ERK5 regulation in naïve T‐cell activation and survival

Abstract

ERK5 has been implicated in regulating the MEF2-dependent genes Klf2 and nur77 downstream of the TCR and the maintenance of expression of CD62L on peripheral T cells. Based on this data, knockout of ERK5 would be predicted to compromise T-cell development and the maintenance of T cells in the periphery. Using an ERK5 conditional knockout, driven by CD4-CRE or Vav-CRE transgenes resulting in the loss of ERK5 in T cells, we have found that ERK5 is not required for T-cell development. In addition, normal numbers of T cells were found in the spleens and lymph nodes of these mice. We also find that TCR stimulation is not a strong signal for ERK5 activation in primary murine T cells. ERK5 was found to contribute to the induction of Klf2 but not nur77 mRNA following TCR activation. Despite the reduction in Klf2 mRNA, no effect was seen in ERK5 knockouts on either the mRNA levels for the Klf2 target genes CD62L, CCR7 and S1P, or the cell surface expression of CD62L. These results suggest that while ERK5 does contribute to Klf2 regulation in T cells, it is not essential for the expression of CD62L or T-cell survival. IntroductionMitogen-activated protein kinase (MAPK) cascades are important mediators of cellular responses to a variety of signals, including growth factors, cytokines and cellular stresses. Fourteen MAPK isoforms have been identified in mammalian cells, which can broadly be divided into four groups, the classical MAPK (ERK1 and ERK2), p38 MAPK, JNK and atypical MAPK, which include ERK5, ERK3 and ERK8 [1][2][3][4][5].ERK5 is an unusual MAPK, as it contains a large C-terminal domain in addition to the MAPK domain [2,6,7]. The precise role of the C-terminal domain is unclear; however, it has been shown to be involved in the regulation of ERK5 sub-cellular localisation [8]. The C-terminal domain has also been suggested to act as a transcriptional co-activator for the MEF2 transcription factors [9]. In cells, ERK5 is activated in response to specific growth factors including EGF, as well as by some stresses, such as sorbitol and hydrogen peroxide [10,11]. Like other MAPK, ERK5 is activated by phosphorylation on its TXY motif downstream of a MAPK kinase. MEK5 was originally proposed as the kinase responsible for ERK5 activation, based on its interaction with ERK5 in a yeast two-hybrid assay [12]. This finding was later confirmed by the observation that embryonic fibroblasts isolated from MEK5 knockout mice were unable to activate ERK5 [13]. MEK5 is activated downstream of a MAPK kinase kinase à These authors contributed equally to this study. 2534(MAP3 K), most probably MEKK2. ERK5 signalling has been reported to be deficient in EGF and FGF stimulated embryonic fibroblast cells from MEKK2 knockout mice suggesting that MEKK2 is the predominant MAP3 K for MEK5, downstream of these signals [14,15]. It is not clear, however, if MEKK2 is the only MAP3 K able to activate the ERK5 pathway. Mouse knockouts of either ERK5 or MEK5 are embryonic lethal, however knockouts of MEKK2 are viable and do not exhibit obvious phen...

Phosphorylation of Nur77 by the MEK-ERK-RSK Cascade Induces Mitochondrial Translocation and Apoptosis in T Cells

“…Consistent with this notion, it was reported recently that Nur77 is regulated by the ERK5 MAPK cascade either through transcriptional up-regulation or posttranslational modification mechanism in T cells (16,18). However, conditional ablation of ERK5 in T cells affects neither transcription of Nur77 nor T cell development in thymus (19), suggesting the role of the MAPK cascades in regulation of Nur77-mediated T cell apoptosis should be re-evaluated.…”

Erk5 contributes to maintaining the balance of cellular nucleotide levels and erythropoiesis

“…6C). 7 In contrast to B cell development, thymic T cell precursors in Erk5 -/-VavCre mice showed a distribution similar to that in control mice 7,42 (data not shown). 43 Cell cycle deceleration in bone marrow ter119 C cells of Erk5 -/-VavCre mice…”

“…The Vav-Cre transgene provides efficient excision during an early stage of haematopoietic development when many cell lineage precursors are actively proliferating. 7,41 Haematopoietic excision of Erk5 resulted in enlarged spleen and increased spleen cellularity in mice aged 1-2 months old, whereas bone marrow cellularity was unaltered (Fig. 5B, C, D, E).…”

“…5 Erk5 is required for proliferation of epithelial cells in response to epidermal growth factor, 6 but cells like T lymphocytes have the capacity to proliferate independently of Erk5. 7 During mitosis, Erk5 is phosphorylated in a cdk-dependent manner and translocates to the nuclei. 8,9 Mek5/Erk5 pathway activity correlates with metastatic potential of prostate 10 and renal tumor cells.…”

Programmed Cell Death in T Cell Development

“…However, MEK5 and ERK5 have not been shown to be required for Nur77 induction in response to TCR stimulation. Indeed, ERK5 is not necessary for Nur77 induction upon activation of peripheral T cells (Ananieva et al 2008). Consistent with dominant-negative Nur77 studies, expression of dominant-negative MEK5 inhibits clonal deletion in certain TCR transgenic models (Sohn et al 2008).…”