download report - Istituto Pasteur

P a r t i c i p a n t s :
Laura Belloni, Rossana De Iaco, Natalia Pediconi,
Barbara Testoni, post-doc fellows; Francesca Guerrieri,
Valeria Schinzari, Cecilia Scisciani, PhD students.
C o l l a b o r a t i o n s :
Istituto Tumori Regina Elena and AIRC, Rome Oncogenomic
Center (Dr. Giovanni Blandino, Dr. Maurizio Fanciulli);
NIAMS, NIH, Bethesda, USA (Dr. Vittorio Sartorelli).
Report of activity
Individual cellular programs (i.e. proliferation, differentiation,
senescence, apoptosis) are executed at
the transcriptional level by the selective expression
of subset of genes, which specify the cell phenotype.
The acetyltransferases p300/CBP and PCAF
play an important role in the positive control of
transcription due to their ability to acetylate the eamino
group of lysine residues of both histones
and nonhistone proteins. Their interaction with
HDAC1 and Sir2/Sirt1 supports a model in which
acetyltransferases and deacetylases may be simultaneously
present on the same gene regulatory loci.
p300, CBP and PCAF are subjected to a variety of
covalent modifications, including acetylation, sumolation,
methylation and phosphorylation, that contribute
to their regulation. p300 undergoes
autoacetylation upon activation of its acetyltransferase
activity whereas, in the case of PCAF, both
auto- and p300-mediated acetylation promote its
acetyltransferase activity.
Our research has focused on the DNA damage
response as a prototype cellular response that is
known to involve the recruitment of both p300
and PCAF and aimed to determine the role of
p300 and PCAF acetylation in the specification of
the repertoire of target genes coactivated namely
by E2F1 and p73.
Principal investigator: Massimo Levrero
Professor of Internal Medicine
Dipartimento di Medicina Interna
Tel: (+39) 06 49970892; Fax: (+39) 06 49383333
massimo.levrero@uniroma1.it
57
Molecular genetics of eukaryotes - AREA 3
Histone Acetyltransferase (HAT) autoregulatory loops in the
regulation of DNA damage responses
hSirT1-dependent regulation of the PCAF-
E2F1-p73 apoptotic pathway in response to
DNA damage
The E2F family of transcription factors have critical
roles in the control of cell proliferation and apoptosis.
E2F1 upregulates transcription of several genes
involved in the activation or execution of apoptosis,
including the Apaf-1, caspase 7 and p73 genes. The
E2F1/p73 pathway is thought to play a major role in
DNA damaging drugs-induced apoptosis and tumor
chemosensitivity. In response to DNA damage E2F1
is phosphorylated by Chk2 and acetylated by PCAF.
These post-translational modification potentiate
E2F1 apoptotic activity and direct its selective
recruitment onto the P1p73 promoter. Pre-existing
and newly synthesized TAp73 is then phosphorylated
by the nuclear tyrosine kinase cAbl, acetylated by
p300 and assembled with the WW domain protein
YAP to activate transcription of downstream apoptotic
target genes. The importance of the E2F1/p73
pathway is reinforced by the strong reduction of
p53-independent apoptosis when either PCAF, p73
or YAP expression is abrogated by specific siRNAs in
cells exposed to DNA damage.
We found that the interaction between hSirT1, the
human homologue of the nicotinamide adenine dinucleotide
(NAD)-dependent class III deacetylase Sir2
(silent information regulator 2) and PCAF controls
the E2F1/p73 apoptotic pathway. hSirT1 represses
E2F1-dependent P1p73 promoter activity in untreated
cells and inhibits its activation in response to DNA
damage. hSirT1, PCAF and E2F1 are co-recruited
on the P1p73 promoter. hSirT1 deacetylates PCAF in
vitro and modulates PCAF acetylation in vivo. In cells
exposed to apoptotic DNA damage nuclear NAD+
levels decrease and inactivate hSirT1, without altering
hSirT1 interaction with PCAF and hSirT1 binding
to the P1p73 promoter. Reactivation of hSirT1
by pyruvate, that increases the [NAD + ]/[NADH]
ratio, completely abolish the DNA damage-induced
activation of TAp73 expression, thus linking the