Ivestigating the role of EZH2 in the BASP1/WT1 repressive complex

Abstract

BASP1 is a neuronal signalling protein that was found to be a corepressor of the developmental transcription factor Wilms’ tumour 1 (WT1). Both BASP1 and WT1 are involved in several different types of cancer and can act as both tumour suppressors and oncogenes. Together, they form the BASP1/WT1 repressive complex which can inhibit the transcription of WT1 target genes. Recent studies in understanding the repressive mechanism of this complex showed that BASP1 facilitates the removal of activatory histone marks (H3K4me3 and H3K9ac) and the placement of repressive histone marks (H3K9me3 and H3K27me3). EZH2, a core subunit of the polycomb (PRC2) complex, was found to be recruited to the promoter region of WT1 target genes by BASP1. EZH2 is a histone methyltransferase which places H3K27me3 marks on gene promoters. Whether or not EZH2 is the enzyme that places the BASP1-dependent H3K27me3 mark and is involved in the transcriptional repression mechanism of BASP1 is not known.
This study used three different EZH2 inhibitors to examine the role of EZH2 in BASP1-dependent transcriptional repression in two different cell lines. The work revealed that EZH2 is responsible for placing BASP1-dependent H3K27me3 marks on the promoters of WT1 target genes. However, the BASP1/WT1 complex exhibited different requirements for EZH2 activity in transcriptional repression depending on the specific target gene.
The effects of EZH2 inhibition on BASP1-dependent suppression of cancer cell growth was also studied. The results showed that, in the absence of EZH2, K562 cells had a decreased growth rate and MCF7 cells showed decreased tumorigenicity, suggesting that the BASP1/WT1 complex works with EZH2 to repress growth-promoting genes.
The findings indicate that the BASP1/WT1 complex employs multiple mechanisms to mediate gene repression. The results suggest that EZH2 plays a role in the function of this complex but the effects on transcriptional repression are gene specific.

Date of Award	23 Jan 2020
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Stefan G E Roberts (Supervisor)