Comments on the cross-talk of TGFβ and EGF in cancer
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Інститут експериментальної патології, онкології і радіобіології ім. Р.Є. Кавецького НАН України
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| citation_txt | Comments on the cross-talk of TGFβ and EGF in cancer / M. Jia, S. Souchelnytstkyi // Experimental Oncology. — 2011. — Т. 33, № 3. — С. 170-173. — Бібліогр.: 10 назв. — англ. |
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170 Experimental Oncology 33, 170–173, 2011 (September)
COMMENTS ON THE CROSS-TALK OF TGFβ AND EGF IN CANCER
M. Jia*, S. Souchelnytstkyi
Department of Oncology-Pathology, Karolinska Institutet, Stockholm, Sweden
INTRODUCTION
Transforming growth factor- (TGFβ) acts as a po-
tent tumor suppressor and tumor promoter in a con-
text-dependent manner [1]. Tumor suppressive func-
tions include inhibition of cell proliferation, induction
of apoptosis and regulation of autophagy. As tumors
develop they switch their response to TGFβ and utilize
this factor as a potent promoter of cell motility, inva-
sion, metastasis and tumor stem cell maintenance.
It has been widely proved that misregulation of TGFβ,
i .e. TGFβ over-expression, TGFβ receptor
or Smad2/4 loss or mutation, can result in tumor de-
velopment [2]. Epidermal Growth Factor (EGF) is an-
other potent regulator of cell functions, with predom-
inantly pro-mitogenic role in tumorigenesis [3]. EGF
promotes also cell survival, angiogenesis and differ-
entiation. Deregulation of human epidermal growth
factor receptor (ErbB/HER) pathways by over-expres-
sion or constitutive activation can promote tumorigen-
esis, including angiogenesis and metastasis and
is associated with poor prognosis in many human
malignancies [4].
TGF and EGF initiate signaling events via acting
on different receptors. However, recent reports indi-
cate that many of the components in their intracellular
signaling pathways may be targeted by both growth
factors. Understanding the molecular mechanisms
of how TGFβ and EGF signaling interact at different
stages of cancer is important for development of novel
therapeutics. In this report, we focus on TGF and EGF
signaling, with emphasis on the cross-talk between
their regulatory pathways.
TGFβ SIGNALING AND CANCER
TGFβ signaling is initiated by the binding of TGFβ
ligands to type II TGFβ receptor (TR-II). TβR-II forms
a dimer and recruits type I TGF receptor (TR-I).
Upon formation of a heterotetrameric complex
of 2 TR-II and 2 TR-I, TR-I becomes activated, and
phosphorylates a number of substrates. TGF-β elicits
its biological effects by coordinated activation of the
well studied canonical Smad pathway and several
non-Smad signaling pathways (Fig. 1) [5]. In Smad-
dependent pathway, TβR-I mediated C-terminal
phosphorylation of the receptor-regulated Smads,
Smad2 at Ser465/476 and Smad3 at Ser433/435.
Following phosphorylation, Smads 2 and 3 form het-
eroligomeric complexes with the co-Smad, Smad4,
enter the nucleus, and in cooperation with cofactors
and other sequence specific transcription factors both
positively and negatively regulate gene expression.
TGFβ also activate several Smad-independent path-
ways, including TAK1, RAS, PI3K, PLC, PP2A, SHC,
Rho, Rac and protein synthesis via eEF1A1. TGFβ plays
dual role in cancer development. It acts as a tumor
suppressor in normal epithelial cells and in early stage
of tumor progression. In advanced cancers the growth
inhibitory function of TGFβ is selectively lost, and TGFβ
induces many activities that lead to growth, invasion
and metastasis of cancer cells [1, 2].
TGF-β
TβR II TβR I
Smad signaling
Smad2, Smad3,
Form complex with
Smad4, enter nucleus
Co-regulation
of gene transcription
Non-Smad signaling
Shc, Rho, Rac/CDC42,Par6,
PI3K, PP2A, TAK1, Ras
P
Fig. 1. Schematic presentation TGFβ signaling pathway. TGFβ
binds the type II TGFβ receptor (TβRII) and this complex is able
to recruit and transactivate the type I TGFβ receptor (TβRI). The
ligand-bound TβRII/TβRI receptor complex subsequently acti-
vates downstream Smad-dependent and Smad-independent
signaling. In the Smad-dependent signaling cascade, acti-
vated Smad2 and Smad3 are able to bind Smad4 as homo- and
heterodimers, then translocate to the nucleus where they act
as co-activators or co-repressors of transcription. The Smad-
independent pathways regulated by TGFβ are known to include
Shc, RHO, RAC/CDC42, RAS, TAK1, PI3K, PAR6, PP2A and
protein synthesis (eEF1A1).
