Department of biochemistry and Molecular biology
Paula Traktman, PhD
1997-2015 – Walter Schroeder Professor and Chairman, Department of Microbiology and Molecular Genetics, Medical College of Wisconsin, Milwaukee, WI
1984-1997 - Assistant Professor, Associate Professor and Professor, Cornell University Medical College, New York, NY
1981-1984, Post-doctoral fellow, Harvard Medical School, Boston, MA
1974 AB, Harvard College
Office: DDB-213 Tel: 843-876-2414
Lab: DDB-228 Tel: 843-876-2208
A: Vaccinia Virus
Vaccinia virus is the prototypic poxvirus and was the virus used in the vaccination campaign that led to the global eradication of smallpox. Vaccinia virus replicates solely within the cytoplasm of infected cells, and the 192 kb DNA genome encodes most, if not all, of the functions required for the progression of the viral life cycle. We have focused our attention primarily on viral DNA replication, the role of virally encoded kinases and phosphatases within the infectious cycle, and virion morphogenesis. We are also exploring the interplay between the viral life cycle and cellular bioenergetics. Our work integrates diverse approaches drawn from the disciplines of virology, molecular genetics, cell biology, and biochemistry.
With regard to DNA replication, we are interested in understanding how replication is organized within dedicated cytoplasmic domains, in deciphering the mechanism of replication, and in pursuing a biochemical and genetic investigation of the proteins involved. We are interested in how the core polymerase, processivity factor (A20+UDG), single-strand DNA binding protein (I3), DNA ligase (A50), and FEN-1 like nuclease work together to accomplish faithful DNA replication and repair. Additionally, we are pursuing the hypothesis that the abundant H5 protein serves as a scaffold to support replication within the membrane-delimited cytoplasmic replication domains.
With regard to virion morphogenesis, our current interest is focused on the biogenesis of the poxvirus membrane, which is quite unique and involves the enlargement of planar lipid bilayers within the cytoplasm. We are using a genetic, biochemical, cell biological and ultrastructural approaches to understand how the F10 kinase, a group of regulatory proteins (A6, A11, A30.5, H7, L2), and the two major structural proteins within the membrane (A14 and A17) mediate diversion of membranes from the endoplasmic reticulum (ER) and their remodeling and enlargement. The overall process of virion assembly involves a cascade of protein/protein, protein/DNA, and protein/lipid interactions that serve as an excellent model for the process of cellular organelle biogenesis.
B: VRK1: A cellular protein kinase involved in nuclear architecture, mitotic and meiotic progression, cell proliferation, and oncogenesis.
We became interested in the VRK family of cellular protein kinases because of the sequence similarity between their catalytic domains and that of the vaccinia-encoded B1 kinases. We performed the first thorough characterization of the VRK family (VRK1, nuclear; VRK2, nuclear envelope and ER; VRK3, nuclear pseudokinase) and purified and characterized their biochemical properties. We identified and validated the cellular BANF1 (BAF) protein as a highly efficient substrate for both VRK1. Within the interphase nucleus, BANF1 binds to chromatin and to proteins in the inner nuclear membrane (INM). We have shown that VRK1-mediated phosphorylation of BANF1, which peaks at the onset of mitosis, abrogates BANF’s DNA binding activity and reduces it’s interactions with proteins at the INM. VRK1 depletion leads to aberrant nuclear envelopes in interphase nuclei, and to the abnormal retention of BANF1 on chromosomes during early stages of mitosis (prophase, metaphase and anaphase). These effects have impacts on mitotic fidelity as well as cell proliferation.
Because overexpression of VRK1 has shown to correlate with poor clinical outcome in a subset of breast cancer patients, we have focused much of our work on mammary epithelial cells (normal and malignant). Using a mouse xenograft model, we showed that malignant cells depleted of VRK1 formed smaller tumors than control cells, and that mice receiving this cells did not develop distal metastases. We have also shown that VRK1 overexpression accelerates acinus growth in a 3D culture model, but reduces cell migration in a 2D wound-healing model. We are using a variety of “omic” strategies, as well as cell biological and biochemical approaches, to understand the roles played by VRK1 in regulating cell structure and function in normal and cancerous cells.
Selected Publications | Additional Publications
Boyle KA, Greseth MD, Traktman P. (2015) Genetic confirmation that the H5 protein is required for vaccinia virus DNA replication. Journal of Virology 89(12):6312-27.
Greseth MD, Traktman P. (2014) De novo fatty acid biosynthesis contributes significantly to establishment of a bioenergetically favorable environment for vaccinia virus infection. PLoS Pathogens 10(3):e1004021.
Molitor TP, Traktman P. (2014) Depletion of the protein kinase VRK1 disrupts nuclear envelope morphology and leads to BAF retention on mitotic chromosomes. Molecular Biology of the Cell 25(6):891-903.
Molitor TP, Traktman P. (2013) Molecular genetic analysis of VRK1 in mammary epithelial cells: depletion slows proliferation in vitro and tumor growth and metastasis in vivo. Oncogenesis 2:e48.
Unger B, Mercer J, Boyle KA, Traktman P. (2013) Biogenesis of the vaccinia virus membrane: genetic and ultrastructural analysis of the contributions of the A14 and A17 proteins. Journal of Virology 87(2):1083-97.
Greseth MD, Boyle KA, Bluma MS, Unger B, Wiebe MS, et al. (2012) Molecular genetic and biochemical characterization of the vaccinia virus I3 protein, the replicative single-stranded DNA binding protein. Journal of Virology 86(11):6197-209.
Boyle KA, Stanitsa ES, Greseth MD, Lindgren JK, Traktman P. (2011) Evaluation of the role of the vaccinia virus uracil DNA glycosylase and A20 proteins as intrinsic components of the DNA polymerase holoenzyme. The Journal of Biological Chemistry 286(28):24702-13.
Wiebe MS, Nichols RJ, Molitor TP, Lindgren JK, Traktman P. (2010) Mice deficient in the serine/threonine protein kinase VRK1 are infertile due to a progressive loss of spermatogonia. Biology of Reproduction 82(1):182-93.
Nichols RJ, Wiebe MS, Traktman P. (2006) The vaccinia-related kinases phosphorylate the N' terminus of BAF, regulating its interaction with DNA and its retention in the nucleus. Molecular Biology of the Cell 17(5):2451-64.
Wiebe MS, Traktman P. (2007) Poxviral B1 kinase overcomes barrier to autointegration factor, a host defense against virus replication. Cell Host & Microbe 1(3):187-97
Nichols RJ, Stanitsa E, Unger B, Traktman P. (2008) The vaccinia virus gene I2L encodes a membrane protein with an essential role in virion entry. Journal of Virology 82(20):10247-61.
Mercer J, Traktman P. (2005) Genetic and cell biological characterization of the vaccinia virus A30 and G7 phosphoproteins. Journal of Virology 79(11):7146-61.
Punjabi A, Traktman P. (2005) Cell biological and functional characterization of the vaccinia virus F10 kinase: implications for the mechanism of virion morphogenesis. Journal of Virology 79(4):2171-90.