The P53 Family

This volume offers a comprehensive review of the functions of the p53 family. The contributors examine the normal roles of these transcription factors, their evolution, the regulatory mechanisms that control p53 activity, and the part played by p53 mutations in tumorigenesis.

Limiting genome replication to once per cell cycle is vital for maintaining genome stability. Although polyploidization is of physiologically importance for several specialized cell types, inappropriate polyploidization is believed to promote aneuploidy and transformation. A growing body of evidence indicates that the surveillance mechanisms that prevent polyploidization are frequently perturbed in cancers. Progress in the past several years has unraveled some of the underlying principles that maintain genome stability. This book brings together leaders of the field to overview subjects relating to polyploidization and cancer.

The p53 protein plays a critical role in tumor suppression, as evidenced by its high mutation rate in human tumors and the observation that p53-null mice get cancer with 100% penetrance. p53 is a stress sensor that responds to cellular assaults, such as DNA damage or serum starvation, by inducing downstream effector functions, including apoptosis and cell cycle arrest. p53 itself is a transcription factor that promotes its downstream functions through its ability to transcriptionally activate downstream targets genes, although p53 also has transactivation-independent functions. However, the role that p53 plays in development and the role its target genes play in development and tumor suppression are not well defined. First, we sought to analyze the role of p53 transcriptional activation in development. Using knock-in mice expressing a p53 transactivation domain mutant (p5325,26,53,54), which does not bind Mdm2, we found that developmental defects caused by unrestrained p53 require p53's transactivation ability, as p5325,26,53,54/- mice are viable. Surprisingly, we also found that expression of p5325,26,53,54 in the presence of wild-type p53 induces embryonic lethality and a spectrum of phenotypes characteristic of a congenital syndrome known as CHARGE, including coloboma, inner and outer ear malformations, heart outflow tract defects, and craniofacial defects. We find that p5325,26,53,54 mutant protein is able to stabilize and hyperactivate wild-type p53, driving p53 to inappropriately induce target gene expression and trigger cell-cycle arrest and apoptosis during development. We further find that p53 is activated in CHD7-mutant CHARGE syndrome patient samples and upon genetic ablation of Chd7 in mouse cells. Additionally, p53-heterozygosity is able to partially rescue Chd7 null embryonic phenotypes, indicating that Chd7 deficiency provokes p53 activation and p53-dependent phenotypes. Thus, through the use of p5325,26,53,54 mice, we have uncovered a critical role for transactivation in provoking developmental defects induced by unrestrained p53 and revealed a novel and critical role for p53 in promoting human CHARGE syndrome. Subsequently, we sought to uncover the role of the p53 family as a whole, including the two related transcription factors p63 and p73, in development. While p53 null mice are viable, p63 null mice are perinatal lethal with epidermal and limb defects and p73 null mice typically die within the first two months of life and manifest neuronal defects. To determine if the absence of more severe developmental phenotypes is due to redundancy between the p53 family members, we bred and analyzed compound knockout mice. Analysis of compound knockout embryos revealed viability of all double knockout embryos (p53p63, p53p73, and p53p63) and five allele knockout embryos (double knockout and heterozygous for the remaining gene) during embryogenesis with the only defects detected being accounted for by loss of single p53 family members. Surprisingly, we also identified a single viable triple knockout at E10.5 with normal morphology except for hypoplastic cardiac cushions. Thus, these results suggest that p53 family members are neither critical nor redundant for relatively normal development. We next sought to determine the role of the p53 target gene Siva in both development and tumorigenesis. Our lab previously identified Siva as a p53 target gene critically important for p53-dependent apoptosis. Here we generated a Siva knockout mouse strain using gene-trap technology. Analysis of homozygous Siva mutant mice, revealed mid-gestational embryonic lethality associated with both embryonic and extra-embryonic defects, including developmental delay and defects of neural tube closure, yolk sac vasculature, and chorioallantoic fusion. The defects associated with Siva deficiency resembled those in embryos with loss of key components of TGF [beta]/SMAD signaling pathways, and notably, Siva null embryos displayed reduced SMAD protein levels and aberrant SMAD target gene expression. Thus, loss of Siva results in embryonic lethality associated with defects in SMAD signaling. Due to the embryonic lethality associated with Siva loss, we went on to generate a conditional Siva knockout mouse strain for studies of Siva in tumor suppression. Using a Kras-dependent non-small cell lung cancer model, we found surprisingly that Siva is necessary for efficient tumorigenesis in this model, as Siva-deficiency results in reduced tumor number and tumor burden. Additionally, Siva knockdown in non-small cell lung cancer cell lines resulted in reduced proliferation and tumorigenic potential. Furthermore, Siva loss inhibited mTOR signaling, induced autophagy, and reduced mitochondrial respiration, suggesting that Siva is necessary for normal metabolic function to promote proliferation. Moreover, Siva levels have prognostic ability for human non-small cell lung cancer patient survival. Therefore, our findings reveal that the p53 target gene Siva enables Kras-dependent lung cancer development and is necessary for oxidative phosphorylation, and that Siva levels could be used to estimate the prognosis of non-small cell lung cancer patient survival. Collectively, these results significantly expand our knowledge of the role of p53, the p53 family, and the p53 target gene Siva in development as well as the role of Siva in tumorigenesis. We found that unrestrained p53 results in developmental defects resembling CHARGE syndrome and that compound loss of the p53 family members does not promote profound developmental phenotypes other than those observed in single mutants. Moreover, we found that Siva is necessary for both proper embryonic development and efficient non-small cell lung cancer tumor development through roles in SMAD signaling and metabolism, respectively.

