p53信号通路

p53 Signaling

RT² Profiler™ PCR Array

p53 Signaling Pathway PCR Array

Cellular Senescence PCR Array

DNA Damage Signaling Pathway PCR Array

Cell Cycle PCR Array

SureSilencing RNAi

p53 Signaling Pathway Gene RNAi

Cellular Senescence Gene RNAi

DNA Damage Signaling Pathway Gene RNAi

Cell Cycle Gene RNAi

Cignal™ Reporter Assays

p53 Pathway Reporter Assay Kit

E2F Reporter Assay Kit

EGR1 Reporter Kit

p53 is a tumour suppressor protein that regulates the expression of a wide variety of genes involved in Apoptosis, Growth arrest, Inhibition of cell cycle progression, Differentiation and accelerated DNA repair or Senescence in response to Genotoxic or Cellular Stress. As a transcription factor, p53 is compos ed of an N-terminal Activation Domain, a central specific DNA Binding Domain, and a C-terminal Tetramerization Domain, followed by a Regulatory Domain rich in basic Amino acids. Having a short half-life, p53 is normally maintained at low levels in unstress ed mammalian cells by continuous ubiquitylation and subsequent

degradation by the 26S Proteasome. Nonphosphorylated p53 is ubiquitylated by the MDM2 (Mouse Double Minute-2) ubiquitin ligase. MDM2 binding inactivates p53 by two mechanisms. First, MDM2 binds to the transactivation domain of p53, precluding interaction with the transcriptional machinery. Second, this binding mediates the covalent attachment of ubiquitin to p53. Ubiquitylated p53 is then degraded by the Proteasome. Thus MDM2 acts as a major reg ulator of the tumor suppressor p53 by targeting its destruction. When the cell is confronted with stress like DNA damage, Hypoxia, Cytokines, Metabolic changes, Vi ral infection, or Oncogenes, however, p53 ubiquitylation is suppressed and p53 accumulates in the nucleus, where it is activated and stabilized by undergoing multiple covalent modifications including Phosphorylation and Acetylation (Ref.1 & 2).

Phosphorylation of p53 mostly occurs in the N-terminal activation domain at the Ser6, Ser9, Ser15, Thr18, Ser20, Ser33, Ser37, Ser46, Thr55, and Thr81 residues, with some phosphorylation occurring in the C-terminal linker and basic regions at Ser315, Ser371, Ser376, Ser378, and Ser392. Phosphorylation on most of these sites is induced by DNA damage, with som e, such as Thr55 and Ser376, being repressed upon genotoxic stress. p53 phosphorylation is mediated by several cellular kinases including Chks (Checkpoint Kinases), CSNK1-Delta (Casein Kinase-1-Delta), CSNK2 (Casein Kinase-2), PKA (Protein Kinase A), CDK7 (Cyclin-Dependent Kinase-7), DNA-PK (DNA-Activated- Protein Kinase), HIPK2 (Homeodomain-Interacting Protein Kinase-2), CAK (CDK-Activating Kinase), p38 and JNK (Jun NH2-terminal kinase). Notably, phosphorylation at Ser15 by ATM (Ataxia Telangiectasia Mutated Gene)/ATR (Ataxia-Telangiectasia and Rad3 Related), either directly or through Chk1 (Cell Cycle Checkpoint Kinase-1)/Chk2 (Cell Cycle Checkpoint Kinase-2), or at Ser20 by Chk1/Chk2 has been shown to alleviate the inhibition or degradation of p53, leading to p53 stabilization and activation. The phosphorylation-induced p53 stabilization and activation are mediated through multiple mechanisms and may vary according to the cellular context or microenvironment. HIF-1Alpha (Hypoxia-Inducible Factor-1-Alpha) has been implicated to be involved in p53 stabilization, the precise mechanism by which HIF-1Alpha regulates p53-mediated function remains unknown. Recently, the interaction between p53 and HIF-1Alpha was reported to evoke HIF-1Alpha degradation. Members of the PIAS (Protein Inhibitor of Activated STAT) protein family have also been found to interact with p53. PIAS1 and PIAS-Gamma function as SUMO (Small Ubiquitin Related Modifier-1) ligases for p53. Moreover, the RING finger domain of PIAS1 binds to the C-terminus of the tumor suppressor p53 and catalyzes its sumoylation, a modification which represses p53 activity on a reporter plasmid containing consensus p53 DNA binding sites. PML (Promyelocytic Leukemia) also activates p53 by recruiting it to multiprotein complexes termed PML-nuclear bodies. PML is a tumor suppressor protein and the major component of multiprotein nuclear complexes that have been variably termed Kremer bodies, ND10, PODs (for PML Oncogenic Domains), and PML-NBs (PML-Nuclear Bodies). PML binds directly with p53 and recruits it to PML-NBs. Recruitment to PML-NBs activate p53 by bringing it in close proximity with CBP (CREB-Binding Protein) /p300. BRCA1 (Breast Cancer-1 Gene) and p53 can also physically associate, both in vitro and in vivo and function in a common pathway of tumor suppression. The ability of BRCA1 to biochemically modulate p53 function suggests that this may be a

fundamental role of BRCA1 in tumor suppression (Ref.3, 4 & 5).

Another important modification of p53 is acetylation. p53 is specifically acetylated at Lys370, Lys372, Lys373, Lys381, and Lys382 by p300/CBP and at Lys320 by PCAF (p300/CBP-associated factor). Acetylation has been shown to augment p53 DNA binding, and to stimulate p53-mediated transactivation of its downstream target genes through the recruitment of coactivators. Acetylation may also regulate the stability of p53 by inhibiting its ubiquitination by MDM2. In vivo, acetylation at Lys320, Lys373, and Lys382 is induced by many genotoxic agents, including UV-radiation, IR (Ionizing Radiation), hypoxia, oxidative stress, and even depletion of ribonucleotide pools. p53 can also be deacetylated by HDAC1 (Histone Deacetylase-1) and SIRT1. Human SIRT1 is an enzyme that deacetylates the p53 tumor suppressor protein and has been suggested to modulate p53-dependent functions including DNA damage-induced cell death. p53 deacetylation has been suggested to down-regulate the activation of genes such as Bax and p21WAF1. Phosphorylation and acetylation are interdependent. In deed, phosphorylation at the p53

N-terminus has been shown to enhance its interaction with acetylase p300/CBP and to potentiate p53 acetylation. Activated p53 functions effectively as a transcription factor and induces transcription of several genes. The D NA targets of p53 are consensus