ERK5 kinase activity is dispensable for cellular immune response and proliferation

Abstract

Unlike other members of the MAPK family, ERK5 contains a large C-terminal domain with transcriptional activation capability in addition to an N-terminal canonical kinase domain. Genetic deletion of ERK5 is embryonic lethal, and tissue-restricted deletions have profound effects on erythroid development, cardiac function, and neurogenesis. In addition, depletion of ERK5 is antiinflammatory and antitumorigenic. Small molecule inhibition of ERK5 has been shown to have promising activity in cell and animal models of inflammation and oncology. Here we report the synthesis and biological characterization of potent, selective ERK5 inhibitors. In contrast to both genetic depletion/deletion of ERK5 and inhibition with previously reported compounds, inhibition of the kinase with the most selective of the new inhibitors had no antiinflammatory or antiproliferative activity. The source of efficacy in previously reported ERK5 inhibitors is shown to be off-target activity on bromodomains, conserved protein modules involved in recognition of acetyl-lysine residues during transcriptional processes. It is likely that phenotypes reported from genetic deletion or depletion of ERK5 arise from removal of a noncatalytic function of ERK5. The newly reported inhibitors should be useful in determining which of the many reported phenotypes are due to kinase activity and delineate which can be pharmacologically targeted.) is a member of the mitogen-activated protein kinase (MAPK) family, which includes ERK1/2, JNK1/2/3, and p38α/β/δ/γ (1). However, unlike the other MAPK members, ERK5 contains a unique 400-amino-acid C-terminal domain in addition to the kinase domain. Through the MAPK signaling cascade, mitogenactivated protein kinase kinase 5 (MEK5) activates ERK5 by phosphorylating the TEY motif in the N-terminal activation loop (2). This event unlocks the N-and C-terminal halves, allowing ERK5 to auto-phosphorylate multiple sites in its C-terminal region, which can then regulate nuclear shuttling and gene transcription (3, 4). Noncanonical pathways (including cyclin-dependent kinases during mitosis and ERK1/2 during growth factor stimulation) also exist for phosphorylation of sites in the ERK5 tail (5-7). Although ERK5 has been demonstrated to directly phosphorylate transcription factors (8-10), the noncatalytic C-terminal tail of ERK5 can also interact with transcription factors and influence gene expression (4,11,12).ERK5 can be activated in response to a range of mitogenic stimuli [e.g., growth factors, G protein-coupled receptor (GPCR) agonists, cytokines] and cellular stresses (e.g., hypoxia, shear stress) (13). Like most kinases including MAPK members, ERK5 function is assumed to be driven by its kinase activity. ERK5 deletion is embryonic lethal in mice and a variety of tissue-or development-stage restricted KOs have shown clear phenotypes, suggesting that the catalytic function and/or an aspect of the nonkinase domain(s) have key roles in development and mature organ function (14-18). The availability of the first ERK5 inhibitor ...

Signatures of cell death and proliferation in perturbation transcriptomics data - from confounding factor to effective prediction

“…We also observed a cluster composed of XMD8-92, XMD8-85, BI-2536 and Fedratinib (MAPK7, MAPK7, PLK and JAK2 inhibitors, respectively). Recent experiments support that all of these drugs have a common BET inhibitor effect (Ciceri et al, 2014;Lin et al, 2016) , probably responsible for the signature similarity.…”

Beyond Kinase Activity: ERK5 Nucleo-Cytoplasmic Shuttling as a Novel Target for Anticancer Therapy

“…Several small molecule inhibitors of ERK5 or MEK5 kinase activity have been developed (Table 1) and are very effective in reducing tumor growth in vitro and in vivo in a number of cancers. However, it is also emerging that the oncogenic role of ERK5 may be kinase inhibitor-insensitive [110]. A possible reason for this insensitivity is that ERK5 nuclear accumulation, a crucial event in sustaining cancer cell proliferation [77], is indeed often independent of the kinase activity of MEK5 or ERK5 itself as indicated by the ineffectiveness of ERK5 or MEK5 inhibitors when used as single agents.…”

Oncogenic signaling of MEK5-ERK5

“…Through a noncanonical mechanism involving Hsp90 dissociation, cell division cycle 37 (Cdc37) overexpression induced nuclear translocation of catalytically inactive but transcriptionally active ERK5 and collaborated with overexpressed ERK5 to promote cell proliferation [72]. Another study showed that XMD8-92 exhibited off-target kinase activity on bromodomain-containing protein 4 (BRD4), and using ERK5-selective derivatives, suggested that inhibition of ERK5 kinase activity was not responsible for XMD8-92-mediated anti-proliferative effects [73]. Further research is needed to elaborate on the nuclear function of ERK5 independent of its catalytic status.…”