Download Centennial Retrovirus Meeting

Centennial Retrovirus
Meeting
Prague (Czech Republic), April 29-May 4, 2010
Editors
Rene Daniel, Jiri Hejnar,
Anna Marie Skalka, Jan Svoboda
MEDIMOND
International Proceedings
© Copyright 2010 by MEDIMOND s.r.l.
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Background and Perspectives
It has been my long-lasting dream to welcome in Prague the community of people working with retroviruses. For various reasons, far above our reach, this has not
been possible. Fortunately, even Central Europe is prone to regaining its position
among civilized countries and starts to communicate with the world as one of equal
partners.
This year we are commemorating 100 years that have elapsed since the seminal
discovery of fowl sarcoma, which was shown by Peyton Rous to be first transmissible
among chickens by grafting and later by cell-free filtrate.
I had the privilege to meet Peyton Rous in 1962, when I brought with me our
strain of his virus, which in the meantime underwent many changes. On this occasion
he gave me a collection of his original works (Fig. 1) with a short dedication, which
represents the most precious recognition I ever received. On this page are listed his
discovery papers. What is even more impressive is the way how systematically and in
depth he analysed his viral agent. In one of his early papers (Fig. 2) he recognized that
the resistance to his virus differed from tissue incompatibility raised against transplanted
tissues, but documented that in early stages of tumor passaging both overgrowth of
tumor cells and virus infection were involved.He also clearly postulated, as given in
Fig. 3, that some tissue injury favors virus-induced oncogenesis, which becomes, in
a broader sense, the very issue of modern oncology. Because of time limits I cannot
discuss additional essential contributions of Peyton Rous.
In one approach Rous was not successful, namely in transmission of his original
virus isolate to foreign avian species and to mammals (Fig. 4). In this respect, Russian virologists Svet-Moldavsky and Zilber brought the first evidence that RSV is
pathogenic and oncogenic also in rodents.
We obtained first clear data showing that RSV-induced tumours contain the viral
genome in non-infectious state. Very schematically (Fig. 5), this genome is kept over
the years in every cell and even cell clone population, and therefore we concluded that
is it integrated there as a provirus which means that it behaves as a new cell genetic
information.Infectious virus could have been rescued from such virogenic cells by
associating them with permissive chicken fibroblasts. As is shown in the bottom part
of the figure, the provirus existence was independently proposed by Howard Temin,
who isolated chicken so-called non-producing cells (NP) that kept the transformed
morphotype in the absence of virus production. As will be discussed later, the lack
of virus production in NP cells was due to the defectiveness of the RSV strain em©2010 by MEDIMOND s.r.l.
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Fig. 1
Fig. 2
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Fig. 3
Fig. 4
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Fig. 5
ployed and infectious virus could be recovered from them by superinfection with
any non-acutely transforming avian retrovirus. In our case it turned out that such an
association leads to cell fusion (Fig. 6), and there is a correlation between the arising heterokaryons and the degree of virus rescue. In fact, this has been a first clear
example showing that retrovirus is under a cell controle.
Recently, we have re-examined the process of virus rescue using more sensitive
techniques. We established that the virus rescued by cell fusion is regularly produced
in the amounts of 15 FFU/ml. In addition, as shown in Fig. 7, the viral glycoprotein
is detectable in 20 % of polynucleated cells since the 2nd day after the fusion using
specific labelled virus receptor. The proportion of positive multikaryons later reaches
30 %. The permissive chicken cell is either supplying a missing function or inactivating
a repressor function in the non-permissive cell. Curiously enough, this function seems
not to be present in terminally differentiated chicken nucleated erythrocytes. At the
molecular level, virogenic cells show clear depression in viral env mRNA synthesis,
However after cell fusion synthesis of env mRNA increases at least 10 times (Fig.
8). From additional experiments we know that the env mRNA representation in the
cytoplasm increases after cell fusion. It should be mentioned that in addition to the
very low env mRNA amount in virogenic cells, at least two anomalously spliced env
RNA species are present, the amount of which is, however, not changed by cell fusion.
The present studies are directed toward depicting the critical functions provided by
chicken fibroblasts and required for virus rescue. Such studies may shed light on the
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Fig. 6
Fig. 7
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Fig. 8
principal question: Which molecular mechanisms are involved in blocking infectious
virus production in foreign species cells and what events allow its deblocking?
The original RSV kept in the USA was shown by Rubin and Vogt to be defective,
in contrast to several European RSV strains, which are not. There is no explanation
for this fact, and therefore we have to admit that the harder conditions for science in
Europe in those days would not allow the defective virus state to be kept.
Of special importance to RSV studies was the quantitative focus assay established
by Temin and Rubin (Fig. 9), which made possible the exact determination of virus
transformation titers. This assay had later been extended to the study of retroviral
and other oncogenes. The quantitative studies of RSV performed by Rubin, Temin,
Vogt, Hanafusa and others established the virus life cycle and opened the way to the
classification of virus strains and mutant analysis, both systematically followed in
Peter Vogt’s laboratory.
