The RAS-dependent ERF Control of Cell Proliferation and Differentiation Is Mediated by c-Myc Repression

Abstract

The ERF transcriptional repressor is a downstream effector of the RAS/ERK pathway that interacts with and is directly phosphorylated by ERKs ETS2-repressor factor (ERF)3 is a ubiquitously expressed transcriptional regulator of the ETS family of transcription factors, with tumor suppressor activity, that is regulated by the RAS/ERK signaling pathway. ERF is shown to be bound and phosphorylated both in vivo and in vitro by ERKs (1, 2). It interacts specifically with active and inactive ERKs via two distinct FXF motifs and can effectively block ERK-substrate interaction (3). In the absence of growth factors, ERF is dephosphorylated and located in the nucleus, whereas upon mitogenic stimulation and in exponentially growing cells, it is actively transported into the cytoplasm through a CRM-dependent mechanism (4). Phosphorylation-deficient ERF mutants are able to reverse RAS-induced tumorigenicity and arrest fibroblasts in the G 0 /G 1 phase of the cell cycle, determining ERF as a bona fide ERK substrate and an effector of the RAS/ERK pathway (2-4). ERF-mediated cell cycle arrest can be abolished by the overexpression of cyclins D and E or the inactivation of the retinoblastoma protein, providing a strong link with cell cycle regulation (2, 4). Homozygous deletion of Erf leads to a block of chorionic trophoblast differentiation, the absence of chorioallantoic fusion, persisting chorion layer, the absence of labyrinth formation, expansion of the giant cell layer, diminishing of the spongiotrophoblast layer, and eventual embryo death by 10.5 dpc (5). Trophoblast stem cell lines derived by Erf Ϫ/Ϫ embryos exhibit delayed differentiation kinetics and decreased expression of spongiotrophoblast terminal differentiation markers suggesting that the ERF is required for extraembryonic ectoderm and trophoblast stem cell differentiation. Thus, there is emerging evidence for ERF contribution in cell cycle inhibition and promotion of differentiation. However, relevant downstream ERF targets have not yet been identified, rendering unclear its mechanism of action.c-MYC is a ubiquitously expressed transcription factor that in physiological levels binds about 10% of the human promoters (6) and regulates crucial cell functions such as proliferation, differentiation, apoptosis, metabolism, and cell growth (for review see Ref. 7). c-MYC induces the activity of cyclin-cyclindependent kinase complexes or affects directly the expression of cell cycle regulators (8 -15), suggestive of its role in cell cycle progression and consistent with the severely retarded proliferation of the c-Myc Ϫ/Ϫ primary mouse fibroblasts because of G 1 and G 2 phase lengthening (16,17). Heterozygous c-Myc fibroblasts show slower growth rates (18), whereas c-MYC controls mammalian and fly body size in a dose-dependent manner (19 -21), indicating that subtle perturbations in c-MYC levels lead to profound defects in cell and organismal physiology.Tight regulation of c-Myc expression is achieved in transcriptional, post-transcriptional, translational, and post-transl...

ERF and ETV3L are retinoic acid-inducible repressors required for primary neurogenesis

“…Erf and Etv3 are cell cycle inhibitors in certain cell types (Klappacher et al, 2002;Sawka-Verhelle et al, 2004;Sgouras et al, 1995;Verykokakis et al, 2007). Since RARs act early in the neuronal differentiation pathway, we hypothesized that ERF and ETV3/3L might act downstream of RARs to promote cell cycle exit and increase neuronal differentiation.…”

EGFR Promotes Lung Tumorigenesis by Activating miR-7 through a Ras/ERK/Myc Pathway That Targets the Ets2 Transcriptional Repressor ERF

“…It seems that multiple mechanisms are controlling the expression, activity, and subcellular localization of ERF, which highlight its physiologic significance in the cell. Recently, ERF was suggested to impose repression checkpoints on a subset of cell cycle control genes (26,27). We have shown that cyclin A, a key factor in the cell Figure 4.…”

Retinoic acid signaling and neuronal differentiation

“…ETV3 was identified as an anti-proliferative factor induced during macrophage differentiation [186,188] and neuronal differentiation [22]. ERF mediates the switch between proliferation and differentiation in macrophages, fibroblasts, extraembryonic ectoderm, and neuroectoderm [22, 167,187,189]. Importantly, both Erf and Etv3 are upregulated by RAR agonists, down-regulated by RAR antagonists, and knockdown of ERF or ETV3 results in paralysis, loss of primary neurons and increased proliferation of undifferentiated neural progenitors.…”

“…The direct targets of ERF repression in neurogenesis are currently unknown. However, since Myc has been identified as an ERF target in fibroblasts [167], it is likely that ERF would also repress n-Myc, a gene that is functionally interchangeable with c-Myc [168]. n-Myc promotes expansion of neural progenitor populations, and would be a good candidate to be repressed by ERF to foster differentiation [169].…”