Background and purpose: High levels of SKP2 are a poor prognostic factor in multiple human cancers and mostly correlate with low p27(KIP1) levels. Prodigiosin is a bacterial tripyrrole pigment with strong proapoptotic activity. Induction of cell cycle blockade underlies one of prodigiosin's anticancer action with unclear mechanisms. The aim of this study was to explore the role of the SKP2-p27(KIP1) axis in prodigiosin's cytostatic effect on human lung adenocarcinoma cells. Experimental approach: Prodigiosin's effects on cell cycle progression and long-term cell proliferation of human lung adenocarcinoma cells were characterized by flow cytometry and colony formation assay, respectively. Real-time RT-PCR and promoter activity analyses were performed for assessing transcriptional control, while cycloheximide chase analysis for protein stability evaluation. Immunoblotting were employed for mechanistic study. Key results: Prodigiosin increased p27(KIP1) expression mainly by stabilizing p27(KIP1) through transcriptional repression of SKP2. Importantly, SKP2 overexpression or p27(KIP1) depletion restored colony formation capacity of prodigiosin-treated cells. Furthermore, prodigiosin induced AKT dephosphorylation, leading to AKT inhibition as revealed by decreased serine 9 phopshorylation of GSK-3beta. Constitutive AKT activation nearly abroagted prodigiosin-induced SKP2 repression. Additionally, prodigiosin down-regulated E2F1, previously reported to mediate PI3K/AKT-induced SKP2 transcription. However, E2F1 overexpression failed to restore SKP2 expression in prodigiosin-treated cells. Conclusions and implications: Transcriptional repression of SKP2 and the consequent accumulation of p27(KIP1) are indispensable for prodigiosin's antiproliferative action. Mechanistically, prodigiosin induces AKT inhibition to down-regulate SKP2 in GSK-3beta- and E2F1-independent manners. Our findings further implicate the potential for developing prodigiosin as a novel class of SKP2-targeting anticancer agent.
Date:
2012-08
Relation:
British Journal of Pharmacology. 2012 Aug;166(7):2095-2108.
