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Hendzel Lab
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Current Laboratory Members
Research Interests
Michael J Hendzel, Ph.D. Principal Investigator
Darin McDonald, M.Sc. Lab Manager
Ismail Ismail, Ph.D. Postdoctoral Fellow
Hilmar Strickfaden, Ph.D.
Postdoctoral Fellow
Mohammed Ali, Ph.D. Postdoctoral Fellow

Recent Publications from Our Laboratory

Polycomb repressive complex 1 is involved in ubiquitin signaling from DNA double-strand breaks.   The polycomb repressive complex 1 (PRC1) is an E3 ubiqutin ligase complex that is responsible for the ubiquitylation of histone H2A and its variants on lysine 119. This plays a critical gene silencing function during development. We recently discovered that this E3 ubiquitin ligase complex also ubiquitylates histone H2A in response to DNA double-strand breaks. The upregulation of this complex in cancer stem cells may confer the radiation resistance commonly observed in cancer stem cells.

Proline Isomerization mediated by Pin1 regulates histone H1 binding.  Histone H1 is known to be regulated by phosphorylation of cdk1/cdk2 consensus target sequences, primarily located in the large carboxy-terminal domain. This domain has long been thought to be unstructured and has not been amenable to crystallization. Currently, it is thought that the C-terminus adopts a defined conformation upon binding to chromatin. In this study, we show that proline isomerization, which can dramatically alter the structure and function of a peptide sequence, takes place within the carboxy-terminal domain. This isomerization is mediated by PIN1 and, surprisingly, counteracts the destabilizing effects of phosphorylation to stabilize the binding of H1 to chromaitn.

Development of a quantitative method for sites of H2AX phosphorylation and the objective measurement of DNA double-strand break-associated foci.  Antibodies that allow the quantification of DNA double-strand breaks are being developed in pre-clinical studies to quantify the damage and persistence of damage caused by radiation treatment or chemotherapeutic agents.  Jianxun Han, a Ph.D. student co-supervised by Dr. Joan Turner, developed a method for objectively measuring DNA damage by quantifying sites of histone H2AX phosphorylation. 

ATM phosphorylates histone H2AX during mitosis and in the absence of DNA damage.  The importance of developing an objective method for measuring double-strand breaks (see above) is highlighted by this study where Kirk McManus, a recent Ph.D. graduate, determined that histone H2AX is phosphorylated at hundreds of sites in the absence of DNA damage.  This phosphorylation is cell cycle-regulated and ATM, a protein important in maintaining genome stability, is required for this phosphorylation.  This may reflect the existence of a second mechanism where ATM contributes to genome stability independent of its role in DNA double-strand break repair.   

Approximately 40% of Canadians are expected to have cancer at some point in their lives and approximately 25% of Canadians are expected to die of cancer.  It is only recently that modern biology has begun to impact upon the clinical treatment of cancer patients.  Despite early successes in so-called rationally designed therapy, much of the fundamental biology that provides the foundation for rationally designed therapy remains to be discovered and characterized.  My research laboratory investigates the basic biology of the genome and the cell nucleus, which houses the genome.  The maintenance of genome stability (mechanisms that ensure the faithful transmission of chromosome number of sequence content), the regulation of DNA double strand break repair, and the regulation of the genome through epigenetic mechanisms are being studied at the level of single cells with the objective of identifying mechanisms that have the potential to be translated into novel rationale therapies.  We are currently funded by the Canadian Institutes of Health Research

Current Research Taking Place in Our Laboratory

A HeLa cell treated with a protein methylation inhibitor for 2 hours.  The treatment results in a failure to properly align the chromosomes during metaphase

Genome Stability and Epigenetics in Cancer.

Epigenetics describes the coding for information in the genome that is important in the control of cell phenotype but is not directly encoded in the DNA.  It is now appreciated that 50% or more of the cumulative changes in a cell necessary to convert it into a cancer cell is epigenetic, rather than genetic, in origin.  We are currently studying how epigenetic modifications of chromatin function in organizing and regulating the genome during interphase and mitosis.  In collaboration with Drs. Robert Campbell, Gordon Chan, J.B. Rattner, and Alan Underhill, we are developing reagents and drugs to exploit the requirement for histone methylations in maintaining genome stability.  Read more about this research.

 

A pair of mouse embryonic fibroblast cells stained with an antibody recognizing phosphorylated histone H2AX.  The cells have been exposed to ionizing radiation prior to staining generating the charactgeristic "γH2AX" foci at sites of DNA damage.

DNA Damage and DNA Damage Repair.             Many current cancer therapies, including radiation therapy, kill cancer cells by introducing double-strand breaks in the DNA.  We have found a novel function for nuclear actin in repairing DNA double-strand breaks and are working to identify novel actin-related targets to enhance the effectiveness of radiation therapy.  In collaboration with Dr. Joan Turner, we are investigating how changes in genome organization alter the ability of cells to repair radiation-induced double-strand breaks (and thereby fail to kill cells).  We are also collaborating with Drs. Guy Poirier and Jean-Yves Masson to determine how cells sense and signal the existence of DNA double-strand breaks.  Collectively, these studies have the objective of identifying mechanisms to improve cancer therapies that work through the introduction of double-strand breaks in the DNA.  Read more about this research.

A mouse fibroblast stained for DNA (blue), transfected with SC35-GFP (a fluorescently tagged RNA splicing factor) and microinjected with 40 nm beads.  A contour map was prepared from the colour fluorescence images. 

Nuclear Dynamics and Genome Regulation.           One of the frontiers in cell and cancer cell biology is to determine the dynamic properties of important cellular proteins inside of living cells.  These studies complement genomics and proteomics studies by providing the details of the spatial and temporal regulation that takes place inside of living cells.  Our laboratory is particularly interested in the dynamics of nuclear proteins that take place in the orchestration of genome regulation, chromatin structure, and genome repair.  In collaboration with Dr. John Th'ng, we are studying the regulation of the histone H1 protein during cellular transformation and terminal differentiation.  We are also characterzing the basic physical properties of the living nucleus in order to understand how these properties influence the regulation of the genome in normal and cancer cells.  This is transdisciplinary work involving collaborations with Dr. Gerda de Vries (Mathematics) and Dr. Jack Tuszynski (Biophysics and Computational Biology).  Read more.