ERK-associated changes in E2F4 phosphorylation, localization and transcriptional activity during mitogenic stimulation in human intestinal epithelial crypt cells

Abstract

BackgroundThe transcription factor E2F4 controls proliferation of normal and cancerous intestinal epithelial cells. E2F4 localization in normal human intestinal epithelial cells (HIEC) is cell cycle-dependent, being cytoplasmic in quiescent differentiated cells but nuclear in proliferative cells. However, the intracellular signaling mechanisms regulating such E2F4 localization remain unknown.ResultsTreatment of quiescent HIEC with serum induced ERK1/2 activation, E2F4 phosphorylation, E2F4 nuclear translocation and G1/S phase transition while inhibition of MEK/ERK signaling by U0126 prevented these events. Stimulation of HIEC with epidermal growth factor (EGF) also led to the activation of ERK1/2 but, in contrast to serum or lysophosphatidic acid (LPA), EGF failed to induce E2F4 phosphorylation, E2F4 nuclear translocation and G1/S phase transition. Furthermore, Akt and GSK3β phosphorylation levels were markedly enhanced in serum- or LPA-stimulated HIEC but not by EGF. Importantly, E2F4 phosphorylation, E2F4 nuclear translocation and G1/S phase transition were all observed in response to EGF when GSK3 activity was concomitantly inhibited by SB216763. Finally, E2F4 was found to be overexpressed, phosphorylated and nuclear localized in epithelial cells from human colorectal adenomas exhibiting mutations in APC and KRAS or BRAF genes, known to deregulate GSK3/β-catenin and MEK/ERK signaling, respectively.ConclusionsThe present results indicate that MEK/ERK activation and GSK3 inhibition are both required for E2F4 phosphorylation as well as its nuclear translocation and S phase entry in HIEC. This finding suggests that dysregulated E2F4 nuclear localization may be an instigating event leading to hyperproliferation and hence, of tumor initiation and promotion in the colon and rectum.

E2F4 as a single multifactorial target against Alzheimer’s disease

“…Our results support this hypothesis since the mutation of the conserved Thr249/T251 motif of mouse E2F4, which is susceptible to be phosphorylated (21), is crucial for maintaining neuronal quiescence and brain homeostasis in the presence of elevated levels of A. This is consistent with our previous observation that E2F4 is associated with phosphoThr immunoreactivity in cortical neurons from APP/PS1 mice (27), and that E2F4 phosphorylation can lead to cell cycle progression (25,75). In stressed neurons, E2F4 phosphorylation could favor the expression of mitotic regulators (25,74), and cell cycleindependent genes involved in the etiology of AD, thus explaining the capacity of E2F4DN to restore normal E2F4 function and prevent several AD-associated processes.…”

Novel functions for the transcription factor E2F4 in development and disease

“…For instance, ERK1/2-mediated phosphorylation of E2F4 on serines S244 and S384 promotes its nuclear localization in proliferating intestinal cells 38 . Phosphorylation of E2F4 on threonines T261 and T263 by p38 MAPK allows it to bind and activate cell cycle genes during cell cycle re-entry of neurons (Fig.…”

Integrative Genomic Analyses Yield Cell-Cycle Regulatory Programs with Prognostic Value

“…In the case of E2F4 , there are no significant changes in mRNA expression but our analysis shows it exhibits significantly increased regulatory activity. This suggests that the regulatory activity of E2F4 cannot be reflected by mRNA level presumably due to post-transcriptional and post-translational regulation (36, 37). In fact, it has been shown that E2F phosphorylation and localization can be regulated by MEK/ERK activation, leading to changes in its transcriptional activity (36).…”