Dr. Hoyun Lee

Office: /N.E.O.R.C.C.
Lab: /N.E.O.R.C.C.

Mailing Address:
Dr. H. Lee
Regional Cancer Program
Northeastern Ontario Regional Cancer Centre of the
Hôpital Régional de Sudbury Regional Hospital
41 Ramsey Lake Road
Sudbury Ontario P3E 5J

Telephone:
Voice: (705) 522-6237, ext 2703
FAX: (705) 523-7326

Internet:
hlee@hrsrh.on.ca

www.neorcc.on.ca

Current Position

Scientist, Cancer Care Ontario
Associate Professor of Medicine and Biochemistry, the University of Ottawa
Affiliate Associate Professor of Biochemistry and Biology, Laurentian University.

Education, Training and Previous Positions

1995 - 1996 Assistant Professor of Research, the Departments of Radiation Oncology, the University of Virginia Medical School
1992 - 1994 Research Associate/Postdoctoral Fellow, the Department of Biochemistry and Genetics, the University of Virginia Medical School
1988 - 1992 Ph.D., Molecular Virology. The University of Guelph, Ontario, 1992
1996 - 1998 M.Sc., Microbiology. The University of Guelph, Ontario, 1988

Awards and Honours

2001 Premier's Research Excellence Award (PREA)
1994 Young Investigator Award, Radiation Research Society
1994 Travel Award, Radiation Research Society

Other Scholarly Activities

2002 - Present Grant Review Panel member, National Cancer Institute of Canada (NCIC)
1999 - 2003 Grant Review Panel member, MRC/CIHR

Research Funding

(1) National Cancer Institute of Canada (NCIC # 016072). PI, Hoyun Lee

$119,054 per year (July 1, 2005 - June 30, 2009)
$121,554 per year (July 1, 2009 – June 30, 2010)
Title: The regulation of proliferating nuclear antigen (PCNA) functions.

(2) Canadian Institutes of Health Research (CIHR)
$106,964 per year for three years (October 2002- September 2005)
Title: The role of Dbf4 in the control of chromosome replication and the S-phase checkpoint.

(3) Natural Sciences and Engineering Research Council of Canada (NSERC)
$25,00 per annum for four years (April 2002- March 2006).
Title: Determining the hamster Cdc7 and Dbf4 amino acid residues that are required for kinase activity.

(4) Canadian Breast Cancer Foundation. PI, Hoyun Lee
$150,926 (2005 – 2007)
Title: Developing effective combined modalities using radiation and chemical compounds to treat breast cancer: targeting the P13K-Akt signal pathway

(5) Premier=s Research Excellence Award (2001-2005), $150,000

(6) Northern Cancer Research Foundation, $80,000 per year

(7) FedNor (2004/5), $27,500

(8) Ontario Research and Challenge Fund - Group grant (2000-2005)

Laboratory Staff

Research Projects

The Cdc7-Dbf4 complex may also be able to turn off DNA replication when a cell faces a crisis occurred by genotoxic agents such as ionising radiation or chemotherapeutic agents, which mechanism is called checkpoint. Although the deregulation of checkpoint mechanisms may result in tumorigenic development, its main consequence is cell death by continuous replication or cell division with unrepaired damage. Both radiation treatment and chemotherapy often kill cancer cells by rendering severe damage to their DNA. Cancer cells are generally vulnerable to radiation and anti-cancer drugs because they are actively dividing. However, cancer cells can develop amazing abilities to survive from the damage rendered by radiation and chemotherapeutic drugs, resulting in failure of cancer therapy. It is thought that operation of the checkpoint mechanism plays an important role for the increased survival of cancer cells to a challenge by genotoxic agents. While examining the regulation of cell division processes several years ago, I discovered that mammalian cells operate an effective turn-off mechanism in response to radiation at the very beginning of DNA replication. Recently, we and others have found several lines of evidence that the Cdc7-Dbf4 complex may play a critical role in this checkpoint control mechanism. To gain a better understanding about how these two proteins are involved in this biologically interesting and clinically important control mechanism, we set out the following two specific objectives:

Firstly, we want to determine as to how mammalian Cdc7 and Dbf4 regulate the activation of DNA replication. We hypothesize that the protein levels, timing of expression (i.e., making proteins), interactions with other proteins, and the localization of these proteins within the cell play important regulatory roles. Secondly, we want to determine how Cdc7 and Dbf4 proteins transiently arrest DNA replication and cell-cycle progression in response to radiation to increase cells’ survivability. We think that protein modifications, protein-protein interactions, and subcellular translocation of Cdc7 and Dbf4 proteins play important regulatory functions.

