Jean Cook, PhD

RESEARCH INTERESTS:

Integrating DNA replication control with checkpoint signaling.

Our lab studies DNA replication licensing, which is the process that renders individual chromosomal segments competent to be duplicated. Licensing involves the construction of a multiprotein complex at replication origins called the pre-replication complex, or "preRC." In order to duplicate vast eukaryotic genomes, preRCs must be assembled at thousands of individual origins, but each of those origins must only be permitted to initiate replication once per cell cycle. PreRC assembly is under very tight regulation to prevent re-replication, which could lead to genome instability, cell death, or cancer.

PreRC assembly is only permitted during the G1 period of the cell cycle (A), and only in cellular environments that are compatible with cell division. For example, if the DNA is damaged, specific preRC proteins are inhibited or degraded so that cells don't duplicate their chromosomes inappropriately. Cells employ a variety of "checkpoint" signaling pathways to coordinate progression through the cell division cycle with a wide variety of extracellular and intracellular information. We seek to understand how the preRC assembly process is linked to these signaling pathways (B). It's clear that cancer cells have mutations that disrupt cell cycle checkpoints, but we still don't fully understand how those checkpoints are supposed to operate in normal cells. Our primary focus is on the regulation and function of two critical preRC proteins, Cdc6 and Cdt1. Some of the questions currently under study are:

• How is the replication licensing factor Cdc6 recognized by the checkpoint pathway for degradation after DNA damage?
• What happens to Cdc6 and/or Cdt1 when cell experience other forms of stress?
• How do cells behave when replication licensing is blocked?
• How do cells behave when replication licensing is hyperactive?

We manipulate various replication and checkpoint proteins in human cell lines using a variety of molecular genetic tools. We deplete proteins from cells using siRNA techniques, overproduce proteins using recombinant plasmid or viral vectors, and inhibit activities with pharmacological reagents. Ultimately we hope to achieve a greater understanding of normal cell cycle control, so that future tools for cancer diagnosis and therapy can be developed. 

RECENT PUBLICATIONS:

Hall JR, Lee HO, Bunker BD, Dorn ES, Rogers GC, Duronio RJ, Cook JG. CDT1 and CDC6 are destablized by rereplication-induced DNA damage. J Biol Chem. 2008 Jul 10.

McCall CM, Miliani de Marval PL, Chastain PD 2nd, Jackson SC, He YJ, Kotake Y, Cook JG, Xiong Y. HIV-1 Vpr-binding protein VprBP, a WD40 protein associated with the DDB1-CUL4 E3 ubiquitin ligase, is essential for DNA replication and embryonic development. Mol Cell Biol. 2008 Jul 7.

Hall JR, Kow E, Nevis KR, Lu CK, Luce KS, Zhong Q, Cook JG. Cdc6 stability is regulated by the Huwe1 ubiquitin ligase after DNA damage. Mol Biol Cell. 2007 Sep;18(9):3340-50.

Braden WA, Lenihan JM, Lan Z, Luce KS, Zagorski W, Bosco E, Reed MF, Cook JG, Knudsen ES. Distinct action of the retinoblastoma pathway on the DNA replication machinery defines specific roles for cyclin-dependent kinase complexes in prereplication complex assembly and S-phase progression. Mol Cell Biol. 2006 Oct;26(20):7667-81.