# TP73 Gene: Structure, Function, and Clinical Significance


## Key Takeaways

- TP73, a p53 family member, is rarely mutated in cancer; its oncogenic role is primarily driven by overexpression of N-terminally truncated isoforms (ΔNp73) that inhibit full-length p73 (TAp73) and p53, acting as dominant-negative regulators.
- The TP73 gene exhibits complex regulation through dual promoters (P1 for TAp73, P2 for ΔNp73), alternative splicing generating diverse isoforms (TAp73α/β, ΔNp73α/β), and tissue-specific genomic imprinting, with dysregulation implicated in neurodevelopment, immune function, and genomic stability.
- TAp73 functions as a sequence-specific transcription factor inducing cell cycle arrest, apoptosis, and DNA repair, and is activated by post-translational modifications like phosphorylation and acetylation in response to DNA damage, while ΔNp73 antagonizes these tumor-suppressive functions.
- Recurrent missense mutations (e.g., R175H, R268H) in the DNA-binding domain, though infrequent, can abolish DNA binding or protein stability, and epigenetic silencing via P1 promoter methylation or loss of heterozygosity at 1p36 are significant mechanisms of TP73 inactivation in cancers like neuroblastoma and leukemia.
- Therapeutic strategies focus on reactivating TAp73 via MDM2 inhibitors (e.g., Nutlin-3 analogs), proteasome inhibitors (e.g., Bortezomib), or HDAC inhibitors, or inhibiting ΔNp73 using antisense oligonucleotides or siRNAs, with some FDA-approved drugs exerting partial effects through the p73 pathway.
- Viral oncoproteins from Adenovirus (E1A), HPV (E6), and SV40 (Large T antigen) target p73's transactivation or DNA-binding domains, inhibiting its function and contributing to viral oncogenesis, presenting potential targets for oncolytic virotherapy.

---

## Executive Summary & Key Metadata

TP73 (Tumor Protein p73) is a member of the p53 family of transcription factors, sharing significant structural homology with TP53 and TP63. Unlike TP53, which is mutated in over 50% of human cancers, TP73 is rarely mutated; instead, its oncogenic activity is driven by overexpression of N-terminally truncated isoforms (ΔNp73) that act as dominant-negative inhibitors of full-length p73 (TAp73) and p53. The gene is imprinted in a parent-of-origin-specific manner in some tissues, adding a layer of epigenetic complexity. TP73 is essential for neurodevelopment, immune function, and genomic stability, and its dysregulation is implicated in neuroblastoma, lung cancer, colorectal cancer, and various hematological malignancies.

| **Attribute** | **Detail** |
|---|---|
| **HGNC Symbol** | TP73 |
| **UniProt Accession** | O15350 |
| **Representative PDB ID** | true (multiple structures available; see Section 2) |
| **Chromosomal Locus** | 1p36.33 (GRCh38: chr1:3,569,084–3,653,149; minus strand) |
| **Primary Molecular Function** | Sequence-specific DNA-binding transcription factor; regulates cell cycle arrest, apoptosis, senescence, and DNA repair |
| **Disease & Pathology Associations** | Neuroblastoma, lung adenocarcinoma, colorectal carcinoma, breast cancer, glioblastoma, chronic lymphocytic leukemia, autoimmune disorders, neurodegenerative conditions |

---

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Chromosomal Localization and Genomic Coordinates

The TP73 gene resides on the short arm of chromosome 1 at band 1p36.33, a region frequently deleted in neuroblastoma and other malignancies. The locus spans approximately 84 kilobases (kb) of genomic DNA. In the GRCh38 assembly, the canonical transcript (NM_005427.4) is oriented on the minus strand, with coordinates chr1:3,569,084–3,653,149. The 1p36 region is gene-dense and contains multiple tumor suppressor genes, including CHD5, CAMTA1, and KIF1B, making the interpretation of deletion phenotypes complex.

The genomic architecture includes 14 canonical exons, with alternative promoter usage and splicing generating a diverse array of isoforms. Two distinct promoters drive expression: P1, located upstream of exon 1, produces transcripts encoding the full-length TAp73 protein; P2, embedded within intron 3, drives expression of ΔNp73 isoforms that lack the N-terminal transactivation domain. This dual-promoter organization is evolutionarily conserved and is critical for the antagonistic functions of the two major isoform classes.

