Translationally regulated C/EBP beta isoform expression upregulates metastatic genes in hormone-independent prostate cancer cells.
BACKGROUND
C/EBP beta is a transcription factor regulating key biological processes including cellular growth and differentiation and its increased expression correlates with tumor invasiveness. Recently, the increased expression of C/EBP beta was reported in proliferative inflammatory atrophy of the prostate, associating with increased COX-2 expression and androgen receptor (AR) downregulation.


METHODS
C/EBP beta expression was determined in DU-145, PC-3 and LNCaP cells by immunoblotting. Transient transfection of C/EBP beta expression vectors was performed to investigate translational regulation of its isoform expression. Reporter gene analysis was performed to investigate transcriptional activity of C/EBP beta on metastatic gene expression.


RESULTS
We determined that transcriptionally active, full-length C/EBP beta isoforms were dominantly expressed in hormone-independent DU-145 and PC-3 cells, while transcription-repressing truncated isoform was dominant in hormone-dependent LNCaP cells. Our results further showed lack of full-length isoform expression from the transiently transfected C/EBP beta expression vector in LNCaP cells compared to that in PC-3 cells transfected with the same vector, while the expression of truncated isoform was comparable in both cell lines. Interestingly, however, the most upstream initiation site A null mutation restored translation of full-length isoform in LNCaP cells. These results suggest that full-length C/EBP beta isoform expression in LNCaP cells may be suppressed at the upstream initiation sites, likely at site A. Most importantly, C/EBP beta overexpression significantly upregulated promoter activities of IL-8, COX-2, and anti-apoptotic Bfl-1 genes.


CONCLUSIONS
Our study demonstrates that C/EBP beta is an important transcription factor upregulating metastatic gene expression and that its isoform expression is differentially regulated at the translational level in prostate cancer cells.
Department of Molecular Biology and Immunology, University of North Texas Health Science Center, Fort Worth, Texas 76107-2699, USA. mkim@hsc.unt.edu
Myoung H
MH
Kim
Jerel
J
Fields
Jerrel
J
Field
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000230:Adenocarcinoma / Q000378:metabolism* / Q000473:pathology; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D016209:Interleukin-8 / Q000235:genetics / Q000378:metabolism*; D008297:Male; D015778:Minor Histocompatibility Antigens; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D014176:Protein Biosynthesis; D020033:Protein Isoforms; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D011944:Receptors, Androgen / Q000378:metabolism; D015854:Up-Regulation / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; C096816:BCL2-related protein A1; D022782:CCAAT-Enhancer-Binding Protein-beta; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D016209:Interleukin-8; D015778:Minor Histocompatibility Antigens; D010750:Phosphoproteins; D020033:Protein Isoforms; D019253:Proto-Oncogene Proteins c-bcl-2; D011944:Receptors, Androgen; D051546:Cyclooxygenase 2