A visual guide to restoring the guardian of the genome

p53 the VIP

The p53 protein is concerned in a dizzying array of wholesome physiological features. In lots of circumstances, p53 controls these features by regulating gene expression. p53 instantly regulates greater than 300 genes with many extra not directly affected1.

Graphic showing p53 and the various physiological functions it is involved in

Infographic: Lucy Studying-Ikkanda

Centre of consideration

The gene that produces p53 (generally known as TP53) is probably the most well-studied gene within the human genome, having been cited in additional than 10,000 papers since its discovery in 19792.

Bar chart comparing the number of cited papers on TP53 compared with EGFR and TNF

Supply: NCBI-NLM as of 25 January 2022; Infographic: Lucy Studying-Ikkanda

A wholesome perform

Wholesome cells categorical low ranges of p53. The protein is generally trapped in an inhibited state, and these inactive p53 molecules are swiftly damaged down. Inactive p53 molecules have a mean half-life of simply 9 minutes3.

Graphic illustrating the main functional domains in p53

Infographic: Lucy Studying-Ikkanda

A regulatory protein referred to as MDM2 retains p53 in its inactive state. Underneath regular circumstances, MDM2 provides chemical modifications to p53 that mark it for destruction by the cell.

Graphic showing destructive interaction between p53 and MDM2

Infographic: Lucy Studying-Ikkanda

Numerous mobile stressors could cause MDM2 to separate from p53. When this occurs, p53 is shuttled from the cytoplasm into the nucleus. Many of those stress triggers are instantly linked to most cancers.

Graphic showing the effect of stress on MDM2 and p53

Infographic: Lucy Studying-Ikkanda

Contained in the nucleus, 4 molecules of p53 assemble right into a tetramer that binds to particular response-element sequences in DNA.

Graphic showing DNA bound by a p53 tetramer

Infographic: Lucy Studying-Ikkanda

The goal genes can produce a variety of responses, relying on the severity of the stress. For gentle stress, p53 would possibly put cell division on maintain whereas it triggers DNA restore, or tunes mobile metabolic exercise. For extreme stress, p53 can put cells right into a state of everlasting development arrest or set off cell loss of life via apoptosis.

Graphic showing the cellular outcomes of p53 reacting to mild and severe stress

Infographic: Lucy Studying-Ikkanda

Damaged or blocked

The perform of p53 will be misplaced owing to mutations within the TP53 gene, or due to the dysfunction of proteins that regulate p53. In both case, these issues give most cancers the inexperienced mild to progress.

Tumours with mutant p53. The TP53 gene is mutated in additional than 50% of tumours4. Round 80% of p53 mutations have an effect on amino acids within the protein’s DBD, inflicting it to misfold and likewise interfering with the popularity of goal genes4. Even one mutated copy of TP53 can gasoline tumour formation, given {that a} faulty p53 protein mixed with different, regular p53 proteins will kind a non-functional tetramer. Some research counsel that mutant p53 additionally inflicts injury by accumulating as aggregates of misfolded proteins5.

Graphic showing possible problems resulting from mutated p53

Infographic: Lucy Studying-Ikkanda

Tumours with wild-type p53. Even when TP53 just isn’t mutated, p53 perform can nonetheless be disrupted. For instance, some tumours produce extreme MDM2 that retains p53 trapped in an inactive state.

Graphic showing p53 constrained by an excess of MDM2

Infographic: Lucy Studying-Ikkanda

Most cancers set free

Lack of p53 perform can promote tumorigenesis and most cancers development in a number of methods.

Graphic showing how loss of p53 function can promote tumorigenesis

Infographic: Lucy Studying-Ikkanda

An opportunity of therapy

Even after 40 years of analysis, clinicians nonetheless lack medicine that may particularly goal tumours with p53 dysfunction. However a number of promising therapeutic methods at the moment are present process trials.

Tumours with mutant p53. Some small-molecule medicine can bind mutant p53 in a means that restores regular folding. A number of such medicine at the moment are in preclinical or early-stage medical improvement6. Nevertheless, this strategy requires remedy to be tailor-made to every affected person’s specific TP53 mutation.

Graphic illustrating how mutated p53 might be correcetd by administration of a drug

Infographic: Lucy Studying-Ikkanda

Tumours with wild-type p53. Medicine that block MDM2’s capacity to inhibit p53 would possibly supply an answer for tumours that produce an extra of MDM27. A number of corporations at the moment have such candidate medicine in medical trials.

Graphic illustrating how drugs that block MDM2 might allow p53 to function

Infographic: Lucy Studying-Ikkanda

Potent companions

The p53-oriented medicine examined up to now have proven minimal or modest efficacy on their very own. However by serving to to normalize p53 perform, these medicine might be utilized in mixture with current therapeutic methods to offer them a lift.

Apoptosis inducers. There are a number of proteins that tumour cells can exploit to inhibit cell loss of life. Restoring p53 perform drives the degradation of certainly one of these, generally known as MCL-1. Combining this therapy with medicine that knock out related proteins, corresponding to BCL-2, would possibly due to this fact promote apoptosis extra successfully than both therapy alone.

Immune-cell activators. The lack of p53 perform places tumours into an immunosuppressed state. Restoring regular perform may prime tumours to answer medicine such because the checkpoint inhibitor pembrolizumab.

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