Cell Type-specific Inhibition of the ETS Transcription Factor ER81 by Mitogen-activated Protein Kinase-activated Protein Kinase 2

Abstract

Mitogen-activated protein kinase-activated protein kinase 2 (MK2) is an important intracellular mediator of stress signals. In this report, a novel target of MK2 has been identified, the ETS transcription factor family member ER81, whose dysregulation contributes to tumorigenesis and whose normal function is required during development. MK2 phosphorylates ER81 in vitro within its central inhibitory domain, and overexpression of MK2 leads to increased in vivo phosphorylation of ER81. Two serine residues, ER81 amino acids 191 and 216, were identified as MK2 phosphorylation sites. MK2 suppresses basal ER81-dependent transcription, and this suppressive effect is alleviated upon mutation of the MK2 phosphorylation sites in a cell type-specific manner. However, MK2 can also interfere with ER81-mediated transcription independently of serine 191 and serine 216 phosphorylation. Furthermore, MK2 overexpression counteracts the stimulation of ER81 activity by p38 mitogen-activated protein kinase. Altogether, MK2 may regulate ER81 transcriptional activity in a cell type-specific manner and thereby modulate various physiological processes beyond stress responses.Three mitogen-activated protein (MAP) 1 kinase classes exist in the mammalian cell, the growth factor-activated ERK-MAP kinases and two stress-activated protein kinase families, JNK and p38 (1). A plethora of stimuli, including serum, growth factors, cytokines, tumor necrosis factor-␣, UV light, hyperosmolarity, and heat, trigger intracellular signal transduction pathways that lead to the activation of one or more of these MAP kinase classes. Upon activation, MAP kinases functionally regulate many proteins through serine/threonine phosphorylation, including distinct MAPKAP kinases, which in turn phosphorylate and modulate downstream effectors.In particular, MAPKAP kinase 2 (MK2) is stimulated by signals such as heat shock and tumor necrosis factor-␣ via the p38-MAP kinase pathway (2, 3). On the other hand, lack of MK2 activity severely dampens tumor necrosis factor-␣ biosynthesis, causing resistance to lipopolysaccharide-induced endotoxic shock (4). Furthermore, 5-lipoxygenase, which catalyzes important steps in the synthesis of a group of inflammatory mediators, leukotrienes, is a downstream target of MK2 (5), suggesting that MK2 may affect the inflammatory response at different levels.A variety of other proteins are phosphorylated by MK2, implicating the involvement of MK2 in many different physiological processes dependent on these target proteins. Among those are the small heat shock proteins (6), the F-actin-binding lymphocyte-specific protein 1 (7), serum response factor that is involved in the regulation of the c-fos proto-oncogene (8), and the transcription factor CREB, which can be phosphorylated by MK2 upon fibroblast or nerve growth factor stimulation (9, 10).ER81 is a transcription factor of the ETS protein superfamily that is characterized by a highly conserved DNA binding domain (11). Gene regulation mediated by ER81 is dependent on its N-and C-termina...

ERK and p38 MAPK-Activated Protein Kinases: a Family of Protein Kinases with Diverse Biological Functions

“…Similar to many MKs, nuclear MK2 contributes to the phosphorylation of CREB (199), serum response factor (77), and ER81 (85 (134).…”

HER2/Neu- and TAK1-mediated Up-regulation of the Transforming Growth Factor β Inhibitor Smad7 via the ETS Protein ER81

“…ER81 is not only activated by ERK MAPK but also by p38 MAPK (42,68). TAK1 is an MAPK kinase kinase that is capable of activating the p38 MAPK pathway (39, 69 -73), and consistently TAK1 appears to activate ER81 and thereby the Smad7 promoter selectively via the p38 MAPK pathway.…”

Regulation of the ER81 transcription factor and its coactivators by mitogen- and stress-activated protein kinase 1 (MSK1)

“…Four amino acids (S94, T139, T143 and S146) are phosphorylated directly by these MAPKs, and two further serine residues (S191 and S216) are phosphorylated by a non-MAPK protein kinase(s). Although one such protein kinase, MAPKAP kinase 2, has been shown to phosphorylate ER81 on S191 and S216, it appears not to be the relevant in vivo kinase upon MAPK stimulation, since MAPKAP kinase 2 rather inhibits than activates ER81 function (Janknecht, 2001). This implicates that another protein kinase is responsible for S191 and S216 phosphorylation upon MAPK stimulation.…”

“…MSK1 was immunoprecipitated with anti-Flag monoclonal antibodies (M2, Sigma) and utilized in in vitro kinase assays employing GST fusion proteins as substrates essentially as described (Janknecht, 2001). Reaction products were separated by SDS-polyacrylamide gel electrophoresis (PAGE) and phosphorylated proteins revealed by autoradiography of the dried gel.…”

“…ER81 expression is undetectable during early stages of embryogenesis, but has been observed in many tissues at later stages (Chotteau-Lelievre et al, 1997, 2001). In addition, ER81 is not ubiquitously and evenly expressed in the adult; for instance, barely, if at all any ER81 mRNA has been detected in liver or skeletal muscle, whereas brain and heart tissue display a high level of ER81 expression (Brown and McKnight, 1992;Jeon et al, 1995;Monte et al, 1995).…”