Role of p27(Kip1) in cAMP- and TGF-beta2-mediated antiproliferation in rabbit corneal endothelial cells

Invest Ophthalmol Vis Sci. 2001 Dec;42(13):3142-9.


Purpose: To determine whether p27(Kip1) plays a role in antiproliferation mediated by antimitogens (cAMP and TGF-beta2) in rabbit corneal endothelial cells (CECs).

Methods: Cell proliferation was assayed using a colorimetric method to determine the number of viable cells. Subcellular localization of cell cycle-regulatory proteins was determined by immunofluorescent staining, and expression of the proteins was analyzed by immunoblot analysis.

Results: When cells were treated with cAMP or TGF-beta2, serum-mediated cell proliferation was inhibited in a dose-dependent manner. Simultaneous treatment of the two antimitogens did not show a synergistic effect on inhibition of cell growth. Expression of cell cycle-regulatory proteins, such as cyclin-D1, cyclin-E, cdk2, cdk4, p21(Cip1), and p27(Kip1) was determined using immunofluorescent staining. A strong nuclear staining was observed for p27(Kip1). The other proteins were not stained or were only very faintly stained. Treatment of cells with either cAMP or TGF-beta2 did not change the staining potential of any proteins other than p27(Kip1), but all cells were positive for nuclear p27(Kip1) when treated with either TGF-beta2 or cAMP. In contrast, mitogen (FGF-2)-containing medium decreased the number of p27(Kip1)-positive cells. When the expression level of p27(Kip1) was determined using immunoblot analysis in the cells treated either with FGF-2 alone or with a concomitant treatment with FGF-2 and cAMP for 24 hours, FGF-2 markedly decreased the p27(Kip1) level, and cAMP prevented the decrease in p27(Kip1) level induced by FGF-2. No such phenomenon occurred during a short-term exposure of cells to either FGF-2 or cAMP or to a combination of the two. When cells were stained for phosphorylated p27(Kip1), FGF-2 markedly enhanced the staining of phosphorylated p27(Kip1) in nuclei, whereas both cAMP and TGF-beta2 prevented the phosphorylation of p27(Kip1).

Conclusions: These findings suggest that both antimitogens upregulate the expression of p27(Kip1) as they prevent the decrease of the p27(Kip1) level mediated by mitogen. Furthermore, cAMP and TGF-beta2 may inhibit the G(1)-to-S transition by blocking phosphorylation of p27(Kip1), which is a prerequisite for nuclear export of the inhibitor molecule for degradation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 8-Bromo Cyclic Adenosine Monophosphate / pharmacology*
  • Animals
  • Cell Cycle Proteins / metabolism
  • Cell Cycle Proteins / physiology*
  • Cell Division / drug effects
  • Cell Division / physiology
  • Cells, Cultured
  • Cyclin-Dependent Kinase Inhibitor p27
  • Endothelium, Corneal / cytology*
  • Endothelium, Corneal / drug effects
  • Endothelium, Corneal / metabolism
  • Rabbits
  • Transforming Growth Factor beta / pharmacology*
  • Transforming Growth Factor beta2
  • Tumor Suppressor Proteins / physiology*


  • Cell Cycle Proteins
  • Transforming Growth Factor beta
  • Transforming Growth Factor beta2
  • Tumor Suppressor Proteins
  • Cyclin-Dependent Kinase Inhibitor p27
  • 8-Bromo Cyclic Adenosine Monophosphate