| 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.S phase kinase-associated protein 2 (Skp2) interacts with cyclin A/CDK2 and mediates G1 to S and G2 to M phase transitions by targeting the cyclin-dependent kinase (CDK) inhibitors p27, p21, and p130 for ubiquitination and subsequent proteolysis Overexpression of Skp2 results in deregulated proliferation and genetic instabilities typical of cancer cells Research studies have shown that increased Skp2/decreased p27 levels are associated with many aggressive lymphomas and human carcinomas such as colon, breast, prostate and lung cancers Several recent research studies have demonstrated that Skp2 is subject to phosphorylation-dependent regulation by a network of pro-proliferative Ser/Thr kinases. It appears as though phosphorylation of Skp2 at Ser64 by CDK2 Ser72 by Akt1 and Thr417 by PIM1 promotes stabilization of Skp2, possibly constituting an additional mechanism for Skp2 oncogenicity.
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