Pharmaceutical Sciences Faculty Publications
RSK-Mediated Phosphorylation in the C/EBP{beta} Leucine Zipper Regulates DNA Binding, Dimerization, and Growth Arrest Activity
Document Type
Article
Publication Date
6-1-2010
Journal Title
Molecular and Cellular Biology
ISSN
1098-5549
Volume
30
Issue
11
First Page
2621
Last Page
2635
DOI
10.1128/MCB.00782-09
PubMed ID
20351173
PubMed Central® ID
PMC2876527
Abstract
The bZIP transcription factor C/EBPbeta is a target of Ras signaling that has been implicated in Ras-induced transformation and oncogene-induced senescence (OIS). To gain insights into Ras-C/EBPbeta signaling, we investigated C/EBPbeta activation by oncogenic Ras. We show that C/EBPbeta DNA binding is autorepressed and becomes activated by the Ras-Raf-MEK-ERK-p90(RSK) cascade. Inducible phosphorylation by RSK on Ser273 in the leucine zipper was required for DNA binding. In addition, three other modifications (phosphorylation on Tyr109 [p-Tyr109], p-Ser111, and monomethylation of Arg114 [me-Arg114]) within an N-terminal autoinhibitory domain were important for Ras-induced C/EBPbeta activation and cytostatic activity. Apart from its role in DNA binding, Ser273 phosphorylation also creates an interhelical ge' salt bridge with Lys268 that increases attractive electrostatic interactions between paired leucine zippers and promotes homodimerization. Mutating Ser273 to Ala or Lys268 to Glu decreased C/EBPbeta homodimer formation, whereas heterodimerization with C/EBPgamma was relatively unaffected. The S273A substitution also reduced the antiproliferative activity of C/EBPbeta in Ras(V12)-expressing fibroblasts and decreased binding to target cell cycle genes, while a phosphomimetic substitution (S273D) maintained growth arrest function. Our findings identify four novel C/EBPbeta-activating modifications, including RSK-mediated phosphorylation of a bifunctional residue in the leucine zipper that regulates DNA binding and homodimerization and thereby promotes cell cycle arrest.
Keywords
Amino acid sequence, cell cycle, DNA, growth substances, leucine zippers, phosphorylation, protein
Recommended Citation
Lee, Sook; Shuman, Jon D.; Guszczynski, Tad; Sakchaisri, Krisada; Sebastian, Thomas; Copeland, Terry D.; Miller, Maria; Cohen, Michael S.; Taunton, Jack; Smart, Robert C.; Xiao, Zhen; Yu, Li-Rong; Veenstra, Timothy D.; and Johnson, Peter F., "RSK-Mediated Phosphorylation in the C/EBP{beta} Leucine Zipper Regulates DNA Binding, Dimerization, and Growth Arrest Activity" (2010). Pharmaceutical Sciences Faculty Publications. 277.
https://digitalcommons.cedarville.edu/pharmaceutical_sciences_publications/277