The extremophile Alvinella pompejana, an annelid worm living on the edge of hydrothermal vents in the Pacific Ocean, is an excellent model system for studying factors that govern protein stability. Low intrinsic stability is a crucial factor for the susceptibility of the transcription factor p53 to inactivating mutations in human cancer. Understanding its molecular basis may facilitate the design of novel therapeutic strategies targeting mutant p53. By analyzing expressed sequence tag (EST) data, we discovered a p53 family gene in A. pompejana. Protein crystallography and biophysical studies showed that it has a p53/p63-like DNA-binding domain (DBD) that is more thermostable than all vertebrate p53 DBDs tested so far, but not as stable as that of human p63. We also identified features associated with its increased thermostability. In addition, the A. pompejana homolog shares DNA-binding properties with human p53 family DBDs, despite its evolutionary distance, consistent with a potential role in maintaining genome integrity. Through extensive structural and phylogenetic analyses, we could further trace key evolutionary events that shaped the structure, stability, and function of the p53 family DBD over time, leading to a potent but vulnerable tumor suppressor in humans.

All of us have lurking in our DNA a most remarkable gene, which has a crucial job - it protects us from cancer. Known simply as p53, this gene constantly scans our cells to ensure that they grow and divide without mishap, as part of the routine maintenance of our bodies. If a cell makes a mistake in copying its DNA during the process of division, p53 stops it in its tracks, summoning a repair team before allowing the cell to carry on dividing. If the mistake is irreparable and the rogue cell threatens to grow out of control, p53 commands the cell to commit suicide. Cancer cannot develop unless p53 itself is damaged or prevented from functioning normally. Perhaps unsurprisingly, p53 is the most studied single gene in history. This book tells the story of medical science's mission to unravel the mysteries of this crucial gene, and to get to the heart of what happens in our cells when they turn cancerous. Through the personal accounts of key researchers, p53: The Gene that Cracked the Cancer Code reveals the fascination of the quest for scientific understanding, as well as the huge excitement of the chase for new cures - the hype, the enthusiasm, the lost opportunities, the blind alleys, and the thrilling breakthroughs. And as the long-anticipated revolution in cancer treatment tailored to each individual patient's symptoms begins to take off at last, p53 remains at the cutting edge. This timely tale of scientific discovery highlights the tremendous recent advances made in our understanding of cancer, a disease that affects more than one in three of us at some point in our lives.

The discovery of microRNAs and its role as gene expression regulators in human carcinogenesis represents one of the most important scientific achievements of the last decade. More recently, other non-coding RNAs have been discovered and its implications in cancer are emerging as well, suggesting a broader than anticipated involvement of the non-coding genome in cancer. Moreover, completely new and unexpected functions for microRNAs are being revealed, leading to the identification of new anticancer molecular targets. This book represents a comprehensive guide on non-coding RNAs and cancer, spanning from its role as cancer biomarkers, to providing the most useful bioinformatic tools, to presenting some of the most relevant discoveries, which indicates how these fascinating molecules act as fine orchestrators of cancer biology.

​​The Hippo signaling pathway is rapidly gaining recognition as an important player in organ size control and tumorigenesis, and many leading scientists are showing increased interest in this growing field and it's relation to cancer. The chapters in this volume cover virtually all aspects of tumor biology, because members of the Hippo Pathway have been associated with numerous well-established cell signaling pathways, just to name a few; Ras, Wnt, TGFbeta and p53. Moreover, Hippo signaling is not solely involved in regulating “classic” tumor characteristics such as cell proliferation, survival and growth, but is also diversely involved in cell-autonomous and non-cell-autonomous differentiation, migration and organ size control. The primary audience are researchers interested in basic science in the areas of tumor suppression, cell cycle and size regulation, development and differentiation.

