KITLG and neoplasm: Of these, the S-phase kinase-associated protein 2 (SKP2) plays a critical role in coordinating the G1/S transition, cell cycle progression, forms a substrate recognition subunit of SCF ubiquitin-protein ligase complex, and inhibits the tumor suppressor function of FOXO1. Over expression of SKP2 was found in many tumor types, consistent with a role of an oncogene, and is associated with poor clinical outcome [33].