 Edward M. Johnson, Ph.D.
Professor and Chairman
Lewis Hall, #3174b
Office: (757) 446-5662
Email:
johnsoEM@evms.edu
Education
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B.A., Pomona College,
Claremont, CA
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Ph.D., Yale University,
New Haven, CT
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Postdoctoral Training,
The Rockefeller University, New York, NY
Research Interests
Areas of interest:
AIDS, DNA replication, neurovirology, virology,
environmental carcinogenesis, nucleic acids, cancer,
cell cycle, tumor suppressors, lung cancer, chromatin,
gene, transcription, brain pathology, HIV.
Work in the laboratory of
Dr. Edward M. Johnson is concerned with control of DNA
replication in cancer and AIDS. A major project
involving lung cancer aims to elucidate the mechanism by
which cells distinguish newly-replicated DNA, and its
associated proteins, in S and G2 phases of the cell
cycle and prevent that DNA from reinitiating replication
in the same cycle. A primary hypothesis is that
alterations in activity of an MCM4, 6, 7 helicase
complex, necessary for initiation or reinitiation, are
mediated by Cdk-dependent phosphorylation.
We are pursuing findings
that Cyclin A/Cdk2 and sequence-specific single-stranded
DNA-binding protein, Pura, are colocalized with once-replicated DNA in S and
G2, that Pura modulates activity of Cdk2 and that Pura
colocalizes with MCM7 on chromatin. We shall ascertain
using chromatin immunoprecipitation (ChIP) and re-ChIP
with successive antibodies the location and timing of
assembly and dissociation of MCM4, 6 and 7 helicase
components and the helicase inhibitor, MCM2, upstream of
the c-MYC gene in the cell cycle of small-cell
lung carcinoma cells and normal controls. We are
examining whether Pura modulates the MCM4, 6, 7 helicase,
either by association with Cyclin A/Cdk2 or by DNA
unwinding. Results allow identification of links between
control of initiation of replication and imposition of
checkpoint controls that are critical in preventing
progression to cancer.
Another major project
involves an opportunistic infection of the brain, caused
by the virus JCV, in AIDS patients. We have hypothesized
that activation of JCV in glial cells of the brain is
influenced by HIV-1 infection. We have found that JCV
late gene transcription is stimulated by the HIV-1 Tat
protein through action at sequence elements bound by the
cellular protein, Pura.
A complex between Tat and Pura
acts to stimulate
transcription at both the HIV-1 TAR RNA element and the
JCV late promoter. The complex also interacts with
T-antigen to enhance JCV DNA replication. Pura
is a frequent partner of Cyclin/Cdk complexes, as is
another Tat-binding protein, Cyclin T1.
We are exploring the
dynamics of the interactions between Tat, T-antigen and
Pura during the
course of JCV infection of oligodendrocytes and are
determining whether transcriptional activation involves
activity of Cyclin T1/Cdk9. We are detailing the
mechanism by which Tat enhances replication initiated at
the JCV origin in human oligodendrocytes both in vivo
and using a new in vitro system. We are also examining
the ability of TAT and Pura to interact
with Smad effectors of the TGF-β pathway. Results will
help elucidate pathways of activation of HIV-1 and JCV
in the brain and will help target particular molecular
interactions for therapy.
Selected Publications
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Weinreb, D.B., Desman,
G.T., Amolat-Apiado, M.J.M., Burstein, D.E., Godbold,
J.H., Jr. and Johnson, E.M. (2006) Polyoma
virus infection is a prominent risk factor for
bladder carcinoma in immunocompetent individuals.
Diagnostic Cytopath., 34, 201-203.
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Johnson, E.M.,
Kinoshita, Y., Weinreb, D.B., Wortman, M.J., Simon,
R., Khalili, K., Winckler, B.and Gordon, J. (2006)
Role of Pura in Targeting mRNA to Sites of
Translation in Hippocampal Neuronal Dendrites. J.
Neurosci. Res., 83, 929-943.
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Wang, H., Wang, M.,
Reiss, K., Darbinian-Sarkissian, N., Johnson, E.M.,
Iliakis, G., Amini, S., Khalili, K. and Rappaport,
J. (2007). Evidence for the involvement of Pura in response to DNA replication stress.
Cancer Biol. Ther. 6, in press.
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Kinoshita Y, Johnson
EM. Site-specific loading of an MCM protein
complex in a DNA replication initiation zone
upstream of the c-MYC gene in the HeLa cell
cycle. J. Biol.Chem. 2004; 279(34):35879-89.
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Johnson EM,
Kinoshita Y, Daniel DC. A new member of the MCM
protein family encoded by the human MCM8
gene, located contrapodal to GCD10 at
chromosome band 20p12.3-13. Nucleic Acids Research
2003; 31:2915-2925.
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Khalili K, Del Valle L,
Muralidharan V, Gault WJ, Darbinian N, Otte J, Meier
E, Johnson EM, Daniel DC, Kinoshita Y, Amini
S, Gordon J. Pura is
essential for postnatal brain development and
developmentally-coupled cellular proliferation as
revealed by genetic inactivation in the mouse. Mol
Cell Biol 2003; 23:6857-6875.
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Johnson EM. The
Pur protein family: clues to function from recent
studies on cancer and AIDS. Anticancer Research
2003; 23:2093-2100.
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Liu H, Johnson EM.
Distinct proteins encoded by alternative transcripts
of the PURG gene, located contrapodal to WRN
on chromosome 8, determined by differential
termination/ polyadenylation. Nucleic Acids Res
2002; 30:2417-2426.
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Barr SM, Johnson EM.
Ras-induced colony formation and
anchorage-independent growth inhibited by elevated
expression of Pura
in NIH3T3 cells. J Cell
Biochem 2001; 81:621-638.
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Daniel DC, Schiller RJ,
Liu H, Wortman MJ, Gan L, Mellen JS, Chang CF,
Gallia GL, Khalili K, Johnson EM. Coordinate
effects of human immunodeficiency virus type-1
protein, Tat, and cellular protein, Pura
, on DNA replication
initiated at the JC virus origin. J Gen Virol 2001;
82:1543-1553.
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Lezon-Geyda K, Najfeld
V, Johnson EM. Deletions of PURA, at
5q31, and PURB, at 7p13, in myelodysplastic
syndrome and progression to acute myelogenous
leukemia. Leukemia 2001; 15:954-962.
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Wortman MJ, Krachmarov
CP, Kim JH, Gordon RG, Chepenik LG, Brady JN, Gallia
GL, Khalilik K, Johnson EM. Interaction of
HIV-1 Tat with Pura in nuclei
of human glial cells: characterization of
RNA-mediated protein-protein binding. J Cell Biochem
2000; 77:65-74.
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