| Background |
Members of the F-box family of proteins are characterized by the approximate 40 amino acid F-box motif named after cyclin F F-box proteins constitute one of the four subunits of the Skp1-Cullin-F-box (SCF) ubiquitin ligase complex. The substrate specificity of SCF complexes is determined by the interchangeable F-box proteins, which act as adaptors by associating with phosphorylated substrate proteins and recruiting them to the SCF core. F-box proteins contain two fundamental domains: the F-box motif mediates binding to Skp1 and a leucine rich repeat (LRR) domain mediates substrate interactions.Skp2 (S phase kinase-associated protein 2) interacts with cyclin A/CDK2 and mediates proper G1 to S and G2 to M phase transitions by targeting the cyclin-dependent kinase (CDK) inhibitors p27, p21, p130 and the FOXO1 transcription factor for ubiquitylation and subsequent proteolysis (3,4,5,6). Skp2 protein expression is low in G0 and early G1 phase, increases during late G1 phase, and peaks during S and G2 phases. Inactivation of Skp2 results in S/G2-phase arrested cells with endoduplication and multiple centrosomes Overexpression of Skp2 results in increased CDK activity and contributes to the deregulated proliferation and genetic instabilities typical of cancer cells Increased Skp2/decreased p27 levels are associated with many aggressive lymphomas and human carcinomas such as colon, breast, prostate and lung cancers.
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