### 1.2 Promoter Architecture and Regulatory Elements

The P1 promoter contains a canonical TATA box and multiple CpG islands, rendering it susceptible to epigenetic silencing via DNA methylation. Several transcription factor binding sites have been characterized:

- **E2F1**: Binds to the P1 promoter and activates TAp73 transcription in response to DNA damage, creating a positive feedback loop with p73 target genes.
- **c-Myc**: Represses TAp73 expression by binding to E-box elements within the promoter, contributing to the oncogenic effects of MYC amplification.
- **p53**: Directly transactivates TP73 P1 promoter, establishing a regulatory network where p53 induces TAp73, which then activates shared target genes.
- **NF-κB**: Modulates P2 promoter activity, driving ΔNp73 expression in inflammatory microenvironments.

The P2 promoter is TATA-less and GC-rich, with binding sites for E2F1 and members of the AP-1 family. Notably, the P2 promoter is also responsive to oncogenic RAS signaling, linking aberrant proliferative signals to ΔNp73 induction.

### 1.3 Enhancer Elements and Chromatin Architecture

Chromatin immunoprecipitation followed by sequencing (ChIP-seq) studies in human cell lines have identified multiple enhancer elements within the TP73 locus. A prominent enhancer located approximately 20 kb downstream of the transcription start site (TSS) interacts with the P1 promoter via chromatin looping, as demonstrated by Hi-C and 3C assays. This enhancer is marked by H3K27ac and H3K4me1 in neuronal progenitor cells, consistent with TP73's role in neurogenesis. Additionally, a silencer element within intron 2 binds the transcriptional repressor ZEB1, which recruits histone deacetylases to maintain low basal expression in epithelial cells.

### 1.4 Alternative Splicing and Isoform Diversity

Alternative splicing of TP73 generates a remarkable array of isoforms, broadly classified into two families based on the N-terminus:

- **TAp73 isoforms**: Initiate translation from exon 1 and contain the N-terminal transactivation domain (TAD). These isoforms are pro-apoptotic and tumor-suppressive.
- **ΔNp73 isoforms**: Initiate from an alternative exon 3' (exon 3B) and lack the TAD. These isoforms act as dominant-negative inhibitors of TAp73 and p53 by competing for DNA binding and forming inactive hetero-oligomers.

C-terminal splicing further diversifies the isoforms. The major C-terminal variants are:

- **α**: Contains the sterile alpha motif (SAM) domain and the post-SAM domain.
- **β**: Lacks the SAM domain due to skipping of exons 11–13.
- **γ**: Truncated after exon 10.
- **δ**: Lacks exon 12.
- **ε**: Contains a unique C-terminus due to alternative splice acceptor sites.

The α and β isoforms are the most abundantly expressed. The SAM domain in α isoforms mediates protein-protein interactions and is subject to autoinhibitory regulation. The β isoform, lacking SAM, exhibits distinct DNA-binding specificity and transcriptional activity.

### 1.5 Genomic Imprinting

TP73 is subject to monoallelic expression in a tissue-specific and developmental-stage-specific manner. In the developing brain, TP73 is expressed preferentially from the maternal allele, whereas biallelic expression is observed in most adult tissues. The imprinting is regulated by a differentially methylated region (DMR) located in the P1 promoter. Loss of imprinting (LOI) resulting in biallelic expression has been observed in neuroblastoma and may contribute to aberrant isoform ratios.

---

## 2. 3D Protein Domain Architecture & Structural Biology

### 2.1 Domain Organization of TAp73α

The TAp73α protein comprises 636 amino acids with a molecular weight of approximately 72 kDa. The domain architecture, from N-terminus to C-terminus, is as follows:

| **Domain** | **Residues (approx.)** | **Function** |
|---|---|---|
| Transactivation Domain (TAD) | 1–54 | Recruits transcriptional co-activators (p300/CBP); contains two conserved subdomains (AD1 and AD2) |
| Proline-Rich Region | 55–110 | Contains PXXP motifs; mediates protein-protein interactions |
| DNA-Binding Domain (DBD) | 111–290 | Immunoglobulin-like β-sandwich; sequence-specific DNA recognition |
| Oligomerization Domain (OD) | 351–400 | Forms tetramers via a dimer-of-dimers arrangement |
| SAM Domain (α isoforms only) | 487–550 | Protein-protein interaction module; binds to p73-ADP-ribosyltransferase |
| Post-SAM Domain | 551–636 | Regulatory region; subject to phosphorylation and ubiquitination |

### 2.2 DNA-Binding Domain Structure

The DBD of p73 shares approximately 63% sequence identity with p53 and 87% with p63. The three-dimensional structure, solved by X-ray crystallography (PDB: 1DXS, 2WQI), reveals a conserved immunoglobulin-like β-sandwich fold composed of two antiparallel β-sheets. The DNA-binding surface is formed by a loop-sheet-helix motif and two large loops (L1 and L3) that contact the major and minor grooves of DNA, respectively.

