Related Experiment Video
Updated: Jun 7, 2025
Differentiation of Mouse Breast Epithelial HC11 and EpH4 Cells
Published on: February 27, 2020
Differentiation signals induce APOBEC3A expression via GRHL3 in squamous epithelia and squamous cell carcinoma
Nicola J Smith1,2, Ian Reddin1,3, Paige Policelli1,4
1School of Cancer Sciences, Faculty of Medicine, University of Southampton, Southampton, UK.
Abstract:
Two APOBEC DNA cytosine deaminase enzymes, APOBEC3A and APOBEC3B, generate somatic mutations in cancer, thereby driving tumour development and drug resistance. Here, we used single-cell RNA sequencing to study APOBEC3A and APOBEC3B expression in healthy and malignant mucosal epithelia, validating key observations with immunohistochemistry, spatial transcriptomics and functional experiments. Whereas APOBEC3B is expressed in keratinocytes entering mitosis, we show that APOBEC3A expression is confined largely to terminally differentiating cells and requires grainyhead-like transcription factor 3 (GRHL3). Thus, in normal tissue, neither deaminase appears to be expressed at high levels during DNA replication, the cell-cycle stage associated with APOBEC-mediated mutagenesis. In contrast, in squamous cell carcinoma we find that, there is expansion of GRHL3expression and activity to a subset of cells undergoing DNA replication and concomitant extension of APOBEC3A expression to proliferating cells. These findings suggest that APOBEC3A may play a functional role during keratinocyte differentiation, and offer a mechanism for acquisition of APOBEC3A mutagenic activity in tumours.
Insights
APOBEC3A and APOBEC3B enzymes cause cancer mutations. In normal cells, APOBEC3A is in differentiating cells, but in tumors, it’s in replicating cells, suggesting a new cancer mutation mechanism.
Area of Science:
- Molecular Biology
- Cancer Research
- Genetics
Background:
- APOBEC3A and APOBEC3B are DNA cytosine deaminase enzymes.
- These enzymes generate somatic mutations in cancer, driving tumor development and drug resistance.
Purpose of the Study:
- To investigate the expression patterns of APOBEC3A and APOBEC3B in healthy and malignant mucosal epithelia.
- To understand the cell-cycle stage and regulatory factors associated with APOBEC deaminase activity in normal and cancerous tissues.
Main Methods:
- Single-cell RNA sequencing
- Immunohistochemistry
- Spatial transcriptomics
- Functional experiments
Main Results:
- APOBEC3B is expressed in mitotic keratinocytes.
- APOBEC3A expression is primarily in terminally differentiating cells, dependent on GRHL3.
- In squamous cell carcinoma, GRHL3 expands to replicating cells, leading to APOBEC3A expression in proliferating cells.
Conclusions:
- In normal tissue, APOBEC deaminases are not highly expressed during DNA replication.
- Tumorigenic expansion of GRHL3 and APOBEC3A expression in replicating cells suggests a novel mechanism for APOBEC3A-mediated mutagenesis in cancer.
- APOBEC3A may have a functional role in keratinocyte differentiation, with potential implications for tumor development.
Related Concept Videos
01:12Role Of Notch Signalling In Intestinal Stem Cell Renewal
Direct cell-to-cell contact is needed for the activation of Notch signaling. The signal is initiated when a notch ligand binds to a receptor on an adjacent cell, also...
02:33Hedgehog Signaling Pathway
02:23Abnormal Proliferation
03:14Notch Signaling Pathway
The Notch gene came into the limelight in 1914 after the discovery that its mutation in Drosophila melanogaster leads to a serrated (or "notched") wing margin phenotype. It was not...
01:16TGF - β Signaling Pathway
01:24Regulation of Angiogenesis and Blood Supply