Question 1

What does TP53 do?

Accepted Answer

TP53 encodes p53, a transcription factor that acts as the genome's central stress sensor. When DNA is damaged, p53 halts the cell cycle at the G1/S checkpoint via transcriptional activation of p21 (CDKN1A), buying time for repair. If damage is irreparable, p53 shifts its programme toward apoptosis by upregulating BAX, PUMA, and NOXA.

Question 2

Is TP53 a tumor suppressor gene or oncogene?

Accepted Answer

TP53 is a tumor suppressor gene — it is loss of function, not gain of function, that drives cancer. Wild-type p53 actively blocks tumour development; the more than 50% of cancers that carry TP53 mutations lose this brake, allowing genomic instability to accumulate unchecked.

Question 3

What happens when TP53 is mutated in cancer?

Accepted Answer

Cells lacking functional p53 fail to arrest the cell cycle after DNA damage, permitting mutations to accumulate and propagate. TP53 mutations are found in over 50% of all human cancers and are strongly associated with genomic instability, chemotherapy resistance, and poor prognosis.

Question 4

What is Li-Fraumeni syndrome?

Accepted Answer

Li-Fraumeni syndrome is a hereditary cancer predisposition disorder caused by germline TP53 mutations. Carriers face nearly 100% lifetime cancer risk, developing sarcomas, breast cancers, brain tumours, and adrenocortical carcinomas — often at unusually young ages and frequently as multiple primary cancers.

Question 5

Why is TP53 called the guardian of the genome?

Accepted Answer

The phrase reflects p53's role as the hub integrating signals from DNA double-strand breaks (via ATM), oncogene activation (via ARF), and hypoxia (via HIF1A), then deciding whether to arrest, repair, senesce, or eliminate the affected cell. No other single protein controls so many cancer-relevant decisions.

Question 6

What are gain-of-function TP53 mutations and what oncogenic properties do they confer?

Accepted Answer

Gain-of-function (GOF) TP53 mutations — primarily at hotspots R175H, R248W, R248Q, R273H, and R282W — not only lose tumour suppressive activity but acquire new oncogenic properties absent from wild-type p53. GOF p53 proteins: (1) co-activate oncogenic transcription factors (STAT3, ETS2, c-Jun) that wild-type p53 would normally suppress; (2) bind and inactivate p63 and p73, paralogues that compensate for p53 loss in apoptosis; (3) remodel chromatin at novel gene loci promoting invasion and metastasis; (4) are metabolically more stable than wild-type p53, accumulating to high levels (explaining the strong IHC staining of TP53-mutant tumours). GOF mutations are associated with worse prognosis and greater chemotherapy resistance than simple TP53 null mutations, suggesting the mutant protein actively drives malignancy rather than merely losing tumour suppression.

Question 7

Why can MDM2 inhibitors not treat TP53-mutant cancer, and in which patients do they work?

Accepted Answer

MDM2 inhibitors (idasanutlin, navtemadlin, milademetan) work by occupying the p53-binding pocket of MDM2, blocking MDM2-mediated p53 ubiquitination and allowing p53 to accumulate and activate. This mechanism requires functional, wild-type p53 protein — if p53 is structurally damaged by a missense mutation, blocking MDM2 simply allows a non-functional p53 to accumulate without therapeutic benefit and may even be harmful by occupying the remaining p53 signalling machinery. MDM2 inhibitors are therefore selective for TP53 wild-type tumours that overexpress MDM2 — predominantly well-differentiated and dedifferentiated liposarcomas (>90% MDM2 amplification) and a subset of AML and other haematological malignancies. TP53 mutation status must be confirmed before prescribing these agents.

TP53 Gene Function

Overview

More Tumor Suppressor Genes