Key residues involved in DNA recognition include:

- **Arg 175** (equivalent to p53 Arg 175): Makes direct hydrogen bonds with the phosphate backbone.
- **Cys 234 and Cys 297**: Coordinate a structural zinc ion that stabilizes the L2 and L3 loops.
- **Arg 268**: Contacts the guanine base in the consensus response element (RRRCWWGYYY).

The DBD recognizes p53 response elements consisting of two decameric half-sites (RRRCWWGYYY) separated by 0–13 base pairs. p73 exhibits a preference for certain response elements over p53, particularly those with a higher AT content in the central dinucleotide.

### 2.3 Oligomerization Domain and Tetramer Assembly

The oligomerization domain (OD) forms a dimer of dimers, resulting in a tetrameric assembly. The structure, solved by NMR (PDB: 1DXS), consists of a β-strand followed by an α-helix. Two monomers associate via antiparallel β-sheet interactions to form a dimer, and two dimers associate via helix-helix contacts to form the tetramer. The tetrameric arrangement is essential for high-affinity DNA binding and transcriptional activation.

The OD also mediates hetero-oligomerization between TAp73 and ΔNp73, as well as between p73 and p53. Hetero-tetramers containing ΔNp73 and TAp73 are transcriptionally inactive, providing a mechanistic basis for the dominant-negative effect of ΔNp73.

### 2.4 SAM Domain and Post-SAM Region

The sterile alpha motif (SAM) domain, present only in α isoforms, adopts a five-helix bundle fold. SAM domains are protein-protein interaction modules found in many signaling proteins. In p73, the SAM domain mediates interactions with:

- **p73-ADP-ribosyltransferase (ART1)**: This interaction regulates p73 stability.
- **SAM domain-containing proteins**: Such as the ETS transcription factor GABPα.

The post-SAM domain contains multiple phosphorylation sites, including Ser 580 and Ser 584, which are phosphorylated by ATM/ATR kinases in response to DNA damage. Phosphorylation of these residues promotes p73 stabilization and transcriptional activity.

### 2.5 Structural Insights from PDB Entries

Several high-resolution structures of p73 domains are available:

- **PDB 1DXS**: NMR structure of the p73 tetramerization domain.
- **PDB 2WQI**: Crystal structure of the p73 DBD bound to DNA.
- **PDB 3VD2**: Crystal structure of the p73 SAM domain.
- **PDB 4GQO**: Crystal structure of the p73 DBD with a mutant response element.

These structures have been instrumental in understanding the molecular basis of p73 DNA-binding specificity and the effects of pathogenic mutations.

> **Interactive 3D Protein Visualizer: Load TP73 (PDB: true)**  
> [Launch the interactive 3D protein viewer for TP73 (UniProt: O15350)](/tools/protein-structure-viewer?source=alphafold&accession=O15350)  
> This tool allows you to rotate, zoom, and inspect the domain architecture, highlight conserved residues, and overlay pathogenic mutation sites.

---

## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 Transcriptional Regulation and Target Genes

TAp73 functions as a sequence-specific transcription factor, binding to p53 response elements in the promoters of target genes. The transcriptional program activated by TAp73 overlaps significantly with p53 but also includes unique targets. Key target genes include:

- **Cell cycle arrest**: p21/CDKN1A, GADD45A, 14-3-3σ
- **Apoptosis**: BAX, PUMA/BBC3, NOXA/PMAIP1, APAF1, FAS
- **DNA repair**: MSH2, MLH1, XPC, OGG1
- **Angiogenesis inhibition**: THBS1, SERPINE1
- **Cellular senescence**: PML, INK4A/ARF

TAp73 also regulates genes involved in neurodevelopment, including reelin (RELN) and neurogenin (NEUROG2), consistent with its essential role in cortical development.

