Par-4, a pro-apoptotic gene, inhibits radiation-induced NF kappa B activity and Bcl-2 expression leading to induction of radiosensitivity in human prostate cancer cells PC-3.
Ionizing radiation caused induction NF kappa B activity and Bcl-2 protein expression in the radioresistant p53 null human prostate cancer cell line, PC-3. Exposure of PC-3 cells to Ad5-I kappa B super-repressor inhibited radiation-induced Bcl-2 expression indicating that radiation-induced NF kappa B activity is required for the induction of Bcl-2 protein. PAR-4, a novel pro-apoptotic protein is a potent down-modulator of NF kappa B activity and bcl-2 protein expression. This study was undertaken to investigate the impact of PAR-4 expression on radiation-induced NF kappa B activity and Bcl-2 expression and its resultant radiation response in PC-3 cells. Western blot analysis indicated that enforced expression of PAR-4 in PC-3 cells down regulated radiation-induced bcl-2 protein, whereas in vector transfected cells radiation caused an induction of bcl-2 protein. In both transfectant cell lines, the bax protein levels remained unaltered after radiation. When compared to PC-3/Vector cells, PC-3/PAR-4 cells showed significant sensitivity to radiation-induced clonogenic inhibition and apoptosis. Thus, the down-regulation of bcl-2 protein by ectopic PAR-4 expression altered bcl-2: bax ratio in PC-3/PAR-4 cells and this led enhanced radiosensitivity. PAR-4 was found to inhibit the radiation-induced NF kappa B activity and NF kappa B transcriptional activity is essential for bcl-2 upregulation. In PC-3/Vector cells, radiation caused an increase in NF kappa B activity leading to upregulation of bcl-2 protein. However, in PC-3/PAR-4 cells, the radiation-induced NF kappa B activity was inhibited resulting in the transrepression of bcl-2 promoter and down-modulation of bcl-2 protein. In addition, PAR-4 was found to directly inhibit the phosphorylation and degradation of I kappa B alpha, which led to the loss of NF kappa B activity causing repression of endogenous and radiation-induced Bcl-2 protein. Together, these mechanisms suggest that PAR-4 is functionally required to cause radiation-induced apoptosis by abrogating the survival and anti-apoptotic effects of NF kappa B activity and bcl-2 function respectively.
Chendil
Damodaran
D
Department of Radiation Medicine, University of Kentucky, 800, Rose Street, Lexington, Kentucky 40536, USA.
Das
Anindita
A
Dey
Swatee
S
Mohiuddin
Mohammed
M
Ahmed
Mansoor M
MM
D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation / Q000528:radiation effects; D006801:Humans; D020672:I-kappa B Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors* / Q000528:radiation effects; D010766:Phosphorylation; D011471:Prostatic Neoplasms / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000528:radiation effects; D011836:Radiation Tolerance; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D047908:Intracellular Signaling Peptides and Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; C101296:prostate apoptosis response-4 protein; D000072000:NF-KappaB Inhibitor alpha