Our Science – Difilippantonio Website

Michael J. Difilippantonio, Ph.D.

Genetics Branch Cancer Genomics Section Staff Scientist Cancer Genomics Section Genetics Branch / CCR / NCI / NIH 50 South Drive, Rm. 1408 Bethesda, MD 20892-8010 Phone:   301-435-3991 Fax:   301-402-1204 E-Mail:   difilipm@mail.nih.gov

Biography

Dr. Difilippantonio earned his B.S. at the University of Connecticut in Molecular and Cellular Biology and a Certificate in Cytogenetics from the University of Connecticut School of Allied Health. He subsequently worked as a Clinical Cytogenetic Technologist in the laboratory of Dr. David C. Ward at Yale University in the early days of the Human Genome Project where he acquired proficiency in the emerging field of fluorescence in situ hybridization. He earned his Ph.D. in Genetics from Yale University under the mentorship of Dr. David G. Schatz. Dr. Difilippantonio came to NIH in 1998 as a post-doctoral fellow in the laboratory of Dr. Thomas Ried, initially in the National Human Genome Research Institute and now in the National Cancer Institute. Dr. Difilippantonio became a Staff Scientist in 2001. He received the NCI Division of Clinical Sciences Fellowship Advancement Award in 2000 and the Aspen Cancer Conference Young Investigator Award in 2001. He served as Co-chair of the from 2005-2006 and is currently actively involved in the NIH-Staff Scientist / Staff Clinician Organization.

Research

My particular interest is in DNA double strand break repair and its role in the generation of chromosome translocations leading to tumor formation. In my position as a Staff Scientist, however, I am intimately involved in a number of different ongoing projects in the lab as well as with collaborators in other NIH institutes and outside universities. Some of the main projects I am working on are outlined below. These involve the study of human and mouse models of tumorigenesis using a variety of genomic techniques, including fluorescence in situ hybridization (FISH), spectral karyotyping (SKY), comparative genomic hybridization (CGH), immunocytochemistry (ICC), gene expression profiling (microarrays), quantitative real-time PCR (RT-PCR), epifluorescence and confocal microscopy.


Structural Chromosome Aberrations and Cancer:

Tumors are characterized by their inability to maintain the integrity of the genome, either through mutation or rearrangement of genomic sequences. Cells have multiple mechanisms whereby they can repair DNA damage or for those cells in which repair is not possible, induce cell death. The non-homologous end-joining DNA double strand break repair pathway is one such mechanism and involves the coordinated effort of many different proteins. Of particular importance is the DNA-PK complex consisting of the proteins DNA-PKcs, Ku70 and Ku80. Mice deficient for either of the genes encoding the Ku proteins are particularly sensitive to the DNA damaging effects of ionizing radiation. In previous collaborative studies with Dr. Nussenzweig (NCI), we demonstrated that cells in the developing embryos of these mice have a propensity to develop DNA breaks, chromosome rearrangements and aneuploidy even in the absence of IR. Most of these cells, however, either undergo cell death or senescence, resulting in the runted growth of these mice relative to their normal siblings. Breeding of these mice with mice deficient for the protein p53, which is known to induce cell death, results in mice that develop tumors in the B cell lineage at a very early age. These tumors are characterized by a specific chromosomal rearrangement involving the immunoglobulin heavy chain gene (IgH) and the tumor promoting gene c-myc. Such an IgH - c-myc rearrangement is seen in Burkitt's Lymphoma in humans and is believed to result in the misregulated growth characteristic of cancer cells. Further characterization of these tumors revealed that the chromosome translocations were occurring through the process of break-induced replication (BIR). Subsequent amplification of the IgH / c-myc fusion was the result of repeated cycles of breakage-fusion-bridge (BFB) and eventual stabilization of the aberrant chromosome end via telomere capture from another chromosome. We are currently studying the role of DNA-PKcs in the process of tumorigenesis.


Numerical Chromosome Aberrations and Cancer:

The partitioning of genomic material during cell division is critical for maintaining the genomic content of each daughter cell. Centrosomes are one of the primary cellular structures responsible for this process. As such, Dr. Ghadimi (University of Gottingen, Germany) and I are investigating defects in these structures and the proteins that regulate them in order to determine how they can lead to the development of aneuploidy. One model system we are using is colorectal tumors because they can be classified into two categories based on the type of genomic defects they contain. Diploid colorectal tumors have a normal number (1 - 2) of centrosomes (as determined by localization of centrosome proteins) while aneuploid colorectal tumors have localization of centrosome proteins to more than 2 discrete structures. We and others have postulated that these extra structures are directly responsible for the mis-segregation of chromosomes leading to aneuploidy and eventually tumor formation. This is seen very nicely in cells from mice lacking the p53, BRCA1 or ATM genes where aberrant partitioning of chromosomes is clearly visible. We are therefore using this system to understand the events leading up to aneuploidy and tumor formation.


The Effects of Genomic Alterations on Gene Expression:

Following on the heels of earlier studies by Dr. Upender in our lab showing that introduction of an additional copy of a chromosome into cells results in an average increase in the expression levels of genes located on that chromosome, we are performing a similar analysis in tumors and tumor-derived cell lines in collaboration with Dr. Ghadimi (Germany) and Dr. Dharmarwardana (NCI). Because aneuploid tumors contain multiple chromosomes in a numerically unbalanced state, the effect is perhaps not surprisingly less pronounced. There remains in tumor cells, however, a high concordance between chromosome copy number and gene expression, particularly for those chromosomes that are characteristically affected in a particular tumor type.

This page was last updated on 9/11/2008.