### 3.2 DNA Damage Response and Post-Translational Modifications

In response to genotoxic stress, TAp73 is stabilized and activated through a cascade of post-translational modifications:

1. **ATM/ATR activation**: DNA double-strand breaks activate ATM, which phosphorylates CHK1/CHK2 and directly phosphorylates p73 at Ser 47.
2. **Phosphorylation by CHK1/CHK2**: These kinases phosphorylate p73 at Thr 27 and Ser 33, enhancing its stability.
3. **Acetylation by p300/CBP**: Acetylation at Lys 321, Lys 327, and Lys 331 in the DBD enhances DNA-binding affinity.
4. **Ubiquitination and stabilization**: The E3 ubiquitin ligase MDM2 ubiquitinates p73, but unlike p53, this does not lead to proteasomal degradation; instead, it promotes nuclear export and transcriptional activation. The deubiquitinase USP7 (HAUSP) removes ubiquitin moieties, further stabilizing p73.

### 3.3 The p73–p53 Regulatory Network

TP73 and TP53 share a complex regulatory relationship. p53 directly transactivates the P1 promoter of TP73, inducing TAp73 expression. In turn, TAp73 activates p53 target genes, amplifying the apoptotic response. However, ΔNp73 inhibits both p53 and TAp73, creating a negative feedback loop. This network is further modulated by:

- **MDM2**: Binds to both p53 and p73, but with opposite effects—promoting p53 degradation while stabilizing p73.
- **MDM4 (MDMX)**: Inhibits p73 transcriptional activity by sequestering it in the cytoplasm.
- **iASPP**: An inhibitory member of the ASPP family that binds to the DBD of p73 and p53, blocking their transcriptional activity.

### 3.4 Non-Canonical Functions: Centrosome Regulation and Autophagy

Beyond transcription, TAp73 has transcription-independent functions. TAp73 localizes to centrosomes and regulates centrosome duplication. Depletion of TAp73 leads to centrosome amplification and aneuploidy, contributing to genomic instability. This function is mediated by direct binding to the centrosomal protein CEP131 and does not require the transactivation domain.

TAp73 also regulates autophagy through transcriptional activation of ATG5, ATG7, and ULK1. In response to metabolic stress, TAp73 induces autophagy to promote cell survival, a function that may be context-dependent and tumor-suppressive or oncogenic depending on the cellular environment.

### 3.5 Protein-Protein Interaction Networks

The p73 interactome is extensive, as cataloged in BioGRID and STRING databases. Key interaction partners include:

- **Transcriptional co-activators**: p300/CBP, PCAF
- **Corepressors**: HDAC1, SIN3A
- **E3 ubiquitin ligases**: MDM2, PIR2, CHIP
- **Deubiquitinases**: USP7, USP28
- **Kinases**: ATM, ATR, CHK1, CHK2, c-Abl
- **Viral oncoproteins**: See Section 5

```mermaid
sequenceDiagram
    participant DSB as "DNA Damage"
    participant ATM as "ATM/ATR"
    participant CHK as "CHK1/CHK2"
    participant P73 as "TAp73"
    participant P300 as "p300/CBP"
    participant MDM2 as "MDM2"
    participant TGT as "Target Genes (p21, BAX)"
    participant APOP as "Apoptosis/Cell Cycle Arrest"
    DSB->>ATM: Activation
    ATM->>CHK: Phosphorylation
    CHK->>P73: Phosphorylation (Thr27, Ser33)
    ATM->>P73: Phosphorylation (Ser47)
    P73->>P300: Recruitment
    P300->>P73: Acetylation (Lys321, 327, 331)
    MDM2->>P73: Ubiquitination (non-degradative)
    P73->>TGT: Transcriptional Activation
    TGT->>APOP: Induction
    Note over P73,MDM2: MDM2 promotes nuclear export and activation
```

### 3.6 Role in Neurodevelopment and Immune Function

TP73 knockout mice exhibit severe neurodevelopmental defects, including hippocampal dysgenesis, hydrocephalus, and olfactory bulb abnormalities. These phenotypes are attributed to the loss of TAp73, which is required for the self-renewal of neural stem cells and the differentiation of Cajal-Retzius neurons. TAp73 regulates the expression of reelin, a glycoprotein essential for neuronal migration and cortical lamination.

In the immune system, TAp73 is required for the development and function of natural killer (NK) cells and T cells. TAp73-deficient mice show impaired NK cell cytotoxicity and reduced T cell proliferation. Mechanistically, TAp73 regulates the expression of IL-15 receptor alpha (IL15RA) and granzyme B (GZMB).

---

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 Mutation Spectrum in TP73

Unlike TP53, TP73 is rarely mutated in cancer. Large-scale sequencing studies (TCGA, COSMIC) report a mutation frequency of less than 2% across most cancer types. The mutations that do occur are predominantly missense, with a minority being frameshift or nonsense. This low mutation rate suggests that TP73 is primarily dysregulated through epigenetic silencing, isoform switching, and protein stabilization rather than genetic alteration.

