Nucleophosmin/B23 regulates transcriptional activation of E2F1 via modulating the promoter binding of NF-kappaB, E2F1 and pRB.
Expression of nucleophosmin/B23 and E2F1 and E2F1-dependent transcription increased in U1 bladder cancer cells upon serum stimulation from quiescence. Nucleophosmin/B23-siRNA treatment abrogated such increase of E2F1-dependent transcriptional activity. In identifying physiologically important factors that may occupy E2F1 promoter and regulate its activity in vivo, we found that the pattern of NF-kappaB, E2F1 and pRB recruitment to E2F1 promoter changed in a strikingly dynamic fashion as cells progressed from quiescence into serum-stimulated growth. E2F1 promoter activity in quiescent cells was associated with recruitment of NF-kappaB. NF-kappaB was replaced largely by E2F1 in concert with gene activation during the early stage (12 h) of serum stimulation. At late stage (24 h) of serum stimulation, pRB was then recruited to the E2F1-promoter complex to counterbalance its activity. Upon siRNA-mediated reduction of intracellular nucleophosmin/B23, E2F1 and pRB were recruited to the promoter with the dissociation of NF-kappaB concomitant with gene inactivation. Based on immunoprecipitation experiments, nucleophosmin/B23 was found to be associated with NF-kappaB in cells grown in serum-supplemented but not in serum-deprived medium. Furthermore, nucleophosmin/B23 could also be co-immunoprecipitated with ppRB at the early stage (12 h) but not at the late stage (24 h) of serum stimulation. The results demonstrate a novel mechanism for transcriptional regulation of E2F1 and identify the functional role of nucleophosmin/B23 in modulating the binding of NF-kappaB, E2F1 and pRB to activate E2F1 promoter.
Lin
Chiao Yun
CY
Cancer Biochemistry Laboratory, Department of Pharmacology, College of Medicine, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-San, Tao-Yuan 333, Taiwan, R.O.C.
Liang
Yu Chun
YC
Yung
Benjamin Yat-Ming
BY
D045744:Cell Line, Tumor; D050687:E2F1 Transcription Factor / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D016328:NF-kappa B / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000494:pharmacology / Q000502:physiology*; D000090243:Nucleophosmin; D011401:Promoter Regions, Genetic; D016160:Retinoblastoma Protein / Q000378:metabolism*; D015533:Transcriptional Activation; D015854:Up-Regulation
D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D016328:NF-kappa B; C000716967:NPM1 protein, human; D009687:Nuclear Proteins; D016160:Retinoblastoma Protein; D000090243:Nucleophosmin