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The Role of p21 in Apoptosis, Proliferation, Cell Cycle Arrest, and Antioxidant Activity in UVB-Irradiated Human HaCaT Keratinocytes

Aijun Chen, Xin Huang, Zhenan Xue, Di Cao, Kun Huang, Jin Chen, Yun Pan, Yongliang Gao

(Department of Dermatology, The First Affiliated Hospital, Chongqing Medical University, Chongqing, China (mainland))

Med Sci Monit Basic Res 2015; 21:86-95

DOI: 10.12659/MSMBR.893608

Published: 2015-04-30

BACKGROUND: Skin cancer is the most common cancer in the United States, and ultraviolet B (UVB) radiation-induced DNA damage is the major environmental factor underlying skin cancer development. p21, a p53-inducible protein, plays a key role in the cellular response to UVB-induced DNA damage.
MATERIAL AND METHODS: Through p21 silencing and overexpression, we investigated the role of p21 in apoptosis, proliferation, cell cycle arrest, and oxidative stress in UVB-irradiated HaCaT keratinocytes.
RESULTS: We found that UVB exposure induced significant p21 downregulation (p<0.05) and was associated with significantly increased apoptosis, significantly decreased proliferation, and significantly increased G2 phase arrest (p<0.05) in UVB-irradiated HaCaT keratinocytes. p21 silencing significantly promoted apoptosis, significantly inhibited G2 phase arrest, and significantly inhibited proliferation (p<0.05), but after UVB irradiation, p21 silencing demonstrated a less significant pro-apoptotic effect and a more significant inhibition of G2 phase arrest (p<0.05), which was reflected in significantly higher proliferative activity (p<0.05). p21 overexpression acted in an anti-apoptotic manner in the absence of UVB-induced DNA damage but acted in a pro-apoptotic manner in the presence of UVB-induced DNA damage, displaying an “antagonistic duality” similar to other growth-promoting oncoproteins. p53 expression mirrored p21 expression, suggesting a regulatory feedback mechanism between p21 and p53 expression. p21 overexpression significantly downregulated glutathione peroxidase and superoxide dismutase antioxidant activity (p<0.05) while significantly upregulating hydrogen peroxide and malondialdehyde content (p<0.05), suggesting a role in decreasing antioxidant defense capabilities in UVB-irradiated HaCaT keratinocytes.
CONCLUSIONS: These findings reveal that p21 may play a key role in HaCaT keratinocytes’ response to UVB exposure.

Keywords: Apoptosis - radiation effects, Analysis of Variance, Blotting, Western, Cell Proliferation - radiation effects, Cyclin-Dependent Kinase Inhibitor p21 - metabolism, DNA Damage, DNA Primers - genetics, Flow Cytometry, G2 Phase Cell Cycle Checkpoints - radiation effects, Gene Expression Regulation - radiation effects, Glutathione Peroxidase - metabolism, Humans, Hydrogen Peroxide - metabolism, Keratinocytes - radiation effects, Malondialdehyde - metabolism, Oxidative Stress - radiation effects, Real-Time Polymerase Chain Reaction, Superoxide Dismutase - metabolism, Tumor Suppressor Protein p53 - metabolism, Ultraviolet Rays