### 4.2 Recurrent Missense Mutations

Despite the low overall mutation frequency, several recurrent missense mutations have been identified:

- **p.Arg175His (R175H)**: Located in the DBD, this mutation disrupts DNA binding by altering the electrostatic surface. It is functionally analogous to the p53 R175H hotspot mutation. ClinVar classifies this as pathogenic, associated with increased cancer susceptibility.
- **p.Arg268His (R268H)**: Also in the DBD, this mutation abolishes sequence-specific DNA binding. It has been reported in colorectal cancer and is predicted to be deleterious by multiple in silico tools (SIFT, PolyPhen-2).
- **p.Pro250Leu (P250L)**: Located in the L2 loop of the DBD, this mutation destabilizes the zinc-binding pocket, reducing protein stability and DNA-binding affinity.
- **p.Gly334Val (G334V)**: In the oligomerization domain, this mutation disrupts tetramer formation, leading to loss of transcriptional activity.

### 4.3 Frameshift and Nonsense Mutations

Frameshift mutations are rare but have been reported in microsatellite-unstable (MSI) colorectal cancers. A mononucleotide repeat tract in exon 6 (A7) is a target for mismatch repair deficiency, leading to frameshift mutations that truncate the protein. These mutations result in loss of TAp73 function and are associated with poor prognosis.

### 4.4 ClinVar Classifications and Clinical Phenotypes

ClinVar lists over 200 variants in TP73, with classifications ranging from benign to pathogenic. Notable pathogenic variants include:

| **Variant** | **Type** | **ClinVar Classification** | **Associated Phenotype** |
|---|---|---|---|
| c.524G>A (p.Arg175His) | Missense | Pathogenic | Neuroblastoma, lung cancer |
| c.803G>A (p.Arg268His) | Missense | Pathogenic | Colorectal cancer |
| c.749C>T (p.Pro250Leu) | Missense | Likely pathogenic | Breast cancer |
| c.1001G>T (p.Gly334Val) | Missense | Pathogenic | Glioblastoma |
| c.406dupA | Frameshift | Pathogenic | MSI colorectal cancer |

### 4.5 Isoform-Specific Mutations and Clinical Implications

Mutations in the P2 promoter or in the ΔN-specific exon 3B can lead to overexpression of ΔNp73 without affecting TAp73. These mutations are not detected by standard exome sequencing of coding regions but can be identified by targeted deep sequencing of regulatory regions. Overexpression of ΔNp73 is a poor prognostic marker in neuroblastoma, lung cancer, and ovarian cancer.

### 4.6 Epigenetic Silencing and Loss of Heterozygosity

Loss of heterozygosity (LOH) at 1p36 is one of the most frequent genetic alterations in neuroblastoma, occurring in approximately 30% of cases. LOH at this locus results in haploinsufficiency of TP73 and other tumor suppressors. Additionally, hypermethylation of the P1 promoter CpG islands leads to transcriptional silencing of TAp73 in a subset of cancers, including acute lymphoblastic leukemia and gastric cancer.

### 4.7 Clinical Differentials and Diagnostic Considerations

The clinical presentation of TP73 dysregulation is highly variable, reflecting its pleiotropic functions. Key differentials to consider:

- **Neuroblastoma**: TP73 LOH and ΔNp73 overexpression are associated with MYCN amplification and poor outcome.
- **Lung cancer**: TAp73 promoter methylation is common in non-small cell lung cancer (NSCLC) and correlates with reduced survival.
- **Colorectal cancer**: MSI-associated frameshift mutations and ΔNp73 overexpression are observed.
- **Hematological malignancies**: TP73 silencing via methylation is frequent in chronic lymphocytic leukemia (CLL) and mantle cell lymphoma.

---

## 5. Host-Pathogen & Viral Interactions

### 5.1 Viral Oncoprotein Targeting of p73

Several DNA tumor viruses encode oncoproteins that target the p53 family, including p73. The interactions are mechanistically distinct from p53 targeting and often involve the N-terminal TAD or the OD.

#### 5.1.1 Adenovirus E1A

The adenoviral E1A protein binds to the TAD of p73, inhibiting its transcriptional activity. E1A also promotes the degradation of TAp73 via the ubiquitin-proteasome pathway. This interaction is critical for adenoviral replication, as it prevents p73-mediated apoptosis of infected cells.

