Investigating the Role of BASP1 Lipidation in WT1/BASP1 Mediated Gene Regulation

Abstract

Brain acid soluble protein 1 (BASP1) is a transcriptional corepressor of the Wilms’ Tumour 1 (WT1) transcription factor. Previous work from the lab demonstrated that N-terminal myristoylation of BASP1 facilitates an interaction with nuclear lipids such that PI(4,5)P2 is recruited to WT1 target gene promoters. PI(4,5)P2 is required for the assembly of chromatin remodelling complexes to mediate transcriptional repression. BASP1 also interacts with cholesterol through a cholesterol recognition amino acid consensus (CRAC) domain, although the role of cholesterol in BASP1-dependent transcription regulation is unknown.
In this study, the mechanisms of WT1/BASP1 mediated transcriptional regulation employing nuclear lipids were investigated. This work revealed for the first time that BASP1 mediates the removal of multiple activating histone modifications, H3K9Ac, H3K4me3 and H3K36me3 in a myristoyl-dependent manner. BASP1 was also found to mediate the addition of repressive histone modifications, H3K9me3 and H3K27me3, plus recruitment of EZH2 in a myristoyl-independent manner.
The role of cholesterol in transcriptional repression by BASP1 was also investigated. Using click-chemistry and chromatin immunoprecipitation, it was demonstrated that BASP1 can recruit cholesterol to gene promoters. Nuclear cholesterol was found to be an important component of the WT1/BASP1 repression complex, involved in removing H3K4me3 at specific WT1/BASP1 target genes.
The subnuclear localisation of BASP1 was investigated to explore how BASP1 interfaces the inner nuclear membrane (INM) with chromatin modification and gene regulation. For the first time BASP1 was found to interact with Emerin and recruit several INM proteins to WT1 target gene promoters in a myristoyl-dependent manner. The evidence presented supports a model whereby the interaction between BASP1 and INM components is important for mediating transcriptional repression. These findings implicate PI(4,5)P2 as a linker between BASP1 and INM proteins.
Together the findings reveal critical roles for PI(4,5)P2 and cholesterol in mediating changes to the chromatin environment at WT1/BASP1 target gene promoters.

Date of Award	7 May 2019
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Stefan Roberts (Supervisor) & Karim T A Malik (Supervisor)