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Fred Dick, PhD

Scientist: London Regional Cancer Program, London Health Sciences Centre, London, Ontario
Assistant Professor: Department of Biochemistry, University of Western Ontario, London, Ontario
Cross Appointments: Department of Oncology, Department of Paediatrics

 

University Website
http://www.biochem.uwo.ca/fac/dick/dick.html

 

Mailing Address

London Regional Cancer Program
Room A4-136, Cancer Research Laboratory Program
790 Commissioners Rd. E.
London, Ontario
Canada N6A 4L6

Tel: 519.685.8620
Fax: 519.685.8616
Email: fdick@uwo.ca

Staff and Trainees

Graduate Students:

Sarah Francis, MSc Student, Department of Biochemistry
Project: Characterization of murine mammary gland development
Email Sarah Francis

Christian Isaac, MSc Student, Department of Biochemistry
Project: Cell cycle control of an RB mutant
Email Christian Isaac

Lisa Julian, MSc Student, Department of Biochemistry
Project: Control of E2F1 by pRB
Email Lisa Julian

Laurie Seifried, MSc Student, Department of Biochemistry
Project: Mechanisms of inactivation of pRB by viral oncoproteins
Email Laurie Seifried

Undergraduate Students:

Lindsay Jordan, Summer Student
Project:
Email Lindsay Jordan

Research Technicians:

Alison Martens, Research Technician
Project: Characterization of an RB mutant mouse strain
Email Alison Martens

Research Area

Cell cycle regulation in development and oncogenesis

Key Words

Laboratory

Laboratory research is focused on the fundamental mechanisms that regulate the mammalian cell cycle and how they are disrupted in cancer. This is carried out by using cell culture, in vitro biochemical, and mouse gene-targeting technologies.

Summary of Current Work

The retinoblastoma tumour susceptibility gene (RB-1) was the first tumour suppressor gene to be identified. Although the RB-1 gene was first identified through its role in a rare pediatric cancer, subsequent tumour studies have shown that this gene is sporadically mutated in a wide range of cancers including osteosarcoma, leukemia, and carcinomas derived from the bladder, prostate, breast, and cervix. In addition to direct mutation of the RB-1 gene, its encoded protein (pRB) is functionally inactivated in many tumour cells either by viral proteins that bind to pRB, or through changes in a regulatory pathway that controls the activity of pRB. Regulators include the melanoma tumour suppressor (p16), cyclin D1, and cyclin dependent kinase 4 (cdk4). These regulators, along with pRB, comprise the so called "RB pathway," a regulatory cascade that controls progression through the G1 phase of the cell cycle. Current mutation data indicates that nearly all tumour cells contain mutations or gene silencing events that effectively lead to inactivation of pRB. This establishes that pRB is necessary for restricting entry into the cell cycle and preventing cancer.

Tumour mutations in the RB pathway end with RB-1, leaving in question how pRB is mechanistically capable of blocking cell cycle entry.

Biochemical models of pRB function argue that it regulates the cell cycle by repressing transcription of genes that are required for cell cycle entry. pRB is believed to repress transcription by binding to E2F transcription factors that are present on the promoters of cell cycle regulated genes. Chromatin remodelling enzymes such as mammalian SWI/SNFs or histone deacetylases (HDACs) are in turn tethered to pRB and effectively silence transcription. The components of this repressor complex then block gene expression until the G1 to S transition of the cell cycle when cyclin/cdks phosphorylate and inactivate pRB and transcription is induced.

Very few mutations in the genes encoding E2Fs or chromatin remodelling enzymes have been described in tumour cells. Furthermore, previous analysis of cancer causing mutant alleles of RB-1 have shown them to lose many functions in addition to transcriptional repression. The lack of tumour derived mutations that specifically cripple transcriptional repression by pRB leaves this model unproven. For this reason other proposed mechanisms for pRB negatively regulating the cell cycle and preventing cancer must be considered. Alternative mechanisms that have been proposed for pRB to act as a tumour suppressor include directly regulating S-phase entry by blocking the initiation of DNA synthesis. Another attractive model involves pRB actively promoting cellular differentiation. Differentiation of precursor cells into neurons, adipocytes, or myotubes removes them from the cell cycle and prevents further proliferation. For a more in depth look at pRB function in cell cycle control and cancer please see the following review articles.

Understanding the fundamental biochemical function(s) that pRB performs as a negative regulator of the cell cycle and tumour suppressor will be the focus of my laboratory.

Current Projects

Structure-Function Studies of pRB in Cell cycle Arrest, Cellular Differentiation, and DNA Damage

The Retinoblastoma Tumour Suppressor protein is known to participate in cell cycle control, cellular differentiation, and the response to DNA damaging agents. In cell culture assays of pRB function a single domain, called the Large Pocket, has been shown to be necessary and sufficient to mediate a cell cycle arrest or to induce differentiation. Unfortunately, a precise mechanistic description of pRB function in these assays has been impossible because many proteins bind this domain. Knowing precisely which protein-protein interactions by pRB are necessary for it to exert control over the cell cycle, differentiation, and DNA damage is essential to understanding why it is a tumour suppressor. During my post-doctoral research I have generated mutant alleles that encode pRB proteins with very specific interaction defects with chromatin remodelling enzymes and E2F transcription factors. This experimental breakthrough has created an exciting new opportunity to investigate the need for many of these interacting proteins in pRB function in cell cycle, differentiation, and DNA damage assays. In particular, analysis of pRB interactions with E2F transcription factors have revealed that the pRB Large Pocket domain contains two binding sites for E2Fs. The two E2F binding sites have unique specficity for individual members of the E2F family of proteins. Investigating how pRB uses these separate binding sites to control different E2F transcriptional activities will be of particular interest.

Tumour Susceptibility of Rb Mutant Mice

Experiments in the preceding section have generated a number of interesting mutants of the RB-1 gene. While the study of these mutants in cellular and biochemical assays provide a valuable insight into pRB function, they do not address which activities are necessary in vivo for pRB to act as a tumor suppressor gene in a multicellular organism. Studies of the mouse RB-1 gene (called Rb) have shown that loss of one copy of this gene predisposes mice to cancer much the same way RB-1 mutations predispose humans to cancer. Using gene targeting technology I have begun to establish mutant mouse strains that carry specific mutations in Rb that are designed to prevent binding of pRB to chromatin remodelling enzymes and E2F transcription factors. The tumor predisposition of mice whose pRB molecules lack these specific interactions will establish which biochemical functions are essential for pRB to prevent cancer.

The first of these mice to be established carries a mutation in the binding site that is used by viral oncoproteins and chromatin remodelling enzymes. Viral proteins and chromatin remodelling enzymes are thought to use a common peptide sequence motif called "LXCXE" to bind to pRB. For this reason the mutant allele is named after this motif. This gene-targeted knock-in mouse (shown with a wild-type sibling) has a number unique phenotypes that could not have been predicted from prior cell culture experiments. This demonstrates the value of a thorough in vivo analysis of these mutants. It will be interesting to determine whether these mice are predisposed to cancer.

PubMed Publications

See my publications on PubMed