Phosphorylation of C/EBPα Inhibits Granulopoiesis

Abstract

CCAAT/enhancer-binding protein ␣ (C/EBP␣) is one of the key transcription factors that mediate lineage specification and differentiation of multipotent myeloid progenitors into mature granulocytes. Although C/EBP␣ is known to induce granulopoiesis while suppressing monocyte differentiation, it is unclear how C/EBP␣ regulates this cell fate choice at the mechanistic level. Here we report that inducers of monocyte differentiation inhibit the alternate cell fate choice, that of granulopoiesis, through inhibition of C/EBP␣. This inhibition is mediated by extracellular signal-regulated kinases 1 and/or 2 (ERK1/2), which interact with C/EBP␣ through an FXFP docking site and phosphorylate serine 21. As a consequence of C/EBP␣ phosphorylation, induction of granulocyte differentiation by C/EBP␣ or retinoic acid is inhibited. Our analysis of C/EBP␣ by fluorescent resonance energy transfer revealed that phosphorylation induces conformational changes in C/EBP␣, increasing the distance between the amino termini of C/EBP␣ dimers. Thus, myeloid development is partly regulated by an ERK1/2-mediated change in the conformation of C/EBP␣ that favors monocyte differentiation by blocking granulopoiesis.

Proteomic identification of C/EBP-DBD multiprotein complex: JNK1 activates stem cell regulator C/EBPα by inhibiting its ubiquitination

“…JNK1 is a stress-regulated kinase and C/EBPa is known to be post-translationally modified by small ubiquitin-like modifier, ubiquitin and phosphorylation (Mahoney et al, 1992;Behre et al, 2002b;Subramanian et al, 2003;Ross et al, 1999Ross et al, , 2004. Therefore, we hypothesized, under stress conditions JNK1 physically associate, phosphorylates C/ EBPa and thereby inhibits its ubiquitination.…”

Transcriptional dysregulation during myeloid transformation in AML

“…Phosphorylation of CEBPA at serine 21 is mediated by extracellular signal-regulated kinases 1 and/or 2, which recognize serine 21 of CEBPA as a substrate through an FXFP docking motif (Ross et al, 2004). This phosphorylation induces a conformational change in CEBPA such that the transactivation domains of two CEBPA molecules within a dimer move further apart.…”

Src-family kinases play an essential role in differentiation signaling downstream of macrophage colony-stimulating factor receptors mediating persistent phosphorylation of phospholipase C-γ2 and MAP kinases ERK1 and ERK2

“…45,48 Myeloid transcription factors are also phosphorylated by MAPK, such as AML-1 49 and members of the C-EBP family. 50,51 Thus, it is possible that the graded influence of MAPK on myeloid progenitor cell fate may be relayed through differential regulation of major myeloid transcription factors. Abnormal activation of the MAPK pathway is found in many cases of acute myeloid leukemia, especially in those exhibiting activating mutations in Ras or Flt-3.…”