14-3-3 Proteins Play a Role in the Cell Cycle by Shielding Cdt2 from Ubiquitin-Mediated Degradation

Abstract

Cdt2 is the substrate recognition adaptor of CRL4^Cdt2 E3 ubiquitin ligase complex and plays a pivotal role in the cell cycle by mediating the proteasomal degradation of Cdt1 (DNA replication licensing factor), p21 (cyclin-dependent kinase [CDK] inhibitor), and Set8 (histone methyltransferase) in S phase. Cdt2 itself is attenuated by SCF^FbxO11-mediated proteasomal degradation. Here, we report that 14-3-3 adaptor proteins interact with Cdt2 phosphorylated at threonine 464 (T464) and shield it from polyubiquitination and consequent proteasomal degradation. Depletion of 14-3-3 proteins promotes the interaction of FbxO11 with Cdt2. Overexpressing 14-3-3 proteins shields Cdt2 that has a phospho-mimicking mutation (T464D [change of T to D at position 464]) but not Cdt2(T464A) from ubiquitination. Furthermore, the delay of the cell cycle in the G₂/M phase and decrease in cell proliferation seen upon depletion of 14-3-3γ is partly due to the accumulation of the CRL4^Cdt2 substrate, Set8 methyltransferase. Therefore, the stabilization of Cdt2 is an important function of 14-3-3 proteins in cell cycle progression.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.00838-14.

ACKNOWLEDGMENTS

We thank members of the Dutta laboratory for discussion, suggestions, and helpful comments. We are grateful to Michele Pagano (NYU Cancer Institute) for providing phospho-Cdt2 antibody.

This work is supported by R01 grants CA60499 and CA166054 to A. Dutta.