As one of the most common hyperproliferative skin diseases,psoriasis vulgaris is characterized by keratinocyte hyperproliferation,profound changes in keratinocyte maturation and turnover rate. Inaddition, an abnormal resistance of psoriatic keratinocytes toapoptosis may contribute to the epidermal hyperplasia (Wrone-Smithet al., 1997).Progression of cells from G 1 to S phase is regulated via pRbphosphorylation by cyclin D complexed with CDK 4 and 6, which arein turn regulated by CDKI, such as p16 INK4 protein (Beasley et al.,2003).