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Cyclin B1 Regulates Its Regulator

The Skp, Cullin, F-box-containing complex (SCF complex) is a multiprotein complex that catalyzes the ubiquitination of proteins destined for proteasomal degradation. Protein substrates are recognized by an F-box protein and delivered to an E3 ligase through the bridging protein, Skp. Cullin acts as a scaffold for the complex. NIPA (nuclear interaction partner of ALK) is the F-box protein of an SCF complex (SCF^NIPA) that targets nuclear cyclin B1 for ubiquitination in interphase. Phosphorylation of NIPA in late G₂ phase and mitosis inactivates the complex, allowing for accumulation of cyclin B1.

Model of NIPA phosphorylation at G2/M.

In this paper of the week, Florian Bassermann and colleagues identify the region of NIPA that mediates cyclin B1 binding. Furthermore, they show that cyclin B1/Cdk1 phosphorylates NIPA during mitosis. This suggests that cyclin B1/Cdk1 contributes to the mitotic inactivation of the SCF^NIPA complex via a negative feedback loop and thus may be involved in the regulation of its own nuclear abundance in early mitosis.

FOOTNOTES

See referenced article, J. Biol. Chem. 2007, 282, 15965-15972

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