Alterations in TGFβ signaling have been associated
with solid tumor initiation, progression and metastasis
[1, 2, 5]. TGFβ1 overexpression has been reported
in breast, colon, esophageal, gastric, lung, pancre-
atic and prostate cancer. High levels of TGFβ1 have
also been detected in the serum of patients with
colon and liver cancer. However, downstream sig-
naling component mutations, loss of expression
and attenuation have been detected in many solid
carcinomas. In particular, it has been shown that the
central mediators of TGFβ signaling TGFβR1, TGFβR2,
Smad2 and Smad4 are frequently lost, mutated or at-
tenuated in human carcinomas. Intragenic mutation,
down-regulation and loss of TGFβR2 expression have
been observed in bladder, breast, colon, esophageal,
lung, ovarian, pancreatic and prostate cancers. Loss
of expression, down-regulation and mutation have also
*Correspondence: E-mail: min.jia@ki.se
Abbreviations: EMT — epithelial-mesenchymal transition; EGF —
epidermal growth factor; TGFβ — transforming growth factor-β.
Exp Oncol 2011
33, 3, 170–173
Experimental Oncology 33, 170–173, 2011 (September) 171
been demonstrated in association with TGFβR1 in bili-
ary, bladder, breast, gastric, liver, ovarian, pancreatic
and prostate cancers. Smad4 mutation, deletion and
loss of expression has been reported in biliary, blad-
der, breast, cervical, colon esophageal, intestine, liver,
lung, ovarian and pancreatic cancers. Smad2 de-
regulation seems to be less frequent than Smad4,
however mutation and deletion has been observed
in cervical, colon, liver and lung cancer. Interestingly,
with the exception of gastric, extravillus trophoblast
and colon cancer, Smad3 is often maintained in hu-
man carcinomas suggesting that it may have a role
different from Smad2 in carcinoma cells that favors
tumor progression.
EGF SIGNALING AND CANCER
The epidermal growth factor (EGF) receptor fam-
ily consists of four related receptors: EGFR (EGFR
or ErbB1), ErbB2 (Neu/HER2), ErbB3 (HER3) and
ErbB4 (HER4). These receptors are differently acti-
vated by ligands including EGF, TGF, amphiregulin
(SDGF), cellulin (BTC), epiregulin (EREG), heparin-
binding EGF-like growth factor (HB-EGF) and the
neuregulins (NRG1, NRG2, NRG3 and NRG4) [3, 6].
Binding of ligands to the extracellular domains of ErbB
receptors initiates their homodimerization or heterodi-
merization with other ErbB receptors, and phosphory-
lation of tyrosine residues within their cytoplasmic
domains. Autophosphorylation of receptors leads
to a number of protein-protein interactions, that in turn
activate downstream growth and survival signals such
as the mitogen-activated protein kinase (MAPK) and
phosphoinositol 3-kinase/v-akt murine thymoma viral
oncogene homolog (PI3K/AKT) pathways (Fig. 2) [6].
P
SRC
STAT3/5
Ras-Raf-Erk
Nck-Jnk
Chl SHP1/2
PLCγ-PKCPI3K-Akt-mT0R
EGF ligand
EGFR dimer
Fig. 2. Schematic presentation of EGFR signaling pathway.
EGFR signaling pathway is initiated by binding of ligands to the
extracellular domain of ErbB receptors, which results in receptor
dimerization, tyrosine kinase activation and transphosphoryla-
tion (P). The activated ErbB receptors are able to interact with
different signaling molecules that transmit the signal in the cell,
including Chl, Src, PI3K, PLC, STAT, Ras, Nck-Jnk and SHP1/2.