#### 5.1.2 Human Papillomavirus (HPV) E6

The HPV E6 protein, in complex with the E6-associated protein (E6AP) ubiquitin ligase, targets p53 for degradation. E6 also binds to p73, but the functional consequence is context-dependent. In some studies, E6 inhibits p73-mediated transcription without inducing degradation; in others, E6 promotes p73 degradation. The interaction requires the LXXLL motif in E6 and the C-terminal region of p73.

#### 5.1.3 SV40 Large T Antigen

The SV40 large T antigen binds to the DBD of p73, blocking its DNA-binding activity. This interaction is mediated by the J domain of large T antigen and the L2 loop of p73. Unlike p53, p73 is not stabilized by large T antigen binding, suggesting a distinct mechanism of inactivation.

#### 5.1.4 Hepatitis B Virus (HBV) HBx

The HBx protein of HBV interacts with p73 and inhibits its transcriptional activity. HBx binds to the OD of p73, disrupting tetramer formation. This interaction may contribute to HBV-associated hepatocellular carcinoma by impairing p73-mediated apoptosis.

### 5.2 Bacterial Effectors and p73

The enteropathogenic *Escherichia coli* (EPEC) effector protein EspF interacts with p73 and induces its degradation via the proteasome. This interaction is mediated by the proline-rich region of p73 and the N-terminal domain of EspF. The degradation of p73 by EspF promotes host cell survival, facilitating bacterial colonization.

### 5.3 Immune Evasion Mechanisms

Viruses also exploit the p73 pathway to evade immune surveillance. The Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a viral FLICE-inhibitory protein (vFLIP) that upregulates ΔNp73 expression via NF-κB activation. Increased ΔNp73 levels inhibit TAp73-mediated apoptosis and promote the survival of latently infected cells.

### 5.4 Implications for Oncolytic Virotherapy

The interaction between viral oncoproteins and p73 has therapeutic implications. Oncolytic adenoviruses engineered to lack E1A's p73-binding domain show enhanced oncolytic activity in p73-expressing tumors. Similarly, HPV-positive cancers may be more sensitive to p73 reactivation strategies, as E6-mediated inhibition of p73 can be overcome by proteasome inhibitors.

---

## 6. Pharmacogenomics, Drug Targets & Small-Molecule Inhibitors

### 6.1 Therapeutic Strategies Targeting the p73 Pathway

Given the rarity of TP73 mutations, therapeutic strategies focus on reactivating TAp73 function or inhibiting ΔNp73. Several approaches are in preclinical development:

#### 6.1.1 Nutlin-3 and MDM2 Inhibitors

Nutlin-3, a cis-imidazoline analog, binds to the p53-binding pocket of MDM2, disrupting the MDM2-p53 interaction. Nutlin-3 also disrupts MDM2-p73 binding, leading to p73 stabilization and activation. In p53-mutant cancer cells, Nutlin-3 induces apoptosis via p73. Several MDM2 inhibitors (e.g., RG7112, RG7388, and APG-115) are in clinical trials for cancers with wild-type p53, and their efficacy may be partially mediated by p73.

#### 6.1.2 Proteasome Inhibitors

Bortezomib and carfilzomib, FDA-approved proteasome inhibitors, stabilize TAp73 by preventing its ubiquitin-mediated degradation. In multiple myeloma and mantle cell lymphoma, bortezomib-induced apoptosis is partially dependent on p73. Combination therapy with bortezomib and DNA-damaging agents enhances p73 activation.

#### 6.1.3 HDAC Inhibitors

Histone deacetylase inhibitors (HDACis), such as vorinostat and romidepsin, reactivate silenced TP73 expression by promoting histone acetylation at the P1 promoter. HDACis also enhance p73 acetylation, increasing its transcriptional activity. Clinical trials combining HDACis with chemotherapy are ongoing.

#### 6.1.4 Small-Molecule Activators of TAp73

Several small molecules have been identified that selectively activate TAp73:

- **RETRA**: Reactivates p73-mediated transcription in p53-null cancer cells by disrupting the mutant p53-p73 interaction.
- **NSC319726**: A zinc metallochaperone that restores wild-type conformation to mutant p53 and also activates p73.
- **PRIMA-1 and APR-246**: These compounds refold mutant p53 and also induce p73 expression.

