PIP-box-mediated degradation prohibits re-accumulation of Cdc6 during S phase

J Cell Sci. 2014 Mar 15;127(Pt 6):1336-45. doi: 10.1242/jcs.145862. Epub 2014 Jan 16.


Cdc6 and Cdt1 initiate DNA replication licensing when cells exit mitosis. In cycling cells, Cdc6 is efficiently degraded from anaphase onwards as a result of APC/C-Cdh1 activity. When APC/C-Cdh1 is switched off again, at the end of G1 phase, Cdc6 could thus re-accumulate, risking the re-licensing of DNA as long as Cdt1 is present. Here, we carefully investigated the dynamics of Cdt1 and Cdc6 in cycling cells. We reveal a novel APC/C-Cdh1-independent degradation pathway that prevents nuclear Cdc6 re-accumulation at the G1-S transition and during S phase. Similar to Cdt1, nuclear clearance of Cdc6 depends on an N-terminal PIP-box and the Cdt2-containing CRL4 complex. When cells reach G2 phase, Cdc6 rapidly re-accumulates but, at this time, Cdt1 is mostly absent and expression of Cdc6 is limited to the cytoplasm. We propose that Cdk1 contributes to the nuclear export of Cdc6 at the S-to-G2 transition. In summary, our results show that different control mechanisms of Cdc6 restrain erroneous licensing of DNA replication during G1, S and G2 phase.

Keywords: CRL4–Cdt2; Cdc6; Cdt1; Cell cycle; PCNA; PIP-box.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Antigens, CD
  • CDC2 Protein Kinase
  • Cadherins / metabolism
  • Cell Cycle Proteins / chemistry
  • Cell Cycle Proteins / metabolism*
  • Cell Line, Tumor
  • Cell Nucleus / metabolism
  • Conserved Sequence
  • Cyclin-Dependent Kinases / metabolism
  • DNA Replication
  • Humans
  • Nuclear Proteins / chemistry
  • Nuclear Proteins / metabolism*
  • Proteolysis
  • S Phase*
  • Ubiquitin-Protein Ligases / metabolism


  • Antigens, CD
  • CDC6 protein, human
  • CDH1 protein, human
  • Cadherins
  • Cell Cycle Proteins
  • DTL protein, human
  • Nuclear Proteins
  • Ubiquitin-Protein Ligases
  • CDC2 Protein Kinase
  • CDK1 protein, human
  • Cyclin-Dependent Kinases