Depletion of Pleckstrin homology domain leucine-rich repeat protein phosphatases 1 and 2 by Bcr-Abl promotes chronic myelogenous leukemia cell proliferation through continuous phosphorylation of Akt isoforms

J Biol Chem. 2009 Aug 14;284(33):22155-22165. doi: 10.1074/jbc.M808182200. Epub 2009 Mar 4.

Abstract

The constitutive activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway commonly occurs in cancers and is a crucial event in tumorigenesis. Chronic myelogenous leukemia (CML) is characterized by a reciprocal chromosomal translocation (9;22) that generates the Bcr-Abl fusion gene. The PI3K/Akt pathway is activated by Bcr-Abl chimera protein and mediates the leukemogenesis in CML. However, the mechanism by which Bcr-Abl activates the PI3K/Akt pathway is not completely understood. In the present study, we found that pleckstrin homology domain leucine-rich repeat protein phosphatases 1 and 2 (PHLPP1 and PHLPP2) were depleted in CML cells. We investigated the interaction between PHLPPs and Bcr-Abl in CML cell lines and Bcr-Abl+ progenitor cells from CML patients. The Abl kinase inhibitors and depletion of Bcr-Abl induced the expression of PHLPP1 and PHLPP2, which dephosphorylated Ser-473 on Akt1, -2, and -3, resulting in inhibited proliferation of CML cells. The reduction of PHLPP1 and PHLPP2 expression by short interfering RNA in CML cells weakened the Abl kinase inhibitor-mediated inhibition of proliferation. In colony-forming unit-granulocyte, erythroid, macrophage, megakaryocyte; colony-forming unit-granulocyte, macrophage; and burst-forming unit-erythroid, treatment with the Abl kinase inhibitors and depletion of Bcr-Abl induced PHLPP1 and PHLPP2 expression and inhibited colony formation of Bcr-Abl+ progenitor cells, whereas depletion of PHLPP1 and PHLPP2 weakened the inhibition of colony formation activity by the Abl kinase inhibitors in Bcr-Abl+ progenitor cells. Thus, Bcr-Abl represses the expression of PHLPP1 and PHLPP2 and continuously activates Akt1, -2, and -3 via phosphorylation on Ser-473, resulting in the proliferation of CML cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line, Tumor
  • Cell Proliferation
  • Fusion Proteins, bcr-abl / metabolism*
  • Gene Expression Regulation, Neoplastic*
  • HL-60 Cells
  • Humans
  • K562 Cells
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / metabolism*
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / pathology
  • Nuclear Proteins / metabolism*
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoprotein Phosphatases / metabolism*
  • Phosphorylation
  • Protein Isoforms
  • Proto-Oncogene Proteins c-akt / metabolism*
  • U937 Cells

Substances

  • Nuclear Proteins
  • Protein Isoforms
  • Phosphatidylinositol 3-Kinases
  • Fusion Proteins, bcr-abl
  • Proto-Oncogene Proteins c-akt
  • PHLPP1 protein, human
  • PHLPP2 protein, human
  • Phosphoprotein Phosphatases