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Cell division is one of the most basic processes of living organisms, yet the mechanisms regulating this complicated process remain unclear at many points. Understanding the regulators that are involved in different stages of the cell cycle is critical to determining how and why cells lose normal controls and checkpoints, resulting in transformation and oncogenesis. This understanding can lead the way toward identifying new drug targets or novel therapies to fight cancer.
The research in this laboratory is focused on understanding the regulation of the onset of DNA replication or S phase in vertebrates. This point in the cell cycle is a major checkpoint of cell division where cells must correctly and with high fidelity initiate the replication of the genome following mitosis while ensuring that replication occurs only once per cell cycle. Premature entry into S phase due to aberrantly high cyclin-dependent kinase (CDK) activity or low CDK inhibitor activity has been shown to cause genomic instability, a hallmark of cancer cells.
Using mammalian cells and egg extracts from the frog, Xenopus laevis, we have shown that Cip-type CDK inhibitors are targeted for ubiquitination and degradation during DNA polymerase switching in a manner that is dependent upon chromatin, Proliferating Cell Nuclear Antigen (PCNA), and the ubiquitin ligase called CRL4Cdt2. Our studies have sought to understand the molecular mechanisms that regulate the onset of DNA replication initiation and to understand how these mechanisms are altered in cancer cells. Studies have shown that Cip/Kip-type CDK inhibitors are frequently expressed at aberrantly low levels in cancer cells while their genes are not mutated. Instead, we hypothesize that the machinery that controls CDK inhibitor turnover is misregulated in cancer cells. In support of this hypothesis, our recent studies show that Cdt2, the substrate targeting component of CRL4Cdt2, is upregulated in many cancers and Cdt2 upregulation correlates with poor patient survival. We hope to understand how Cdt2 is misregulated in cancer cells and to discover methods to reverse this cancer phenotype.
Another project in the laboratory seeks to understand how Retinoblastoma (Rb) in conjunction with the replication protein, MCM7, and the signaling molecule TGFβ, aids in preventing prostate and other cancers. Our studies have identified a non-canonical function of Rb that inhibits the transition between pre-replication and pre-initiation complex formation through Rb’s binding to MCM7. This non-canonical function of Rb is not dependent upon transcriptional repression of E2F and instead appears to involve direct Rb binding to origins of replication. Our studies are focused on understanding the molecular mechanisms of this non-canonical function of Rb and its role in tumor suppression.
An additional area of research in the laboratory focuses on understanding how the tumor suppressor protein complex, BRCA1-BARD1, contributes as an ubiquitin ligase to prevent breast cancer. Our studies have identified USP7 as a negative regulator of BRCA1-BARD1-mediated ubiquitination and we hope to understand how this negative regulator of BRCA1-BARD1 may function in the progression of breast cancer.
- Zhu XN, Kim DH, Lin HR, Budhavarapu VN, Rosenbaum HB, Mueller PR, Yew PR: (2013) Proteolysis of xenopus Cip-type CDK inhibitor, p16Xic2, is regulated by PCNA binding and CDK2 phosphorylation. Cell Div. 8(1): 5. DOI: 10.1186/1747-1028-8-5. [ePub ahead of print.]
- Lu Y, Li J, Cheng D, Parameswaran B, Zhang S, Jiang Z, Yew PR, Peng J, Ye Q, and Hu Y: (2012) The F-box protein FBX044 mediates BRCA1 ubiquitination and degradation. J Biol Chem. 287(49): 41014-22.
- Yew PR and Philpott A: (2011) The Xenopus cell cycle: an overview. In Protocols in Cell Cycle Control (Methods in Molecular Biology). Edited by Gavin Brooks and Katrina Bicknell. Humana Press.
- Nair BC, Nair SS, Chakravarty D, Challa R, Manavathi B, Yew PR, Kumar R, Tekmal RR, and Vadlamudi RK: (2010) Cyclin-dependent kinase-mediated phosphorylation plays a critical role in the oncogenic functions of PELP1. Cancer Res. 70(18): 7166-75.
