# First functional evidence that a rare germline TP53β variant drives senescence-associated immune suppression and impairs apoptosis and cell migration in breast cancer patients

## TL;DR

A rare TP53β variant is linked to immune suppression, reduced cell death, and impaired migration in breast cancer patients.

## Contribution

First ex vivo evidence showing a rare TP53β variant impairs immune function and contributes to chemoresistance in breast cancer.

## Key findings

- TP53β N340D variant increases cellular senescence and impairs apoptosis and migration.
- The variant reduces PBMC proliferation and migration, suggesting altered immune recruitment.
- Functional genomics supports the pathogenicity of TP53β N340D in a Li-Fraumeni-like syndrome context.

## Abstract

•Germline TP53β N340D variant disrupts peripheral blood mononuclear cell function.•TP53β N340D variant increases cellular senescence and impairs apoptosis and migration.•Functional genomics provides evidence for rare germline variant classification.•Pathology-supported genetic testing utilizes functional genomics for interpretation.•First ex vivo evidence supporting the pathogenicity of the TP53β N340D variant.

Germline TP53β N340D variant disrupts peripheral blood mononuclear cell function.

TP53β N340D variant increases cellular senescence and impairs apoptosis and migration.

Functional genomics provides evidence for rare germline variant classification.

Pathology-supported genetic testing utilizes functional genomics for interpretation.

First ex vivo evidence supporting the pathogenicity of the TP53β N340D variant.

Pathology-supported genetic testing (PSGT), a personalized medicine framework established in South Africa, led to the identification of a rare germline tumour suppressor protein 53 (TP53) beta-isoform (β) variant (NM_001126114.3, c.1018A>G, p.N340D) in a family with the Li-Fraumeni-like syndrome. While protein modeling predicted structural alterations consistent with impaired function, its pathogenicity remained unclear.

To determine the functional impact of the TP53β N340D variant on cell proliferation, cell death, senescence, migration, and anti-tumour activity using a translational ex vivo model.

Peripheral blood mononuclear cells (PBMCs) were isolated from female controls and breast cancer patients, with or without the TP53β N340D variant. Lipopolysaccharide (LPS)- and phytohemagglutinin-L (PHA-L)-stimulated proliferation was evaluated by a water-soluble tetrazolium 1 (WST-1) assay. Doxorubicin (DXR)-induced cell death was assessed using a WST-1 assay, flow cytometry, and western blotting. A senescence-associated beta-galactosidase assay and western blotting determined senescence. Migration and anti-tumour activity were assessed using a Transwell assay and co-culturing PBMCs with BT-549 spheroids.

The TP53β N340D variant impaired DXR-induced cell death (p < 0.001), supported by reduced late apoptosis and decreased CASP3 and PARP activation. TP53β N340D PBMCs exhibited increased senescence (p < 0.01), potentially contributing to chemoresistance. Reduced LPS- and PHA-L-stimulated proliferation was dependent on cancer status. The variant reduced PBMC migration (p < 0.01), suggesting altered immune recruitment. Although anti-tumour activity appeared reduced in TP53β N340D PBMCs, spheroid size remained unchanged.

This study provides supporting evidence for the pathogenicity of the TP53β N340D variant and highlights the importance of integrating functional genomics into PSGT to enhance medical decision-making.