Akt-induced phosphorylation of N-CoR at serine 1450 contributes to its misfolded conformational dependent loss (MCDL) in acute myeloid leukemia of the M5 subtype

PLoS One. 2013 Aug 5;8(8):e70891. doi: 10.1371/journal.pone.0070891. Print 2013.

Abstract

The nuclear receptor co-repressor (N-CoR) is a key component of the generic co-repressor complex that plays an important role in the control of cellular growth and differentiation. As shown by us recently, the growth suppressive function of N-CoR largely relies on its capacity to repress Flt3, a key regulator of cellular gorwth during normal and malignant hematopoesis. We further demonstrated how de-repression of Flt3 due to the misfolded conformation dependent loss (MCDL) of N-CoR contributed to malignant growth in acute myeloid leukemia (AML). However, the molecular mechanism underlying the MCDL of N-CoR and its implication in AML pathogenesis is not fully understood. Here, we report that Akt-induced phosphorylation of N-CoR at the consensus Akt motif is crucial for its misfolding and subsequent loss in AML (AML-M5). N-CoR displayed significantly higher level of serine specific phosphorylation in almost all AML-M5 derived cells and was subjected to processing by AML-M5 specific aberrant protease activity. To identify the kinase linked to N-CoR phosphorylation, a library of activated kinases was screened with the extracts of AML cells; leading to the identification of Akt as the putative kinase linked to N-CoR phosphorylation. Consistent with this finding, a constitutively active Akt consistently phosphorylated N-CoR leading to its misfolding; while the therapeutic and genetic ablation of Akt largely abrogated the MCDL of N-CoR in AML-M5 cells. Site directed mutagenic analysis of N-CoR identified serine 1450 as the crucial residue whose phosphorylation by Akt was essential for the misfolding and loss of N-CoR protein. Moreover, Akt-induced phosphorylation of N-CoR contributed to the de-repression of Flt3, suggesting a cross talk between Akt signaling and N-CoR misfolding pathway in the pathogenesis of AML-M5. The N-CoR misfolding pathway could be the common downstream thread of pleiotropic Akt signaling activated by various oncogenic insults in some subtypes of leukemia and solid tumors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Amino Acid Substitution
  • Cell Line, Tumor
  • Enzyme Activation
  • Gene Expression Regulation, Leukemic
  • HEK293 Cells
  • Humans
  • Leukemia, Monocytic, Acute / enzymology*
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Nuclear Receptor Co-Repressor 1 / genetics
  • Nuclear Receptor Co-Repressor 1 / metabolism*
  • Phosphorylation
  • Protein Conformation
  • Protein Folding
  • Protein Processing, Post-Translational
  • Protein Stability
  • Proteolysis
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Serine / metabolism

Substances

  • NCOR1 protein, human
  • Nuclear Receptor Co-Repressor 1
  • Serine
  • Proto-Oncogene Proteins c-akt