Abstract: 【Abstract】 Objective To investigate the effects of cyclin A2 （CCNA2） and cyclin-dependent kinase 1 （CDK1） on cell cycle- and apoptosis-related protein expression in HaCaT cells exposed to ultraviolet B （UVB） radiation. Methods The transcriptome sequencing dataset GSE86406 from patients with solar dermatitis （SD） was obtained from the Gene Expression Omnibus （GEO） database. Through differential gene expression analysis, Kyoto Encyclopedia of Genes and Genomes enrichment analysis, and protein-protein interaction network analysis, CCNA2 and CDK1 were identified to be key genes involved in the pathogenesis of SD. Their effects on the function of human keratinocytes were further explored in vitro. Human keratinocyte HaCaT cells were divided into a normal control （NC） group （cultured under standard conditions） and a UVB group （irradiated at a cumulative dose of 30 mJ/cm2）. The expression of CCNA2 and CDK1 was determined by Western blot analysis. CCNA2 and CDK1 were overexpressed separately or co-overexpressed in HaCaT cells, followed by UVB irradiation （i.e., a CCNA2 + UVB group, a CDK1 + UVB group, and a CCNA2 + CDK1 + UVB group）, and the NC group and UVB group served as controls. Flow cytometry was performed to analyze changes in the cell cycle, while Western blot analysis was employed to determine the expression of proliferation-related proteins （Ki-67 and proliferating cell nuclear antigen ［PCNA］） and apoptosis-related proteins （B-cell lymphoma 2 ［Bcl-2］, Bcl-2-associated X protein ［Bax］, caspase-3, and cleaved caspase-3）. Co-immunoprecipitation assay was performed to investigate the interaction between CCNA2 and CDK1. Results Analysis of GEO sequencing data from human SD samples showed that the expression of CCNA2 and CDK1 was significantly lower in the SD group than in the healthy control group （log2FC = -1.16, -1.13, t = -6.71, -5.47, respectively, both P < 0.001）. Western blot analysis revealed that CCNA2 and CDK1 protein expression was significantly lower in the UVB group than in the NC group （t = 5.93, 6.39, P = 0.004, 0.003, respectively）. Compared with the UVB group （G1 phase: 65.66% ± 0.30%, S phase: 27.56% ± 0.43%, G2 phase: 6.77% ± 0.28%）, the CCNA2 + UVB group （G1 phase: 69.31% ± 0.61%, S phase: 21.53% ± 0.44%, G2 phase: 9.16% ± 0.58%） and the CCNA2 + CDK1 + UVB group （G1 phase: 69.15% ± 0.30%, S phase: 20.02% ± 0.11%, G2 phase: 10.83% ± 0.34%） showed increased percentages of HaCaT cells in G1 and G2 phases and decreased percentages of HaCaT cells in S phase （all P < 0.001）, while the CDK1 + UVB group （G1 phase: 56.16% ± 0.27%, S phase: 36.36% ± 0.28%, G2 phase: 7.48% ± 0.34%） exhibited decreased percentages of HaCaT cells in G1 phase （P < 0.001）, increased percentages of HaCaT cells in S phase （P < 0.001）, and no significant difference in the percentages of HaCaT cells in G2 phase （P = 0.102）. As Western blot analysis further revealed, compared with the UVB group （Ki-67: 0.92 ± 0.18; PCNA: 0.54 ± 0.10; Bax: 1.98 ± 0.29; Bcl-2: 0.46 ± 0.10; cleaved caspase-3: 2.05 ± 0.20）, both the CCNA2 + UVB group and CDK1 + UVB group exhibited increased Ki-67 expression （1.75 ± 0.18, 1.70 ± 0.13, respectively, both P < 0.05）, no significant change in PCNA expression （0.99 ± 0.13, 1.00 ± 0.01, respectively, both P > 0.05）, reduced Bax expression （1.18 ± 0.67, 0.79 ± 0.19, respectively, both P < 0.05）, and increased Bcl-2 expression （0.88 ± 0.06, 0.86 ± 0.07, respectively, both P < 0.05）, the CCNA2 + UVB group showed no significant change in cleaved caspase-3 expression （1.55 ± 0.04, P > 0.05）, while the CDK1 + UVB group revealed reduced cleaved caspase-3 expression （0.93 ± 0.07, P < 0.001）; moreover, compared with the CCNA2 + UVB group and/or CDK1 + UVB group, the CCNA2 + CDK1 + UVB group showed further upregulation of Ki-67 and Bcl-2 expression （2.15 ± 0.14, 0.91 ± 0.02, respectively, both P < 0.01）, further downregulation of Bax and cleaved caspase-3 expression （0.73 ± 0.05, 0.71 ± 0.08, respectively, both P < 0.01）, and upregulation of PCNA expression （1.33 ± 0.12, P < 0.01）. Co-immunoprecipitation assay confirmed the interaction between CCNA2 and CDK1. Conclusion CCNA2 could interact with CDK1 to cooperatively promote the cell cycle progression and proliferation of keratinocytes, but inhibit their apoptosis.

Key words: Dermatitis, Solar dermatitis, CCNA2, CDK1, Cell cycle, Cell proliferation, Apoptosis