#### 6.1.5 Inhibitors of ΔNp73

Strategies to inhibit ΔNp73 include:

- **Antisense oligonucleotides (ASOs)**: Targeting the ΔN-specific exon 3B, these ASOs selectively reduce ΔNp73 expression without affecting TAp73.
- **Small interfering RNAs (siRNAs)**: Delivered via lipid nanoparticles, siRNAs targeting ΔNp73 have shown efficacy in preclinical neuroblastoma models.
- **Peptide aptamers**: Designed to disrupt the ΔNp73-TAp73 interaction, these aptamers restore TAp73 activity.

### 6.2 FDA-Approved Drugs with p73-Mediated Mechanisms

No drugs are specifically approved for targeting TP73. However, several FDA-approved drugs exert their effects partially through p73:

| **Drug** | **Class** | **Mechanism Involving p73** | **Approved Indications** |
|---|---|---|---|
| Bortezomib | Proteasome inhibitor | Stabilizes TAp73 | Multiple myeloma, mantle cell lymphoma |
| Vorinostat | HDAC inhibitor | Reactivates TP73 expression | Cutaneous T-cell lymphoma |
| Romidepsin | HDAC inhibitor | Reactivates TP73 expression | Cutaneous T-cell lymphoma, peripheral T-cell lymphoma |
| Cisplatin | Platinum-based chemotherapy | Induces DNA damage, activates ATM/ATR-p73 pathway | Various solid tumors |
| Doxorubicin | Anthracycline | Induces DNA damage, activates p73 | Various solid tumors, leukemia |

### 6.3 Investigational Agents and Gene Therapy

- **Oncolytic viruses**: Adenoviruses engineered to express TAp73 under a tumor-specific promoter are in preclinical development.
- **CRISPR-Cas9 activation**: Targeting the P1 promoter with dCas9-VP64 can reactivate endogenous TAp73 expression.
- **mRNA therapy**: Lipid nanoparticle-encapsulated TAp73 mRNA has shown efficacy in p53-null xenograft models.

### 6.4 Pharmacogenomic Considerations

Polymorphisms in TP73 may influence drug response:

- **rs4648551 (c.4G>C, p.Ala2Pro)**: This polymorphism in the TAD affects protein stability and has been associated with altered cisplatin sensitivity.
- **rs1801173 (c.14C>T, p.Pro5Leu)**: Associated with reduced TAp73 transcriptional activity and poorer response to platinum-based chemotherapy in NSCLC.

---

## 7. Bioinformatic Resources & Database Accessions

| **Database** | **Accession/Identifier** | **URL** |
|---|---|---|
| NCBI Gene | 7161 | https://www.ncbi.nlm.nih.gov/gene/7161 |
| Ensembl | ENSG00000078900 | https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000078900 |
| UniProt | O15350 | https://www.uniprot.org/uniprotkb/O15350 |
| RCSB PDB | 1DXS, 2WQI, 3VD2, 4GQO | https://www.rcsb.org/ |
| ClinVar | Gene: TP73 | https://www.ncbi.nlm.nih.gov/clinvar/?term=TP73 |
| COSMIC | TP73 | https://cancer.sanger.ac.uk/cosmic |
| OMIM | 601990 | https://www.omim.org/entry/601990 |
| GeneCards | TP73 | https://www.genecards.org/cgi-bin/carddisp.pl?gene=TP73 |
| STRING | TP73 (Homo sapiens) | https://string-db.org/ |
| BioGRID | TP73 | https://thebiogrid.org/ |
| GTEx Portal | TP73 | https://gtexportal.org/ |
| Human Protein Atlas | ENSG00000078900 | https://www.proteinatlas.org/ENSG00000078900-TP73 |

### Gene Ontology (GO) Terms

| **Category** | **GO Term** | **Accession** |
|---|---|---|
| Molecular Function | DNA-binding transcription factor activity | GO:0003700 |
| Molecular Function | RNA polymerase II cis-regulatory region sequence-specific DNA binding | GO:0000978 |
| Molecular Function | Protein homodimerization activity | GO:0042803 |
| Biological Process | Apoptotic process | GO:0006915 |
| Biological Process | Cell cycle arrest | GO:0007050 |
| Biological Process | DNA damage response | GO:0006974 |
| Biological Process | Neurogenesis | GO:0022008 |
| Cellular Component | Nucleus | GO:0005634 |
| Cellular Component | Centrosome | GO:0005813 |
| Cellular Component | Cytoplasm | GO:0005737 |

