Down-Regulation and Growth Inhibitory Role of C/EBPα in Breast Cancer

Abstract

CCAAT/enhancer binding proteins (C/EBP) are a family of transcription factors that regulate proliferation and differentiation in a variety of tissues. The purpose of this study was to explore the possibility that C/EBPalpha is involved in breast cancer. We quantified C/EBPalpha mRNA expression levels in 24 primary breast tumors, 16 normal breast samples, and 8 breast cancer cell lines using quantitative real-time reverse transcription-PCR assay. C/EBPalpha protein levels were further determined by immunohistochemical analysis. To examine the consequence of C/EPBalpha expression in breast cancer, we stably transfected an inducible C/EPBalpha expression vector into three breast cancer cell lines. Low expression of C/EBPalpha mRNA was found in 83% of primary breast cancer samples. Immunohistochemical study further showed either a markedly reduced or undetectable expression of C/EBPalpha protein in 30% of breast cancer specimens. The other 70% of breast cancers had C/EBPalpha expression in both the cytoplasm and nucleus; in control, C/EBPalpha was localized to the nucleus in the normal ductal cells. C/EBPalpha expression was associated with estrogen- and progesterone receptor-negative status. Induction of C/EBPalpha expression in these cell lines resulted in growth inhibition accompanied by G0-G1 cell cycle arrest and reduced anchorage-independent cell growth. C/EBPalpha expression was associated with down-regulation of c-myc and up-regulation of p21, PPARgamma, and the breast epithelial differentiation marker, maspin. These results suggest that reduced expression of C/EBPalpha may play a role in the development and/or progression of breast cancer.