Andrei
Thomas-Tikhonenko, Ph.D.
Associate Professor of
Pathology
Department
of Pathobiology
University of
Pennsylvania
3800 Spruce Street, Room 367E
Philadelphia, PA 19104-6051
215-573-5138 (office), 215-898-9963
(laboratory)
215-746-0380 (fax)
Graduate
Program: CELL
GROWTH & CANCER
(part of CAMB)
CURRENT LAB
MEMBERS:
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Duonan Yu MD, PhD Courtesy Appointment |
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Michael Dews PhD Senior Research Investigator |
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Diana Cozma MD Research Associate |
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Elaine Chung PhD Postdoctoral researcher
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Yuting Zhao Graduate Student Spring '07 rotation |
SOME FORMER LAB MEMBERS:
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Cinzia Sevignani, Ph.D. -> Research Instructor at the Kimmel Cancer Center, Thomas Jefferson University |
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Jeffrey Ilardi, M.D. -> Resident in Psychiatry, Harvard Medical School |
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Gautam Rajpal -> Gradute Program, University of Michigan |
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Anna Azvolinsky -> Gradute Program, Princeton University |
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Ankoor Shah -> Columbia University School of Medicine |
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Andrea Park -> Research Analyst, The Lewin Group - Healthcare
Management division |
My laboratory studies the mechanisms of
neoplastic transformation by the Myc oncoprotein as
well as host responses to malignant growth, in particular tumor
surveillance
based on anti-angiogenesis (suppression of blood vessel growth). Myc is
a
transcription factor which regulates a perplexingly large number of
genes. In
the recent years, the interactions between Myc and other nuclear
proteins and between
Myc and promoter elements in genomic DNA have been exhaustively
characterized.
Yet to what extent these interactions define the oncogenic potential of
Myc in
vivo is understood only fragmentarily. On the other hand, the use of
model
organisms has revealed potent effects of Myc on normal and pathological
development, but many underlying molecular mechanisms remain to be
elucidated. Our
goal is to understand gene regulation by Myc in the context of tumor
progression. Thus, our research is directed towards: A. Identifying Myc target
genes in cell types corresponding to naturally occurring Myc-induced
tumors; and B. Establishing
the functional significance
of these target genes for tumorigenesis in vivo.
Our
effort began with the discovery that Myc overexpression leads to
down-regulation
of thrombospondin-1, a secreted glycoprotein (Journal of
Biological
Chemistry, 1996). Since thrombospondin-1 was known to inhibit
angiogenesis, we hypothesized that by reducing its levels, Myc can
promote the
ingrowth of blood vessels. At that point, the role of Myc in tumor
angiogenesis
was not recognized. To put our hypothesis to a test, we demonstrated
that
transient overexpression of Myc indeed confers upon rodent fibroblasts
the
angiogenic phenotype (Cell Growth & Differentiation, 2000).
The
effects of Myc on neovascularization were independently observed by
several Myc
laboratories, and recently it has been shown that down-regulation of
thrombospondin-1
by Myc underlies the pro-angiogenic activity of Ras, another potent
oncoprotein. The question still remained whether Myc can trigger the
angiogenic
switch in genetically complex tumors.
Myc promotes
angiogenesis in
murine colon carcinomas by a microRNA-mediated mechanism. To assess the angiogenic effects of Myc in a
bona
fide tumor context, we established a new mouse model of colon
cancer. In
this model, primary colonocytes deficient in the p53 tumor suppressor
are
sequentially transformed by Ras and Myc oncoproteins. We discovered
that
Ras/p53-null cells were very weakly angiogenic on their own. This was
surprising, since mutations in both Ras and p53 had been reported to
promote
vascularization. However, in our system microvascular densities and
overall
growth rates became robust only after overexpression of Myc.
Interestingly, the
pro-angiogenic effects of Myc correlated with down-regulation of
several
proteins with thrombospondin-1 type repeats (TSR), including
thrombospondin-1
itself (Tsp1) and connective tissue growth factor (CTGF). Previously we
demonstrated that rather than affecting the thrombospondin-1 promoter,
Myc
decreases Tsp1 mRNA half-life (Nucleic Acids Research, 2000).
More recently, microRNAs have emerged as important regulators of mRNA
stability, and at least one microRNA cluster (miR-17-92) is directly
activated
by Myc. Provocatively, both Tsp1 and CTGF are predicted targets
for
repression by miR-17-92. Consistent with this prediction, miR-17-92
knock-down
with antisense 2'-O-methyl oligoribonucleotides partly restored Tsp1
and CTGF
expression, and conversely, transduction of Ras-only cells with a
miR-17-92-encoding retrovirus reduced Tsp1 and CTGF levels.