- Kim DH, Budhavarapu VN, Herrera CR, Nam HW, Kim YS, and Yew PR: (2010) The CRL4Cdt2 ubiquitin ligase mediates the proteolysis of cyclin-dependent kinase inhibitor Xic1 through a direct association with PCNA. Mol Cell Biol. 30(17): 4120-33.
- Wise H, Philpott A, Yew PR, and Richard-Parpaillon L: (2009) Cell cycle regulation during early development in Xenopus. In Cell Cycle and Development in Vertebrates. P. 71-88. Edited by Jacek Z. Kubiak, Maria A. Ciemerych, and Laurent Richard-Parpaillon. ISBN 978-81-308-0327-2. Research Signpost.
- Philpott A and Yew PR: (2008) The Xenopus cell cycle: an overview. Mol Biotechnol. 39(1): 9-19.
- Boix-Perales H, Horan I, Wise H, Lin HR, Chuang LC, Yew PR, and Philpott A: (2007) The E3 ubiquitin ligase Skp2 regulates neural differentiation independent from the cell cycle. Neural Dev. 2: 27.
- Lin HR, Chuang LC, Boix-Perales H, Philpott A, and Yew PR: (2006) Ubiquitination of cyclin-dependent kinase inhibitor, Xic1, is mediated by the Xenopus F-box protein xSkp2. Cell Cycle. 5(3): 304-14.
- Block K, Appikonda S, Lin HR, Bloom J, Pagano M, and Yew PR: (2005) The acidic tail domain of human Cdc34 is required for p27Kip1 ubiquitination and complementation of a cdc34 temperature sensitive yeast strain. Cell Cycle. 4(10): 1421-7.
- Chuang LC and Yew PR: (2005) Proliferating cell nuclear antigen recruits cyclin-dependent kinase inhibitor Xic1 to DNA and couples its proteolysis to DNA polymerase switching. J Biol Chem. 280(42): 35299-309. (Selected as a JBC Paper of the Week.)
- Chuang LC, Zhu XN, Herrera CR, Tseng HM, Pfleger CM, Block K, and Yew PR: (2005) The C-terminal domain of the Xenopus cyclin-dependent kinase inhibitor, p27Xic1, is both necessary and sufficient for phosphorylation-independent proteolysis. J Biol Chem. 280(42): 35290-8.
- Philpott A and Yew PR: (2005) The Xenopus cell cycle: an overview. In Cell Cycle Control: Mechanisms and Protocols (Methods in Molecular Biology), Volume 296, p. 95-112. Edited by Tim Humphrey and Gavin Brooks. ISBN 978-1-58829-144-8 (Print); 978-1-59259-857-1 (Online). Humana Press.
- Chauhan D, Li G, Hideshima T, Podar K, Shringarpure R, Mitsiades C, Munshi N, Yew PR, and Anderson KC: (2004) Blockade of ubiquitin-conjugating enzyme CDC34 enhances anti-myeloma activity of Bortezomib/Proteasome inhibitor PS-341. Oncogene. 23(20): 3597-602.
- Block K, Boyer TG, and Yew PR: (2001) Phosphorylation of the human ubiquitin-conjugating enzyme, CDC34, by casein kinase 2. J Biol Chem. 276(44): 41049-58.
- Yew PR: (2001) Ubiquitin-mediated proteolysis of vertebrate G1- and S-phase regulators. J Cell Physiol. 187(1): 1-10.
- Chuang LC and Yew PR: (2001) Regulation of nuclear transport and degradation of the Xenopus cyclin-dependent kinase inhibitor, p27Xic1. J Biol Chem. 276(2): 1610-7.
- Yew PR and Kirschner MW: (1997) Proteolysis and DNA replication: the CDC34 requirement in the Xenopus egg cell cycle. Science. 277(5332): 1672-6.