Lecture Summaries

1 Introduction to the course First, we will get to know each other! Then we will go over the syllabus, including expectations and goals of the class, an overview of the course, and an introduction to the first two papers. We will also discuss strategies for reading primary scientific papers.
2 p53 first described p53 was first identified as a cellular protein complexed with the large T protein of the cancer-causing simian virus 40 virus (SV40). When researchers made anti-sera (antibody) directed against the virus T protein (antigen) and precipitated the protein complex generated by the antibody and T antigen, a non-viral protein with a molecular mass of around 53 kDa came along for the ride. We will discuss the serendipitous discovery of p53 and the early hypothesis that this cellular protein might play a broad role in cancer development.
3 An oncogene turned out to be a tumor suppressor Oncogenes are genes that when mutated or amplified promote cancer development. In the early years, p53 was thought to be a oncogene. Several research labs cloned the p53 gene from cancer cells and showed that these cancer-derived p53 sequences could enhance tumor formation in cells. However, p53 derived from wild-type non-cancer cells repressed cell growth. We will discuss how this enigma was solved by comparing the DNA sequences of the various p53 clones used in the laband determined that those clones actually carried mutations in the p53 coding region. This observation provided the first indication that p53 is a tumor suppressor gene.
4 p53 mutation in cancer A tumor suppressor gene has two hallmarks: humans carrying loss-of-function mutations in that gene should be susceptible to cancer, and its loss should confer a cancer-prone phenotype in experimental animal models. We will discuss how p53 mutations were found in the hereditary Li-Fraumeni syndrome, a genetic disease characterized by early-onset cancers. We will also discuss the observation that, in human colorectal tumors, the wild-type p53 gene is frequently lost by mutations, deletions or a combination of both.
5 p53 and cancer mouse models Mouse cancer models provide the second important evidence that p53 is a tumor suppressor gene. A knockout mouse is a genetically engineered mouse in which one or more genes have been deleted through a targeted mutation. Knockout mice are important for studying the role of genes in cancer and other diseases. p53-knockout mice, first described in 1992, frequently develop cancer (mostly lymphomas, tumors derived from white blood cells). We will discuss how these p53-knockout mice were generated and how their cancer biology was characterized.
6 p53 and programmed cell death (apoptosis) Programmed cell death (apoptosis), a natural way by which cells die, is a tightly controlled process required for embryonic development and adult tissue homeostasis. Apoptosis deregulation is a hallmark of multiple diseases, including cancer, in which cells that should die instead survive and proliferate. We will discuss the general features of apoptosis, the main constituents of the apoptotic machinery and how p53 functions as a master regulator of apoptosis.
7 p53 and cell cycle regulation The cell cycle consists of the series of events that take place in a cell as it divides and replicates. The cell cycle is tightly regulated in normal cells. Cancer often involves an increased rate of cell division and dysregulation of the cell cycle. We will discuss how p53 regulation of the cell cycle was discovered and how a key cell cycle gene, p21WAF1, was found to be a direct transcriptional target of p53.
8 p53, DNA damage and genome integrity Cells maintain a genome capable of replication and self repair. A genome consists of chromosomes, each with two complementary strands of DNA. The DNA is under constant assault from stress, such as radiation and environmental mutagens. Cancer cells exhibit increased genomic instability, such as chromosomal rearrangements and duplications. Cells normally will stop in the cell cycle if DNA is damaged. Several proteins have been identified that act to halt the cell cycle until DNA damage is repaired. Among these proteins p53 has been shown to maintain genome integrity by halting the cell cycle of damaged cells and by promoting the action of DNA repair genes. This function of p53 has led to, its being known as the "guardian of our genome."
9 Field trip Trip to a pharmaceutical company
10 p53 and Mdm2 A common means to explore the biochemical function of a protein of interest is by identifying other proteins with which it interacts. Probably the most important protein–protein interaction of p53 was discovered in 1992, when Mdm2 (previously described as a putative oncogene) was shown to bind tightly to p53 and inhibit its biochemical activity. Since then, Mdm2 has emerged as the key cellular regulator of p53, effectively down-regulating p53 protein in normal cells. We will discuss how Mdm2 was discovered and how Mdm2 forms a negative feedback loop with p53.
11 p53 and microRNA MicroRNAs are small RNAs that are not translated into proteins. microRNAs are generated from large RNAs and recognize and bind to target RNAs to inhibit their translation. The human genome encodes >500 microRNAs, many of which play important roles in development and disease. We will discuss the mir-34 family of microRNAs, identified as p53-regulated microRNAs with important functions in cell cycle regulation and cell death.
12 p53 restoration therapy The p53 pathway has been the target of an active area of drug discovery. Because p53 has potent anti-cancer effect by inducing apoptosis and cell cycle arrest, restoration of p53 has been proposed as a potential cancer therapy. We will discuss genetic mouse models in which p53 can be re-activated to induce tumor shrinkage. A small molecule drug that re-folds mutant p53 into its functional tumor suppressive structural conformation will be discussed.
13 Final class After the oral presentations, we will discuss an overview of what has been learned about the connections between p53 and cancer throughout the semester.