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Objective   To explore the effect and mechanism of ultraviolet B (UVB) on melanin synthesis and premature senescence in human immortalized keratinocytes (HaCaT) cells.Methods   HaCaT cells were irradiated with 0, 20, 50, 80, 100, 150, and 200 mJ/cm 2  of UVB. NaOH method was used for melanin content assay, cellular tyrosinase (TYR) activity was determined by 3,4-Dihydroxy-L-phenylalanine (L-DOPA) oxidation to dopachrome, premature senescence was analyzed by senescence-associated beta-galactosidase (SA-β-gal) staining kit, and the levels of p21, p16, p62, and GATA4 proteins were detected by Western blotting. Premature senescence was inhibited by the inhibitors of ataxia telangiectasia mutated (ATM) or ataxia telangiectasia and Rad3–related (ATR), and the p53 signaling pathway was activated by Nutlin-3. The mRNA levels of senescence-associated secretory phenotype (SASP) factors including tumor necrosis factor alpha (TNF-α), vascular endothelial growth factor A (VEGF-A), and interleukin-8 (IL-8) were measured by real-time quantitative polymerase chain reaction in HaCaT cells after 80 mJ/cm 2  of UVB irradiation.Results   The melanin level increased significantly with the elevation of irradiation dose ( F = 28.19, 43.82, 143.60, P &lt; .05), reaching the peak at the dose of 80 mJ/cm 2 . The tyrosinase activity increased significantly ( F = 84.50, P &lt; .05), the percentage of premature senescence increased ( F = 16.31, P &lt; .05), the levels of p62 decreased, and the level of GATA4 increased obviously with the increase of UVB dose after irradiation. The UVB-induced promotion of GATA4 level was significantly inhibited by being treated with ATM or ATR inhibitor. However, this did not occur in the Nutlin-3-treated group. The mRNA and protein expression of TNF-α increased significantly at 72 h at 80 mJ/cm 2  of UVB irradiation.Conclusions   Melanin contents increased first and decreased afterward with the increasing of UVB irradiation. The decrease of p62-mediated selective autophagy was accompanied by the accumulation of GATA4 after different doses of UVB irradiation. Activation of this p62/GATA4 pathway depends on the ATM and ATR but is independent of p53, and the SASP factor was activated in HaCaT cells at 80 mJ/cm 2  of UVB irradiation.

Effect of Ultraviolet B Irradiation on Melanin Content Accompanied by the Activation of p62/GATA4-Mediated Premature Senescence in HaCaT Cells