p16 expression in psoriatic lesions following therapy with propylthiouracil, an antithyroid thioureylene.
Plaque formation is a characteristic finding in patients with psoriasis and reflects cytokine-induced keratinocyte proliferation and/or impaired apoptosis of keratinocytes. Antithyroid thioureylenes such as propylthiouracil (PTU) and methimazole (MMI) are effective in the treatment of plaque psoriasis. Following PTU and MMI treatment, proliferative cell nuclear antigen (PCNA) expression is significantly reduced, suggesting that these medications have an antiproliferative effect. p16 is an antiapoptotic protein that is present in relative abundance in psoriatic plaques and is believed to play a potential role in the persistent senescence and impaired apoptosis of the keratinocytes in the plaque. This study examined p16 expression in biopsy samples of eight patients with plaque psoriasis given 300 mg of propylthiouracil in divided doses for 3 months. Despite significant clinical and histological improvement with PTU treatment, p16 expression was essentially unchanged, suggesting that the beneficial effect of PTU in psoriasis is not mediated through a decrease in p16 expression. The effect of PTU on other antiapoptotic proteins such as bcl-xL remains to be determined.