Importantly,
miR-17-92-transduced cells formed larger, better perfused tumors. These
findings establish a role for microRNAs in non-cell-autonomous
Myc-induced
tumor phenotypes (Nature Genetics, 2006) . Neoplastic
growth is
also attenuated by other Myc-regulated TSR proteins, such as clusterin.
We
discovered that down-regulation of clusterin by Myc boosts both
proliferation
and neovascularization of primary colonocytes. In addition, clusterin
attenuates neoplastic transformation of epithelial cells during skin
carcinogenesis (Cancer Research, 2004). These findings
demonstrate how Myc shapes the angiogenic phenotype of solid tumors.
However,
leukemias and lymphomas, whose reliance on blood vasculature is less
obvious,
are also known to overexpress Myc. This poses a question: what are
crucial Myc
targets in hematopoietic cells?
Myc regulates
B-cell differentiation markers of
therapeutic importance. To
determine
the contribution of Myc to hematological malignancies, we developed
another
non-transgenic mouse model based on transduction of p53-null bone
marrow cells
with Myc-encoding retroviruses. We demonstrated that overexpression of
Myc combined
with inactivation of p53 suffices for B-lymphomagenesis (Oncogene,
2002).
We also determined that some Myc- transformed cells possess dual
B-myeloid
potential and differentiate into macrophage-like cells following
spontaneous
down-regulation of the Pax5 transcription factor (Blood, 2003).
Interestingly, Pax5 appears to be an oncogene in its own right and
cooperates
with Myc in many non-Hodgkin lymphomas. Moreover, the propensity of
some of our
cell lines to silence Pax5 afforded a unique opportunity to study, in
collaboration with other laboratories, the role of Pax5 in B-cell
differentiation. One such study co-authored by Kathryn Calame's
(Columbia), David
Schatz's (HHMI-Yale) and our laboratories, was published last year (Nature
Immunology, 2004). In that paper, we established that Pax5
controls
commitment to the B cell lineage via the loss of histone 3 methylation
in the
V(H) immunoglobulin locus.
To
gain a better understanding of the role of Myc in lymphomagenesis, we
used a
conditional mutant of Myc (MycER), which requires the presence of a
synthetic
estrogen for its activity. MycER/p53-null lymphomas were generated, and
the
role of Myc in tumor sustenance was studied using estrogen-deprivation.
We
discovered that inactivation of Myc does not cause overt tumor
regression, as
observed in one-hit transgenic systems. Instead, it merely suppresses
cell
cycle progression, leading to stasis and eventual relapse. However, the
hallmark
of surviving MycOFF
cells
is overexpression of the interleukin-10 receptor and CD20, two
well-known
therapeutic targets. Thus, targeting Myc, while moderately effective on
its
own, shapes the phenotype of quiescent neoplastic cells and sensitizes
them to
other molecular therapies (Cancer Research, 2005; Ann N Y Acad
Sci, 2005).
This
experimental system proved to be very useful in the analysis of other
Myc
targets first identified in cultured cells. Already it has spawned
numerous
collaborations and joint publications with investigators interested in
gene
regulation by Myc, for example Chi Dang (
Myc targets and
anti-tumor surveillance. Our studies on Myc-induced lymphomas led to
the
conclusion that Myc profoundly down-regulates responses to several
tumor-suppressive cytokines, including interferon gamma (IFNg).
This prompted us to investigate the mechanisms underlying
anti-neoplastic effects of IFNg and to re-assess its
therapeutic potential. We discovered that production of retrovirally
encoded (Cancer
Letters, 2001) or infection-induced interferon gamma strongly
inhibits
tumor angiogenesis and/or neoplastic growth (Cancer Biology &
Therapy,
2003). Importantly, it is this inhibition of angiogenesis, not
bystander immunity, that underlies well-documented resistance to tumors
during
infection. This became apparent when we observed tumor resistance in
acutely
infected mice lacking major cytotoxic responses, for instance T- and
tumoricidal NK-cells (Journal of Immunology, 2001). Our
discovery
represented a major development in the field of tumor surveillance and
was
featured in numerous commentaries (Lancet,
Drug Discovery Today, ScientificAmerican.com, etc). One provocative
corollary of our work is that anti-tumor vaccines should be evaluated
not only
for the ability to elicit cytotoxic immunity but also for their
anti-angiogenic
effects.
In
the future, we will continue to develop and refine in vivo mouse models
that
recapitulate genetic defects in naturally occurring human neoplasms.
Our
overall hypothesis is that in order to be clinically beneficial,
inactivation
of Myc would have to be combined with adjuvant molecular therapies.
