The do's and don'ts of p53 isoforms

2009 ◽  
Vol 390 (10) ◽  
Author(s):  
Reiner U. Jänicke ◽  
Vilma Graupner ◽  
Wilfried Budach ◽  
Frank Essmann
Keyword(s):  
Decision Process ◽  
Target Genes ◽  
Decision Processes ◽  
Dominant Negative ◽  
Alternative Promoters ◽  
Selective Activation ◽  
Cycle Arrest ◽  
P53 Isoforms ◽  
Transcription Factor P53 ◽  
P53 Target Genes

Abstract Upon DNA damage and other stresses, the transcription factor p53 elicits numerous responses including DNA repair, cell cycle arrest and apoptosis, properties that make p53 the prototype tumor suppressor. In addition, p53 also transactivates genes whose products act in an anti-apoptotic manner providing strong evidence that p53 exhibits both tumor suppressive and tumorigenic functions. Although several events were postulated to contribute to the p53-mediated decision process, the precise mechanism(s) that governs p53 activities is still elusive. Recently, it was found that the p53 gene allows expression of at least nine different isoforms that arise from multiple splicing events and the usage of alternative promoters. Several of these isoforms were shown to critically interfere with the function of the full-length p53 mainly by acting in a dominant-negative manner. However, an isoform-dependent selective activation of p53 target genes was also observed. Furthermore, certain p53 isoforms are aberrantly expressed in various tumors strongly implying their involvement in tumorigenic events. Thus, p53 isoforms may represent crucial determinants in p53-mediated decision processes whose precise functions (their do's and don'ts) are only beginning to emerge.

scholarly journals Regulation of p53 Target Gene Expression by Peptidylarginine Deiminase 4

2008 ◽  
Vol 28 (15) ◽  
pp. 4745-4758 ◽  
Author(s):  
Pingxin Li ◽  
Hongjie Yao ◽  
Zhiqiang Zhang ◽  
Ming Li ◽  
Yuan Luo ◽  
...  
Keyword(s):  
Target Gene ◽  
Target Genes ◽  
Peptidylarginine Deiminase ◽  
Uv Treatment ◽  
Rna Pol Ii ◽  
Pol Ii ◽  
Cycle Arrest ◽  
P53 Target Gene ◽  
P53 Target Genes ◽  
P21 Promoter

ABSTRACT Histone Arg methylation has been correlated with transcriptional activation of p53 target genes. However, whether this modification is reversed to repress the expression of p53 target genes is unclear. Here, we report that peptidylarginine deiminase 4, a histone citrullination enzyme, is involved in the repression of p53 target genes. Inhibition or depletion of PAD4 elevated the expression of a subset of p53 target genes, including p21/CIP1/WAF1, leading to cell cycle arrest and apoptosis. Moreover, the induction of p21, cell cycle arrest, and apoptosis by PAD4 depletion is p53 dependent. Protein-protein interaction studies showed an interaction between p53 and PAD4. Chromatin immunoprecipitation assays showed that PAD4 is recruited to the p21 promoter in a p53-dependent manner. RNA polymerase II (Pol II) activities and the association of PAD4 are dynamically regulated at the p21 promoter during UV irradiation. Paused RNA Pol II and high levels of PAD4 were detected before UV treatment. At early time points after UV treatment, an increase of histone Arg methylation and a decrease of citrullination were correlated with a transient activation of p21. At later times after UV irradiation, a loss of RNA Pol II and an increase of PAD4 were detected at the p21 promoter. The dynamics of RNA Pol II activities after UV treatment were further corroborated by permanganate footprinting. Together, these results suggest a role of PAD4 in the regulation of p53 target gene expression.

scholarly journals FLIP(L) determines p53 induced life or death

2019 ◽  
Author(s):  
Andrea Lees ◽  
Alexander J. McIntyre ◽  
Fiammetta Falcone ◽  
Nyree T. Crawford ◽  
Christopher McCann ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Arrest ◽  
Cell Fate ◽  
Target Genes ◽  
Hdac Inhibitors ◽  
Caspase 8 ◽  
Cycle Arrest ◽  
P53 Activation ◽  
P53 Target Genes ◽  
Mdm2 Inhibitor

AbstractHow p53 differentially activates cell cycle arrest versus cell death remains poorly understood. Here, we demonstrate that upregulation of canonical pro-apoptotic p53 target genes in colon cancer cells imposes a critical dependence on the long splice form of the caspase-8 regulator FLIP (FLIP(L)), which we identify as a direct p53 transcriptional target. Inhibiting FLIP(L) expression with siRNA or Class-I HDAC inhibitors promotes apoptosis in response to p53 activation by the MDM2 inhibitor Nutlin-3A, which otherwise predominantly induces cell-cycle arrest. When FLIP(L) upregulation is inhibited, apoptosis is induced in response to p53 activation via a novel ligand-independent TRAIL-R2/caspase-8 complex, which, by activating BID, induces mitochondrial-mediated apoptosis. Notably, FLIP(L) depletion inhibits p53-induced expression of the cell cycle regulator p21 and enhances p53-mediated upregulation of PUMA, with the latter activating mitochondrial-mediated apoptosis in FLIP(L)-depleted, Nutlin-3A-treated cells lacking TRAIL-R2/caspase-8. Thus, we report two previously undescribed, novel FLIP(L)-dependent mechanisms that determine cell fate following p53 activation.