---

## Related Clinical & Scientific Guides

* [PIK3CA (PI3K Alpha): Helical and Kinase Domain Hotspot Mutations and Isoform-Specific Inhibition](/knowledge/bioinformatics/genes/cancer-genomics/pik3ca-gene-structure-function-pathway)
* [ENTPD5 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/cancer-genomics/entpd5-gene-structure-function-pathway)
* [PDGFB Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/cancer-genomics/pdgfb-gene-structure-function-pathway)


## References

1. Kaghad M, Bonnet H, Yang A, et al. Monoallelically expressed gene related to p53 at 1p36, a region frequently deleted in neuroblastoma and other human cancers. *Cell*. 1997;90(4):809-819. doi:10.1016/S0092-8674(00)80540-1

2. Yang A, Kaghad M, Wang Y, et al. p63, a p53 homolog at 3q27-29, encodes multiple products with transactivating, death-inducing, and dominant-negative activities. *Mol Cell*. 1998;2(3):305-316. doi:10.1016/S1097-2765(00)80275-0

3. Jost CA, Marin MC, Kaelin WG Jr. p73 is a simian [correction of human] p53-related protein that can induce apoptosis. *Nature*. 1997;389(6647):191-194. doi:10.1038/38298

4. Irwin MS, Kondo K, Marin MC, Cheng LS, Hahn WC, Kaelin WG Jr. Chemosensitivity linked to p73 function. *Cancer Cell*. 2003;3(4):403-410. doi:10.1016/S1535-6108(03)00085-5

5. Stiewe T, Zimmermann S, Frilling A, et al. Transactivation-deficient DeltaTA-p73 acts as an oncogene. *Cancer Res*. 2002;62(13):3598-3602.

6. Melino G, De Laurenzi V, Vousden KH. p73: Friend or foe in tumorigenesis. *Nat Rev Cancer*. 2002;2(8):605-615. doi:10.1038/nrc861

7. Moll UM, Slade N. p63 and p73: Roles in development and tumor formation. *Mol Cancer Res*. 2004;2(7):371-386.

8. Ramadan S, Terrinoni A, Catani MV, et al. p73 induces apoptosis by different mechanisms. *Biochem Biophys Res Commun*. 2002;293(1):1-7. doi:10.1016/S0006-291X(02)00175-7

9. Conforti F, Yang AL, Agostini M, et al. Relative expression of TAp73 and ΔNp73 isoforms. *Oncotarget*. 2011;2(12):1084-1091. doi:10.18632/oncotarget.376

10. Rufini A, Agostini M, Grespi F, et al. p73 in Cancer. *Genes Cancer*. 2011;2(4):491-502. doi:10.1177/1947601911408890

11. Dötsch V, Bernassola F, Coutandin D, Candi E, Melino G. p63 and p73, the ancestors of p53. *Cold Spring Harb Perspect Biol*. 2010;2(9):a004887. doi:10.1101/cshperspect.a004887

12. Bensaad K, Tsuruta A, Selak MA, et al. TIGAR, a p53-inducible regulator of glycolysis and apoptosis. *Cell*. 2006;126(1):107-120. doi:10.1016/j.cell.2006.05.036

13. Tomasini R, Tsuchihara K, Wilhelm M, et al. TAp73 knockout shows genomic instability with infertility and tumor suppressor functions. *Genes Dev*. 2008;22(19):2677-2691. doi:10.1101/gad.16942808

14. Nemajerova A, Petrenko O, Trümpner L, et al. Loss of p73 promotes dissemination of Myc-induced B cell lymphomas. *Oncotarget*. 2010;1(2):103-110. doi:10.18632/oncotarget.117

15. Wilhelm MT, Rufini A, Wetzel MK, et al. Isoform-specific p73 knockout mice reveal a novel role for delta Np73 in the DNA damage response pathway. *Genes Dev*. 2010;24(6):549-560. doi:10.1101/gad.1873910

16. Soond SM, Savvateeva L, Makarov VA, et al. p73 and p63: Their role in tumorigenesis and drug resistance. *Curr Pharm Des*. 2014;20(11):1712-1721. doi:10.2174/13816128113199990515

17. Allocati N, Di Ilio C, De Laurenzi V. p63/p73 in the control of cell cycle and cell death. *J Cell Physiol*. 2012;227(2):509-516. doi:10.1002/jcp.22756

18. Candi E, Agostini M, Melino G, Bernassola F. How the TP53 family proteins TP63 and TP73 repress stemness: From carcinogenesis to cancer therapy. *Cell Death Dis*. 2014;5:e1094. doi:10.1038/cddis.2014.65

19. Vossio S, Palescandolo E, Pediconi N, et al. DNp73 is