"The embryonic stress response to DNA damage during organogenesis was examined using the model teratogen, hydroxyurea. Intraperitoneal administration of hydroxyurea (400 mg/kg or 600 mg/kg) to timed pregnant CD-1 mice on gestational day 9 significantly affected the expression of ~1300 transcripts in the embryo within three hours. Pathway analysis predicted that the P53 signaling pathway was the most activated in response to hydroxyurea. The steady-state levels of P53 and its phosphorylation increased dramatically in hydroxyurea-exposed embryos. The nuclear localization of phosphorylated P53 was increased significantly in the embryo heart and rostral and caudal neuroepithelia. Hydroxyurea also induced P53 transcriptional activity, leading to the upregulation of P53 downstream targets involved in DNA damage repair, cell cycle arrest and apoptosis. Using a Trp53 null transgenic mouse model, the effects of treatment with hydroxyurea on P53 family members, P63 and P73, were determined in the gestational day 9 embryo. Appreciable amounts of P63 and P73 were detected under normal conditions; hydroxyurea did not affect their steady-state or phosphorylation levels. Trp63 and Trp73 transcript levels were affected by hydroxyurea treatment, although only Trp73 levels were P53-dependent. As transcription factors, neither P63 nor P73 were capable of compensating for the absence of P53 in upregulating the expression of downstream targets involved in cell cycle arrest (Cdkn1a, Rb1) or apoptosis (Fas, Pmaip1) in response to hydroxyurea exposure. Hydroxyurea induction of Caspase-3 and MST-1 cleavage, markers for apoptosis and DNA damage repair, required the presence of P53. Thus, P53 is the main member of the P53 family that responds to genotoxic stress in the organogenesis-stage embryo.To determine whether P53 acts as a suppressor or inducer of hydroxyurea embryotoxicity, Trp53+/+, Trp53+/- and Trp53-/- embryos were exposed in utero on gestational day 9 with saline or hydroxyurea (200 or 400 mg/kg). On gestational day 18, Trp53-/- fetuses from the saline treatment group were found to exhibit a higher rate of malformations compared to their Trp53+/+ littermates. Hydroxyurea treatment induced a dose-dependent increase in resorptions and congenital malformations; these included hypoplastic tails and fore- and hind-limb syndactly, oligodactyly and amelia. In the 200 mg/kg treatment group, hydroxyurea exposed fetuses lacking P53 had a higher rate of malformations than their Trp53+/+ littermates and the rate of resorptions was elevated in these fetuses after exposure to 400 mg/kg hydroxyurea. Thus, the organogenesis stage embryo responds to hydroxyurea-induced stress by activating the P53 signaling pathway that mediates DNA damage repair, cell cycle arrest and apoptotic factors to suppress hydroxyurea embryotoxicity. " --

Written with the busy practice in mind, this book delivers clinically focused, evidence-based gynecology guidance in a quick-reference format. It explores etiology, screening, tests, diagnosis, and treatment for a full range of gynecologic health issues. The coverage includes the full range of gynecologic malignancies, reproductive endocrinology and infertility, infectious diseases, urogynecologic problems, gynecologic concerns in children and adolescents, and surgical interventions including minimally invasive surgical procedures. Information is easy to find and absorb owing to the extensive use of full-color diagrams, algorithms, and illustrations. The new edition has been expanded to include aspects of gynecology important in international and resource-poor settings.

TP53 gene mutations are present in more than half of all human cancers. The resulting proteins are mostly full-length with a single amino acid change and are abundantly expressed in cancer cells. Some of the mutant p53 proteins gain oncogenic functions (GOF) through which it actively contribute to the aberrant cell proliferation, increased resistance to apoptotic stimuli and ability to metastasize. Gain of function mutant p53 proteins can transcriptionally regulate the expression of a large plethora of target genes. This mainly occurs through the formation of oncogenic transcriptional competent complexes that include mutant p53 protein, known transcription factors, posttranslational modifiers and scaffold proteins. Mutant p53 protein can also transcriptionally regulate the expression of microRNAs, small non-coding RNAs that regulate gene expression at the posttranscriptional level. Each microRNA can putatively target the expression of hundred mRNAs and consequently impact on many cellular functions. Thus, gain of function mutant p53 proteins can exert their oncogenic activities through the modulation of both non-coding and coding regions of human genome. Over the past 3 decades, the regulation of p53 has been extensively studied. However, the regulation of mutant p53 remained largely unexplored. This snapshot focuses on recent discovery of mutant p53 GOF and regulation.