The oncogenic serine/threonine kinase Pim-1 directly phosphorylates and activates the G2/M specific phosphatase Cdc25C

Int J Biochem Cell Biol. 2006 Mar;38(3):430-43. doi: 10.1016/j.biocel.2005.10.010. Epub 2005 Nov 8.


The proto-oncogene Pim-1 encodes a serine-threonine kinase which is a downstream effector of cytokine signaling and can enhance cell cycle progression by altering the activity of several cell cycle regulators among them the G1 specific inhibitor p21(Waf), the phosphatase Cdc25A and the kinase C-TAK1. Here, we demonstrate by using biochemical assays that Pim-1 can interact with the phosphatase Cdc25C and is able to directly phosphorylate the N-terminal region of the protein. Cdc25C is functionally related to Cdc25A but acts specifically at the G2/M cell cycle transition point and can be inactivated by C-TAK1-mediated phosphorylation. Immuno-fluorescence experiments showed that Pim-1 and Cdc25C co-localize in the cytoplasm of both epithelial and myeloid cells. We find that phosphorylation by Pim-1 enhances the phosphatase activity of Cdc25C and in transfected cells that are arrested in G2/M by bleomycin, Pim-1 can enhance progression into G1. Therefore, we propose that Pim-1 activates Cdc25C by a direct phosphorylation and can thereby assume the function of a positive cell cycle regulator at the G2/M transition.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • COS Cells
  • Cell Cycle / physiology*
  • Cell Cycle Proteins / metabolism*
  • Chlorocebus aethiops
  • HeLa Cells
  • Humans
  • K562 Cells
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins c-pim-1 / genetics
  • Proto-Oncogene Proteins c-pim-1 / metabolism*
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Signal Transduction / physiology
  • cdc25 Phosphatases / metabolism*


  • Cell Cycle Proteins
  • Recombinant Fusion Proteins
  • MARK3 protein, human
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-pim-1
  • CDC25C protein, human
  • cdc25 Phosphatases