download report - Istituto Pasteur

P a r t i c i p a n t s :
Gianluca Canettieri, Elisabetta Ferretti, professors; Enrico De
Smaele, Lucia Di Marcotullio, Alessandra Ianari, researchers.
Subversion of cerebellar neural progenitor cell development
leads to neoplastic transformation into medulloblastoma,
an aggressive brain malignancy with high
incidence in childhood. Current treatment approaches
have limited efficacy and severe side effects. Therefore,
new risk-adapted therapeutic strategies based on
molecular classification are required. A crucial master
regulator of cerebellar neural progenitor cell development
is represented by the Hedgehog pathway which
displays, when deregulated, a critical role in the pathogenesis
of medulloblastoma. Cross-regulation between
Hedgehog signalling and several tumorigenic pathways
(e.g. the oncogene products of the AP1/jun/fos complex)
plays a role in cell development and tumorigenesis.
Furthermore, deregulation of tumor suppressor
gene function (i.e. Rb) is critical for the formation of
Hedgehog-dependent medulloblastoma. We have investigated
a number of molecular mechanisms involved in
the formation of medulloblastoma (Gulino et al., J Clin
Invest. 2009, in press; Gulino et al., Curr Opin Oncol.
2008, 20:668-75; Gulino et al., Psychoneuroendocrinology
2007, 32:S55-56; Farioli-Vecchioli et al., FASEB J. 2007,
21:2215-25). We have also further dissected the molecular
steps of the regulation of the Hedgehog pathway
as well as of the control of the transcriptional function
of AP1 and Rb proteins. Specific aspects of the
research are described below.
MicroRNA control of cerebellar neural
progenitors and medulloblastoma cells via
targeting of the Hedgehog pathway
MicroRNAs are crucial post-transcriptional regulators
of gene expression and control cell differentiation and
proliferation. MicroRNA expression analysis has
emerged as a powerful tool to identify candidate molecules
playing an important role in a large number of
malignancies. However little is known about their targeting
of specific developmental pathways and, more
specifically, no data are yet available on human primary
medulloblastomas. We have performed a high through-
Principal investigator: Alberto Gulino
Professor of Molecular Pathology
Dipartimento di Medicina Sperimentale
Tel: (+39) 06 4464021; Fax: (+39) 06 4461974
alberto.gulino@uniroma1.it
55
Molecular genetics of eukaryotes - AREA 3
Regulation of the Hedgehog signaling in neural cell development
and disease
put microRNA expression profile analysis in human
primary medulloblastoma specimens to investigate
microRNA involvement in medulloblastoma carcinogenesis.
We identified specific microRNA expression
patterns which distinguish medulloblastoma differing
in histotypes (anaplastic, classic and desmoplastic), in
molecular features (ErbB2 or c-Myc over-expressing
tumors) and in disease risk stratification. MicroRNAs
expression profile clearly differentiates medulloblastoma
from either adult or fetal normal cerebellar tissues.
Only a few microRNAs displayed up-regulated
expression, while most of them were downregulated in
tumor samples, suggesting a tumor growth inhibitory
function. This property has been addressed for miR-9
and miR-125a whose rescued expression promoted
medulloblastoma cell growth arrest and apoptosis
while targeting the pro-proliferative truncated isoform
of TrkC neurotrophin receptor (Ferretti et al., Int J
Cancer 2009, 124:568-77; Laneve et al., Proc Natl Acad
Sci USA 2007, 104:7957-62).
Our microRNA high-throughput profile screening also
revealed a downregulated microRNA signature in
human medulloblastomas with high Hedgehog signaling.
Specifically, we identify miR-125b and miR-326 as
suppressors of the pathway activator Smoothened
together with miR-324-5p which also targets the
downstream transcription factor Gli1. Downregulation
of these microRNAs allows high levels of Hedgehogdependent
gene expression leading to tumor cell proliferation.
Interestingly, the downregulation of miR-324-
5p is genetically determined by medulloblastoma-associated
deletion of chromosome 17p. Of note, we also
report that while microRNA expression is downregulated
in cerebellar neuronal progenitors, it increases
along differentiation, thereby allowing cell maturation
and growth inhibition. These findings identify a novel
regulatory circuitry of the Hedgehog signaling pathway
and suggest that misregulation of specific
miRNAs, leading to its aberrant activation, sustains
cancer development.
In conclusion, specific microRNA deregulation signatures
characterize medulloblastomas and discriminate
tumor subsets with distinct properties thus representing
potential targets for novel therapeutic strategies.