p53 gene mutations in human tumors Greenblatt et al. (1995) Cancer Res. 54: %

p53 and Ink4a are the two most frequently mutated genes in human tumors

p53 (low) p53 (high) Cell cycle arrest Apoptosis Cellular Stresses (e.g. DNA damage) The Basic Paradigm of p53 Function

The Discovery of p53

SV40 large T protein binds to p53

Li Fraumeni Syndrome An inherited neoplastic disease with autosomal dominant trait Characterised by multiple primary neoplasms in children and young adults A predominance of soft tissue sarcomas (e.g. breast)

Li Fraumeni Syndrome: Childhood and Adult Onset Cancers

Typical Li Fraumeni Syndrome Pedigree In approximately 70% of Li-Fraumeni cases, affected family members carry a germline mutation of one allele of the TP53 tumour suppressor gene.

Inactivation of p53 in Friend murine erythroleukemia

p53 Mutant Mice Develop Cancer

p53 Mutations in Human Tumors are Found with High Frequency In the DNA Binding Domain In 143 families reported: point mutations (85%) deletions (9%) splice mutations (3.5%) insertions (2%)

Ribbon ModelSpace Filling Model p53 Binds DNA The most common mutation changes arginine 248, colored red here. Notice how it snakes into the minor groove of the DNA (shown in blue and green), forming a strong stabilizing interaction. When mutated to another amino acid, this interaction is lost. Other key sites of mutation are shown in pink, including arginine residues 175, 249, 273 and 282, and glycine 245.

p53 Binds DNA as a Tetramer

p53 Functions in Cell Cycle Checkpoints

p53 Mutant Cells Lack Cell Cycle Checkpoint Function

p53 activates p21 (WAF1) El-Deiry et al. (1993) Cell 75:817

The Structure of RAD9 BRCT domains required for oligomerization in response to DNA damage BRCT domains are found in BRCA1 Rad9 and BRCA1 both may act as scaffolds FHA domains bind specific phosphopeptides Rad53=Chk2 Toh and Lowndes, Biochem Soc Trans : SCD=S/T Cluster Domain

The Function of RAD9 (Rad53=chk2) (Rad9 similar to BRCA1) (Mec1=ATM) Toh and Lowndes, Biochem Soc Trans :242-6.