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2004 Scientific Report

equired for its

equired for its essential replication function. Determining how the DNA damage checkpoint pathway may alter the activity of Cdc7p-Dbf4p kinase or modulate DNA replication and repair is an ongoing and exciting area of research. Lastly, we are examining the abundance of CDC7 and DBF4 in normal and human cancer cell lines. Semiquantitative RT-PCR performed on the NCI60 set of human tumor cell lines has indicated that both CDC7 and DBF4 exhibit increased expression in some of these cancer cell lines. Importantly, CDC7 protein abundance is also increased in a subset of these cell lines but is not detectable in normal tissues. We are currently examining how human CDC7-DBF4 kinase activity may influence normal and tumor cell growth. Recent Publications Pappas, Donald L., Jr., Ryan Frisch, and Michael Weinreich. 2004. The NAD + -dependent Sir2p histone deacetylase is a negative regulator of chromosomal DNA replication. Genes and Development 18(7): 769–781. Weinreich, Michael, Madaleine A. Palacios DeBeer, and Catherine A. Fox. 2004. The activities of eukaryotic replication origins in chromatin. Biochemica et Biophysica Acta 1677(1–3): 142–157. Bose, M.E., K.H. McConnell, K.A. Gardner-Aukema, U. Müller, M. Weinreich, J.L. Keck, and C.A. Fox. 2004. The origin recognition complex and Sir4 protein recruit Sir1p to yeast silent chromatin through independent interactions requiring a common Sir1p domain. Molecular and Cellular Biology 24(2): 774–786. From left to right: VanDussen, DeWard, Hammond, Frisch, Pappas, Weinreich 58

Laboratory of Cell Signaling and Carcinogenesis Bart O. Williams, Ph.D. Dr. Williams received his Ph.D. in biology from Massachusetts Institute of Technology in 1996. For three years, he was a postdoctoral fellow at the National Institutes of Health in the laboratory of Harold Varmus, former Director of NIH. Dr. Williams joined VARI as a Scientific Investigator in July 1999. Laboratory Members Staff Charlotta Lindvall-Weinreich, M.D., Ph.D. Sheri L. Holmen, Ph.D. Troy A. Giambernardi, Ph.D. Cassandra Zylstra, B.S. Students Holli Charbonneau Nicole Evans Jason Koning Aaron Massie Jose Toro Research Interests My laboratory’s long-term interest is to understand how alterations in the Wnt signaling pathway cause human disease. Wnt signaling is an evolutionarily conserved process that has been adapted to function in the differentiation of most tissues within the body. Given its central role in growth and differentiation, it is not surprising that alterations in the pathway are among the most common events associated with human cancer. In addition, several other human diseases, including osteoporosis, have been linked to alterations in the regulation of Wnt signaling. Recently, my laboratory has focused on understanding the role of Wnt signaling in bone formation. Our interest is not only from the perspective of normal bone development, but also in trying to understand whether aberrant Wnt signaling plays any role in the predisposition of some common tumor types (for example, prostate or breast tumors) to metastasize to and grow in the bone. The long-term goal of this work is to provide insights that could be used in developing strategies to lessen the morbidity and mortality associated with skeletal metastasis. Wnt signaling in normal bone development Recently, several groups reported that mutations in the Wnt receptor, Lrp5, caused changes in bone density in human patients. We have characterized a mouse strain deficient for Lrp5 and shown that it recapitulates the low-bone-density phenotype seen in human patients deficient for Lrp5. We have furthered this study by showing that mice carrying mutations in both Lrp5 and the related Lrp6 protein have even more severe defects in bone density. We are currently performing experiments to directly test whether a Lrp5 deficiency causes changes in bone density due to aberrant signaling through ß-catenin. To do this, we have created mice carrying an osteoblast-specific deletion of Lrp5. These mice die within five weeks of birth due to profound deficiencies in bone development. A reciprocal experiment was also performed, in which mice were missing the Apc gene specifically in osteoblasts (and therefore were expressing elevated levels of ß-catenin). In this case, the mutant mice again died very shortly after birth. Their death was associated with a dramatic overgrowth of bone to the point where very little marrow cavity was present (Fig. 1). Our current work on this project is aimed at addressing the molecular mechanisms that underlie the phenotypic observations. We have isolated osteoblasts from these mice and are analyzing them in tissue culture to determine their ability to produce and mineralize osteoid. Also, we are identifying potential downstream mediators of Wnt signaling in osteoblasts via microarray-based expression analysis. We are designing experiments to test the time frame during which activation of Wnt signaling can have effects on bone density. One approach is to use doxycycline-inducible systems to activate ß-catenin signaling in vivo. Another approach is to control the timing of ß-catenin induction in primary osteoblasts. Wnt signaling in prostate development and cancer The activation of the Wnt signaling pathway has been shown in a significant percentage of 59

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