With this
in mind, we hope to exploit biologically significant targets of Myc
(such as thrombospondin-1
and interleukin-10 receptor) for the development of new cancer
therapeutics.
POSSIBLE ROTATION PROJECTS
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Regulation of the thrombospondin-1 and related genes by Myc via a microRNA-based mechanism. The main goal of this project is to determine whether neoplastic growth by Myc-transformed colonocytes could be suppressed via enforced expression of these proteins and whether tumor suppression is due to cell-autonomous (e.g., cell cycle progression) or non-cell-autonomous (e.g., angiogenesis) processes. |
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The interplay between Myc, p53, and Pax5 in B-lymphomagenesis. We are interested in validating these genes as therapeutic targets. Our experimental data indicate that inactivation of Myc and Pax5 affects primarily cell cycle progression and B-cell differentiation, while re-activation of p53 results in immediate and wide-spread apoptosis and tumor regression. |
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Anti-angiogenic and tumoristatic properties of
murine pro-inflammatory cytokines. We have already established that
sustained production of interferon gamma blocks tumor growth, as does
the deficiency in interleukin-10. We are now investigating the role of
their downstream effectors, STAT1 and STAT3, in tumor cell
proliferation, survival, and neovascularization. |
PRINCIPAL PUBLICATIONS (click on titles to view full text)
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T.-C.Chang,
D.Yu, Y.-S.Lee, D.E.Arking, K.M.West, C.V.Dang, A.Thomas-Tikhonenko*,
and J.T. Mendell* (2007) "Widespread microRNA repression by c-Myc
promotes tumorigenesis", NATURE GENETICS, in press (* - corresponding
authors) |
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S.Thiyagarajan,
N.Bhatia, S.Reagan-Shaw, D.Cozma, A.Thomas-Tikhonenko,
N.Ahmad, and V.S.Spiegelman (2007) "Role of Gli2 transcription factor
in growth and tumorigenicity of prostate cells", CANCER RESEARCH,
67(22):10642-10646 |
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D.Yu, M.Carroll, and
A.Thomas-Tikhonenko (2007) "p53 status dictates
responses of B-lymphomas to monotherapy with proteasome inhibitors", BLOOD, 109(11): 4936-4943 |
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J.Liu,
S.Kumar, D.Yu, S.A.Molton, M.McMahon, M.Herlyn, A.Thomas-Tikhonenko, and
S.Y.Fuchs (2007) "Oncogenic BRAF
regulates β-Trcp expression and NF-κB activity in human melanoma cells",
ONCOGENE, 26(13), 1954-1958 |
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R.K.Amaravadi, D.Yu,
J.J.Lum, T.Bui, M.A.Christophorou, G.I.Evan, A.Thomas-Tikhonenko, and
C.B.Thompson (2007) "Autophagy
inhibition enhances therapy-induced apoptosis in a Myc-induced model of
lymphoma", J
CLIN INVEST, 117(2):326-336 |
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M.Dews,
A.Homayouni, D.Yu, C.Sevignani, K.Sathi, E.Wentzel E.E.Furth, G.Enders,
J.Mendell,
and A.Thomas-Tikhonenko
(2006) "Augmentation
of tumor angiogenesis by the Myc-activated microRNA cluster", NATURE GENETICS, 38(9):1060-1065 |
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S.Hodawadekar,
F.Wei, D.Yu, A.Thomas-Tikhonenko,
and M.L.Atchison (2006) "Epigenetic
histone modifications do not control Igκ locus contraction and
intranuclear localization in cells with dual B-cell-macrophage
potential", J Immunol,
26(6):2373-2386 |
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K.A.O'Donnell,
D.Yu, K.I.Zeller, J.-W.Kim, F.Racke, A.Thomas-Tikhonenko, and
C.V.Dang (2006) "Activation
of transferrin receptor 1 by c-Myc enhances
cellular proliferation and tumorigenesis", Mol Cell Biol,
26(6):2373-2386 |
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D.Yu, D.Cozma, A.Park,
and A.Thomas-Tikhonenko (2005) "Functional
validation of genes implicated in lymphomagenesis: an in vivo selection
assay
using a Myc-induced B-cell tumor", Ann N Y Acad Sci, 1059:145-159 |
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X.Zhang,
L.M.DeSalle, J.H.Patel, A.J.Capobianco, D.Yu, A.Thomas-Tikhonenko
and S.B.McMahon (2005) "Metastasis-associated protein 1
