Associate Member
Department of Molecular and Cellular Biology
Roswell Park Cancer Institute
Elm and Carlton Streets
Buffalo, NY 14263
Telephone : (716)845-7691
Fax : (716)845-8899
E-mail: william.burhans@roswellpark.org

General Research Interest

DNA replication, cancer, aging, genome evolution

Current Program

DNA replication, checkpoints and apoptosis
DNA replication stress, cancer and aging
Gene silencing and genome evolution

Laboratory Personnel

Martin Weinberger PhD - Senior Research Associate

Description of Research

Research in our laboratory is focused on defects in DNA replication and how they contribute to neoplasia and other age-related diseases. Accumulating evidence points to DNA replication stress — i.e., inefficient DNA replication that leads to genome instability — as an important component of early stages of cancer. Replication stress develops in preneoplastic cells downstream of the activation of oncogenic growth-signaling pathways and contributes to oncogene-induced senescence. Recent studies suggest the paradigm-shifting notion that oncogene-induced senescence and other cellular responses to replication stress, and not acute responses to DNA damage, are responsible for the tumor-suppressing properties of p53 and other tumor suppressor proteins. Thus, replication stress is emerging as a critically important factor in neoplasia. Recent findings in our laboratory indicate that replication stress downstream of aberrant growth signaling is also an important factor in aging.

We have been examining the roles of replication stress in cancer and aging in three related projects.

In Project 1 (DNA replication, checkpoints and apoptosis) we are investigating how defects in initiation of DNA replication induce genome instability and apoptosis. These studies are based on our discovery (in collaboration with the Baumann laboratory at Roswell Park) that in mammalian and budding yeast, a highly conserved protein required for initiation of DNA replication in all eukaryotes is targeted for destruction by multiple cell death pathways in response to a variety of apoptotic triggers (Blanchard et al., 2002). Subsequent studies established that in budding yeast, loss-of-function mutations in initiation proteins cause apoptotic phenotypes by inducing replication stress and DNA damage in cells with defective checkpoints (Burhans et al., 2003; Weinberger et al., 2005). In collaboration with the Huberman laboratory at Roswell Park, we determined that mutations in initiation proteins or in a cyclin-dependent kinase required for mitosis induce apoptotic phenotypes in fission yeast as well (Marchetti et al., 2006). These findings are consistent with our model that destruction of initiation proteins plays a causal role in apoptosis related to defects in the dual roles of these proteins in DNA replication and checkpoint regulation, which leads to uncoupling of DNA replication from the cell cycle (Burhans et al., 2002). Our findings also suggest new therapeutic strategies for treating cancer that involve targeting of initiation proteins.

In Project 2 (Replication Stress, Aging and Cancer) we are investigating how replication stress arises downstream of the inappropriate activation of highly conserved growth-signaling pathways. Many of these experiments employ budding yeast as a model organism. Many other studies of replication stress-induced genome instability have also employed yeasts. However, most of these studies examined cycling populations of cells. Our experiments employ budding yeast cells driven by nutrient depletion into a non-cycling, quiescent state. These conditions more accurately reflect the conditions under which many preneoplastic cells arise in mammals during cellular differentiation. The results of our experiments indicate that replication stress arises as a consequence of excessive or imbalanced growth signaling under conditions that are suboptimal for replicating chromosomes. Our experiments also suggest that replication stress caused by deregulated growth signaling is an important determinant of chronological lifespan of budding yeast and other eukaryotes, including humans. They suggest that caloric restriction and mutational inactivation of growth signaling pathways extend lifespan in part by promoting a tighter G1 arrest during differentiation that inhibits inappropriate entry into S phase, and thus replication stress (Weinberger et al., 2007).

In Project 3 (DNA replication, gene silencing and genome evolution) is based on our recent discovery that in rapidly cycling budding yeast cells, the highly conserved Origin Recognition Complex (ORC), which is required for initiation of DNA replication in all eukaryotes, represses transcription of a large number of genes that are normally induced by nutrient deprivation (Ramachandran et al., 2006). When nutrients are available, these genes are maintained silent by ORC and/or other proteins because expression of these genes leads to the induction of a G1 cell cycle arrest, which is incompatible with growth. This G1 arrest — which is induced by many other stresses, in addition to nutrient deprivation — protects cells from replication stress associated with the suboptimal conditions for replicating DNA that likely exist in stressed cells. Our findings suggest that replication stress played a particularly important role in the evolution of the budding yeast genome after an ancient whole genome duplication event (Burhans et al., 2006). They provide a framework for understanding how quiescence is globally regulated by chromatin structure and other factors. This framework may illuminate some of the details of mechanisms underlying differentiation and stress resistance in mammalian cells and how dysregulation of these mechanisms contribute to aging and age-related diseases, including cancer and neurodegeneration.

