Functions and Mechanisms of the ERK5 MAP Kinase in Pluripotent Stem Cells

  • Helen Brown

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

ERK5 is a MAPK which is an important regulator of stem cell pluripotency, maintaining naïve pluripotency and suppressing differentiation. Interestingly, ERK5 differs from other MAPKs as it possesses an extended C-terminal domain containing a transcriptional activation domain. However, the biological functions of the ERK5 signalling pathway have not been systematically investigated. In this thesis, I employed quantitative proteomics to identify novel targets of ERK5 signalling, which I subsequently validated biochemically. This screen identified two projects to pursue. Firstly, ANNEXIN A2 and S100A10, which form a heterotetrameric membrane-bound complex, were upregulated in response to ERK5 signalling, implicating ERK5 in membrane dynamics. Secondly, ZSCAN4 isoforms were upregulated by ERK5 signalling, suggesting a role for ERK5 in regulating early embryonic genes and stem cell rejuvenation.

I next dissected the signalling pathway controlling expression of these proteins, and found that ERK5 regulates expression of Anxa2, S100a10, and Zscan4 mRNA through KLF2, a transcription factor key to naïve pluripotency and known to be induced downstream of ERK5. I also confirmed a role for ERK5 regulating cell morphology and telomere elongation through these novel targets. Furthermore, I identified a feedback mechanism by which ERK5 transcriptionally induces KLF2, but also post-translationally regulates KLF2, through phosphorylation which promotes ubiquitylation and subsequent degradation. As such, ERK5 can both switch on and switch off the expression of downstream targets, such as ZSCAN4, consistent with the dynamic expression profile of these genes.
Date of Award2021
Original languageEnglish
SupervisorGreg Findlay (Supervisor) & Marios Stavridis (Supervisor)

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