Phosphorylation of serine 21 modulates the proliferation inhibitory more than the differentiation inducing effects of C/EBPα in K562 cells

Valentina Fragliasso, Yuri Chiodo, Giovanna Ferrari-Amorotti, Angela Rachele Soliera, Gloria Manzotti, Sara Cattelani, Olivia Candini, Giulia Grisendi, Jenny Vergalli, Samanta Antonella Mariani, Clara Guerzoni, Bruno Calabretta

Research output: Contribution to journalArticlepeer-review


The CCAAT/enhancer binding protein α (C/EBPα) is a transcription factor required for differentiation of myeloid progenitors. In acute myeloid leukemia (AML) cells expressing the constitutively active FLT3-ITD receptor tyrosine kinase, MAP kinase-dependent phosphorylation of serine 21 (S21) inhibits the ability of C/EBPα to induce granulocytic differentiation. To assess whether this post-translational modification also modulates the activity of C/EBPα in BCR/ABL-expressing cells, we tested the biological effects of wild-type and mutant C/EBPα mimicking phosphorylated or non-phosphorylatable serine 21 (S21D and S21A, respectively) in K562 cells ectopically expressing tamoxifen-regulated C/EBPα-ER chimeric proteins. We show here that S21D C/EBPα-ER induced terminal granulocytic differentiation of K562 cells almost as well as wild-type C/EBPα-ER, while S21A C/EBPα-ER was less efficient. Furthermore, wild-type C/EBPα suppressed the proliferation and colony formation of K562 cells vigorously, while S21D and S21A C/EBPα mutants had more modest anti-proliferative effects. Both mutants were less effective than wild-type C/EBPα in suppressing endogenous E2F-dependent transactivation and bound less E2F-2 and/or E2F-3 proteins in anti-C/EBPα immunoprecipitates. Together, these findings suggest that mutation of S21 more than its phosphorylation inhibits the anti-proliferative effects of C/EBPα due to reduced interaction with or impaired regulation of the activity of E2F proteins. By contrast, phosphorylation of serine 21 appears to have a modest role in modulating the differentiation-inducing effects of C/EBPα in K562 cells.

Original languageEnglish
Pages (from-to)1704-1713
Number of pages10
JournalJournal of Cellular Biochemistry
Issue number5
Publication statusPublished - May 2012



ASJC Scopus subject areas

  • Biochemistry
  • Cell Biology
  • Molecular Biology


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