell cycle transition, apoptosis and/or caspase activation. We have used a dual approach, measuring whether overexpression of wild-type IRF-1 or a dominant negative IRF-1 (dnIRF-1) produce opposing effects on breast cancer cell proliferation in vitro or tumorigenicity in athymic nude mice. Mechanistic studies determined the effects of blocking endogenous IRF-1 expression on cell cycle transition by flow cytometry, on apoptosis by Annexin V staining, and on caspase activation by fluorescent substrate cleavage. IRF-1 mRNA (P ≤ 0.001) and protein (P ≤ 0.001) are highly expressed in non-tumorigenic, normal, mammary epithelial cells, with intermediate expression in tumorigenic, but non-metastatic, cells and very low expression in metastatic cell lines. In MCF-7 cells transfected with a wild-type IRF-1 (MCF-7/IRF-1), IRF-1 mRNA expression inversely correlates with the rate of cell proliferation (r = −0.91; P = 0.002). Conversely, expression of dnIRF-1 in both MCF-7 (MCF-7/dnIRF-1; p53 wild-type) and T47D cells (T47D/dnIRF-1; p53 mutant) increases cell proliferation (P ≤ 0.001). In athymic nude mice, the incidence of MCF-7/IRF-1 xenografts is reduced (P = 0.045), whereas MCF-7/dnIRF-1 xenografts exhibit a significantly higher tumor incidence (P ≤ 0.001). Effects of IRF-1/dnIRF-1 are mediated through changes in the rates of apoptosis and not through cell cycle regulation. MCF-7/dnIRF-1 cells exhibit a 50% decrease in basal apoptosis (P = 0.007) and a significant reduction in caspase 8 activity (P = 0.03); similar effects occur in T47D/dnIRF-1 cells, where the effects on apoptosis appear to be mediated through inhibition of caspases 3/7 (P < 0.001) and caspase 8 (P = 0.03). These data establish a functional role for IRF-1 in the growth suppression of breast cancer cells and strongly implicate IRF-1 as a tumor suppressor gene in breast cancer that acts, independent of p53, to control apoptosis.

Keywords: CCS-IMEM, improved minimal essential medium supplemented with 5% charcoal stripped calf serum; EGFP, enhanced green fluorescent protein; ERα, estrogen receptor-alpha; ER+/−, estrogen receptor positive/negative; IRF-1, interferon regulatory factor-1; NPM, nucleophosmin

Journal Article.  8174 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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