AP-1 protein induction during monopoiesis favors C/EBP: AP-1 heterodimers over C/EBP homodimerization and stimulates fosB transcription

Sunhwa Hong, Alyza M. Skaist, Sarah J. Wheelan, Alan D. Friedman

Research output: Contribution to journalArticlepeer-review

Abstract

AP-1 proteins heterodimerize via their LZ domains to bind TGACGTCA or TGACTCA, whereas C/EBPs dimerize to bind ATTGCGCAAT. We demonstrate that intact C/EBPα also heterodimerizes with c-Jun or c-Fos to bind a hybrid DNA element, TGACGCAA, or more weakly to TGATGCAA. A 2:1 ratio of c-Jun:C/EBα or c-Fos:C/EBα was sufficient for preferential binding. Semiquantitative Western blot analysis indicates that the summation of c-Jun, JunB, and c-Fos levels in differentiating myeloid cells is similar to or exceeds the entirety of C/EBα and C/EBα, indicating the feasibility of heterodimer formation. Induction of AP-1 proteins during monocytic differentiation favored formation of C/EBP:AP-1 heterodimers, with C/EBα homodimers more evident during granulopoiesis. Approximately 350 human and 300 murine genes contain the TGACGCAA motif between -2 kb and +1 kb of their transcription start sites. We focused on the murine Fosb promoter, which contains a C/EBP:AP-1 cis element at -56 and -253, with the hFOSB gene containing an identical site at -253 and a 1-bp mismatch at -56. C/EBα:AP-1 heterodimers bound either site preferentially in a gel-shift assay, C/EBα:c-Fos ER fusion proteins induced endogenous Fosb mRNA but not in the presence of CHX, C/EBP and AP-1 proteins bound the endogenous Fosb promoter, mutation of the -56 cis element reduced reporter activity fivefold, and endogenous FosB protein was expressed preferentially during monopoiesis versus granulopoiesis. Increased expression of Jun/Fos proteins elevates C/EBP:AP-1 heterodimer formation to potentially activate novel sets of genes during monopoiesis and potentially during other biologic processes.

Original languageEnglish (US)
Pages (from-to)643-651
Number of pages9
JournalJournal of Leukocyte Biology
Volume90
Issue number4
DOIs
StatePublished - Oct 2011

Keywords

  • C-fos
  • C-jun
  • Leucine zipper
  • Myeloid

ASJC Scopus subject areas

  • Immunology and Allergy
  • Immunology
  • Cell Biology

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