HaCaT cells, obtained from the Korea Cell Line Bank (Seoul, Korea), were maintained at 37 °C in a humidified atmosphere under 5% CO2 in RPMI 1640 or Dulbecco’s modified Eagle’s medium (DMEM, Invitrogen Gibco BRL, Gaithersburg, MD, USA), containing 10% heat-inactivated foetal bovine serum, 100 U/ml of penicillin, and 100 μg/ml of streptomycin. Solubilised PSC was added to the media to reach the indicated concentration for the PSC treatment. The PSC solution at the indicated concentration was incubated for 30 min, removed from the plate, and washed with PBS once, then seeded with cells.