The characterisation of a functional interaction between Ikaros and Foxp1 in pre-B-cells and acute lymphoblastic leukaemia
Author(s)
Bond, Jonathan
Type
Thesis
Abstract
B-lymphopoiesis is characterised by orderly progression through a series of
stages of differentiation, each of which is associated with specific patterns of protein
expression and cellular proliferation. These processes require a high degree of
regulation by the coordinated action of a series of transcription factors that are critical
for appropriate stage-specific gene expression.
We describe a novel interaction between Ikaros and Foxp1, two transcription
factors that are essential for normal B-lymphopoiesis, and which frequently exhibit
abnormal expression in B-lymphoid malignancy. By co-immunoprecipitation, we have
demonstrated physical association between the DNA-binding domains of these
proteins in vivo, which is recapitulated in a cell-free system in vitro. In functional
experiments, ectopic overexpression of Foxp1 by retroviral infection of pre-B-cells
resulted in an increased proportion of cells in the G2 phase of the cell cycle. This
phenotype was associated with increased transcription of Gpr132, a gene which
encodes the G2A protein that is known to induce G2/M cell cycle arrest in mammalian
cells.
The phenotypic effects of Foxp1 overexpression were abolished by coinfection
with Ikaros, which abrogated induction of Gpr132 expression by Foxp1, and
caused displacement of Foxp1 from the Gpr132 gene, as shown by chromatin
immunoprecipitation. Co-infection of IK6 (an Ikaros isoform which lacks the Foxp1
interaction domain and which is frequently expressed in B-cell acute lymphoblastic
leukaemia) had no effect on Gpr132 expression or Foxp1 occupancy of the Gpr132
gene, and failed to abolish the phenotypic effects of Foxp1 overexpression.
Our results contribute to a growing understanding of transcription factor
interplay during normal lymphopoiesis, and provide mechanistic insights into the roles
of Ikaros and Foxp1 in lymphocyte cell cycle homeostasis. In addition, these findings
may contribute to the understanding of cell cycle dysregulation and chemotherapeutic
resistance that characterise certain subtypes of acute leukaemia that exhibit aberrant
expression of these proteins.
stages of differentiation, each of which is associated with specific patterns of protein
expression and cellular proliferation. These processes require a high degree of
regulation by the coordinated action of a series of transcription factors that are critical
for appropriate stage-specific gene expression.
We describe a novel interaction between Ikaros and Foxp1, two transcription
factors that are essential for normal B-lymphopoiesis, and which frequently exhibit
abnormal expression in B-lymphoid malignancy. By co-immunoprecipitation, we have
demonstrated physical association between the DNA-binding domains of these
proteins in vivo, which is recapitulated in a cell-free system in vitro. In functional
experiments, ectopic overexpression of Foxp1 by retroviral infection of pre-B-cells
resulted in an increased proportion of cells in the G2 phase of the cell cycle. This
phenotype was associated with increased transcription of Gpr132, a gene which
encodes the G2A protein that is known to induce G2/M cell cycle arrest in mammalian
cells.
The phenotypic effects of Foxp1 overexpression were abolished by coinfection
with Ikaros, which abrogated induction of Gpr132 expression by Foxp1, and
caused displacement of Foxp1 from the Gpr132 gene, as shown by chromatin
immunoprecipitation. Co-infection of IK6 (an Ikaros isoform which lacks the Foxp1
interaction domain and which is frequently expressed in B-cell acute lymphoblastic
leukaemia) had no effect on Gpr132 expression or Foxp1 occupancy of the Gpr132
gene, and failed to abolish the phenotypic effects of Foxp1 overexpression.
Our results contribute to a growing understanding of transcription factor
interplay during normal lymphopoiesis, and provide mechanistic insights into the roles
of Ikaros and Foxp1 in lymphocyte cell cycle homeostasis. In addition, these findings
may contribute to the understanding of cell cycle dysregulation and chemotherapeutic
resistance that characterise certain subtypes of acute leukaemia that exhibit aberrant
expression of these proteins.
Version
Open Access
Date Issued
2013-04
Date Awarded
2013-07
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Dillon, Niall
Publisher Department
Institute of Clinical Science
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)