scholarly journals Reduction of total E2F/DP activity induces senescence-like cell cycle arrest in cancer cells lacking functional pRB and p53

2005 ◽  
Vol 168 (4) ◽  
pp. 553-560 ◽  
Author(s):  
Kayoko Maehara ◽  
Kimi Yamakoshi ◽  
Naoko Ohtani ◽  
Yoshiaki Kubo ◽  
Akiko Takahashi ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Proliferation ◽  
Cell Cycle Arrest ◽  
Cancer Cells ◽  
Target Genes ◽  
Cellular Proliferation ◽  
Human Cancer ◽  
Dominant Negative ◽  
Cycle Arrest ◽  
Risk Of Cancer

E2F/DP complexes were originally identified as potent transcriptional activators required for cell proliferation. However, recent studies revised this notion by showing that inactivation of total E2F/DP activity by dominant-negative forms of E2F or DP does not prevent cellular proliferation, but rather abolishes tumor suppression pathways, such as cellular senescence. These observations suggest that blockage of total E2F/DP activity may increase the risk of cancer. Here, we provide evidence that depletion of DP by RNA interference, but not overexpression of dominant-negative form of E2F, efficiently reduces endogenous E2F/DP activity in human primary cells. Reduction of total E2F/DP activity results in a dramatic decrease in expression of many E2F target genes and causes a senescence-like cell cycle arrest. Importantly, similar results were observed in human cancer cells lacking functional p53 and pRB family proteins. These findings reveal that E2F/DP activity is indeed essential for cell proliferation and its reduction immediately provokes a senescence-like cell cycle arrest.

scholarly journals ΔNp73β Is Active in Transactivation and Growth Suppression

2004 ◽  
Vol 24 (2) ◽  
pp. 487-501 ◽  
Author(s):  
Gang Liu ◽  
Susan Nozell ◽  
Hui Xiao ◽  
Xinbin Chen
Keyword(s):  
Cell Growth ◽  
Target Genes ◽  
Expression System ◽  
Dominant Negative ◽  
Activation Domain ◽  
P53 Family ◽  
Cycle Arrest ◽  
Family Protein ◽  
Alternatively Spliced ◽  
Cell Type Specific

ABSTRACT p73, a p53 family protein, shares significant sequence homolog and functional similarity with p53. However, unlike p53, p73 has at least seven alternatively spliced isoforms with different carboxyl termini (p73α-η). Moreover, the p73 gene can be transcribed from a cryptic promoter located in intron 3, producing seven more proteins (ΔNp73α-η). ΔNp73, which does not contain the N-terminal activation domain in p73, has been thought to be transcriptionally inactive and dominant negative over p53 or p73. To systemically analyze the activity of the ΔN variant, we generated stable cell lines, which inducibly express ΔNp73α, ΔNp73β, and various ΔNp73β mutants by using the tetracycline-inducible expression system. Surprisingly, we found that ΔNp73β is indeed active in inducing cell cycle arrest and apoptosis. Importantly, we found that, when ΔNp73β is expressed at a physiologically relevant level, it is capable of suppressing cell growth. We then demonstrated that these ΔNp73β activities are not cell type specific. We showed that the 13 unique residues at the N terminus are required for ΔNp73β to suppress cell growth. We also found that, among the 13 residues, residues 6 to 10 are critical to ΔNp73β function. Furthermore, we found that ΔNp73β is capable of inducing some p53 target genes, albeit to a lesser extent than does p73β. Finally, we found that the 13 unique residues, together with the N-terminal PXXP motifs, constitute a novel activation domain. Like ΔNp73β, ΔNp73γ is active in transactivation. However, unlike ΔNp73β, ΔNp73α is inactive in suppressing cell growth. Our data, together with others' previous findings, suggest that ΔNp73β may have distinct functions under certain cellular circumstances.

