# APOBEC3B Does Not Promote Tumor Progression in Tp53 Hemizygous Mice

## TL;DR

This study shows that APOBEC3B overexpression does not speed up tumor progression in mice with one copy of the Tp53 gene.

## Contribution

A well-validated APOBEC3B transgenic mouse model was developed and used to test its role in tumor progression.

## Key findings

- A3B overexpression did not accelerate tumor development in Tp53 hemizygous mice.
- Tumors with A3B expression had more high-VAF mutations, but they lacked the APOBEC mutation signature.
- The A3B transgenic mouse model is validated and suitable for future research.

## Abstract

DNA cytosine deaminase APOBEC3B (A3B) is one of the endogenous sources of somatic mutations in many types of human cancers and is associated with tumor progression rather than tumorigenesis. However, it remains uncertain whether APOBEC3B‐induced mutations accelerate tumor progression or not. In this paper, we established a mouse model with A3B overexpression and investigated whether the introduction of A3B overexpression accelerates tumor development in Tp53 hemizygous mice.

We established A3B transgenic mouse by microinjection and selected the mouse which has only one A3B transgene by genomic qPCR and southern blotting using the probe against the transgene. A3B expression was validated by qPCR, immunoblotting, immunohistochemistry and in vitro CDA assays using lysates of this transgenic mouse liver, spleen and bone marrow. We interbreed this transgenic mouse model with CAG‐Cre and Tp53 knockout mice and observed differences in tumor progression and survival between Tp53 hemizygous mice and Tp53 homozygous mice irrespective of A3B expression. Finally, comprehensive genomic mutation analysis was done using the developed tumors.

We established A3B transgenic mouse which has only one transgene. A3B expression and its CDA activity were confirmed in liver cells and tumor tissues of mice overexpressing A3B. Tp53 hemizygous mice developed osteosarcomas, spindle and pleomorphic sarcomas, and squamous cell carcinomas, however we did not observe any difference in tumor development between the mice with or without A3B expression. The tumor with A3B expression has more high‐VAF mutations than the one without A3B, but these mutations are not APOBEC signature.

We developed a Cre inducible A3B transgenic mouse model bearing single copy of A3B gene. Although the introduction of A3B overexpression did not accelerate tumor development in Tp53 hemizygous mice, our mouse model with A3B overexpression is well‐validated and useful for further research.