C/EBPbeta regulates metastatic gene expression and confers TNF-alpha resistance to prostate cancer cells.
BACKGROUND
CCAAT/enhancer-binding protein beta (C/EBPbeta) is a transcription factor and consists of three isoforms, transcription-activating A/B (C/EBPbeta-AB) and transcription inhibitory C (C/EBPbeta-C). We previously reported that C/EBPbeta-C was predominantly expressed in hormone-dependent LNCaP cells, while C/EBPbeta-AB forms were predominant in hormone-independent prostate cancer (HI-PCa) cells.


METHODS
Reporter gene analysis was performed to investigate transcriptional activity of C/EBPbeta on metastatic gene expression upon TNF-alpha treatment. NF-kappaB activation and C/EBPbeta protein upregulation were determined by immunoblotting. WST assay was used to determine the role of C/EBPbeta in TNF-alpha-induced cell death.


RESULTS
We first determined that the C/EBPbeta-C overexpression or siRNA-mediated C/EBPbeta depletion decreased TNF-alpha-induced promoter activities of Bfl-1, IL-6, and IL-8 genes. IL-6 and IL-8 are autocrine growth factors of HI-PCa cells and Bfl-1 is an anti-apoptotic protein whose function in prostate cancer is yet to be determined. Secondly, we determined differential regulation of C/EBPbeta by TNF-alpha. In DU-145 cells, C/EBPbeta was upregulated by TNF-alpha, but downregulated in LNCaP cells, although NF-kappaB was activated in both cells. This result suggested cell-type specific activation of signaling pathways leading to C/EBPbeta upregulation, which was distinct from that leading to NF-kappaB activation. Most importantly, C/EBPbeta depletion decreased cell growth and sensitized DU-145 cells to TNF-alpha-induced cell death. Conversely, overexpression of C/EBPbeta-A in LNCaP cells increased resistance to TNF-induced cell death and TNF-induced promoter activities of IL-6 and Bfl-1.


CONCLUSIONS
Our study, for the first time, demonstrated that C/EBPbeta regulated cell growth and conferred TNF-alpha resistance to PCa cells, in part, via regulation of metastatic gene expression. Prostate 69: 1435-1447, 2009. (c) 2009 Wiley-Liss, Inc.
Kim
Myoung H
MH
Department of Molecular Biology and Immunology, University of North Texas Health Science Center, Fort Worth, Texas, USA. mkim@hsc.unt.edu
Minton
Alena Z
AZ
Agrawal
Vikas
V
D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism*; D016923:Cell Death / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D017930:Genes, Reporter; D006801:Humans; D015850:Interleukin-6 / Q000235:genetics; D016209:Interleukin-8 / Q000235:genetics; D008297:Male; D015778:Minor Histocompatibility Antigens; D016328:NF-kappa B / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000502:physiology; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000556:secondary; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D034741:RNA, Small Interfering; D014158:Transcription, Genetic / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism / Q000494:pharmacology*
C096816:BCL2-related protein A1; D022782:CCAAT-Enhancer-Binding Protein-beta; C508600:IL6 protein, human; D015850:Interleukin-6; D016209:Interleukin-8; D015778:Minor Histocompatibility Antigens; D016328:NF-kappa B; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha