Phosphorylation of the c-Fos transrepression domain by mitogen-activated protein kinase and 90-kDa ribosomal S6 kinase.

Abstract

Phosphorylation of the C terminus of c-Fos has been implicated in serum response element-mediated repression of c-fos transcription after its induction by serum growth factors. The growth-regulated enzymes responsible for this phosphorylation in early G1 phase of the cell cycle and the sites of phosphorylation have not been identified. We now provide evidence that two growth-regulated, nucleus-and cytoplasm-localized protein kinases, 90-kDa ribosomal S6 kinase (RSK) and mitogen-activated protein kinase (MAP kinase), contribute to the serum-induced phosphorylation of c-Fos. The major phosphopeptides derived from biosyntheticafly labeled c-Fos correspond to phosphopeptides generated after phosphorylation of c-Fos in vitro with both RSK and MAP kinase. The phosphorylation sites identified for RSK and MAP kinase (Ser-374) are in the transrepression domain. Cooperative phosphorylation at these sites by both enzymes was observed in vitro and reflected in vivo by the predominance of the peptide phosphorylated on both sites, as opposed to singly phosphorylated peptides. This study suggests a role for nuclear RSK and MAP kinase in modulating newly synthesized c-Fos phosphorylation and downstream signaling.The product of protooncogene c-fos is implicated in cell proliferation (1-4), differentiation (5), and development (6)(7)(8). To ensure proper expression during these processes, it is subjected to tight regulation at multiple levels. The c-fos gene undergoes rapid and transient transcriptional activation in response to a variety of extracellular stimuli in various cell types (9, 10). The protein synthesis-independent induction is mediated mainly through the serum response element (11), which binds a protein complex composed of a homodimer of serum response factor and p62TCF (12-18). Interestingly, the repression of c-fos gene expression following its activation may also be mediated through the serum response element (19) and the newly synthesized c-Fos protein plays a role in repression of its own promoter (20)(21)(22). The transforming v-Fos protein, which is truncated at the C terminus with five additional point mutations (23), is defective in the transrepression activity (24,25). Upon serum stimulation, c-Fos is more extensively phosphorylated than v-Fos, due to this C-terminal region (23,(25)(26)(27)(28). Phosphorylation of the C terminus has been shown to be responsible for the transrepression activity (29,30), and truncation or mutations that block phosphorylation in this region enhance the transforming capacity of c-Fos (30).c-fos gene induction correlates with the agonist-dependent activation of the mitogen-activated protein kinase (MAP kinase)/90-kDa ribosomal S6 kinase (RSK) signal transduction pathway (31-33). In addition, both kinases are nuclear and cytoplasmic (34), which may be a prerequisite for their participation in regulation ofgene expression. Although MAP The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "adverti...

Signal Transduction in the Liver: C/Ebpβ Modulates Cell Proliferation and Survival

“…1). RSK also modulates the cell cycle through phosphorylation of other transcriptional factors, such as CREB and c-Fos, 11,12 either directly or by altering their binding to CREB binding protein, 13 a key integrator of cellular functions, which is also phosphorylated by RSK 13 (Fig. 1).…”

“…For example, MEKK1 mediates interferon gamma-induced responses through the activation of both p38 (and its target STAT1) and ERK1/2 (and its target C/EBP␤). 22 A mixed response results from the interaction between c-Fos and c-Jun to form the transcriptional factor AP1, [1][2][3] since their activities are stimulated by two MAPK cascades leading to the activation of RSK and JNK1, respectively 1,12 (Fig. 1).…”

Targeting p90 Ribosomal S6 Kinase Eliminates Tumor-Initiating Cells by Inactivating Y-Box Binding Protein-1 in Triple-Negative Breast Cancers

“…This allows RSK to phosphorylate downstream targets involved in tumor growth, invasion, and epithelial-mesenchymal transition [19,23]. These include transcription factors such as Y-box binding protein-1 (YB-1) [22], creb, and c-fos [24] as well as the anti-apoptosis protein BAD [25], the translation factor GSK3b [26], and histone H3 [27,28]. More specifically, RSK phosphorylates YB-1 at S102 leading to nuclear translocation and transcriptional activation [22].…”

Critical role for Rsk2 in T-lymphocyte activation

“…23,24 Rsk family kinases have multiple cellular functions. They are involved in the phosphorylation of histone H3 and remodeling of chromatin in response to epidermal growth factor (EGF) 25 and can regulate gene expression by phosphorylating transcription factors, including c-Fos, 26,27 cAMP-response element-binding protein (CREB), [28][29][30] CREB-binding protein, 31,32 estrogen receptor, 33 ATF4,34 NFATc4, 35 and NF-B/I B␣. 36,37 p90 Rsk2 was also reported to phosphorylate the p34 cdc2 inhibitory kinase Myt1 in frog oocytes, leading to activation of the cyclin-dependent kinase p34 cdc2 that then promotes cell-cycle progression of oocytes through the G2/M phase of meiosis.…”