Adenoid cystic carcinoma (ACC) is a malignant salivary gland tumor, which shows frequent recurrence and metastasis, ultimately with a poor outcome. We previously demonstrated that p27 down-regulation is frequently found and is due to an enhancement of its degradation in ACC. Here we transfected non-degradable p27 mutant (T187A) and wild type gene into ACC cell line. Transfection of T187A mutant gene was more effective on inhibition of cell growth of ACC cells, suggesting that aberration of p27 degradation may be present in ACC. As F-box protein Skp2, which is necessary for ubiquitin-mediated degradation of p27, is involved in p27 down-regulation in various cancers, we examined the Skp2 expression and its correlation with p27 expression in 50 ACC cases. We found Skp2 expression in 36% of ACC cases and inverse correlation between the expression of Skp2 and p27. Moreover, Skp2 siRNA transfection decreased Skp2 protein and accumulation of p27 protein and inhibited the cell growth of ACC cells in vitro. These findings overall suggest that Skp2 may play an important role in ACC development through the down-regulation of p27, and that Skp2 siRNA can be a novel modality of cancer gene therapy for suppression of p27 down-regulation in ACC
