Mutation of the p53 gene is very frequent in breast cancer. In normal cells induction of wild-type p53 function leads to either cell cycle arrest or cell death. Loss of this function can contribute to oncogenic cell transformation. Additionally the presence of mutant forms of p53 in breast tumor cells may actually facilitate the process of tumorigenesis. The properties of mutant p53 proteins in vitro and in breast tumor cell lines will be studied, experiments will focus on analysis of the structure and modification of mutant p53 proteins as well as the effect of cellular signalling on p53 function. Additionally it is planned to establish breast cell lines expressing inducible mutant p53 to determine the effect of such mutants on parameters of cell cycle, growth and death. We have discovered that all mutant forms of pS3 tested are capable of binding specifically to p53 response elements present in p53 target genes at lower but not at physiological temperatures. Furthermore, we have identified a means by which such binding is stabilized at the higher temperature. This will allow us to explore means to develop molecules that might have the outcome of converting pS3 in breast tumor cells from mutant to wild-type in function. One approach will be to develop a yeast- based screen for mutant p53 modifying genes. Such reagents would have clear therapeutic advantages.

The current year (2004) marks the Silver Anniversary of the discovery of the p53 tumor suppressor. The emerging ?eld ?rst considered p53 as a viral antigen and then as an oncogene that cooperates with activated ras in transforming primary cells in culture. Fueling the concept of p53 acting as a transforming factor, p53 expression was markedly elevated in various transformed and tumorigenic cell lines when compared to normal cells. In a simple twist of fate, most of the studies conducted in those early years inadvertently relied on a point mutant of p53 that had been cloned from a normal mouse genomic library. A bona ?de wild-type p53 cDNA was subsequently isolated, ironically, from a mouse teratocarcinoma cell line. A decade after its discovery, p53 was shown to be a tumor suppressor that protects against cancer. It is now recognized that approximately half of all human tumors arise due to mutations within the p53 gene. As remarkable as this number may seem, it signi?cantly underrepresents how often the p53 pathway is targeted during tumorigenesis. It is my personal view, as well as many in the p53 ?eld, that the p53-signaling pathway is corrupted in nearly 100% of tumors. If you are interested in understanding cancer and how it develops, you must begin by studying p53 and its pathway. After demonstrating that p53 functions as a tumor suppressor the ?eld exploded and p53 became a major focus of scientists around the world.

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.

Approximately 50% of human cancers have accumulated missense mutations in the gatekeeping tumor suppressor protein p53, usually resulting in genomic instability and a very poor prognosis. The wild-type p53 protein is required for assessing DNA damage in cells and making the decision to either induce cell cycle arrest to facilitate DNA repair, or to induce a suicide response in those cells with irreparable damage. In human tumors, many hot-spot mutations are found within the DNA-binding domain of p53, rendering it incapable of sequence-specific transactivation of target genes such as p2l, bax, and mdm2. Some of these mutants, in addition to having dominant-negative functions, also gain novel functions by interacting with proteins differently from the wild-type p53 protein. One such gain-of-function p53 mutant possesses an Arg to His substitution at codon l75 (l72 in mice) and has been shown to be involved in the dysregulation of centrosome duplication leading to abnormal mitoses and subsequent aneuploidy. Because centrosome abnormalities and aneuploidy are often seen in high-grade breast tumors, unraveling the mechanism behind the involvement of p53l72 R-H in centrosome dysregulation will help us to understand the progression of mammary carcinogenesis. In order to identify potential indirect target genes regulated by this mutant, we employed a suppressive subtractive hybridization technique to generate a cDNA library specific to p53 null mammary epithelial cells (MECs) expressing the l72 R-H mutant. cDNA made from p53 null mammary epithelial cells transiently transfected with wild-type p53 was subtracted from cDNA made from mutant p53 transfected cells. The subtraction procedure generated a pool of cDNAs differentially expressed in the presence of the mutant protein; many interesting genes were revealed to be candidates for regulation by mutant p53. Some of these include developmental, metabolic, transcriptional,

This book provides the readers with an overview of research on p53, which has been shown to play a role in numerous crucial biological pathways in normal and cancer cells. Leading scientist in the field, who have all made direct contributions to the understanding of the molecular events underpinning p53 function, have been invited to contribute the various chapters, which discuss the current knowledge of the signaling cascades that are activated by mutations in p53 and overexpression of MDM2, frequently found in human cancer and are major causes of oncogenesis. This book features chapters on the molecular basis of oncogenesis induced by gain of function mutation of p53, signaling pathways induced by MDM2 overexpression, control of mutant or wild-type p53 function by MDM2 and MDMX, p53 mutation in hereditary cancer and structural aspects that activate mutant p53 which can be targeted by drug therapy. This book should be useful for scientists at all levels.

Decades of research on the tumor suppressor p53 have revealed that it plays a significant role as a "guardian of the genome," protecting cells against genotoxic stress. In recent years, p53 research has begun to move into the clinic in attempts to understand how p53 is frequently inactivated in-and sometimes even promotes-human cancer. Written and edited by experts in the field, this collection from Cold Spring Harbor Perspectives in Medicine covers the rapid progress that has recently been made in basic and clinical research on p53. The contributors review new observations about its basic biology, providing updates on the functions of its isoforms and domains, the myriad stresses and signals that trigger its activation or repression, and its downstream effects on genome stability and the cell cycle that enforce tumor suppression in different cell and tissue types. They also discuss how p53 dysfunction contributes to cancer, exploring the various inherited and somatic mutations in the human TP53 gene, the impact of mutant p53 proteins on tumorigenesis, and the prognostic value and clinical outcomes of these mutations. Drugs that are being developed to respond to tumors harboring aberrant p53 are also described. This book is therefore essential reading for all cancer biologists, cell and molecular biologists, and pharmacologists concerned with the treatment of this disease.

This work serves as an introduction to the applications of molecular biology in the field of oncology. It provides a basic understanding of the genetic events involved in fully developed human cancer, including research into inherited and acquired gene defects initiating new neoplasms and the subsequent genetic alterations involved in tumor progression. Some of the specific topics explored include gene control, molecular therapy and antibodies, drug resistance, growth factors and receptors, and tumor biology. While intended primarily as an advanced text for oncologists, postgraduate molecular geneticists and molecular biologists, the book will certainly be of interest to other researchers who frequently encounter cancer in their practice.