Dissecting the role of β-catenin in AML by global epigenetic sequencing

Abstract

Wnt–b-catenin signalling regulates diverse developmental and homeostasis processes. Aberrant regulation of this pathway is observed in numerous cancers. b-catenin, whilst largely dispensable in adult haematopoiesis, has a critical role in the development, disease progression and drug resistance of Acute Myeloid Leukaemia (AML). One of the most frequent chromosomal translocations in AML involves KMT2A, also known as Mixed Lineage Leukaemia protein (MLL). MLL-fusions initiate transformation of haematopoietic stem cells (HSCs) and progenitors such as the Granulocyte-Macrophage Progenitors (GMPs) into Leukaemia Stem Cells (LSCs). Recently we demonstrated that b-catenin is required for the development of MLL-ENL transformed LSCs originating from GMPs but not from HSC enriched populations. This study aims to uncover key targets of b-catenin and dissect mechanisms by which b-catenin controls transcription in LSCs arising from distinct cellular haematopoietic populations. To investigate b-catenin targets in AML, haematopoietic progenitors of specific origin were taken from a b-catenin conditional mouse model and transformed by retroviral MLL-ENL expression.

To this end, we performed global transcriptional profiling by RNA sequencing (RNASeq) on transformed cells in the presence or absence of b-catenin. b-catenin has been shown to recruit histone modifying enzymes and other epigenetic regulators; to elucidate mechanisms by which b-catenin modulates its targets in AML, ChIP sequencing (ChIP-Seq) was produced for promoter and enhancer defining histone modifications. b-catenin targets in LSCs were found to be enriched in cytokine signalling and immune pathways and contrast with those in other cell types suggesting that b-catenin may perform unique roles in AML. Interestingly, one of the few genes differentially up regulated in GMP derived LSCs upon b-catenin deletion included Gadd45a, a DNA damage inducible growth arrest mediator. Whilst showing little effect in vitro, Gadd45a overexpression eliminated leukaemia in vivo. Combined global ChIP-Seq and RNA-Seq analyses revealed b-catenin dependant changes at promoter regions suggesting that b-catenin could be actively involved in histone modification. However, further study with improved experimental design is required to ensure that the observed effects are specific to b-catenin activity.

Date of Award	1 Mar 2020
Original language	English
Awarding Institution	King's College London
Supervisor	Eric So (Supervisor) & Boris Lenhard (Supervisor)