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Targeted deletion of Rad9 in mouse skin keratinocytes enhances genotoxin-induced tumor development
Zhishang Hu1, Yuheng Liu, Chunbo Zhang
1National Laboratory of Biomacromolecules, Chinese Academy of Sciences, Beijing, China.
Abstract:
The Rad9 gene is evolutionarily conserved from yeast to humans and plays crucial roles in genomic maintenance, DNA repair, and cell cycle checkpoint controls. However, the function of this gene with respect to tumorigenesis is not well-understood. A Rad9-null mutation in mice causes embryonic lethality. In this study, we created mice in which mouse Rad9, Mrad9, was deleted only in keratinocytes to permit examination of the potential function of the gene in tumor development. Mice with Mrad9(+/-) or Mrad9(-/-) keratinocytes showed no overt, spontaneous morphologic defects and seemed similar to wild-type controls. Painting the carcinogen 7,12-dimethylbenzanthracene (DMBA) onto the skin of the animals caused earlier onset and more frequent formation of tumors and senile skin plaques in Mrad9(-/-) mice, compared with Mrad9(+/-) and Mrad9(+/+) littermates. DNA damage response genes p21, p53, and Mrad9B were expressed at higher levels in Mrad9(-/-) relative to Mrad9(+/+) skin. Keratinocytes isolated from Mrad9(-/-) skin had more spontaneous and DMBA-induced DNA double strand breaks than Mrad9(+/+) keratinocytes, and the levels were reduced by incubation with the antioxidant epigallocatechin gallate. These data suggest that Mrad9 plays an important role in maintaining genomic stability and preventing tumor development in keratinocytes.
Insights
The mouse Rad9 gene (Mrad9) deletion in skin cells accelerates tumor formation. Loss of Mrad9 increases DNA damage, suggesting its role in preventing skin cancer development.
Area of Science:
- Genetics
- Molecular Biology
- Dermatology
Background:
- The Rad9 gene is vital for DNA repair and cell cycle control across species.
- Its specific role in skin tumorigenesis remains unclear.
- Rad9-null mutations are lethal in mice, necessitating conditional deletion studies.
Purpose of the Study:
- To investigate the function of mouse Rad9 (Mrad9) in skin tumor development.
- To determine if Mrad9 deletion in keratinocytes influences susceptibility to chemical carcinogens.
Main Methods:
- Generated mice with keratinocyte-specific deletion of Mrad9 (Mrad9(+/+), Mrad9(+/-), Mrad9(-/-)).
- Applied the carcinogen 7,12-dimethylbenzanthracene (DMBA) to mouse skin.
- Analyzed tumor formation, DNA damage response gene expression (p21, p53, Mrad9B), and DNA double-strand breaks in keratinocytes.
Main Results:
- Mice with Mrad9(-/-) keratinocytes exhibited earlier onset and increased frequency of DMBA-induced tumors and skin plaques.
- Elevated expression of DNA damage response genes (p21, p53, Mrad9B) was observed in Mrad9(-/-) skin.
- Keratinocytes lacking Mrad9 showed higher levels of spontaneous and DMBA-induced DNA double-strand breaks, which were mitigated by an antioxidant.
Conclusions:
- Mrad9 plays a significant role in maintaining genomic stability within keratinocytes.
- Loss of Mrad9 function in skin cells promotes tumor development, highlighting its tumor-suppressive function.
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