BCL6 Regulates Diffuse Large B-Cell Lymphoma Cell Cycle and Apoptosis Checkpoints through Direct Repression of the p300 Histone Acetyl-Transferase.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1413-1413
Author(s):  
Leandro Cerchietti ◽  
Maria E. Figueroa ◽  
Rita Shaknovich ◽  
Ari Melnick
Keyword(s):  
Cell Cycle ◽  
B Cell ◽  
Target Genes ◽  
B Cell Lymphoma ◽  
Dominant Negative ◽  
Mrna Levels ◽  
Histone Acetyl Transferase ◽  
Protein Levels ◽  
P53 Target Genes ◽  
Large B Cell

Abstract The BCL6 oncogenic transcriptional repressor protein is frequently constitutively expressed in Diffuse Large B-cell Lymphomas (DLBCLs). A BCL6 peptidomimetic inhibitor (BPI) that specifically inhibits the repressor activity of BCL6 can induce cell death in DLBCL cell lines and primary tumor tissue, both in vitro and in vivo. Many genes involved in DNA damage, cell cycle and others are targets of BCL6. Among these is the p53 tumor suppressor gene. However, we find that p53 mRNA levels are actually higher in the subset of DLBCL patients with higher BCL6 expression (n=176 cases). Overall, we could readily detect p53 protein expression by immunohistochemistry in 50% of BCL6 positive DLBCL samples (n=350 cases). By studying expression levels of p53 target genes, we show that even in DLBCLs expressing wild-type p53, the protein is not fully active, and a p53 activating peptide was required to trigger p53 activity and execute cellular checkpoints. Accordingly, even though p53 was already present, BCL6 blockade by BPI could still induce a p53 response in DLBCL cells (with only small changes in p53 levels). Based on these results we speculated that BCL6 might inhibit p53 activity through an alternative mechanism such as regulating its activity through post-translational modifications. In accordance with this prediction, we found that BPI can strongly induce expression of the p300 histone acetyl-transferase, which can activate p53 by acetylation. The p300 promoter has two BCL6 binding sites and by chromatin immunoprecipitation (ChIP) assays we show that BCL6 directly binds to these sites. We found that 80% of DLBCL (n=70) express low protein levels of p300 (compared with other B-lymphomas) and the same is apparent from mRNA studies. By performing kinetic studies in DLBCL cells with multiple time points, we show that after BPI treatment, p300 mRNA and then protein levels are induced, after which p53 becomes acetylated and after which p53 target genes (p21, PUMA, NOXA, GADD45 and PIG3) are upregulated. These changes are partially or totally overcome by expression of either a p53-dominant negative or p300-dominant negative construct. In DLBCL cells with p53 mutations, this program is preferentially executed trough p73 and/or p63, which in turn become acetylated by p300. Interestingly, after BPI treatment p300 acetylates BCL6 itself, which further reduces BCL6 activity. This leads to higher BCL6 inhibition and triggering of a signal amplification loop. These findings have significant therapeutic implications, since co-treatment of DLBCL cells with BPI plus histone deacetylase inhibitors such as Trichostatin A or SAHA (i.e. that hyperacetylate p53 and BCL6) resulted in a synergistic effect in killing DLBCL cells. Our studies demonstrated that p300 is a direct target gene of BCL6 with a critical role in determining DLBCL response to treatments that require activation of p53 and/or p53-family members. This can be capitalized on to develop powerful biological therapeutic regiments for DLBCL.

scholarly journals Increased p53 Acetylation By SIRT1 Inhibition Is Required for Optimal Activation of p53 Activity and Significantly Enhances the Ability of HDM2 Inhibitors to Target CML LSC

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 4521-4521
Author(s):  
Yann Pierre Kevin Duchartre ◽  
Ling Li ◽  
Tinisha McDonald ◽  
YinWei Ho ◽  
Yao-Te Hsieh ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Stem Cells ◽  
Transcriptional Activity ◽  
Target Genes ◽  
Myelogenous Leukemia ◽  
Growth And Survival ◽  
Cycle Arrest ◽  
Cd34 Cells ◽  
Induced Apoptosis ◽  
P53 Target Genes

