Robert F. Kalejta, Ph.D.

Associate Professor of Molecular Virology and Oncology

B.S., 1990, Biochemistry, Penn State University
Ph.D., 1997, Biochemistry, University of Virginia
Postdoctoral research: Princeton University

Office: 635A Bock Laboratories
Telephone: Office - (608) 265-5546; Lab - (608) 265-5390
Email: rfkalejta@wisc.edu

Research Interests: Cell cycle progression and DNA replication, viral manipulation of the cell cycle, HCMV replication and pathogenesis, Rb/E2F pathway, ubiquitin-mediated proteolysis, HCMV genetics.

Research Focus: My lab focuses on the mechanisms of mammalian cell cycle progression, and uses human cytomegalovirus as a tool to probe the pathways that lead to oncogenesis. As obligate intracellular parasites, viruses are reliant upon their host cells for their replication, and have evolved ways to commandeer cellular pathways to promote their own survival. Studies of viral regulation of the cell cycle have led to major advances in the field of cell cycle research, including the discovery of oncogenes, the p53 tumor suppressor, and the E2F family of transcription factors, as well as elucidating the role of the retinoblastoma (Rb) family of tumor suppressors in cellular growth control.

Human cytomegalovirus (HCMV) alters the cell cycle in a very unique way. It induces quiescent (G0) cells to re-enter the cell cycle, travel through G1, but then arrests them at the G1/S border before the cell begins to replicate its own DNA. This cell cycle position is favorable for efficient viral replication since all of the building blocks for DNA replication are present but are not being consumed by the host cell for the synthesis of its own genome.

Most of my work has focused on the HCMV pp71 protein. We identified pp71 as a cell cycle regulator and determined its mechanism of action. pp71 utilizes a protein motif with the sequence LXCXD to bind to the three members of the retinoblastoma family of tumor suppressors (Rb, p107 and p130). These proteins control progression through the G1 phase of the cell cycle. Targeting of the Rb family members by pp71 induces quiescent (resting, or G0) cells to re-enter the cell cycle and progress into the S phase. The LXCXD motif is required for this activity. We have also demonstrated that pp71 induces the proteasome-dependent, ubiquitin-independent degradation of the Rb family members, and have identified a region of the protein required for this activity. Determining the molecular mechanism for this unique example of protein degradation and cell cycle regulation will be a major emphasis in my laboratory. In addition, we have begun to explore two other HCMV cell cycle regulatory proteins, UL69 and IE2, to determine the mechanisms they employ to alter the cell cycle, and will utilize new viral genetic techniques to explore the role that the cell cycle alterations induced by pp71, UL69 and IE2 play in both the lytic and latent replication cycles of the virus.

Projects in my lab will include:

-- further defining the mechanism for proteasome-dependent, ubiquitin-independent degradation of the Rb family by pp71
-- determining the mechanism through which UL69 and IE2 modulate cell cycle progression
-- discover the roles that these proteins play during viral infection

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Selected recent publications

Hume, A. J., and Kalejta, R. F.  Regulation of the Retinoblastoma Proteins by the Human Herpesviruses.  Cell Division 4:1, 2009.

Hwang, J., and Kalejta, R. F.  Human Cytomegalovirus Protein pp71 Induces Daxx SUMOylation.  J. Virol., 83:  6591-6598, 2009.

Kamil, J. P., Hume, A. J., Jurak, I., Münger, K., Kalejta, R. F., and Coen, D. M.  Human Papillomavirus 16 E7 Inactivator of Retinoblastoma Family Proteins Complements Human Cytomegalovirus Lacking UL97 Protein Kinase.  Proc. Natl. Acad. Sci. USA, 106:  16823-16828, 2009.

Hume, A. J., Finkel, J. S., Kamil, J. P., Coen, D. M., Culbertson, M. R., and Kalejta, R. F.  Phosphorylation of Retinoblastoma Protein by Viral Protein with Cyclin-Dependent Kinase Function.  Science, 320:  797-799, 2008. For news article about the 2008 Science paper, go to:  http://www.news.wisc.edu/15213

Kalejta, R. F.  Functions of Human Cytomegalovirus Tegument Proteins Prior to Immediate Early Gene Expression.  Curr. Top. Microbiol. Immunol., 325:  101-115, 2008.

Kalejta, R. F.  Tegument Proteins of Human Cytomegalovirus.  Microbiol. Mol. Biol. Rev., 72:  249-265, 2008.

Hwang, J., and Kalejta, R. F.  Proteasome-dependent, Ubiquitin-independent Degradation of Daxx by the Viral pp71 Protein in Human Cytomegalovirus-infected Cells.  Virology, 367:  334-338, 2007.

Saffert, R. T., and Kalejta, R. F.  Human Cytomegalovirus Gene Expression Is Silenced by Daxx-Mediated Intrinsic Immune Defense in Model Latent Infections Established In Vitro.  J. Virol., 81:  9109-9120, 2007.

Saffert, R. T., and Kalejta, R. F. Inactivating a Cellular Intrinsic Immune Defense Mediated by Daxx Is the Mechanism through Which the Human Cytomegalovirus pp71 Protein Stimulates Viral Immediate-Early Gene Expression. J. Virol., 80: 3863-3871, 2006.

Kalejta, R. F. Human Cytomegalovirus pp71: A New Viral Tool to Probe the Mechanisms of Cell Cycle Progression and Oncogenesis Controlled by the Retinoblastoma Family of Tumor Suppressors. J. Cell. Biochem., 93: 37-45, 2004.

Kalejta, R. F., and Shenk, T. Proteasome-dependent, Ubiquitin-independent Degradation of the Rb Family of Tumor Suppressors by the Human Cytomegalovirus pp71 Protein. Proc. Natl. Acad. Sci. USA, 100: 3263-3268, 2003.

Kalejta, R. F., Bechtel J. T., and Shenk, T. Human Cytomegalovirus pp71 Protein Stimulates Cell Cycle Progression by Inducing the Proteasome-dependent Degradation of the Retinoblastoma Family of Tumor Suppressors. Mol. Cell. Biol., 23: 1885-1895, 2003.

Kalejta, R. F., and Shenk, T. The Human Cytomegalovirus UL82 Gene Product (pp71) Accelerates Progression through the G₁ Phase of the Cell Cycle. J. Virol., 77: 3451-3459, 2003.

Kalejta, R. F., and Shenk, T. Manipulation of the Cell Cycle by Human Cytomegalovirus. (Review). Front. Biosci., 7: D295-306, 2002.

Kalejta, R. F., Li, X., Mesner, L. D., Dijkwel, P. A., Lin, H.-B., and Hamlin, J. L. Distal Sequences, but not ori-β/OBR-1, are Essential for Initiation of DNA Replication in the Chinese Hamster DHFR Locus. Mol. Cell, 2: 797-806, 1998.