Cystatin A suppresses ultraviolet B-induced apoptosis of keratinocytes.

Background: Cystatin A is a cysteine proteinase inhibitor abundantly expressed in keratinocytes. Although cystatin A is one of the cornified cell envelope constituents and expressed in the upper epidermis, its precise function is still unknown. Ultraviolet B irradiation (UVB) induces apoptosis accompanied with the activation of cysteine proteinases, caspases.