The EGF family members play important roles
in normal physiological processes including ontogeny,
morphogenesis, migration, differentiation and prolifer-
ation. Deregulation of EGF family members and related
signaling molecules can contribute to tumorigenesis,
invasion and metastasis. In particular, ErbB2 and EGFR
have been implicated in development of many types
of human cancer [3, 4, 6]. Genetic changes that have
been detected in human tumors include gene ampli-
fication leading to receptor overexpression, activating
kinase domain mutations mainly in EGFR, but also
in ErbB2, in-frame deletions in the extracellular domain
of EGFR (EGFR vIII), and coexpression of ErbB ligands
and receptors in tumors. Each alteration promotes
constitutive activation of the receptors.
CROSS-TALK OF TGFβ AND EGF
IN CANCER
Signaling pathways do not act in isolation, but
interplay with each other and form complex signaling
networks. Recent studies have shown that ErbB signal-
ing, which activates both the MAPK (including Erk1/2,
JNK1/2/3, and p38/MAPKs) and phosphatidylino-
sitol-3 kinase (PI3K)/Akt pathways, communicates
intimately with TGFβ/Smad in controlling mammary
epithelial cell biology and breast cancer development
[7]. Other common Smad-dependent regulatory
mechanisms include phosphorylation of Smad2 and
Smad3 by PKC and PKG. MAPKs and Akt bind to and/
or phosphorylate Smads to control their intracellular
distribution and transcriptional activity [2, 7]. MAPKs
and Akt also phosphorylate and regulate a variety
of Smad binding partners in the nucleus, indirectly
affecting the Smads. We focus below on the cross-talk
involving TGF and Smads from one side, and MAPK
and Akt from the other side (Fig. 3).
TGF-β
TF
EGFR
Ras
MAP3K
MAP2K
MAPK
P
P
Smad3
PI3K
AKT
R-Smad
R-Smad
R-Smad
Smad4
Smad4
cytoplasm
nucleus
Plag, CNK
DNA
Fig. 3. Cross-talk between TGFβ and EGF signaling pathway. The
MAPK and PI3K/Akt are linkers (common targets) of TGFβ and
EGF pathways. Their interplay is modulated primarily by Smad
functions. MAPKs and Akt bind and/or phosphorylate R-Smads
to control their intracellular distribution and transcriptional ac-
tivity. MAPKs and Akt also phosphorylate and regulate a variety
of Smad binding partners in the nucleus, indirectly affecting
the Smads. TGFβ stimulates Erk1/2 activation by regulating
Plag1 and CNK.
TGFβ/SMADS AND THE ERBB/MAPK
PATHWAY
A consensus is that HER2/Ras can antagonize
TGFβ-induced apoptosis and cell cycle arrest, while al-
lowing for the pro-migratory and pro-invasive functions
of TGFβ. Therefore, both positive and negative regu-
lations exist between the two pathways. The synergy
between the TGFβ and HER2/Ras/MAPK pathways
often leads to the secretion of TGFβ, which in turn
promote epithelial-to-mesenchymal transition (EMT)
and cell invasion, whereas JNK kinases seem to nega-
tively regulate the autocrine expression of TGFβ1 [7,
172 Experimental Oncology 33, 170–173, 2011 (September)
8]. MEK/Erk has been reported to positively regulate
SMAD3 gene transcription in epithelial and smooth
muscle cells [7].
It has been confirmed that the linker region in Smad
proteins is important for integrating ErbB/MAPK
signals with the TGFβ pathway. Human cancer cells
overexpressing oncogenic Ras are often resistant
to TGFβ-induced cytostasis. MAPK/Erk-mediates
Smad2/3 linker phosphorylation and Smad nuclear
exclusion, which is considered as the reason for the
attenuation of TGFβ induced cytostasis by MAPK
[9]. MAPKs (especially Erk1/2) also phosphorylate
the linker of Smad1/5, which almost always blocks
Smad1/5 nuclear translocation. Phosphorylation
in Smad1 linker region by Erk creates a docking site
for the Smad1/5-specific E3 ubiquitin ligase, Smurf1.
Smurf1 binding not only causes ubiquitination and
degradation of the Smads but also occludes their
interaction with the nuclear pore complex, thereby
preventing Smad nuclear translocation [9]. In addition
to R-Smads, MAPKs also phosphorylate and regulate
the Co-Smad, Smad4, and the inhibitory Smad7. For
instance, MAPK/Erk decreases Smad4 protein stability
[9]. JNK and p38 seem to preferentially phosphorylate
tumor-derived mutant Smad4 and promote its protea-
somal degradation http://www.nature.com/ cr/jour-
nal/v19/ n1/full/cr2008302a.html - bib58. Erk, JNK,
and p38 have all been implicated in the transcriptional
regulation of Smad7, therefore indirectly regulating
TGFβ signaling. On the flip side, TGFβ also regulates
MAPK/Erk signaling. Addition of TGFβ stimulates
Erk1/2 activation in most of the cells. Our lab identi-
fied Plag1 and CNK contribution to TGFβ induced
Erk1/2 activation [8].