2. Molecular mechanisms of tumor cell radiosensitivity
Despite that radiation therapy has considerably improved during the last several decades, local failure after radiation treatments is still a serious problem. This failure is often due to the selection of more radioresistant subpopulations during radiation therapy. We are trying to understand the cellular response to radiation at molecular levels and, eventually, to develop effective combined modality therapies to control cancers using radiation and chemotherapeutic agents.
To initiate a systematic study to determine how breast and cervical cancers are repopulated by more radioresistant cells during radiation treatments, we previously generated model systems by mimicking the fractionation schemes that are used in a clinical setting. The two model systems used for this study were (i) MDA-MB231 that was originally derived from an estrogen-independent and p53-mutated breast cancer cell, and (ii) HeLa cell line, which was from a papilloma virus-positive cervical cancer cell.

Our data showed, among others, that a decrease in apoptotic potential is the single most important factor in gaining radioresistance during fractionated radiation treatments (Radiat Res, 156:739-750 [2001]). Using DNA microarray assays, we have identified that the PI3-kinase-mediated signal transduction and protein degradation pathways are important for determining cell death/survival. We are currently examining as to how these survival mechanisms are differentially regulated in radio-sensitive and -resistant isogenic cells against a radiation challenge.

(3) The structure-function and post-translational modifications of PCNA

Proliferating cell nuclear antigen (PCNA), which functions as a DNA sliding clamp/processivity factor for DNA polymerases ? and ?, is an essential component for eukaryotic chromosome replication. In addition, PCNA is also involved in a wide range of other cellular activities, including DNA damage repair, cell-cycle control, apoptosis and epigenetic inheritance. These diverse functions of PCNA may be regulated largely by post-translational modifications and association with different protein partners. We have recently shown by high-resolution two-dimensional gel electrophoresis that there are three distinct PCNA isoforms that differ in their acetylation status. The Acidic (A), Main (M) and Basic (B) forms are 34 kDa-pI4.52, -pI4.57 and -pI4.62 proteins, respectively. Importantly, the acetylation status was directly relevant to DNA replication efficiency in vitro. We also found, in contrast to the currently accepted single homotrimer-ring model, that mammalian PCNA trimers exist in a cell as a back-to-back doublet complex. Since the double-trimer complex exposes two Front sides, this structure can provide great flexibility in coordinating DNA replication with diverse cellular functions. This is truly an exciting possibility, which will undoubtedly open a new paradigm in our understanding of many cellular functions that are coupled with replication or repair.

(4) Identifying and characterizing effective anticancer compounds

Using our breast cancer model system described above (B), we are currently screening anticancer compounds that can effectively kill radioresistant cancer cells, but not normal cells. Our screening includes known chemotherapeutic agents as well as natural and synthetic chemical compounds. The main objectives of this project are: (i) to isolate compounds that can effectively and specifically kill cancer cells; (ii) to develop effective combined modalities using chemical compounds and radiation treatment; (iii) to modify currently known anticancer compounds to increase specificity and efficacy.

Selected recent publications

Stanislav N. Naryzhny, Helen Zhao and Hoyun Lee. 2005. Proliferating cell nuclear antigen (PCNA) may function as a double-homotrimer complex in the mammalian cell. J. Biol. Chem. 280: 13888-13894.

Helen Zhao, Yong Cai, Robert Lafrenie and Hoyun Lee. 2005. Chloroquine-mediated radiosensitization is due to the destbilization of the lysosomal membrane and subsequent induction of necrotic cell death. Radiat. Res.(in press)

Stanislav N. Naryzhny and Hoyun Lee. 2004. The post-translational modifications of proliferating cell nuclear antigen (PCNA): acetylation, not phosphorylation, plays an important role in the regulation of its function. J. Biol. Chem. 279:20194-20199.

Stanislav N. Naryzhny and Hoyun Lee. 2003. Observation of multiple isoforms and specific proteolysis patterns of PCNA in the context of cell-cycle compartments and sample preparations. Proteomics 3:930-936.

Xing Wu and Hoyun Lee. 2002. Human Dbf4/ASK promoter is activated through the Sp1 and Mlu 1 cell-cycle box (MCB) transcription elements. Oncogene 21 (51): 7786-779621.