Assistant Professor of Molecular Virology and Oncology
B.S., 1990, Biochemistry, Penn State University
Ph.D., 1997, Biochemistry, University of Virginia
Postdoctoral work: 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
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-b/OBR-1,
are Essential for Initiation of DNA Replication in the Chinese Hamster DHFR
Locus. Mol. Cell, 2: 797-806, 1998.
