Identification of Interferon Regulatory Factor (IRF)-5 Tumor Suppressor Function in Human Breast Cancer.

Abstract

Abstract Background: Transcription factors of the IRF family participate in the early host response to pathogens, hematopoietic differentiation and immunomodulation. IRFs can regulate cell growth and apoptosis thereby affecting the susceptibility to and progression of cancer. IRF-1 was recently identified as a tumor suppressor in breast cancer. Early evidence from our lab and others suggests that IRF-5 may also have tumor suppressor activities. Although loss of IRF-5 expression has recently been shown to enhance transformation by Ha-ras, very little is known of IRF-5 tumor suppressor function(s).Material and Methods: Using paraffin-embedded formalin-fixed human breast tissue specimens from 64 patients with varying stages of ductal carcinoma, we analyzed and compared the expression of IRF-1 and IRF-5 by immunofluorescence (IF). Clinical data, such as histological subtype, stage, and receptor expression (ER, PR Her-2) were available for clinicopathological correlations. Protein levels were also determined in normal human breast epithelial MCF-10A, and -12A cells, and in cancer cell lines MCF-7, MDA-MB-231, -468, and T47D by immunoblot and IF. By retroviral infection, we overexpressed IRF-5 in breast cancer cell lines or knocked-down IRF-5 in normal MCF-10A and -12A cells and examined cell growth, apoptosis, metastasis and sensitivity to cytotoxic stress. In vivo tumor suppressor function was determined in NCr nu/nu mice inoculated with MCF-7 or MDA-MB-231 cells expressing or lacking IRF-5.Results: We confirmed recent data on IRF-1 revealing that it is expressed less frequently in tumor tissue of high-grade ductal carcinoma in situ (DCIS) or invasive DC compared with normal breast tissue. Data from patient samples indicate a significant difference between IRF-1 and IRF-5 expression that was distinctly associated with breast cancer disease stages, including early-to-late stage DCIS, suggesting their utilization as prognostic indicators.Similar findings were made in breast cancer cell lines. We demonstrate that forced expression of IRF-5 in breast cancer cells inhibits colony formation, sensitizes cells to cytotoxic stress-induced apoptosis, inhibits metastasis, and tumor formation in nude mice. Conversely, knockdown of IRF-5 in MCF-10A and -12A cells resulted in resistance to stress-induced cell death.Discussion: Data from this study strongly support a tumor suppressor function for IRF-5 in breast cancer. Ultimately, the study is expected to lead us to the identification of new prognostic indicators and therapeutic approaches for the treatment of breast cancer. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 3160.