MAPKs phosphorylate a number of nuclear tran-
scription factors, many of which can physically interact
with Smads and regulate TGFβ responses. The best-
characterized ones in this category are the AP-1 pro-
teins, including members of the Jun, Fos, Maf, and
ATF sub-families [9]. Functional interaction between
Smad and the Jun/Fos family proteins has been widely
studied, and their relationship can be synergistic
or antagonistic depending on their target genes and
other binding partners. Thus, TGFβ and EGF may
coordinate their actions by the cross-talk between
Smad-dependent signaling and Erk1/2 activation.
TGFβ AND THE ERBB/PI3K/AKT PATHWAY
PI3K pathway promotes cell survival, growth,
and motility through Akt-mediated phosphorylation
of a number of proteins. Oncogenic mutations and
protein overproduction of PI3K and Akt are commonly
found in human cancers. The activity of PI3K is coun-
teracted by the tumor suppressor protein PTEN. Loss-
of-function mutations of PTEN also occur at a high
frequency in human cancers [7].
The PI3K/Akt activity is known to alleviate TGFβ-
induced apoptosis and/or cell cycle arrest in multiple
types of cells. Interestingly, Smad3, but not Smad2,
seems to be the primary target of inhibition by PI3K/
Akt, consistent with the indispensable function
of Smad3 in mediating the pro-apoptotic effects
of TGFβ. However, exactly how PI3K/Akt modulates
Smad3 activation remains unanswered.
On the other hand, the PI3K/Akt pathway is also
subjected to TGFβ regulation. Akt activity increases
in response to TGFβ treatment, which seems to be re-
quired for a variety of TGFβ-induced activities, such
as cell migration of HER2-expressing breast cancer
cells, EMT of normal mammary epithelial cells, cell
survival of mouse hippocampal neurons and mesen-
chymal cells, as well as growth stimulation of certain
fibroblasts [7, 9]. It is to be noted that Akt activation
by TGFβ is cell type-dependent and very likely indirect,
often requiring either MAPKs or autocrine actions
of secreted molecules.
Alteration of PTEN function represents another
route for TGFβ to influence Akt activity. TGFβ has
been shown to transcriptionally downregulate PTEN
in Smad4 null pancreatic cancer cells, which, again,
seems to rely on the function of the Ras/MAPK path-
way [7, 8, 9]. In the same cells, TGFβ elicits EMT
by dislodging β-catenin from the adherence junctions,
a process that involves TGFβ-dependent PTEN dis-
sociation from β-catenin and Akt activation. On the
other hand, TGFβ/Smad can reduce Akt activity in he-
matopoietic cells by inducing the expression of SHIP
(SH2 domain-containing 5’ inositol phosphatase),
a lipid phosphatase that removes the 5 position phos-
phate from PIP3.
TARGETING TGFβ AND EGF PATHWAYS
IN CANCER TREATMENT
The genetic and preclinical studies support target-
ing TGFβ signaling as therapeutic strategy for combat-
ing cancer. To date there have been investigated three
approaches to inhibit the TGFβ signaling. They are:
(1) inhibition at the translational level using antisense
oligonucleotides, (2) inhibition of the ligand-receptor
interaction using monoclonal antibodies, and (3) in-
hibition of the receptor-mediated signaling cascade
using inhibitors of TGFβ receptor kinases [1, 2]. For
each of these approaches, several drugs have been
developed and are either in pre-clinical or in early
stages of clinical trials. Some of these have already
been shown to be efficacious in limiting tumor inva-
sion and metastasis in vivo. Among these drugs are
antisence oligos used for treatment of gliomas, and
TβR-I kinase inhibitors used for treatment breast
cancer. One of the challenges of anti-TGFβ therapy
will be in targeting the tumor promoting arm of TGFβ
signaling while maintaining the tumor suppressive arm.
