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The CCAAT/enhancer-binding protein beta-2 isoform (CEBP?-2) upregulates galectin-7 expression in human breast cancer cells.

ABSTRACT: 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/EBP?) 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/EBP?-2 (also known as LAP2), the most transcriptionally active of the C/EBP? isoforms. Our results showed that ectopic expression of C/EBP?-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/EBP?-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/EBP? closely micmicked that of galectin-7, most notably in mammary myoepithelial cells and basal-like breast cancer where galectin-7 is preferentially expressed. Taken together, our findings suggest that C/EBP? is an important mediator of galectin-7 gene activation in breast cancer cells and highlight the different transcriptional mechanisms controlling galectin-7 in cancer cells.

SUBMITTER: Campion CG

PROVIDER: S-EPMC4008383 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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The CCAAT/enhancer-binding protein beta-2 isoform (CEBPβ-2) upregulates galectin-7 expression in human breast cancer cells.

Campion Carole G CG Labrie Marilyne M Grosset Andrée-Anne AA St-Pierre Yves Y

PloS one 20140502 5

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 indu ...[more]

PMID: 24789216

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Project description:IntroductionThe c-Jun coactivator, Jun activation-domain binding protein 1 (Jab1) also known as the fifth component of the COP9 signalosome complex (CSN5), is a novel candidate oncogene whose aberrant expression contributes to the progression of breast carcinoma and other human cancers. The mechanism of Jab1 gene expression and its deregulation in cancer cells remains to be identified. We therefore investigated the transcriptional regulatory mechanisms of Jab1 expression in human breast carcinoma cells.MethodsTo identify potential regulators of Jab1 transcription, we cloned the 5' upstream region of the human Jab1 gene and mapped its transcriptional start site. We identified binding sequences for the CCAAT/enhancer binding protein (C/EBP) and GATA, as well as a signal transducer and activator of transcription-3 (Stat3) consensus sequence overlapping the C/EBP site, using 5'- deletion analysis and a gene reporter assay. Mutational analysis of these binding sites was performed to confirm their roles in promoting Jab1 transcription in breast cancer cells. We further confirmed these binding sites using electrophoretic mobility shift assays (EMSAs) and chromatin immunoprecipitation (ChIP) assays. We also analyzed whether the siRNA-mediated inactivation of Stat3 and Src could reduce Jab1-promoter activity and whether interleukine-6 (IL-6) could mediate increased Jab1 expression through Stat3 signaling.ResultsWe identified binding sequences for C/EBP, GATA, as well as a Stat3 consensus sequence overlapping the C/EBP site in the promoter region of Jab1. C/EBP-beta2 is a potential transcriptional activator of Jab1 and mutation of the C/EBP/Stat3 binding site significantly reduced Jab1-promoter activity. In addition, inhibiting Stat3 significantly reduced Jab1-promoter activation. EMSA and ChIP assays confirmed that C/EBP, GATA1 and Stat3 bind to Jab1 promoter in breast carcinoma cells. We also found that Src, an activator of Stat3, is involved in Jab1-promoter activation. siRNA knockdown of Src reduced the Jab1-promoter activity, similar to the results seen when Stat3 was inhibited in breast carcinoma cells. Interestingly, reactivation of Stat3 in normal mammary epithelial cells (MCF-10A, MCF-10F) is sufficient to reactivate Jab1 expression. Treatment with the cytokine IL-6 resulted in increased Jab1 expression that was blocked by inhibition of Stat3.ConclusionsThese findings reveal a novel mechanism of Jab1 gene regulation and provide functional and mechanistic links between the Src/Stat3 and IL-6/Stat3 signaling axes that are involved in the activation of Jab1 transcription and regulation of this novel oncogenic protein.

Dataset Information

The CCAAT/enhancer-binding protein beta-2 isoform (CEBP?-2) upregulates galectin-7 expression in human breast cancer cells.

Publications

The CCAAT/enhancer-binding protein beta-2 isoform (CEBPβ-2) upregulates galectin-7 expression in human breast cancer cells.

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