(MTA1) is an essential downstream effector of the c-MYC oncoprotein", Proc Natl Acad Sci |
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D.Yu, M.Dews, A.Park,
J.W.Tobias, and A.Thomas-Tikhonenko (2005) "Inactivation
of Myc in two-hit B-lymphomas causes dormancy with elevated levels of
interleukin-10 receptor and CD20: implications for adjuvant therapies",
Cancer Res, 65(12):5454-5461 |
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W. Tang, Y.Li, D.Yu, A.Thomas-Tikhonenko,
V.S.Spiegelman, and S.Y.Fuchs (2005)
"Targeting b-transducin repeat-containing
protein E3 ubiquitin ligase augments the effects of antitumor drugs on
breast cancer cells", Cancer Res, 65(5):1904-1908 |
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K.Johnson, D.L.Pflugh,
D.Yu, D.G.T.Hesslein, K.-I.Lin, A.L.M.Bothwell, A.Thomas-Tikhonenko,
D.G.Schatz, and K.Calame (2004) "B-cell specific loss of histone 3
lysine 9 in the VH locus depends on Pax5", Nature Immunol, 5(8):853-861 |
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M.S. Ricci, Z.Jin, M.Dews,
D.Yu, A.Thomas-Tikhonenko, D.T.Dicker and W.S.El-Deiry (2004) "Direct repression of
FLIP expression by c-myc is a major determinant of TRAIL sensitivity",
Mol Cell Biol, 24(19):8541-55 |
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A.Thomas-Tikhonenko*,
I.Viard-Leveugle*, M.Dews, P.Wehrli, C.Sevignani,
S.Ricci, W.El-Deiry, B.Aronow,
G.Kaya,
J.-H.Saurat, and
L.E. French (2004)
"Myc-transformed
epithelial cells down-regulate clusterin which inhibits their growth in
vitro and carcinogenesis in vivo", Cancer Research, 64
(9), 3126-3136 |
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A.Thomas-Tikhonenko and
M.L.Iruela-Arispe (2004) "Whence
thrombospondin?",
Cancer Biol & Therapy, 3(4):406-407 |
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E.B.Rankin*, D.Yu*, J.Jiang,
H.Shen, E.J. Pearce, M.H.Goldschmidt, D.E.Levy, T.V.Golovkina,
C.A.Hunter, and A.Thomas-Tikhonenko
(2003)
"An essential
role of Th1 responses and interferon gamma in infection-mediated
suppression of neoplastic growth" Cancer Biol &
Therapy, 2(6):687-693 ►Read about this work in
CB&T◄ |
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D.Yu, D.Allman,
J.G.Monroe, M.H.Goldschmidt, M.L.Atchison
and A.Thomas-Tikhonenko (2003) "Oscillation
between B-lymphoid and myeloid lineages in Myc-induced hematopoietic
tumors following spontaneous silencing/reactivation of the EBF/Pax5
pathway" Blood, 101(5):1950-1955 |
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A.Thomas-Tikhonenko
and C.Hunter (2003) "Infection
and
cancer: the common vein",
Cytokines & Growth Factor Reviews, 14(1):67-77 |
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A. Thomas-Tikhonenko
(2002) "Poisoning the
messengers: could tumor endothelial cells acquire drug resistance?"
Cancer Biol & Therapy, 1(3):266-267 |
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D.Yu and A.Thomas-Tikhonenko (2002) "A non-transgenic mouse model for
B-cell lymphoma: in vivo infection of p53-null bone marrow progenitors
by a Myc retrovirus is sufficient for tumorigenesis" Oncogene, 21:1922-1927 |
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D.Yu and A.Thomas-Tikhonenko (2001)
"Intratumoral delivery of an interferon gamma retrovirus-producing
cells inhibits growth of a murine melanoma by a non-immune mechanism"
Cancer Lett, 173:145-154 |
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C.Hunter, D.Yu, M.Gee, C.Ngo, C.Sevignani,
S.Evans, T. Golovkina, M.Goldschmidt, W.F. Lee, and A.Thomas-Tikhonenko
(2001) "Cutting Edge: Systemic inhibition of
angiogenesis underlies resistance to tumors during acute toxoplasmosis"
J Immunol, 166:5878-5881 ►Read about this work in
LANCET ,
SCIENTIFIC
AMERICAN,
or DRUG DISCOVERY
TODAY◄ |
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A.Janz, C.Sevignani, K.Kenyon, C.Ngo, and A.Thomas-Tikhonenko
(2000) "Activation of the Myc oncoprotein
leads to increased turnover of thrombospondin-1 mRNA"
Nucleic Acids Res, 28:2268-2275 |
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C.Ngo, O.Volpert, M.Gee, K.Kenyon, and A.Thomas-Tikhonenko (2000) "An in vivo function for the transforming Myc protein: elicitation of the angiogenic phenotype" Cell Growth & Diff, 11:201-210 |