 Selected Publications (click here to see a list through PubMed)

• Madia , F., Gattazzo , C., Wei, M., Fabrizio, P., Burhans, W.C., Weinberger, M., Galbani, A., Smith, J., Nguyen, C., Huey, S., Comai, L. and Longo, V.D. (2008) "Longevity mutation in SCH9 prevents recombination errors and premature genomic instability in a Werner/Bloom model system". J. Cell Biology 180; 67-81.
• Burhans, W.C. and Weinberger, M. (2007) "DNA replication stress, genome instability and aging" , Nucleic Acids Research,  35: 7545–7556
• Weinberger, M., Feng, L., Paul, A., Smith, D.L., Hontz, R.D., Smith, J.S., Vujcic, M., Singh, K.K., Huberman, J.A. and Burhans, W.C. (2007) DNA replication stress is a determinant of chronological lifespan in budding yeast. PLoS One 2(8):e748. doi:10.1371/journal.pone.0000748"
• Burhans, W.C. and Weinberger, M.  (2007) Yeast endonuclease G: Complex matters of death and of life. Molecular Cell 25: 323-325.
• Maslov, A.Y., Bailey, K.J., Mielnicki, L.M., Freeland, A.L., Sun, X., Burhans, W.C. and Pruitt, S.C. (2007) Stem/Progenitor cell-specific EGFP expression driven by the endogenous Mcm2 promoter. Stem Cells, 25: 132-138.
• Burhans, D.T., Ramachandran, L., Wang, J., Liang, P., Patterton, H. Breitenbach, M. and Burhans, W.C. (2006) Non-random clustering of stress-related genes during evolution of the S. cerevisiae genome. BMC Evolutionary Biology 6; 58.
• Burhans, William C., Carr, A.M. and Wahl, G.M. (2006) DNA Replication and Cancer, in “DNA Replication and Human Diseases”, Cold Spring Harbor Press, N.Y. Melvin DePamphilis, ed.
• Ramachandran, L., Laun, P., Liang, P., Wang, J., Burhans, D.T., Wissing, S, Jarolim, S., Suter, B., Madeo, F., Breitenbach, M., Burhans, W.C. (2006) Evidence for global silencing by ORC of budding yeast genes induced by starvation and other stresses FEMS Yeast Research 6; 763-76.
• Marchetti, M.A., Weinberger, M., Murakami, Y., Burhans, W.C.* and Huberman, J.A.* (2006) Production of reactive oxygen species in response to replication stress and dysregulated mitosis in fission yeast. J. Cell Science 119:124-31 (*co-corresponding authors).
• Weinberger, M., Ramachandran, L., Feng, L., Marchetti, M.A., Huberman, J.A., and Burhans, W.C. (2005) Apoptosis in budding yeast caused by defects in initiation of DNA replication. J. Cell Science 118; 3543-3553.
• Trabold, P. Weinberger, W., Feng, L. and Burhans, W.C. (2005) Altered ORC interactions with DNA induced by DNA damage and their suppression by the heat shock protein Mge1p. J. Biol. Chem. 280: 12413-12421.
• Burhans, W.C., Weinberger, M., Marchetti, M.A., Ramachandran, L., D’Urso, G. and Huberman, J.A. (2003). Apoptosis-like yeast cell death in response to DNA damage and replication defects. Mutation Research 532: 227-243.
• Weinberger, M., Ramachandran, L., and Burhans, W.C. (2003). Apoptosis in yeasts. IUBMB Life 55: 467-472.
• Miao, H., Seiler, J. and Burhans, W.C. (2003). Regulation of cellular and SV40 viral DNA replication origins by Chk1-dependent intrinsic and UVC-induced checkpoints. J. Biol. Chem. 278: 4295-4304.
• Burhans, W.C., Blanchard, F. and Baumann, H. Programmed cell death and origin licensing: a hypothesis. (2002). Cell Death & Differentiation 9: 870-872.
• Marchetti, M., Kumar, S., Hartsuiker, E., Maftahi, M., Carr, A.M., Freyer, G.H., Burhans, W.C., and Huberman, J.A. A single unbranched S-phase DNA damage and replication fork blockage checkpoint pathway. Proc. Natl. Acad. Sci. USA (2002) 99: 7472-7477, 2002.
• Blanchard, F., Rusiniak, M., Sun, X., Sharma, K., Todorov, I., Baumann, H., and Burhans, W.C. Targeted destruction of the DNA replication protein Cdc6 by cell death pathways in mammals and yeast. (2002). Mol. Biol. Cell 13; 1536-1549.

Selected Publications (please click here for a complete PubMed list for Dr. Burhans).