download report - Istituto Pasteur

P a r t i c i p a n t s :
Laura Amicone, Carla Cicchini, Alessandra Marchetti,
researchers; Alice Conigliaro, post-doc fellow; Marta Colletti,
PhD student; Claudio Cavallari, technician.
C o l l a b o r a t i o n s :
Istituto Nazionale per le Malattie Infettive “L. Spallanzani”, Roma
(Dr. Tonino Alonzi, Dr. Veronica Bordoni, Dr. Carmine
Mancone).
Report of activity
The epithelial-to-mesenchymal transition (EMT), by
which an epithelial cell undergoes a conversion to a
mesenchymal cell, dissociates from initial contact
and migrates to secondary sites, is a crucial process
both in development and in late stage of tumor
process. EMT requires loss of epithelial polarity,
alteration in cellular architecture and acquisition of
migration capacity. Hallmarks of EMT include
increased expression of mesenchymal markers,
nuclear localization of β-catenin and production of
transcription factors able to inhibit E-cadherin
expression, in particular Snai1 (Snail). The key role
for Snail family members in triggering EMT has
been well established in vitro and in vivo.
Recently an important role for EMT have been proposed
also in the onset and development of chronic
liver diseases that result from derangements in the
synthesis and degradation of extra-cellular matrix.
In particular, the transition of hepatocytes and
cholangiocytes to a mesenchymal fibrogenic cell
may contribute to pathogenesis of liver fibrosis and
cirrhosis.
A reverse trans-differentiation event, the mesenchymal-to-epithelial
transition (MET), occurs at the
secondary site. During MET, all the EMT markers
are inversely modulated.
Continuous balance between EMT and MET characterizes
the so-called “metastable phenotype”,
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Molecular genetics of eukaryotes - AREA 3
Molecular mechanisms of the epithelial to mesenchymal
transition in hepatocyte
Principal investigator: Marco Tripodi
Professor of Genetics
Dipartimento di Biotecnologie Cellulari ed Ematologia
Sezione Genetica Molecolare
Tel: (+39) 06 4461387; Fax: (+39) 06 4462891
tripodi@bce.uniroma1.it
expression of stem cell plasticity. Metastable stem
cells in fact express both epithelial and mesenchymal
traits, while the dynamic fine regulation of
EMT/MET oscillations permits self-renewal as well
as the generation of differentiating precursors.
In the frame of this project we previously demonstrated
that in hepatocytes i) EMT correlates with
the down-regulation of HNF4α, a master regulator
of hepatocyte differentiation, and ii) EMT “master
gene” Snail is sufficient to reproduce the TGFβinduced
down-regulation of several epithelial markers
and to induce EMT in hepatocytes. Most relevantly,
we found that Snail represses the transcription
of the HNF4α gene through a direct binding to
its promoter demonstrating that Snail control both
epithelial morphogenesis and differentiation
(Cicchini et al., J Cell Physiol. 2006, 209:230-8).
During the last year of the project we collected the
following results:
Role of MAPK in TGFb-mediated EMT of the
hepatocytes
In the attempt to further define the role for signalling
pathways activated by TGFβ in hepatocytes, we analyzed
the MAPK cascade and, in particular, the extracellular
signal-regulated protein kinase 5 (ERK5).
We found that ERK5 is phosphorylated and activated
by TGFβ with a rapid and sustained kinetic,
through a Src-dependent pathway. Interference with
ERK5 activation by means of a specific dominant
negative mutant of MEK5 also allowed to uncover a
role for ERK5 in the TGFβ-induced cellular
responses. In fact, we demonstrated that ERK5 participates
to Snail protein accumulation. We also
found that ERK5 inactivation impedes the TGFβmediated
glycogen synthase kinase-3β inactivation,
thus suggesting this as mechanism responsible for
Snail stabilization. Our results, demonstrating a
novel pathway of TGFβ signalling are reported in
the selected publication Marchetti et al., 2008.