Regulation of BCL6: p38 MAPK signalling and CTCF transcriptional regulation converge at exon 1
Author(s)
Batlle, Ana
Type
Thesis
Abstract
BCL6 is a zinc finger transcriptional repressor, which is highly expressed in
germinal centre B-cells, and is essential for germinal centre formation and T-dependent
antibody responses. Deregulated BCL6 expression is associated with certain non-
Hodgkin’s lymphomas. High expression is observed in breast cancer. Tight lineage and
temporal regulation of BCL6 is, therefore, required for normal immunity and abnormal
regulation occurs in cancer. Regulatory mechanisms have been analysed in two
settings. Firstly, BCL6 is strongly induced by the tyrosine kinase inhibitor, Imatinib, in
chronic myeloid leukaemia lymphoid blast crisis cell lines, and this effect was used in
order to study the effects of phospho-protein signalling on BCL6 expression and a major
finding is that p38 MAPK induced BCL6. Also, p38 is, at least in part, responsible for
BCL6 expression in basal conditions in the germinal centre representative Burkitt’s
lymphoma cell lines and that qualitatively different CD40 stimuli can either induce or
repress BCL6 expression. Luciferase assays showed that p38 acts at a 300bp sequence
immediately 5’ of exon 1, and probably also at more distal sequences. Overall it appears
that the balance between positive and negative regulatory controls BCL6 expression
with inhibitory signalling pathways being predominant in most circumstances. Focusing
on BCL6 exon 1, a binding site for the multifunctional regulator CTCF was identified.
CTCF interacts in vitro and in vivo with this sequence. Reduced expression of CTCF in
germinal centre cells caused a moderate reduction of BCL6 expression. Finally,
although no clear differences were observed in the methylation status of the CTCF
binding site on exon 1, a significant enrichment of active histone modifications at this
site was observed in BCL6 expressing cells, suggesting that CTCF may have a role in
the epigenetic regulation of BCL6.
germinal centre B-cells, and is essential for germinal centre formation and T-dependent
antibody responses. Deregulated BCL6 expression is associated with certain non-
Hodgkin’s lymphomas. High expression is observed in breast cancer. Tight lineage and
temporal regulation of BCL6 is, therefore, required for normal immunity and abnormal
regulation occurs in cancer. Regulatory mechanisms have been analysed in two
settings. Firstly, BCL6 is strongly induced by the tyrosine kinase inhibitor, Imatinib, in
chronic myeloid leukaemia lymphoid blast crisis cell lines, and this effect was used in
order to study the effects of phospho-protein signalling on BCL6 expression and a major
finding is that p38 MAPK induced BCL6. Also, p38 is, at least in part, responsible for
BCL6 expression in basal conditions in the germinal centre representative Burkitt’s
lymphoma cell lines and that qualitatively different CD40 stimuli can either induce or
repress BCL6 expression. Luciferase assays showed that p38 acts at a 300bp sequence
immediately 5’ of exon 1, and probably also at more distal sequences. Overall it appears
that the balance between positive and negative regulatory controls BCL6 expression
with inhibitory signalling pathways being predominant in most circumstances. Focusing
on BCL6 exon 1, a binding site for the multifunctional regulator CTCF was identified.
CTCF interacts in vitro and in vivo with this sequence. Reduced expression of CTCF in
germinal centre cells caused a moderate reduction of BCL6 expression. Finally,
although no clear differences were observed in the methylation status of the CTCF
binding site on exon 1, a significant enrichment of active histone modifications at this
site was observed in BCL6 expressing cells, suggesting that CTCF may have a role in
the epigenetic regulation of BCL6.
Date Issued
2010
Date Awarded
2010-11
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Wagner, Simon D.
Porter, Andy
Delgado, M. Dolores
Sponsor
Foundation Marqués de Valdecilla and Amgen
Creator
Batlle, Ana
Publisher Department
Medicine
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)