Regulation of expression of the early growth response gene-1 (EGR-1) in malignant and benign cells of the prostate.
BACKGROUND
Expression of the early growth response gene-1 (EGR-1) is elevated in prostate cancer and correlates with tumor progression. This study provides insight into the mechanism(s) that regulate EGR-1 expression and activity in malignant and benign prostate cells.


METHODS
Western blotting and in vitro pulse labeling were used to examine EGR-1 protein levels and half-life in malignant (PC-3) and benign (BPH-1) prostate cell lines. EGR-1 functional ability was assessed by transient transfections with an EGR-1 promoter driven luciferase plasmid and electromobility shift assays (EMSAs) to assess DNA binding of the EGR-1 protein. Protein levels of casein kinase II (CKII) were evaluated by Western blotting.


RESULTS
PC-3 cells maintain high steady-state levels of EGR-1 protein, in part due to a longer half-life of EGR-1 protein. BPH-1 cells responded to mitogenic stimuli with increased EGR-1 protein levels, and enhanced transcriptional activity. In contrast, PC-3 cells showed no response to stimuli. DNA binding of EGR-1 was higher in BPH-1 cells than in PC-3 cells. This appears to be related to the heavily phosphorylated state of EGR-1 in PC-3 cells which is correlated with increased levels of CKII found in these cells.


CONCLUSIONS
PC-3 cells maintain a long lasting, heavily phosphorylated pool of EGR-1, which binds poorly to DNA and responds poorly to mitogenic stimulus. BPH-1 cells, in contrast, maintain a more responsive, less phosphorylated EGR-1 pool. These findings suggest that EGR-1 expression and activity is differentially regulated in PC-3 and BPH-1 cell lines.
Department of Urology Research, Mayo Clinic, Rochester, Minnesota, USA.
Gloria R
GR
Mora
Kenneth R
KR
Olivier
Richard F
RF
Mitchell
Robert B
RB
Jenkins
Donald J
DJ
Tindall
D015153:Blotting, Western; D047390:Casein Kinase II / Q000378:metabolism; D045744:Cell Line, Tumor; D004273:DNA, Neoplasm / Q000235:genetics; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*; D051766:Early Growth Response Protein 1; D024202:Electrophoretic Mobility Shift Assay; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D006801:Humans; D017874:Immediate-Early Proteins / Q000096:biosynthesis / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D011470:Prostatic Hyperplasia / Q000235:genetics* / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*; D014158:Transcription, Genetic; D014162:Transfection
D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D017874:Immediate-Early Proteins; D014157:Transcription Factors; D047390:Casein Kinase II