download report - Istituto Pasteur

P a r t i c i p a n t s :
Michela Muscolini, PhD student; Silvana Caristi, technician.
C o l l a b o r a t i o n s :
Centro de Biología Molecular Severo Ochoa, Universidad Autónoma
de Madrid, Cantoblanco, Madrid, Spain (Prof. Balbino Alarcón);
Dipartimento di Biologia Cellulare, Università di Roma Tor Vergata,
(Prof. Mauro Piacentini); Dipartimento di Dermatologia,
Università di Roma Tor Vergata, (Dr. Antonio Costanzo).
Report of activity
The signalling pathway that leads from antigenreceptor
and/or co-receptor triggering to the activation
of transcription factors of the NF-κB family
has a crucial role in the regulation of cell survival,
and is controlled by highly similar molecular
events in B and T cells. Genetic deficiencies in NFκB
family members or signalling components that
act upstream of NF-κB have been linked to
immune deficiencies, whereas aberrant constitutive
NF-κB activation has been associated with the
development of autoimmune and neoplastic disorders.
The understanding of the molecular mechanisms
that control NF-κB activation in lymphocytes
has therefore important implications for the
design of novel and more specific therapies for
immune diseases.
CD28 is one of the most important co-stimulatory
receptors necessary for full T lymphocyte activation.
As a member of the immunoglobulin (Ig) supergene
family, CD28 extra-cellular Ig-like domain binds to
the cognate ligands, B7.1/CD80 or B7.2/CD86 on
the surface of professional antigen presenting cells
(APC), including macrophages, dendritic cells and
activated B lymphocytes. As an integral component
of the immunological synapse, CD28 plays a critical
role in the recruitment of key molecules to the T cell
receptor (TCR), thus lowering the activation threshold
and enhancing TCR-mediated signalling path-
Principal investigator: Loretta Tuosto
Researcher in Molecular Immunology
Dipartimento di Biologia Cellulare e dello Sviluppo
Tel. : (+39) 06 49917595; Fax: (+39) 06 49917594
loretta.tuosto@uniroma1.it
107
Cellular and molecular immunology - AREA 5
CD28 co-stimulatory molecule as a key regulator of T lymphocyte
differentiation and survival: characterisation of the biochemical
pathways and molecules coupling CD28 to NF-kB activation
ways. More recent data evidence that CD28 can also
act as a TCR-independent signalling unit, by delivering
specific signals, which induce NF-κB actvity
and regulate the survival of primary T cells to several
apoptotic stimuli.
In the last years, we focused our research studies
on the characterisation of the biochemical and
molecular mechanisms coupling CD28 to the activation
of NF-κB. We evidenced that CD28 stimulation
by B7 activates, in memory CD4 + T cells, a
non-canonical NF-κB2-like cascade leading to the
selective recruitment of RelA/p52 and RelA/RelA
dimers on the promoter of pro-inflammatory (i.e.
IL-8 and BAFF) as well as anti-apoptotic (Bcl-xL)
genes. We also found that CD28-induced NF-κB
activation rescues T cells form ionising radiation
(IR)-induced apoptosis by interfering with the
binding of active p73, a member of p53 tumour
suppressor family, and transcription of the proapoptotic
gene bax. The analysis of the biochemical
pathways regulating both transcription of antiapoptotic
bcl-xL and repression of bax expression
by RelA/NF-κB revealed a key role exerted by
phosphatidylinositol 3-kinase (PI3K)/Akt. Indeed,
CD28-induced activation of PI3K/Akt pathway
leads to the recruitment of transcriptionally active
complexes, containing RelA/NF-κB and the histone
acetyltransferase p300/CBP, on the promoter
of anti-apoptotic bcl-xL. At the same time,
PI3K/Akt cascade induces the binding of corepressor
complexes, formed by RelA and the histone
deacetylase HDAC1, on the bax gene promoter
thus inhibiting Bax expression and ensuring T
cell survival in response to death stimuli.
CD28 also plays a critical role in regulating actin
remodelling by inducing the early cytoskeleton
rearrangements events required for the recruitment
and activation of signalling molecules to the membrane.
We previously demonstrated that Vav-1, an
exchange factor for Rac-1 and Cdc42 GTP-binding
proteins, is a key upstream regulator of the sig-