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p53 Structure, Function and Therapeutic Applications Provider: Dr.Davood Nourabadi(PhD,medical physiology) mdphysiology.persianblog.ir 2

Common names p53 cellular tumor antigen p53 phosphoprotein p53 tumor suppressor p53 Tumor protein p53 3

Discovery 4

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Cloning of the p53 gene, followed by successive experiments showed that it is actually a tumor suppressor gene Moshe Oren Arnold Levine 6

Gene a 20-Kb gene containing 11 exons and 10 introns,which is located on the small arm of chromosome 17.This gene belongs to a highly conserved gene family containing at least two other members, p63 and p73. one of the most frequently mutated gene in human cancers 7

p53 protein 393aa MW:43.7 KDa Gene: TP53 p53 belongs to an unique protein family which includes three members: p53, p63 and p73. 8

Cont.. p53 seems to have evolved in higher organisms to prevent tumor development, whereas p63 and p73 have clear roles in normal developmental biology they show considerable homology with p53. all three of these proteins can induce apoptosis 9

53 K

p53 have 7 domain include: 1.An acidic N-terminus transcription- activation domain (TAD) or activation domain 1 (AD1) 2.Activation domain 2 (AD2) 3.Proline rich domain Structure of p53 11

4. Central DNA-binding core domain (DBD) most highly conserved region 5. Nuclear localization signaling domain(NLS) 6. Homo-oligomerisation domain (OD) 7. C-terminal Cont... 12

Various intracellular and extracellular stimuli DNA damage (ionizing radiation, UV radiation, application of cytotoxic drugs or chemotherapeutic agents, and infectious virus) Heat shock Hypoxia Oncogene overexpression p53 is activated and triggers diverse biological responses, both at the level of a single cell as well as in the whole organism 13

Damage to DNA: activation of protein kinase including ATM (Ataxia telangiectasia mutated) and ATR (Ataxia telangiectasia and Rad3-related), that enzymes phosphorylate of p53 activated CDKN1A geneproduction p21 14

In response to various types of stress, p53 is accumulated in the nucleus and binds to specific sites in the regulatory regions of p53- responsive genes, and then strongly promotes the transcription of such genes 15

The regulation of p53 level and activity Under normal circumstances, wt p53 is maintained at very low concentrations within the cells and exists mainly in an inactive latent form. In normally growing cells, the half-life of p53 is limited to minutes, whereas cellular stress or exposure to DNA damaging agents prolongs it to hours 16

Activated genes by p53 include: Genes involved in cell cycle arrest DNA repair Apoptosis Senescence-related genes, such as genes for p21Waf1/Cip1, Gadd45 (growth arrest and DNA-damage inducible protein 45) 17

Genes which may be repressed by p53 bcl-2 bcl-X Cyclin B1 MAP4 Survivin 18

p53 locating at the crossroads of complex networks of stress response pathways 19

Function of p53 Its anti-cancer role, p53 works through several mechanisms: It can activate DNA repair proteins when DNA has sustained damage. It can arrest growth by holding the cell cycle at the G1/S regulation point on DNA damage recognition. It can initiate apoptosis, the programmed cell death, if DNA damage proves to be irreparable. 20

Cell-cycle regulation by p53 p53 can induce cell cycle arrest in the G1, G2 and S phases of the cell cycle it provides additional time for the cell to repair genomic damage before entering the critical stages of DNA synthesis and mitosis. Cyclin-dependent kinase (CDK) inhibitor, p21 is perhaps the best known downstream target of p53 among the various p53 target gene products identified. p21 binds cyclin-CDK complexes. 21

p53 Cell cycle control involves several checkpoints and checkpoint (molecular breaking) mechanisms 22

MDM2: murine double minute which in humans is identified as Hdm2 23

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Induction of apoptosis Apoptotic gene: products of these genes may induce apoptosis through either an extrinsic pathway or an intrinsic pathway, namely the death receptor pathway and the mitochondrial pathway, respectively. It has been suggested that the intrinsic apoptotic pathway is primarily utilized in p53-mediated apoptosis, whereas the extrinsic pathway is used to augment the apoptotic response. 27

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The intrinsic apoptotic pathway is engaged when cells are challenged by stress and is dominated by the Bcl-2 family proteins. In the regulation of the intrinsic pathway, pro-apoptotic gene products such as Bax, Bid localize to the mitochondria and promote the loss of mitochondrial membrane potential and release of cytochrome c, resulting in the formation of the apoptosome complex with Apaf-1 and caspase 9. 29

In cell death extrinsic pathway, p53 can promote apoptosis through activation of the death receptors located at the plasma membrane and lead to inhibition of the production of IAPs (inhibitor of apoptosis proteins). 30

Therapeutic applications of p53 p53 can be a useful biomarker in carcinogenesis. useful in studying the efficacy of chemopreventive agents p53-MDM2 interaction as the basis of a drug development strategy. 31

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