The role of extracellular signal-regulated kinases (ERKs) in T lymphocytes

Abstract

The aim of this study was to evaluate the role of the MAP kinases ERK1/2 in naïve and effector CD8 T lymphocytes. Initial experiments showed that inhibition of ERK1/2 activation impaired protein synthesis and reduced cell growth and proliferation of T cell antigen receptor (TCR) stimulated naïve CD8 T cells. On the basis of this data, proteomics analysis of the impact of inhibiting ERK1/2 on the TCR stimulated CD8 T cell proteome was performed. These studies identified 8609 proteins in TCR activated CD8 T cells. The impact of ERK1/2 inhibition was to reduce expression of 1910 proteins and increase expression of 220 proteins. The proteins whose expression was reduced in TCR activated T cells lacking active ERK1/2 proteins included eukaryotic initiation factors, glucose and amino acid transporters, cytokines like IL-2, cytolytic molecules such as granzyme B, surface molecules such as CD25 and transcription factors like EGR1. These results provide a comprehensive understanding of the role of ERK1/2 in antigen receptor signaling in naïve T cells.

The second part of this study consisted of the evaluation of the ERK1/2 role in TCR activated cytotoxic T lymphocytes (CTLs). These studies identified 7627 proteins in TCR re triggered CTLs. The impact of ERK1/2 inhibition was to reduce expression of 101 proteins and increase expression of 75 proteins.The proteins whose expression was reduced in TCR re-triggered CTLs lacking active ERK1/2 proteins included cytokines, chemokines, and transcription factors. However, loss of ERK1/2 activity did not affect expression of eukaryotic initiation proteins, cytolytic molecules and amino acid or glucose transporters. These data provide a comprehensive understanding of the role of ERK1/2 in antigen receptor signaling in CTL and reveal differences in the impact of ERK1/2 inhibition in naive T cells versus effector CTL.

ERK1/2 phosphorylates different substrates, including the p90 ribosomal S6 kinases (RSKs).In the last part of this study I used genetically modified mice to evaluate whether the effects caused by inhibition of MEK1/2 in T cells are mediated by RSKs. T cells express RSK1 and RSK2. The data show no discernible impact of deleting RSK1 on T cell phenotypes. TCR activated RSK2 in null T cells showed reduced production of IL-2, which suggests that RSK2 mediates production of this cytokine downstream of ERK1/2. However, deletion of RSKs did not phenocopy the effects of ERK1/2 inhibition on TCR induced cell growth and proliferation. Hence, further studies are required to identify relevant ERK1/2 substrates in T cells.

Date of Award	2016
Original language	English
Awarding Institution	University of Dundee
Supervisor	Doreen Cantrell (Supervisor)