The CCAAT/Enhancer-Binding Protein Beta-2 Isoform (CEBPb-2) Upregulates Galectin-7 Expression in Human Breast Cancer Cells

Galectin-7 is considered a gene under the control of p53. However, elevated expression of galectin-7 has been reported in several forms of cancer harboring an inactive p53 pathway. This is especially true for breast cancer where galectin-7 expression is readily expressed in a high proportion in basal-like breast cancer tissues, conferring cancer cells with increased resistance to cell death and metastatic properties. These observations suggest that other transcription factors are capable of inducing galectin-7 expression. In the present work, we have examined the role of CCAAT/enhancer-binding protein beta (C/ EBPb) in inducing expression of galectin-7. C/EBP proteins have been shown to contribute to breast cancer by upregulating pro-metastatic genes. We paid particular attention to C/EBPb-2 (also known as LAP2), the most transcriptionally active of the C/EBPb isoforms. Our results showed that ectopic expression of C/EBPb-2 in human breast cancer cells was sufficient to induce expression of galectin-7 at both the mRNA and protein levels. In silico analysis further revealed the presence of an established CEBP element in the galectin-7 promoter. Mutation of this binding site abolished the transcriptional activity of the galectin-7 promoter. Chromatin immunoprecipitation analysis confirmed that C/EBPb-2 binds to the endogenous galectin-7 promoter. Analysis of galectin-7 protein expression in normal epithelia and in breast carcinoma by immunohistochemistry further showed the expression pattern of C/EBPb closely micmicked that of galectin-7, most notably in mammary myoepithelial cells and basal-like breast cancer where galectin-7 is preferentially expressed. Take