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.
Kim
Myoung H
MH
Department of Molecular Biology and Immunology, University of North Texas Health Science Center, Fort Worth, Texas 76107-2699, USA. mkim@hsc.unt.edu
Fields
Jerel
J
Field
Jerrel
J
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