p27 is regulated independently of Skp2 in the absence of Cdk2

Biochim Biophys Acta. 2014 Feb;1843(2):436-45. doi: 10.1016/j.bbamcr.2013.11.005. Epub 2013 Nov 21.

Abstract

Cyclin-dependent kinase 2 (Cdk2) is dispensable for mitotic cell cycle progression and Cdk2 knockout mice are viable due to the compensatory functions of other Cdks. In order to assess the role of Cdk2 under limiting conditions, we used Skp2 knockout mice that exhibit increased levels of Cdk inhibitor, p27(Kip1), which is able to inhibit Cdk2 and Cdk1. Knockdown of Cdk2 abrogated proliferation of Skp2(-/-) mouse embryonic fibroblasts, encouraging us to generate Cdk2(-/-)Skp2(-/-) double knockout mice. Cdk2(-/-)Skp2(-/-) double knockout mice are viable and display similar phenotypes as Cdk2(-/-) and Skp2(-/-) mice. Unexpectedly, fibroblasts generated from Cdk2(-/-)Skp2(-/-) double knockout mice proliferated at normal rates. The increased stability of p27 observed in Skp2(-/-) MEFs was not observed in Cdk2(-/-)Skp2(-/-) double knockout fibroblasts indicating that in the absence of Cdk2, p27 is regulated by Skp2-independent mechanisms. Ablation of other ubiquitin ligases for p27 such as KPC1, DDB1, and Pirh2 did not restore stability of p27 in Cdk2(-/-)Skp2(-/-) MEFs. Our findings point towards novel and alternate pathways for p27 regulation.

Keywords: Cdk2; Cyclin-dependent kinase; Knockout mice; Skp2; p27.

Publication types

  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigens, Polyomavirus Transforming / metabolism
  • Body Size
  • Cell Proliferation
  • Crosses, Genetic
  • Cyclin-Dependent Kinase 2 / deficiency*
  • Cyclin-Dependent Kinase 2 / metabolism
  • Cyclin-Dependent Kinase Inhibitor p27 / metabolism*
  • Embryo, Mammalian / cytology
  • Female
  • Fibroblasts / cytology
  • Fibroblasts / enzymology
  • Gene Silencing
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Organ Size
  • Protein Stability
  • S-Phase Kinase-Associated Proteins / metabolism*
  • Ubiquitin-Protein Ligases / metabolism

Substances

  • Antigens, Polyomavirus Transforming
  • S-Phase Kinase-Associated Proteins
  • Cyclin-Dependent Kinase Inhibitor p27
  • Ubiquitin-Protein Ligases
  • Cdk2 protein, mouse
  • Cyclin-Dependent Kinase 2