HMGB1 and HMGB2 cell-specifically down-regulate the p53- and p73-dependent sequence-specific transactivation from the human Bax gene promoter.
The recently cloned gene p73 is a close homologue of p53, which is a crucial tumor suppressor gene for preventing the malignant transformation of cells by inducing cell cycle arrest and apoptosis. Previous reports have shown that architectural DNA-bending/looping chromosomal proteins HMGB1 and HMGB2 (formerly known as HMG1 and HMG2), which function in a number of biological processes including transcription and DNA repair, interact in vitro with p53 and stimulate p53 binding to DNA containing p53 consensus sites. Here, we report that HMGB1 physically interacts with two splicing variants of p73, alpha and beta (pull-down assay), and enhances binding of p73 to specific cognate DNA sites (gel-shift assay). Both HMG box domains of HMGB1, A and B, interact with p73alpha. Association of HMGB1 with p73, like the demonstrated ability of HMGB1 to stimulate p73 binding to different p53-responsive elements, requires the oligomerization region and/or region between DNA-binding domain and oligomerization domain of p73 (residues 312-381). Transient transfections revealed that ectopically expressed or endogenous HMGB1 and HMGB2 (antisense strategy) significantly inhibit in vivo both p73alpha/beta- and p53-dependent transactivation from the Bax gene promoter (and much less from Mdm2 and p21(waf1) promoters) in p53-deficient SAOS-2 cells. In contrast, HMGB1 and HGMB2 stimulate p73- or p53-dependent transactivation in p53-deficient H1299 cells, irrespective of the promoter used. Our results suggest that ubiquitously expressed HMGB1 and HMGB2 have potential to cell- and promoter-specifically down- or up-regulate in vivo transcriptional activity of different members of the p53 family. A possible mechanism of HMGB1-mediated modulation of p73- and p53-dependent transactivation is discussed.
Stros
Michal
M
Institute of Biophysics, Academy of Sciences of the Czech Republic, Kralovopolská 135, 612 65 Brno, Czech Republic. stros@ibp.cs
Ozaki
Toshinori
T
Bacikova
Alena
A
Kageyama
Hajime
H
Nakagawara
Akira
A
D017398:Alternative Splicing; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics*; D015536:Down-Regulation; D016147:Genes, Tumor Suppressor; D016158:Genes, p53 / Q000235:genetics*; D005982:Glutathione Transferase / Q000378:metabolism; D024243:HMGB1 Protein / Q000378:metabolism*; D024261:HMGB2 Protein / Q000378:metabolism*; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics*; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D051736:Proto-Oncogene Proteins c-mdm2; D016329:Sp1 Transcription Factor / Q000378:metabolism; D015533:Transcriptional Activation; D014162:Transfection; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins; D015854:Up-Regulation; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D004268:DNA-Binding Proteins; D024243:HMGB1 Protein; D024261:HMGB2 Protein; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016329:Sp1 Transcription Factor; C000606460:TP73 protein, human; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins; D051028:bcl-2-Associated X Protein; D008156:Luciferases; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D005982:Glutathione Transferase