Abstract BCR-ABL tyrosine kinase inhibitors (TKI) are effective in inducing remissions and prolonging survival in chronic myelogenous leukemia (CML) patients, but do not eliminate leukemia stem cells (LSCs) that are responsible for establishment, maintenance and recurrence of the disease. We have shown that the NAD-dependent SIRT1 deacetylase is overexpressed in CML LSC (Li et al., Cancer Cell, 21:266, 2013). SIRT1 participates in the maintenance, growth and treatment resistance of CML LSC by deacetylation and inhibition of the p53 pathway that regulates cell cycle and apoptosis. Inhibition of SIRT1 using RNAi and the small molecule SIRT1 inhibitor Tenovin-6 (TV-6) inhibits growth and survival of CML LSC by itself and results in enhanced targeting of LSC in combination with TKI treatment. The effects of SIRT1 inhibition are related at least in part to enhanced acetylation of the p53 protein associated with enhanced p53 transcriptional activity. Here we examined the efficacy of an alternative strategy to activate p53, using inhibition of the p53 regulatory protein HDM2, in activating p53 transcriptional activity and inhibiting CML LSC growth and survival compared to SIRT1 inhibition. Nutlin-3 (Nut-3) is a small molecule HDM2 inhibitor that disrupts the p53-HDM2 interaction which has proceeded to clinical trials. Treatment of CML CP CD34+ cells with Nut-3 (1, 2, 5µM) increased expression of the p53 target genes p21 (associated with cell cycle arrest) and NOXA and PIG3 (associated with apoptosis), inhibited proliferation and induced apoptosis to a significantly lesser extent than TV-6 (1, 2 µM) (Nut 5 µM vs TV 2 µM ; p<0.0003) . However, Nutlin-3 enhanced p53 target gene expression and inhibited proliferation and survival of normal CD34+ cells to a similar extent as CML CD34+ cells. This was in contrast to TV-6 which although inhibiting proliferation of both CML and normal CD34+ cells, selectively induced apoptosis in CML compared to normal CD34+ cells. Treatment of CML CD34+ cells with the combination of Nut-3 (2, 5µM) and TV-6 (1µM) significantly increased the expression of p53 target genes (p21, PIG3, NOXA), and enhanced apoptosis of CML CD34+ cells compared to Nut-3 or TV-6 alone. 32D-BCR-ABL cells transduced with lentivirus vectors expressing p53 shRNA demonstrated significantly reduced apoptosis following treatment with the combination of Nut-3 and TV-6 compared to cells expressing control shRNA, indicating that the effects of this treatment are p53 dependent. Our results indicate that enhancement of p53 acetylation by SIRT1 inhibition is required for optimal activation of p53 transcriptional activity and induction of apoptosis in CML LSC. These results further support SIRT1 as a valid therapeutic target in CML, and suggest that addition of SIRT1 inhibitors may significantly enhance the ability of HDM2 inhibitors to eliminate CML LSC. Table 1 : Effects of Nutlin-3, Tenovin-6 or combination on the expression of apoptosis/cell cycle arrest related-genes, apoptosis and proliferation in cord blood and CML CD34+ cells. Figure 1 Figure 1. SEM values ; significance, compared to controls: ***p<0.001. ****p<0.0001. Key words : Chronic Myelogenous Leukemia (CML), hematopoietic stem cells, p53, SIRT1. Disclosures No relevant conflicts of interest to declare.

scholarly journals PERP, an apoptosis-associated target of p53, is a novel member of the PMP-22/gas3 family

2000 ◽  
Vol 14 (6) ◽  
pp. 704-718 ◽  
Author(s):  
Laura D. Attardi ◽  
Elizabeth E. Reczek ◽  
Corinna Cosmas ◽  
Elizabeth G. Demicco ◽  
Mila E. McCurrach ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Target Genes ◽  
Sequence Similarity ◽  
Cell System ◽  
Dependent Manner ◽  
Apoptosis Pathway ◽  
Adenovirus E1a ◽  
Cycle Arrest ◽  
P53 Target Genes

The p53 tumor suppressor activates either cell cycle arrest or apoptosis in response to cellular stress. Mouse embryo fibroblasts (MEFs) provide a powerful primary cell system to study both p53-dependent pathways. Specifically, in response to DNA damage, MEFs undergo p53-dependent G1 arrest, whereas MEFs expressing the adenovirus E1A oncoprotein undergo p53-dependent apoptosis. As the p53-dependent apoptosis pathway is not well understood, we sought to identify apoptosis-specific p53 target genes using a subtractive cloning strategy. Here, we describe the characterization of a gene identified in this screen, PERP, which is expressed in a p53-dependent manner and at high levels in apoptotic cells compared with G1-arrested cells. PERP induction is linked to p53-dependent apoptosis, including in response to E2F-1-driven hyperproliferation. Furthermore, analysis of the PERP promoter suggests that PERP is directly activated by p53. PERP shows sequence similarity to the PMP-22/gas3 tetraspan membrane protein implicated in hereditary human neuropathies such as Charcot–Marie–Tooth. Like PMP-22/gas3, PERP is a plasma membrane protein, and importantly, its expression causes cell death in fibroblasts. Taken together, these data suggest that PERP is a novel effector of p53-dependent apoptosis.

scholarly journals The Selective Activation of p53 Target Genes Regulated by SMYD2 in BIX-01294 Induced Autophagy-Related Cell Death

PLoS ONE ◽  
2015 ◽  
Vol 10 (1) ◽  
pp. e0116782 ◽  
Author(s):  
Jia-Dong Fan ◽  
Pin-Ji Lei ◽  
Jun-Yi Zheng ◽  
Xiang Wang ◽  
Shangze Li ◽  
...  
Keyword(s):  
Cell Death ◽  
Target Genes ◽  
Selective Activation ◽  
Related Cell ◽  
P53 Target Genes
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