Essential component of a SCF-type E3 ligase complex, SCF(NIPA), a complex that controls mitotic entry by mediating ubiquitination and subsequent degradation of cyclin B1 (CCNB1). Its cell-cycle-dependent phosphorylation regulates the assembly of the SCF(NIPA) complex, restricting CCNB1 ubiquitination activity to interphase. Its inactivation results in nuclear accumulation of CCNB1 in interphase and premature mitotic entry. May have an antiapoptotic role in NPM-ALK-mediated signaling events. Protein modification; protein ubiquitination. Interacts with the NPM-ALK fusion protein in a tyrosine phosphorylation-dependent manner. Interacts with SKP1. Component of a SCF(NIPA) E3 complex with SKP1, RBX1 and CUL1 when not phosphorylated on Ser-354. Interacts with CCNB1. Widely expressed. Highly expressed in heart, skeletal muscle and testis. Expressed in brain, placenta, lung, kidney, liver, pancreas, spleen, thymus, prostate, ovary small intestine and colon. Weakly or not expressed in leukocytes. Weakly expressed in G0/G1 phases, abundant during S and G2/M phases, and strongly decreases thereafter. The F-box-like region is required for the interaction with SKP1. Phosphorylated. Phosphorylated on Ser residues at G2/M phase, but not during S and G0 phases. May also be weakly phosphorylated on Tyr residues. Ser-354 phosphorylation, a major site during the course of cell-cycle-dependent phosphorylation, results in its dissociation from the SCF(NIPA) complex, thereby preventing CCNB1 degradation leading to mitotic entry. Reported to contain a F-box domain (PubMed:16009132). Such domain is however not predicted by any detection method.