UVB-Induced Cellular Stress Assays

Cells were harvested with trypsin-EDTA (Biosera, Budapest, Hungary) and then seeded in six-well plates for the hypoxanthine phosphoribosyltransferase (HPRT) gene mutation assay or 24-well plates for all other experiments. At ~80% confluence, cells were pretreated with 25 μM ABT-888 (PARP1 inhibitor, veliparib, Selleckchem, Houston, TX, USA), 10–50 μM resveratrol (Abcam, Cambridge, UK), 5–25 μM spironolactone (Selleckchem, Houston, TX, USA), or 0.5–4 μg/mL As₂O₃ (Sigma-Aldrich, St. Louis, MO, USA) solution. In the case of veliparib treatment, we chose the concentration that caused marked inhibition of PARP1 protein, according to our previous [29 (link)] and current experiments (Figure S9). For the other chemicals, we identified three different concentrations due to their more complex and not fully understood mode of action—based on prior published data [26 (link),27 (link),30 (link),31 (link),32 (link)]. As₂O₃ was dissolved in 1 M NaOH (Sigma-Aldrich, St. Louis, MO, USA) and diluted in Dulbecco’s phosphate-buffered saline (DPBS; Biosera, Budapest, Hungary). Other chemicals were dissolved in dimethyl sulfoxide (DMSO, Sigma-Aldrich, St. Louis, MO, USA). Pretreated cells were incubated for 120 min at 37 °C before UVB irradiation.