Finally, the proviral DNA step in the retrovirus cell cycle was explained by the
discovery of reverse transcriptase made by Baltimore and Temin, and by successful
transfection experiments using DNA isolated from virogenic cells.
Now, I would like to return to Peyton Rous and recall his far-sighted testament
(Fig. 10). Let’s comment on the inferences of today (Fig. 11). There is large evidence
that retroviral structures, together with retroelements and their products, constitute
about half of our genome. What is the evolutionary consequence of this “movable
feast”- these are words of Ernst Hemingway, or let’s place it also into another perspective as a movable disaster? How both these extremes are orchestrated remains
to be solved.
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Fig. 9
Fig. 10
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Fig. 11
Retroviruses and retroelements are movable not only within species, but also among
related and unrelated species. That is why we have acquired deadly diseases such as
HIV causing AIDS, HTLV, and probably others. The transmissibility of retroviruses
is governed by reshaping of the virus genome, integration site in the cell genome,
and a series of cell control functions. Especially the latter ones are among the best
antiviral strategies.
As a consequence of their life cycle, retroviruses belong among the best candidates for vector constructs that can be employed in gene therapy. However, we should
know more about their safety and targeting in the cell genome, excluding them from
integration in the vicinity of protooncogenes. In fact, retroviruses provided the key to
the definition of principal oncogenes, the structure of which has been well defined.
However, less clear are the ways how they trigger cell transformation.
Finally, we face a great task how to elicit efficient anti-retrovirus resistance, both
in acquired and natural immunity. Working with avian retroviruses, we have been
repeatedly unsuccessful in eliciting protection, with the exception of oncogene v-src
mediated tumorigenesis. In case of acquisition of twelve new aminoacids during vsrc genesis produced a new epitope recognized by immune reaction. Hopefully more
efficient approaches will provide the required success in protection against retrovirus
infection.
Index
Front page ........................................................................................................................... I
Foreword ............................................................................................................................. III
Action at the Cell Surface
Pathogenesis of HIV Nef in Thymocytes
Paul Jolicoeur, Pavel Chrobak, Nathalie Bouchard, Munir M. Rahim, Joël Guertin,
Elena Priceputu and Zaher Hanna ....................................................................................... 1
Identification of Essential Host Cell Factors
Novel host factors essential for HIV-1 replication: their importance in HIV-1
life cycle.
Rato S., Maia S., Brito P.M., Resende L., Ramos A., Pereira C.F., Moita L.F. , Goncalves J. . ... 7
Insights from Studies of Intracellular Trafficking
Analysis of the N-terminus of nucleocapsid protein of Mason-Pfizer monkey
virus: its role in the particle assembly.
Bohmová K, Hadravová R., Štokrová J., Ruml T., Pichová I. and Rumlová M. ...................... 13
Retrovirus Evolution
Towards a retrovirus database, RetroBank
Blomberg Jonas, Sperber Göran, Jern Patric, Benachenhou Farid . .................................... Abelson Virus Target Cell Development
Stuart, B. and Rosenberg, N. . .............................................................................................. 19
23
Cellular Defenses
HIV-1 Vif binds to APOBEC3G mRNA and regulates its translation
Marquet R., Mercenne G., Bernacchi S., Richer D., Bec G., Henriet S., & Paillart J.-C. . ....... 27
©2010 by MEDIMOND s.r.l.
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Epigenetic Effects on Retroviral Gene Expression and Oncogenesis
Epigenetic regulation of the HIV promoter and approaches to persistent retroviral infection
David M. Margolis, MD FACP ............................................................................................... Influence of antipsychotic medication on endogenous retrovirus (ERV) expression in brain cells
Diem O., Schäffner M., Frohnmeyer M., Hemby S.E., Frank O., Seifarth W., Leib-Mösch, C. .
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Mechanisms of Disease
Avian leukosis virus integrations activate oncogenes, microRNA-155, and
TERT in lymphomas
Withers, J.B., Bolisetty, M.T. and Beemon, K.L. .................................................................... 45
Anti-viral Strategies: Drugs and Vaccines
Discovery of Novel Compounds From Betula papyrifera That Inhibit HIV-1
Maturation
Dorr C, Kolomitsyna O, Yemets S, Somia N, Krasutsky P and Mansky LM ........................... 53
HIV-1 gp120 glycosylation is cell type-specific and influences reactivity with
HIV-1-specific antibodies
Raska M., Elliott M.C., Hall S., Czernekova L., Zachova K., Moldoveanu Z., Brown R.,
Mestecky J., Novak J. .......................................................................................................... 55
Trends in Retroviral Therapy
Prospects of anti-HIV therapy
De Clercq Erik ...................................................................................................................... Retrovirus Transduced Human Mesenchymal Stem Cells in Targeted Gene
Therapy for Cancer
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Altaner C., Altanerova V., Cihova M., Matuskova M., Kucerova L. . ....................................... 67
Author Index ........................................................................................................................ 75