EGFR and ErbB receptors have been especially
explored as targets for cancer treatments, because
overexpression and mutations of these receptors
are frequently observed in human malignancies.
A variety of small molecule kinase inhibitors target-
ing EGFR (e.g. erlotinib: Tarceva™) and monoclonal
antibodies targeting EGFR (e.g. cetuximab: Erbitux)
and HER2 (e.g. trastuzumab: Herceptin™) have been
Experimental Oncology 33, 170–173, 2011 (September) 173
developed and some of them are used for treatment
of lung and breast cancer [3]. Anti-EGFR therapy has
shown significant efficacy for some patients. However,
no therapeutic response was seen in high number
of other cancer patients. In addition, patients initially
responsive to anti-EGFR therapy develop resistance
over time of treatment. Potential mechanisms of re-
sistance to EGFR-targeted therapy may be depen-
dent on EGFR gene amplification and mutations, and
on activation of alternative signaling pathways which
bypass the EGFR pathway.
Using targeted agents to inhibit multiple signaling
pathways has emerged as a new paradigm for antican-
cer treatment. This approach is based on preclinical
and clinical data showing potent anti-tumor activity
of single drugs inhibiting multiple molecular targets
or combination therapies involving multiple drugs with
selective or narrow target specificity [10]. In a study
comparing the multi-targeting tyrosine kinase in-
hibitor SU11248—whose targets include VEGFR and
PDGFR—with agents targeting only PDGFR (imatinib)
or VEGFR (SU10944) in mouse xenograft models,
the most robust anti-tumor and anti-angiogenic ef-
fects were observed with SU11248. Moreover, the
efficacy of imatinib combined with SU10944 was
generally similar to that of SU11248 monotherapy,
suggesting that the anti-tumor and anti-angiogenic
effects of SU11248 included additional effects related
to VEGFR and PDGFR inhibition [10]. This suggests
that optimal therapeutic approaches to cancer may in-
volve targeting multiple molecules in different signaling
pathways. Therefore, combination of drugs targeting
EGF and TGFβ or development of drugs targeting com-
mon components of both pathways may confer better
therapeutic effects than single treatments.
ACKNOWLEDGEMENT
This work was supported by the Swedish Research
Council, the Swedish Institute, and the Swedish Can-
cer Foundation to S.S.
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Copyright © Experimental Oncology, 2011
|
| id | nasplib_isofts_kiev_ua-123456789-138639 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1812-9269 |
| language | English |
| last_indexed | 2025-11-28T13:50:46Z |
| publishDate | 2011 |
| publisher | Інститут експериментальної патології, онкології і радіобіології ім. Р.Є. Кавецького НАН України |
| record_format | dspace |
| spelling | Jia, M. Souchelnytskyi, S. 2018-06-19T10:49:01Z 2018-06-19T10:49:01Z 2011 Comments on the cross-talk of TGFβ and EGF in cancer / M. Jia, S. Souchelnytstkyi // Experimental Oncology. — 2011. — Т. 33, № 3. — С. 170-173. — Бібліогр.: 10 назв. — англ. 1812-9269 https://nasplib.isofts.kiev.ua/handle/123456789/138639 This work was supported by the Swedish Research Council, the Swedish Institute, and the Swedish Cancer Foundation to S.S. en Інститут експериментальної патології, онкології і радіобіології ім. Р.Є. Кавецького НАН України Experimental Oncology Short communications Comments on the cross-talk of TGFβ and EGF in cancer Article published earlier |
| spellingShingle | Comments on the cross-talk of TGFβ and EGF in cancer Jia, M. Souchelnytskyi, S. Short communications |
| title | Comments on the cross-talk of TGFβ and EGF in cancer |
| title_full | Comments on the cross-talk of TGFβ and EGF in cancer |
| title_fullStr | Comments on the cross-talk of TGFβ and EGF in cancer |
| title_full_unstemmed | Comments on the cross-talk of TGFβ and EGF in cancer |
| title_short | Comments on the cross-talk of TGFβ and EGF in cancer |
| title_sort | comments on the cross-talk of tgfβ and egf in cancer |
| topic | Short communications |
| topic_facet | Short communications |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/138639 |
| work_keys_str_mv | AT jiam commentsonthecrosstalkoftgfβandegfincancer AT souchelnytskyis commentsonthecrosstalkoftgfβandegfincancer |