Regulation of p27 by S-phase kinase-associated protein 2 is associated with aggressiveness in non-small-cell lung cancer.

PURPOSE: The F-box protein S-phase kinase-associated protein 2 (Skp2) is one of the positive regulators of the cell cycle that promote ubiquitin-mediated proteolysis of the cyclin-dependent kinase inhibitor p27. In this study, we investigated the significance of Skp2 expression in human non-small-cell lung cancer (NSCLC). PATIENTS AND METHODS: Clinicopathologic features and immunohistochemical expression of Skp2 and p27 proteins were studied in 138 patients with NSCLC. Survival analyses were performed using the Kaplan-Meier method and the Cox regression model. To analyze the role of Skp2 in vitro, NSCLC cells were transfected with an Skp2-expressing vector or small interfering RNA. RESULTS: Skp2 was overexpressed in males, smokers, patients with squamous cell carcinomas, and patients with poorly differentiated cancers (P = .034, < .0001, < .0001, and .002, respectively). The multivariant analysis revealed that Skp2 expression is an independent prognostic factor for survival in NSCLC. An inverse relationship of Skp2 with p27 expression was observed (P = .012), and patients with both a higher expression of Skp2 and a lower expression of p27 showed a significantly unfavorable prognosis (P = .0002). In vitro ectopic expression of Skp2 in NSCLC cells reduced the protein level of p27. Conversely, induction of Skp2 siRNA increased the protein level of p27, leading to growth inhibition in NSCLC cells. CONCLUSION: Skp2 overexpression is closely associated with the suppression of p27 and the aggressiveness in NSCLC. It also could be a therapeutic target in NSCLC.